Article

Recent advances in the solar water heating systems: A review

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  • Penn State Erie, The Behrend College
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... Many researches had been performed to evaluate exclusive varieties of solar structures in one-of-a-kind areas of the arena to better apprehend the conduct of sun water heating structures within the domestic. Ghorab et al. [22] carried out an in depth evaluation and evaluation of the performance of the solar system for home warm water, which incorporates an ACS recirculation loop in Indian climatic situations for common family employment (2 kids and a pair of adults); the gadget that has been studied is illustrated inside the following scheme: ...
... Schematic of solar domestic hot water system [22] the use of a information logger, Ghorab et al. [22] amassed statistics on the temperature, float and standing of various gadgets within the solar system (thermocouples, glide meters, pulse meters, etc.); the statistics had been taken each 10 seconds and then saved in a memory for evaluation. These records collected and analyzed are used to estimate lengthy-term overall performance underneath actual device circumstances: A. common sun tank temperature at specific out of doors climate situations B. heat exchanger temperature profiles C. solar tank and recirculation loop temperatures D. DHW temperature, nature gas consumption, and DHW load ...
... Schematic of solar domestic hot water system [22] the use of a information logger, Ghorab et al. [22] amassed statistics on the temperature, float and standing of various gadgets within the solar system (thermocouples, glide meters, pulse meters, etc.); the statistics had been taken each 10 seconds and then saved in a memory for evaluation. These records collected and analyzed are used to estimate lengthy-term overall performance underneath actual device circumstances: A. common sun tank temperature at specific out of doors climate situations B. heat exchanger temperature profiles C. solar tank and recirculation loop temperatures D. DHW temperature, nature gas consumption, and DHW load ...
Article
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Climate trade and power have turn out to be the fashion of universal discussions in current years. It's far genuine that using conventional fossil fuels has a negative effect on our planet, consequently, inside the totality of renewable electricity moves. However, in the modern-day kingdom, the sector can't but absolutely depend upon renewable power for its wishes. Alternatively, the use of maximum opportunities for renewable strength might have a positive impact on climate exchange. Many styles of renewable energy, wind strength, tidal energy, solar power, and so on. They can be exploited. The most common renewable power is sun energy, it can be used for special functions (power era thru photovoltaic / thermal systems, water heating for domestic functions, and so on.). Governments round the arena encourage the use of solar water heating for domestic use, for its simple use, low renovation requirements and the performance of solar heating systems. The objective of this work is to observe a solar water heating gadget in a residential constructing, expand a numerical model primarily based at the photo approach to are expecting the thermal behavior of the solar device and compare the outcomes with the actual facts amassed by means of the system sun. An energy meter referred to as SunEye.
... The auxiliary energy source with installed SWHS is a small capacity of about 1 kW electric heater. The SWHS types are mainly divided into two main groups, the active systems and the passive system [19][20][21][22]. ...
... It does not work when no electric current. It should be supplied with the control system and it may require the use of freeze-resistant heat transfer fluid, which made this system not available in the Iraqi market [19,20]. ...
... Therefore, these systems are simpler and cheaper than the active systems and they are available in the Iraqi market. The passive SWHSs found in the Iraq market is divided into two types [19][20][21]: ...
... Though they have better performance in producing high temperatures, when compared to FPCs, they are not competitive as a result of high initial costs [82]. The basic components of the ETC, are shown in Figure 2.4. ...
... ETC consists of evacuated tubes (glass-glass seal) to minimize heat losses, copper heat pipes for rapid heat transfer and aluminium casing to provide durability and structural integrity to the system. ETC minimizes the heat losses due to convection and radiation [82]. Alike to FPCs, ETCs collect both direct and diffuse radiation, however, their efficiency is higher at low incidence angles. ...
Book
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In South Africa, more than 40% of the energy produced, is estimated to be consumed in the commercial sector. Organizations, such as universities in South Africa, are faced with increased pressure to manage energy demands and escalating energy costs. This has resulted in the country currently facing ambiguous tariff increases, at short intervals, by the power utilities and rolling blackouts that could possibly lead to a grid shutdown. On the other hand, most institutions were not designed to be energy efficient, as they were mostly constructed in an era when energy optimization did not offer sufficient financial benefits. Therefore, energy efficiency is seldom viewed as a core university function. Standard electric storage tank-water heaters (ESTWHs) are the most used systems for sanitary water heating and are a major contributor to the undesirable high morning and afternoon peaks in energy demand. Another reason is that these systems rely solely on thermostat systems for operation control, with no other energy management activities (or technologies) in place. In addition, the thermostat automatically switches ON/OFF, to heat water to the end user’s set desired thermal level throughout the day, whenever the temperature drops below the set point, due to standby losses. All these things, therefore, add to the cost of the monthly bills of the users. Using renewable energy source water heating systems, such as air-source heat pump water heaters (ASHPWHs) and solar water heaters (SWHs), may further assist to reduce excessive energy demand and the cost of hot water production. However, these stand-alone water heating systems are insufficient, in the case of a great deal of hot water production whereby continuous energy supply is needed. This is due to the slow heating processes of the ASHPWHs and SWHs being solely dependent on thermal heat from the sun to heat the water. Furthermore, like the ESTWHs, the electricity-driven HP units on the market use primary thermostat control systems, which may further contribute to the energy consumption during the peak period. Solar-assisted heat pump water heaters (SAHPWHs), are a possible solution to the escalating electricity charges, faced by the South African community, particularly for the continuous demand for sanitary hot water in the commercial sector, such as university student residences. The solar system may provide a great amount of thermal energy to supply the heat pump unit during the time when the sun is available, while the heat pump vii consumes a minimal amount of energy, during the time when there is minimal to no solar energy available, to heat the water. These SAHPWH technologies may be a solution to assist with reducing the high energy demand, which will further help alleviate the pressure on the electricity supply grid. Additionally, implementing an optimal energy control scheme, to load shifting by the TOU tariff plan, may help alleviate demand strain on the supply grid, as well as optimize energy savings, while maintaining the consumer’s thermal comfort level. In this study, an IDX-SAHPWH system, operating under an optimal energy control scheme, integrated with the load shifting by TOU pricing plan, is proposed for the commercial sector. A student residence was used as a case study. A mathematical model of the proposed system was developed and the optimal control problems formulated for the operation. The Solving Constraint Integer Programs (SCIP) solver, in the MATLAB interface optimization toolbox, was used for the simulations, with the considered computational variables taken at 20-minute intervals. The baseline model was further simulated using the same component sizing, as well as under the same climate conditions. From the simulation results, the proposed system, under the optimal energy control scheme integrated with the load shifting by TOU pricing plan, operates optimally, as it avoids the peak and standard periods of the TOU tariffs, which guarantees savings in energy and costs, as compared to the baseline ESTWH. The proposed system ensures that water is heated during the off-peak period to the highest temperature that will be able to maintain the thermal level of the consumers, throughout the high TOU tariff periods. The techno-economic analysis of the optimally controlled proposed system and the baseline systems were conducted and presented for a project lifespan of 20 years. All cost aspects were considered in the analysis and, from the results obtained, the IDX-SAHPWH system showed significant savings. The cost savings obtained from the winter and summer seasons, as well as annual, are 76.0 %, 75.6 % and 75.8 %, respectively. The break-even point of the project is during the 9th month of the first year of the project, with a possible savings of 71.5 % at the end of the project's lifetime. It may therefore be concluded that the aim of this study has been met as the IDX-SAHPWH system, when operated with the optimal energy control scheme, integrated with the load shifting by TOU pricing plan, shows a very significant savings in costs, while viii maintaining the thermal comfort level of the consumers. Furthermore, the system may contribute to the load reduction during peak energy usage periods on the electricity grid supply. As a result, this system can be used in any commercial enterprise, that has a high demand for sanitary water heating.
... Domestic water heating has long been cited as one of the primary sources of energy consumption in the building sector [1]- [3], accounting for 42% of global energy demand [4]- [6]. The pervasive use of energy in buildings contributes significantly to global energy concern [7]. ...
... Hence, the HP can be regarded as a secondary heat source for the hybrid system. The useful heat gain by HP is determined using (3). In this study, hot water is drawn from the thermal storage tank at a rate equal to hot water load demand. ...
Conference Paper
Domestic water heating is becoming more recognized as a significant source of energy consumption in buildings. The pervasive use of non-renewable fossil-based water heating technologies comes at a high cost and significantly contributes to the climate crisis. Thus, the Nigerian energy situation necessitates the prompt adoption of sustainable energy systems and the efficient application of hybrid in order to achieve net-zero energy in buildings. This paper presents a mathematical model of a hybrid solar/heat pump water heating system. The proposed system consists of solar thermal collector, storage tank, heat pump, and grid system. The proposed model aims to reduce grid energy costs by optimizing the switching control of the heat pump water heater. Control variable is the heat pump water heater switch. The mathematical model is based on energy balance equations, and the optimization problem is a mixed integer nonlinear. The economic benefits of this hybrid technology in terms of cost savings and energy reduction are promising. The proposed model can save about 56% of energy consumption and N192.08/day of cost savings is achievable with the hybrid system. Adoption of this hybrid technology has the potential to significantly reduce energy consumption while compensating for energy shortages in the majority of African countries.
... have two form such as flat collectors and vacuum tube collectors. Expression 1 gives the mathematical model of thermal collectors which is based on the standard second-order equation of collectors' performance as follows [30]. ...
... Auxiliary water heaters: which are used to meet the hot water needs of users, there are type of auxiliary water heaters coupled to a solar water heater, electric auxiliary solar water heating system and natural gas solar water heating system, more details can be found in the literature [30]. In this paper, the first type is considered, i.e. electricity as an auxiliary energy source is used to heat water in parallel with solar energy in order to improve water heating system performance. ...
Article
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In this paper, the comprehensive performance analysis based on technical, economic and environmental aspects of using a solar water heating system in Algeria is carried out. Optimal tilt angle received solar radiation, system yield and efficiency, solar faction, CO2 emissions are the parameters analyzed. Among the simulated tilt angles from 0° to 90°, the optimal angle is found 30 degrees. The simulation results reveal that the solar irradiation received, system yield, solar fraction and CO2 emissions are 7149 kWh/year, 3032 kWh/year, 72% and 1659 kg/year, respectively. The solar coverage (%) and CO2 emission (kg) are (93-1445), (88-1532), (83-1592), (77-1633) and (72-1659) for hot water temperatures of 40°C, 45°C, 50°C, 55°C and 60°C, respectively.
... Latent heat thermal energy storage systems have thrust area in space vehicles, battery thermal management, refrigeration, house cooling, solar energy system, solar dryers and with respect to the present article, also in solar water heater (Plytaria et al. 2019;Verma, Shashidhara, and Rakshit 2019;Heera 2020;Saxena 2020). Incorporation of phase-change material (PCM) for storing excess solar energy during sunshine hours in solar water heater was one of the major applications considered for such materials (Shukla et al. 2013;Kaushik 2018, 2020;Palanikumar et al. 2021). ...
... Nowadays, the market is predominated by mainly two types of solar water heater: (1) flat plate solar water heaters and (2) evacuated tube solar water heaters. However, due to better thermal efficiency of evacuated tube solar water heater over flat plate solar water heater, preference is generally given to evacuated tube solar water heater (Shukla et al. 2013;Panchal and Thakkar 2016;Panchal et al. 2020;Mevada, Panchal, and Sadasivuni 2021). Based on the water flow manner, the heaters are further classified as (1) external pump assisted forced convection system also known as active solar water heating system and (2) thermosyphonic governed natural circulation system which is also named as passive solar water heating system. ...
Article
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The intake of hot water helps in keeping the body healthy, hydrated and protected against harmful bacteria, protozoa and viruses. As per WHO, the exposure of 55°C temperature for 20 min, can kill coronavirus and also other disease-causing organisms. The present study aims at maintaining hot water temperature of 55°C and above, with the use of phase-change material (PCM) within the solar water heating system for application in households and hospitals. A detailed performance evaluation for PCM integrated solar water heating system has been carried out. The phase-change behaviour of paraffin wax-6035 incorporated within copper tube in three different configurations (without fin, single fin and triple fin) is studied using CFD analysis. The results show that single fin configuration can maintain the required output water temperature sufficiently long enough to provide hot water during off-sunshine hours and is recommended for implementation.
... The active systems include fluid heater collectors, which system works using electrical pumps, controllers, and valves to move working fluids through the collectors. Forced circulation (FC) is the name given to this system, which can be used in either an open-loop mode or a closed-loop (indirect) mode (Shukla et al., 2013). ...
... Secondly, this system does not provide moving (mechanical) fluid, but radiation absorption temperature gradients move fluid and energy. The passive system utilises the natural convection heat transfer method to flow solar liquids between the collector and the tank without mechanical devices (Shukla et al., 2013). ...
Article
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The increasing energy demand and continuous confrontation of energy generation costs are preceded by a terrible depletion of fossil fuel power reserves and increased environmental pollution. In the recent years, renewable energy grew quickly to face the responsibility of the unforeseen energy problem. Flat plate solar collectors (FPSC) are well-known and widely used, thus utilised in low and medium thermal different domestic applications. However, FPSCs are less efficient due to their limited ability of solar energy to be converted into thermal energy due to the inefficient heat transfer in solar fluids on the collector’s flow tubes. In recent decades, new technologies have enabled the manufacturing of particles in nanometre dimensions (usually less than 100 nm), suspended consistently and stable in traditional solar liquid or so-called nanofluid (NF) and have improved the effects of thermophysical features. The use of NFs as an innovative solar fluid can be reasonably considered as a powerful method of increasing the performance of the FPSC. This paper provides recent advances related to experimental and theoretical studies on NFs applications in the FPSC. Several parameters affecting the thermal efficiency of FPSC are extensively analysed, including the type of nanoparticles (NP)s, size/shape of the NPs, NPs concentration, mass flow rate and solar radiance. This paper also provides a comprehensive review and analysis of progress in the field of NFs, such as the applications of NFs, types, preparation, thermophysical properties, stability, chemical and physical methods for stability, mathematical formulas, and stability evaluation. Finally, the main challenges and future trends mentioned by the researchers while using NFs in solar thermal collectors such as the viscosity, instability, corrosion, operation cost, pumping power, pressure drop and behaviour of surfactant usage, which are assumed helpful to newcomers, are the focus areas of this research.
... It is a system with component of absorber, glazing, and insulation capable of transforming the sun's radiation into heat which is then transfers to a working fluid usually water or air (Patil and Deshmukh, 2015). According Shukla et al., (2013) defines solar collector as a heat exchanger that converts solar energy to useful heat which is transferred to the fluid flowing through the collector. Solar collectors can be basically classified into three types namely; uncovered (unglazed), flat plate, and evacuated tubular collectors (Jesk, 2008;Soltrain, 2017). ...
Article
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The quest for solution to the high cost of energy and the environmental impact emanating from century long overdependence on fossil fuel has propelled several research efforts in renewable alternative energy sources. Nigeria with an annual average of global horizontal irradiation of about 1.4kWh/m 2 in the coastal region, 2.4kWh/m 2 in the Northern region, and seven (7) or more hours of daily sunshine significantly demonstrates solar thermal potential. Solar energy can provide sufficient energy to heat up water to a desired temperature for both domestic and industrial applications with cost reduction in energy and its associated consumption. The study presents a review of literatures on Solar Water Heating (SWH) as well as Solar Thermal Energy Storage Systems (STES). Findings from the review show that solar water heating systems indicate good potential for cost reduction in fossil fuel consumption and its associated environmental concerns with well design solar water heating systems. The use of sensible heat storage materials for underground thermal energy storage (UTES) demonstrates high prospect for solar thermal energy storage for thermal application. The pertinent of laboratory investigation of sensible materials for their physical and thermal properties for heat storage and transfer characteristics in addition to modeling, simulation, and validation is fundamental to overcoming the challenge of daily and seasonal solar thermal systems load demand during solar radiation off peak period.
... Experimental results of mass and thermal flow rate on solar hot water systems revealed that the energy collection would be reduced for a higher flow rate (8). The heat pipe ETSC is more efficient than the FPC of a solar water heating system because it produces a high temperature, but the initial cost of ETSCs is higher than FPC (9). All evacuated tubes are the cheapest, simplest and more cost-effective than the electric water heater with 50° C operating temperature, suitable for domestic applications. ...
... Solar PV generation is also increasing but at a slower pace. Usually, the solar-thermal conversion efficiency is about 70% but the solar photovoltaic electricity conversion system efficiency is about 17% [13]. Accordingly, as seen from the global installed capacities, solar water heating systems are popular due to their ease of maintenance and operation. ...
Article
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In the present work, solar water heating systems having nominal water usage of 24 cubic meters per day are considered. To identify the better option, both technologically and economically, a typical geographical location in Saudi Arabia, namely Abha, is considered. Internal rate of return (IRR) values for the solar collectors with glazing are found to be higher as compared with that of the unglazed type. The glazed type collectors are found to be more efficient, provide greater savings in fuel consumption, and result in the reduction of greenhouse gas (GHG) emissions. The findings of this study can be used for locations with similar types of climatic conditions in any part of the world.
... A standard SWHS consist of solar collectors, where the conversion of solar energy to heat takes place, and a hot water storage tank. Conventionally, two main topologies can be used for the operation of the solar collectors in a SWHS: the natural circulation of the heat transfer fluid and the forced circulation via a pump [7][8][9]. In the scientific literature, natural circulation systems are often called passive SWHSs, but a more widely used term is thermosyphon SWHSs. ...
Article
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The main categories of solar water heating systems (SWHSs) are the thermosyphon and the forced circulation (FC). This paper presents an experiment carried out with the aim to compare the energy performance of the FC with a thermosyphon SHWS. Identical SWHSs were installed side by side at the University of West Attica in Athens, Greece. Domestic hot water load was applied to both systems via a microcontroller-based dispensing unit which mimics the demand profile. The trial period comprised the last two months of spring (April and May). For the first law assessment, two energy indicators were utilized: the solar fraction (SF) and the thermal efficiency of the system (η th). On days with distinctive weather conditions, both systems obtained approximately equal SF and η th values, without a specific preference between the ambient conditions and the type of SWHS. Regarding a four-day nonstop operation, the FC overperformed the thermosyphon system at both energy indicators. Namely, for the FC and the thermosyphon SWHS, the SF was calculated to be 0.62 and 0.48, and the η th was 68.2% and 53.3%, respectively.
... Solar heaters are one of the most widespread solar systems, and there are millions of these systems distributed in various countries of the world (Smyth, Eames and Norton, 2006). Solar heaters are among the applications that do not need relatively high temperatures, as the boiling point of water does not exceed 100 o C. Solar heaters are classified into two main classes (Shukla et al., 2013). First, the thermo-siphon system. ...
Article
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The use of solar energy to heat water is the more critical application of solar energy. Researchers are trying to develop different methods to improve the efficiency of solar water heaters to meet the increasing demand for hot water due to global population growth. To reduce the cost and increase the efficiency of solar heaters, the solar collector and the storage tank are combined into one part, and this system is called solar storage collector. It can be defined as geometric shapes filled with water, painted black, and placed under the influence of sunlight to gain the largest amount of solar energy. This article presents the various designs of solar storage collector. This review showed that design variables and design shape significantly affect the efficiency of the solar heating system. Climate and operational factors also have a strong influence on the performance of solar heating. Furthermore, scientists and researchers have also used nanotechnology, solar cells, and mirrors to improve other stored solar collectors' performance. Finally, recently published articles indicate an increase in interest in improving the efficiency of solar storage collector by creating new designs that enhance the economic and practical viability.
... In the midst of various renewable sources, solar energy is the most generous and can serve as a sustainable source. Society has long recognized the advantage of solar technologies in multiple fields [1][2][3][4][5][6][7]. Fig. 1 represents solar technologies, including solar desalination, solar cooking, solar-powered car, solar furnace, solar-powered laser, solar water heater, cabinet solar dryer, solar power plant, etc. ...
Article
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The rapid exhaustion of conventional energy sources and global environmental concerns are opening new opportunities to utilize sustainable and renewable energy. Amid the various renewable sources, solar energy is a promising, inexhaustible, and abundant form of freely available energy. The solar-driven laser system is one of the most acceptable technologies to harness solar power. Solar-powered laser converts the broadband solar radiation directly into the monochromatic, collimated, and coherent laser beam. The emitted laser beam may be widely used in space and terrestrial applications, including free-space optical communication, renewable energy cycle, asteroid deflection, space debris removal, material processing, nano-material production, and electric vehicles. The paper starts with a discussion of solar-powered lasers with distinct gain mediums such as liquid, gas, and solid. This paper illustrates details about the solar-powered solid-state lasers, which have the advantage of inherent high energy density and compactness, relatively low pumping threshold, and potential for efficient solar to laser power conversion. A comprehensive review of solid-state solar laser's construction, working principle, energy conversion process, and beam shaping are also presented. The state‐of‐the‐art procedures have been summarized for laser collection efficiency and laser output power. The power density of solar radiations received on the earth's surface is low and insufficient for lasing action. Hence, the solar concentrators are described in detail to enhance the energy density. Furthermore, the different Nd: YAG laser rods and pumping schemes are explained to reduce the thermal lens effect. Finally, the review is concluded with a conclusion and perspectives.
... Compared to solar systems, hybrid gas and solar water-heating systems include an auxiliary system based on natural gas. Interested readers can consider reviews about solar water heating, including Ibrahim et al. (2014), Shukla et al. (2013), and Wang et al. (2015). Resilience is one of the growing trends in the energy supply chain. ...
Chapter
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Supply chain disruptions in energy management negatively impact businesses’ performance. In its seventh objective, sustainable development tries to guarantee that all people have access to inexpensive, dependable, sustainable, and contemporary energy. However, many people worldwide suffer from energy supply chain disruption. For example, the 2019 World Bank report shows that 759 million people still live without electricity. The problem herein is energy scarcity as well as energy supply chain disruptions that create an unreliable business environment. In the energy sector, regulators have made a call for supply chain resilience, which refers to a capability to identify and avoid energy disruptions or quickly return to normal activity after a disruption. Integration of renewable energy sources through a hybrid energy supply chain can mitigate this problem. This chapter provides an assessment of sustainable development based on empirical data for integrating two sources of energy, with a focus on environmental, economic, and social impacts. To collect data for evaluating the impacts, field experiments are performed as well as the life cycle assessment analysis. The results show that integrated energy systems, such as hybrid solar energy with natural gas systems, produce lower environmental impacts compared to fossil-fuel-based energy systems. Moreover, integrated energy systems create more job opportunities and alleviate energy poverty.
... Table 1 illustrates the hot water devices, sensors, transducers and data loggers used in the study. T-Minol 130 flow meters 1 5 12 bits S-TMB temperature sensors 4 6 12 bits S-THB ambient temperature and relative humidity sensor 1 7 ...
Article
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This paper ascertained the performance of the evacuated tube solar water heater (SWH) coupled with an auxiliary electric heater with reference to the replaced electric water heater with the same storage tank capacity (200 L) in a building. It also examines the influence of the uptake of the SWHs in the community due to different campaign methods. The study evaluated the performance of a 4 kW electric water heater and a 2 kW input SWH with an auxiliary electric heater, and quantified the annual energy and cost savings. A survey using questionnaires was conducted among 150 residences in Dimbaza based on the house representative’s perceptions to replace their electric water heaters with solar water heaters (based on the monetary saving inscribed on the solar water heaters, the sensitization of the target population on the environmental benefits of the solar water heaters and both the monetary savings and environmental benefits). The findings revealed that by replacing the electric water heater with the solar water heater with an auxiliary electric heater, the annual electricity savings due to hot water heating was 4408.99 kWh and the net present value payback period was 4.32 years. The desire of the household representatives to replace their existing electric water heaters with solar water heaters due to the campaign strategies increased from 75 to 126. This study is capable of providing a mechanism to increase the penetration of solar water heaters and justifying the techno-economic viability of solar water heaters.
... The reader can get in-depth information regarding the uses and difficulties of nanofluids by visiting this website. return to the analysis by Saidur et al. [21]. ...
Article
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This article provides a thorough analysis of current developments in the use of nano fluids in the sun collectors with heat pipes. Theoretical, numerical, and experimental papers that are current and relevant to the Applications of nanotechnology in this class of solar collectors. To provide a thorough overview of the effect of the nano fluid in enhancing heat pipe solar collectors, a large body of literature has been thoroughly researched and summarized. The effectiveness of heat pipe solar collectors can be significantly increased by using nano fluid, it was discovered certain tools.
... ETCs are more expensive than FPCs despite being more efficient collectors [38]. Though they have high initial costs, as compared to FPCs, ETCs are better performers in producing high temperatures, of above 200 • C, and further have minimal heat losses, due to convection and radiation [41]. ...
Article
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Although traditional electric storage tank water heaters (ESTWHs) are the most frequently used systems in the world, they are known to be among the highest energy consumers, due to their inefficiency in converting electrical energy to thermal energy. These systems have grown increasingly hostile to consumers, as power prices have risen. Therefore, the need to reduce energy consumption of hot water production, while maintaining the users’ thermal comfort level, has led to the development of more energy-efficient technologies. In this paper, a review of renewable energy water heating systems, particularly air-source heat pump water heaters (ASHPWHs), solar water heaters (SWHs) and solar-assisted heat pump water heaters (SAHPWHs), as well as the background literature of the studies on these systems, carried out in South Africa, under the energy management schemes, is presented.
... flat plate collector has long life and absorber of solar radiation falling in it. The effectiveness of FPC for solar energy reduced due to high temperature and thermal performance and heat transfer coefficient loss are poor [29].In flat plate collector the thermal losses depend upon many parameters like wind velocity, number of glasses covers and wind velocity [30].When the wind loss coefficient increases, the solar collector's FPC efficiency declines [31]. Chen et al. [32] carried out the experiment on FPC efficiency and compare the efficiency of plate collector with different types of collectors. ...
Article
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"The aim of the article is describes the performance of Flat Plate Collector in solar thermal water heater system. It highlights the importance of single glazed system and double-glazed system and evaluates how single glazing system and double-glazing system effects on the performance of FPC in solar thermal water heater.
... Solar energy utilization devices primarily include flat plates, vacuum tubes, and focusing collectors. The photothermal conversion components on the surface of heat absorbers are coated with a selective absorption material [21]. The Flat-plate collectors typically operate at temperatures below 100 • C, and they are physically large and occupy a lot of space; also, they are slower to start and have a high heat loss ratio. ...
Article
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The primary objective of this study is to address the embankment frost heave issues in cold regions with an active heating method. The applicability of various heat sources was compared with the heating demands of embankments, and the results demonstrated that the seasonally frozen areas of China are rich in solar energy resources. A specialized device for heating embankments, comprising a solar collector section and an embankment heater section, was developed. The device integrates energy conversion, storage, and transfer with no moving parts and can therefore be used for self-driven operations on an “isolated island”. Performance tests showed that the maximum heating temperature exceeds 60 °C with an average range of 20–40 °C, which increases with solar radiation. The effective heat utilization rate of the soil is approximately 26%. A predictive model that considers latitude and the daily ordinal number was proposed for heating temperature. The long-term heating performance of the embankment was numerically simulated. The results revealed that the heating mode in all seasons is capable to overcome the limitations of existing insulation measures and effectively enhance the potential of frost-resistant embankments in winter.
... Some active techniques such as helically twisted tape, rod fitted twist, and full-length twisted tape inserted inside the pipe, have also been used to increase heat transfer. These active techniques have been reported to cause high-pressure drop penalties on pump systems [43][44][45][46]. The high pressure drops penalties have been reported as a major disadvantage in the active system. ...
Article
This study reports on the performance of delta-shaped obstacles in a solar water heating system (SWHS) by means of experimental analysis and optimization. The influence of different parameter combinations such as Reynolds number (200, 600, 1000, 1400, 1800), pitch ratio (0.5, 1, 1.5), blockage ratio (0.15, 0.20, 0.25), and angle of attack (45 •) on Nusselt number, friction factor and thermo-hydraulic performance of SWHS were analyzed. For the combination of Reynolds number = 1800 and pitch ratio = 0.5, the Nusselt number remained highest for 0.25 of blockage ratio, whereas the friction factor remained lowest for a blockage ratio of 0.15. The maximum thermo-hydraulic efficiency was achieved using Reynolds number = 200, pitch ratio = 0.5, and blockage ratio = 0.20. The obtained results were intensely dependent on parameter combinations without any pronounced trend. Therefore, criteria importance through inter-criteria correlation (CRITIC) and complex proportional assessment (COPRAS) approach was implemented to find optimal design alternative. The results of the hybrid CRITIC-COPRAS approach showed that the combination of Reynolds number = 1800, pitch ratio = 0.5, blockage ratio = 0.20, and angle of attack = 45 • is the best alternative for maximum thermal enhancement in SWHS. The sensitivity analysis proved the robustness of the results that the first-ranked alternative is the most dominant in all scenarios.
... In order to reduce the energy footprint of DHW systems in the residential sector, optimizing strategies aim at (i) decarbonizing and increasing the efficiency of hot water production technologies (Ahmadi et al., 2018;Fabrizio et al., 2014;Shukla et al., 2013), (ii) reducing losses through hot water distribution systems within buildings (Bøhm, 2013;Cholewa et al., 2019), (iii) decreasing hot water use through technological or behavioral measures (Binks et al., 2017;Tiefenbeck et al., 2016) and (iv) recovering heat from wastewater at multiple levels, from the household drain to the wastewater treatment plant (Frijns et al., 2013;Nagpal et al., 2021). However, it is not yet clear which strategy has more potential and what combinations may yield the best results for the least effort. ...
Article
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Domestic hot water systems are large energy consumers. With the aim of reducing the energy footprint of these systems, we selected and simulated five technologies across a wide range of technology readiness levels: established technologies – pipe insulation and low-flow faucets –, relatively new technologies – shower drain heat exchangers and an innovative pipe system – and a novel experimental technology – a heat exchanger connected to membrane bioreactor for on-site greywater treatment. Using the WaterHub modeling framework, we simulated the technologies alone and in combination and compared the energetic performance of fifteen scenarios with a validated reference domestic hot water system. Low-flow appliances as standalone technologies performed best with 30% less energy required for the boiler tank, but combining low-flow appliances with a membrane bioreactor heat exchanger performed best overall (50% reduction). Deep insights into the temperature dynamics at all locations in the system led to the identification of technological competition patterns to prevent and synergies to exploit. Through our results, we are able to discuss and recommend further investigations regarding critical aspects like hygiene and economic performance.
... In the direct systems, water is directly circulated in the collector to be heated by solar energy. On the other hand, in the indirect active system, the water is circulated in a heat exchanger, where it absorbs heat from the heat transfer fluid that circulates through the collector [6]. ...
Article
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Solar Water Heating (SWH) systems have been extensively investigated during the past decades to optimize their performance and configuration. In fact, a lot of research work has been conducted to improve the SWH system components such as the solar collector and heat transfer fluids while less studies have been devoted to improving performance through control strategies. In this paper, a comprehensive comparison and control are introduced for four configurations of SWH systems to investigate their performance under different solar radiation conditions. It is, in fact, a great challenge to regulate the outlet temperature of a SWH system under a time-varying solar radiation during the day. Hence, two controllers, namely robust and Proportional-Integral-Derivative (PID), are utilized to work in harmony in order to control the water temperatures of four SWH systems under clear and cloudy skies solar radiation conditions. Various open- and closed-loop tests are conducted, in simulation, on the proposed four SWH systems to compare their responses in terms of regulating the outlet water temperature to a desired level with a minimum energy consumption. The simulation results show the effectiveness of the proposed closed-loop control algorithms in regulating the outlet water temperature in the presence of time-varying solar radiation. Moreover, the results also show that energy consumed within the closed-loop system was 14%, 67%, 36%, and 44% less than the energy consumed within the open-loop system 1, 2, 3, and 4, respectively, under clear sky solar radiation condition. On the other hand, the energy consumed within the closed-loop system was 23%, 88%, 52%, and 58% less than the energy consumed within the open-loop system 1, 2, 3, and 4, respectively, under cloudy sky solar radiation condition. This confirms the superiority of the closed-loop system performance over the open-loop system performance. Furthermore, the results of this study show that the optimal SWH system configuration depends on the dominant nature of the solar radiation in the region at which the SWH system is installed.
... Over the last decades, the efficiency of widely used oil or gas boilers has increased significantly, with modulating and condensing boilers as flagship examples [12]. The trend, however, is to avoid fossil fuels through the use of air-, water-or ground-sourced electric heat pumps [13,14], the integration of renewables like solar, wind or biomass [15], the development of district heating networks [16,17], and perhaps most importantly an increased hybridization of all of the above [18]. Integrating DHW and SH may be challenging for some of these systems due to large differences in the required water temperature for DHW and SH as well as uncertainties regarding hot water demand. ...
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*Thanks to intense research efforts, modern low-energy buildings consume only a fraction of the space heating loads of their older counterparts. However, reducing their energy footprint further requires optimization of domestic hot water systems. This is a difficult task, because the relationship between water and energy in domestic systems is intricate and complex. In general, the intrinsic uncertainty and variability of water demand makes the planning and assessment of new technologies challenging, but also risks related for instance to water pathogens like Legionella Pneumophila impose trade-offs that diminish the performance of energy-saving measures. In this short communication, we argue that truly sustainable solutions will only be found if a multi-scale, multi-disciplinary mindset is adopted by the community. We show how the collaboration and knowledge integration between experts of various fields, notably urban water specialists and building engineers, is a prerequisite to resolve some of the most pressing issues on the way to optimizing domestic hot water systems. Through concrete examples, we describe how a new, common modeling framework has already triggered the required knowledge integration, and how it could be expanded further to integrate additional disciplines.
... Com a crescente demanda energética e a proposição de novas técnicas de geração de energia elétrica e no intuito de economizar a fatura de luz, têm-se investido em aquecedores de água domésticos para suprir essa demanda, bem como investir em tecnologias sustentáveis e de viabilidade econômica. Segundo Shukla (2012), o aquecimento de água nas residências é responsável por cerca de 20% do consumo de energia em uma família. Nesse contexto, o uso de um sistema de aquecimento solar (SAS) para redução do consumo energético doméstico é promissor. ...
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A busca por tecnologias renováveis e eficientes estão sendo constantes e a energia proveniente da radiação solar é um importante mecanismo para a diversificação da matriz energética nacional. Nesse contexto, várias formas de utilização desse mecanismo são buscadas, por especialistas. Dentre esses, pode-se citar o sistema de aquecimento solar, pois se trata de um sistema perene, mais rentável e sustentável, por se tratar de uma energia advinda da radiação solar. Assim, o objetivo propor um dimensionamento de um sistema de aquecimento solar para água utilizando coletores de placa plana na cidade de Brasília. O método utilizado para tanto foi baseada na norma ABNT NBR 15569:2020 e foi seccionada em duas partes as quais foram local de instalação e dimensionamento através da norma citada. Sendo assim, Com a análise dos cálculos do dimensionamento do sistema de aquecimento solar para uma residência localizada na cidade de Brasília, foi observado que a área coletora necessária foi de 3,15 m2 e com isso serão utilizados 2 coletores para a residência em questão, visto que a diferença de 0,15 m2 não é viável para a dição de outro coletor. Palavras-chave: Energia renovável, Radiação solar, Sustentabilidade.
... The solar collector's efficiency was related significantly to the total efficiency of a solar system. For this reason, solar collectors are essential elements of every solar system (Shukla et al., 2013). In recent years, various kinds of solar collectors have really been developed and researched, particularly the FPCs (Cerón et al., 2015;Jiandong et al., 2015;Jing et al., 2014;Makhanlall and Jiang, 2015;Subiantoro and Ooi, 2013;, certain evacuated glass solar tube collectors (ETSCs) (Li et al., 2010;Kim et al., 2007), as well as U-shaped evacuated solar tube collectors (Eslami-nejad and Bernier, 2011;Tong et al., 2015). ...
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This research paper presents a detailed review about the recent advances concerned with the heat pipe-evacuated tube solar collectors. The reviewed papers covered various subjects related with this type of the collectors such as enhancement techniques, its structure designing and the methods used to modify it. Moreover, the effects of integration of (CPCs), types of working fluids and using of storage systems on the performance of this collector were reviewed and summarized in different tables. Depending on the reviewed papers, various conclusions and recommendations were outlined to be very useful to the readers and give them a clear road map to produce more future papers about the heat pipe- solar collector systems.
... The hot water storage tank, like the solar collector, is an essential component of the SWHS that influences the system's performance. The tank stores the collected thermal energy and delivers the hot water to end-users at the preferred temperature [53]. Concrete, plastic, fiber glass, and steel are the most common materials used to construct storage tanks. ...
Article
Solar water heating systems can be used in any climate. However, their performance varies depending on the quantity of solar energy available in the region, and more importantly, the temperature of the water entering the system – the colder the incoming water, the higher the operating efficiency of the solar water heater. One of the noble benefits of solar water heating systems is the ability to save money, which is a reason that motivates most people to adopt them. In this study, a thermosyphon solar water heater was built and experimentally tested in an open field in Minna, Niger State-Nigeria, to determine the maximum water temperature and stability of water temperature in a 300-litre storage tank for use in commercial beauty salons. The systems' performance was evaluated on partly cloudy and clear sunny days. The maximum outlet water temperature of the collector was 70.0 °C and 84.0 °C on partly cloudy and clear sunny days, respectively. The maximum temperature values of stored water obtained were 67.0 °C and 78.0 °C on partly cloudy and clear sunny days, respectively. The maximum thermal efficiency values of the solar collector obtained on partly cloudy and clear sunny days were 81.0% and 81.5%, respectively. The respective quantitative values of the collector's operational parameters – the energy absorption (FR(τα)) and the energy loss (FRUL) characteristics – were 0.621 and 2.66 on the partly cloudy day and 0.622 and 2.25 on the clear sunny day. Thus, the thermosyphon solar water heater can meet the hot water needs of beauty salons in Nigeria.
... The use of renewables for the production of hot water, led by solar technologies, form a mature set of strategies aiming at decarbonizing DHW production. Among the most prominent solar energy-harvesting technologies, we cite photovoltaics (PV), solar thermal collectors, and the promising combination of both into single devices (PV/T) (Shukla et al. 2013). Research efforts in the field of nearly-zero energy buildings are focusing on the integration of solar technologies into the building energy system, towards hybrid systemse.g., PV providing electricity for a heat pump compressor is often more efficient than solar thermal collectors (Good et al. 2015) -or improved architectural integration, for instance building-integrated photovoltaics (BIPV) (Wu and Skye 2021). ...
Chapter
The article presents the results of studying the possibility of using solar collectors in the small business sector, in particular, to meet the needs of hot water supply for a medium size hotel located in Tashkent. The research methodology and the hot water supply system with its technical characteristics were described in detail. The study used the f-method to determine part of the load on hot water covered by solar collectors. An economic analysis of the proposed system is carried out using Life Cycle Saving method (LCS). The special computer program is developed based on both methods to simulate thermal and economic performance of proposed system. Results show that in spite of high level of solar irradiance in Tashkent region, installing and exploiting solar water heater system seems to be uneconomical. Due to relatively low price of conventional fuel, natural gas and electricity, investing in solar water heating system at all range of solar collector area is not economically attractive.
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Given the imminent energy depletion status, solar energy has drawn sufficient attraction from the researchers. In the building section, the solar heating possesses a significant potential for bringing down corresponding energy consumption. However, it calls for latent heat storage to tackle the time-domain incompatibility caused by solar intermittency. Phase change material (PCM) integrated solar heating system has been studied sufficiently and abundant advances have been achieved. There are reviews about PCM integrations with solar heating system applied in individual building component, energy storage unit, material enhancement, systematic efficiency improvement, etc. However, most former studies only looked into the above-mentioned aspects respectively. Consequently, there is scarce of comprehensive review over PCM applications deployed in solar building heating systems. Herein, the present manuscript gives a brief review over relevant investigations and corresponding developments. Solar heating system and relative PCM integration are review respectively and conjunctively. And the authors concluded that the PCM integration with building enclosure structure would be the most effective way for thermal efficiency improvement of solar building heating systems. Apart from that, future research recommendations for relevant studies are drawn. Firstly, proper operating mechanism of solar heating coupled with PCM technology synergism for universal climates has not been developed yet. When established, it would bring along an exponential growth in the system universality. Moreover, there is huge necessity of engineering standard/criteria for relevant application projects. Last but not the least, desired comprehensive evaluating/investigating methodologies would be put on agenda for related research projects. Besides, this manuscript also expounds some perspectives on future development of PCM solar heating applications.
Chapter
The operation of a low-temperature solar thermal system using artificial neural network (ANN) models of its components (flat-plate solar collector, internal heat exchanger, and stratified tank), and its workings with dynamic and static modes, has been simulated. The ANN models of these components, used as blocks, have been previously formulated using the experimental data of solar irradiance, ambient temperature, flow and temperature of the working fluid and water supplied to the tank, and stratification temperatures in eight levels of the tank, measured under the continental Mediterranean climate conditions of central Iberian Peninsula. The simulation, executed in intervals of 1 minute, was run on 2 days for each month of 1 year. The f-chart method was used to validate the neural simulation under the same conditions (without stratification) for 10 years, resulting in an average deviation of the performance of 1.85%. The results for 1 day at stratification temperatures show a root mean square error value of 0.77°C in dynamic operation mode and of 0.13°C in static operation mode.
Article
Solar thermal evaporation (STE) is a promising advanced technique to purify contaminated water under the influence of solar light. Naturally, cement has served as a binder in masonry-related applications and possesses light-absorbing properties. Herein, we fabricated a cost-effective high-durable cement/carbon/polyurethane foam (CCPF) composite material as a solar-driven evaporator. It provided an excellent evaporation rate of ∼2.4 kg m⁻² h⁻¹ under one sun (1 kW/m²) illumination. The CCPF exhibits a high solar light absorbance due to the presence of carbon. Also, the high-interconnected porous foam provides the self-floating ability to maximize heat localization. Simultaneously, the interconnected crisscross porous foam and the porous activated carbon coat on the air-water interface behave like a highly concentrated dye water filter, salt-water filter, and high density muddy water filter. Moreover, the super hydrophilic surface of CCPF and the addition of polyurethane (PU) foam ensure adequate water supply. Complete wastewater filtering ability was confirmed by UV–Vis spectral analysis. As-fabricated composite can attain the maximum surface temperature of 62 °C under one sun illumination for 1 h. The stability and adhesive strength of the coating were confirmed from successive 60 days of water treatment. No carbon was excreted from the device even after 60 days of the experiment. The small size solar still setup was fabricated with an area of 30 × 30 cm² to show the performance of the device under ambient conditions. Collection of 140–160 ml ultrapure water from the device under ∼0.6 kW/m² varying solar intensity (environment temperature 30–32 °C) in 4–5 h. Therefore, this easily fabricated, cost-effective, highly stable CCPF solar-driven evaporator can be used as a strategy for high water production on a potential scale for the long term.
Article
This study reports on the performance of delta-shaped obstacles in a solar water heating system (SWHS) by means of experimental analysis and optimization. The influence of different parameter combinations such as Reynolds number (200, 600, 1000, 1400, 1800), pitch ratio (0.5, 1, 1.5), blockage ratio (0.15, 0.20, 0.25), and angle of attack (45°) on Nusselt number, friction factor and thermo-hydraulic performance of SWHS were analyzed. For the combination of Reynolds number = 1800 and pitch ratio = 0.5, the Nusselt number remained highest for 0.25 of blockage ratio, whereas the friction factor remained lowest for a blockage ratio of 0.15. The maximum thermo-hydraulic efficiency was achieved using Reynolds number = 200, pitch ratio = 0.5, and blockage ratio = 0.20. The obtained results were intensely dependent on parameter combinations without any pronounced trend. Therefore, criteria importance through inter-criteria correlation (CRITIC) and complex proportional assessment (COPRAS) approach was implemented to find optimal design alternative. The results of the hybrid CRITIC-COPRAS approach showed that the combination of Reynolds number = 1800, pitch ratio = 0.5, blockage ratio = 0.20, and angle of attack = 45° is the best alternative for maximum thermal enhancement in SWHS. The sensitivity analysis proved the robustness of the results that the first-ranked alternative is the most dominant in all scenarios.
Book
As a part of the global clean energy transition, the increased deployment of ground-mounted PV systems depends on the availability of land. In some regions, scarce land resources can lead to competition between agriculture and PV land use, threatening both food and energy security. Agrivoltaics is a method to combine agricultural and electricity production on the same unit of land, which significantly increases land-use efficiency and has the potential to contribute towards mitigation of related land-use conflicts. Additionally, agrivoltaics is expected to stabilize agricultural yields in regions that are vulnerable to the effects of climate change by providing weather protection and shading and might contribute to strengthen and vitalize rural economies and livelihoods. Adolf Goetzberger and his colleague Armin Zastrow were the first to propose the concept of agrivoltaics in the early 1980s. However, it was only about 10 years ago that agrivoltaics gained traction. In Japan, pioneer Akira Nagashima analyzed crop growth below PV modules within the first research pilot systems in 2004 and promoted the technology under the heading of “solar sharing” which led to the first governmental support scheme implemented in 2012. In 2014, China installed the first large-scale agrivoltaic systems and, still, today remains the country with the largest installed capacity in the world. France was the first European country to systematically support agrivoltaics with regular tenders starting in 2017. This development was largely driven by the research of Christian Dupraz at the French Institut National de la Recherche Agronomique and the Sun’Agri R&D program. Other countries that implemented or plan to implement governmental supporting schemes are the United States of America in the state of Massachusetts, South Korea, India, Israel, Germany, and Italy. An overview of the policies of those countries can be found in Section 5.7. In 2021, agrivoltaics emerged as a market-ready technology with a globally installed capacity of more than 14 GWp. In most subtropical and semiarid regions, however, agrivoltaics remains widely unknown even though the technical potential appears to be very high especially in these regions.
Chapter
Artificial Neural Networks for Renewable Energy Systems and Real-World Applications presents current trends for the solution of complex engineering problems in the application, modeling, analysis, and optimization of different energy systems and manufacturing processes. With growing research catering to the applications of neural networks in specific industrial applications, this reference provides a single resource catering to a broader perspective of ANN in renewable energy systems and manufacturing processes. ANN-based methods have attracted the attention of scientists and researchers in different engineering and industrial disciplines, making this book a useful reference for all researchers and engineers interested in artificial networks, renewable energy systems, and manufacturing process analysis.
Article
The development of proper storage medium for renewable sources with high intermittency (such as solar or wind) is an essential steps towards the growth of green energy development and enabling them to compete with fossil fuel resources in the current market. While the emerging of new generation of storage mediums, such as lithium based batteries is revolutionizing the world of renewable energy storage systems, many counties are still far behind in the growing market of storage technologies due to budget-related issues and hindering policies. In other world for many countries investment on new technologies which are still under the experimental stage of marketing, is too risky. It is more efficient for such countries to focus on well-developed and reliable storing technologies. This is the main reason why fossil fuel systems still thriving significantly in this field. Under these circumstances relying on “water-based” storage systems to compete with fossil fuels dominancy is an efficient solution due to various advantages of water-based systems including high specific heat, non-toxicity, lower costs, chemical stability, availability and high capacity rate during charge and discharge. While liquid water storage are highly suitable for operating temperature of 20–80 °C, using the steam accumulation form of such medium is easily suitable for high temperature applications such as power generation or other industrial applications. Aside from thermal applications of water-based storages, such systems can also take advantage of its mechanical energy in the form of pumped storage systems which are vastly use for bulk energy storage applications and can be used both as integrated with power grid or standalone and remote communities. The main goal of this study is to comprehensively explore the exciting water-based storage systems (including ice and steam) in terms of technical advances, economic growth and environmental challenges which have been significantly overlooked in the previous similar studies.
Article
SDG implementation in the industrial sector of Pakistan is significant for its economic growth, sustainable industrialization, innovation, and sustainable production. Integration of solar thermal collectors in the textile industry will encompass sustainable development goals (SDG 7,9,12,13). Meeting these goals in the thermal sector of Pakistan is becoming increasingly challenging due to the limited resources and harmful emissions from conventional fuels. In this study, the technical feasibility of two non-concentrating collectors, Flat Plate Collector (FPC) and Evacuated Tube Collector (ETC) was investigated for the application of preheating of feedwater of boilers. Choosing the better performing collector for a range of regional and climatic variations across Pakistan, a comparative analysis of three fuels (coal, oil, and natural gas) has been carried out by using TRNSYS and RETScreen for economic analysis and GHG emission mitigation, respectively. The overall best results have been observed in Quetta. For this city replacement of coal has shown the highest GHG emission mitigation potential of 182,326 tonnes of CO2 and the highest NPV for oil (1509.4 million PKR) among the three fuels studied. Based on the results, it can be deduced that this work can be further extended to concentrating thermal technologies as well. Since real-time industrial data has been used, the insights will promote solar thermal technology in Pakistan.
Chapter
The energy transition is one of the greatest challenges of our time. While photovoltaics (PVs) became the cheapest technology for generating electricity in many regions, the rising development of ground-mounted PV requires large areas and, hence, competes with other land use forms such as agriculture. Agrivoltaics enables dual use of land for both agriculture and PV power generation considerably increasing land-use efficiency, allowing for an expansion of PV capacity on agricultural land while maintaining farming activities. In recent years, agrivoltaics has experienced a dynamic development mainly driven by Japan, China, France, and Germany. In this chapter, we provide an overview of the current state of agrivoltaics starting with a definition and classification of typical systems. Section 5.2 sheds light on basic agricultural implications in agrivoltaic systems such as light availability, further microclimatic impacts, and crop selection. In Section 5.3, we address typical technical structures and agricultural applications distinguishing between interspace PV and overhead PV systems. Section 5.4 outlines relevant characteristics of PV modules used for agrivoltaics including standard crystalline silicon and thin-film cell technologies as well as emerging module technologies. Section 5.5 provides an economic analysis of agrivoltaic systems based on a location in southern Germany and Section 5.6 summarizes the most relevant facts about the preliminary German standard DIN SPEC 91434 published in April 2021. In Section 5.7, we present the results of a case study on societal implications conducted in southern Germany within the research project APV-RESOLA. Section 5.8 provides brief country profiles of the existing policies around the world while Section 5.9 concludes and outlines perspectives of agrivoltaics.
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The operating temperature of the photovoltaic (PV) cell is essential in converting the renewable radiant energy emitted by the sun into direct current to meet various energy demands. It should be remembered that the photovoltaic efficiency and temperature of the solar PV cell are indirectly proportional. The performance of the PV module can be greatly enriched by minimizing the operating temperature of the semiconducting PV cells, and this is accomplished by removing the surplus heat from the PV module. This paper proposes a novel sandwich- glazed photovoltaic (SGPV) module as an alternative to the standard PV module for overheating protection and assessment of the photovoltaic, thermal, and overall efficiency of the sandwich-glazed photovoltaic thermal (SGPV/T) system. Effects on photovoltaic efficiency and temperature distribution in the SGPV/T system and the standard PV module are also compared. Furthermore, the programmed electrical and thermal models are simulated using MATLAB for comparative analysis. Experiments were conducted in India under the climatic conditions prevailing at Coimbatore (latitude: 11.10ºN; longitude: 76.96ºE). Subsequently, the performance and outlet water temperature of the SGPV/T system are significantly improved with an average photovoltaic, thermal, and overall efficiency of 9.67, 41.34, and 66.78%, respectively.
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This manuscript discusses one of the proposed methods for storing solar energy. Applications of PCMs, mono and binary nanofluids and molten salts as storage materials in solar energy are the major important techniques explained. A summary of various other solar energy storage materials that are currently under application is also presented. This paper overlooks the most current research in this specific field through the main focus of measuring absorption efficiency and effects of different particles on it with changed concentration and assessing thermophysical and storage properties of discussed materials. Presented studies expressed extraordinary efficiency enhancement and other outcomes of these materials. However, there are many problems associated with these materials that hindered their commercialization. These major problems include high costs, corrosion and erosion, pressure drop and friction factor appreciation and instability are also discussed.
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There is a pressing need to decarbonize our energy sector to limit the effects of climate change. Electrification in the buildings and transportation sectors is being proposed as a critical solution. This paper discusses the impact of rapid electrification by comparing the predicted future electricity demand with different scenarios for electricity generation. The effects on primary energy consumption and CO2 emissions are highlighted. Our analysis shows that the composition of the electricity grid plays a key role in determining a better trajectory toward decarbonization. Another key challenge facing the building energy sector is the eventual phasing out of synthetic refrigerants currently used in vapor-compression heating, ventilation, and air-conditioning (HVAC) systems. This article discusses potential solutions for the building energy sector to address these issues and provides engineering solutions that can guide the safe transition to a decarbonized economy without catastrophic shortages of supply or exacerbation of CO2 emissions. Overall, the paper determines that an ∼5.0 quad reduction in building energy usage can be achieved by switching to carbon-free thermal energy where possible and implementing technologies such as desiccant-coated heat exchangers to judiciously manage dehumidification loads. The entirety of the energy saving methods recommended in this article allows for a reduction in predicted carbon emissions by up to 67%, which, combined with carbon capture and other energy saving techniques, could approach a goal of carbon neutral by 2050.
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Solar energy plays the most pivotal role in providing energy demand among all renewable energy resources in today's world. Hence, significant advances are being made to harness solar energy by using ever-evolving technologies such as solar collectors. Evacuated tube collectors have been in the center of attention due to high thermal efficiency and desirable performance in unfavorable weather conditions. This paper provides new insight into how ETSC has changed drastically to improve thermal performance. A full-scale comparison has been drawn between thermosyphon vacuum tube and flat plate units at the commencement to demonstrate the competency and uniqueness of evacuated tube collectors. At the next step, numerous numerical and experimental investigations have been compiled and presented to cover the latest innovations and developments in thermal modifications of evacuated tube collectors concerning the use of PCM, working fluids, and design parameters. Furthermore, to evaluate the thermal efficiency of collectors, mathematical modeling is also presented based on single-tube and the whole collector. Evacuated tube collectors have various residential and industrial applications for water heating, solar drying, solar desalination, and air conditioning which have been discussed extensively. In addition, challenges and obstacles in utilizing evacuated tube collectors have been identified and need to be tackled to reach higher thermal performance. Last but not least, an economic-environmental analysis is presented, which consequently demonstrated that evacuated tube collectors are cost-effective and impose less danger to the environment than flat plate collectors.
Article
Accurate prediction of collector performance is important for optimal planning of solar thermal systems. Here, a novel prediction method combining clustering of data with artificial neural network (ANN) model is presented. A novel all-glass straight-through tube solar collector is employed as reference solar technology. In the present approach, experimental collector performance data was first collected during different weather conditions (sunny, cloudy, rainy days) subject to a clustering analysis to screen out outlier samples. The data was then used to train and verify the neural network models. For the ANN, the Back Propagation (BP) and Convolutional Neural Network (CNN) models were used. For predicting the performance (thermal efficiency) of the solar collector, solar radiation intensity, ambient temperature, wind speed, fluid flow rate, and fluid inlet temperature were used as the input parameters in the model. The prediction accuracy of the neural network models after full-data-screening were superior to that of the pre-screening and partial-screening models. The CNN model provided somewhat better efficiency predictions than the BP model. The R2, RMSE and MAE of the CNN model prediction in sunny conditions with full-screening was 0.9693, 0.0039 and 0.0030, respectively. The average MAPE of the BP and CNN models for all three weather types dropped by 30.7% and 13.8%, respectively, when applying data pre-screening and partial-screening only. The accuracy of the ANN collector prediction model can thus be improved through data clustering, which provides an effective method for performance prediction of solar collectors.
Article
Solar water heating system is inefficient during winter due to the chances of water freezing and higher viscosity at low temperatures. Several investigations are being done to increase the efficiency of the solar water heater using various secondary fluids for different climatic conditions. This paper emphasises on the study of heat transfer and fluid flow behaviour of CO2 based naturally circulated indirect solar water heating system. Subcritical (liquid and vapour) and supercritical CO2 are considered as loop fluid, and the results are compared with water based system. Three-dimensional computational fluid dynamics simulations are carried out for two different weather conditions i.e., winter (278 K) and summer (305 K). Results are obtained for 33° collector inclination angle from horizontal at various operating pressures 50–70 bar for subcritical and 80–100 bar for supercritical CO2. The CO2 based system yields very high Reynolds number (subcritical liquid: ∼160 times; subcritical vapour: ∼204 times; supercritical vapour: ∼260 times) and very high Nusselt number (subcritical liquid: ∼14 times; subcritical vapour: ∼19.5 times; supercritical vapour: ∼48 times) compared to water based system. Supercritical CO2 based system exhibits 12% higher energy efficiency compared to water. Whereas, subcritical vapour based system exhibits 140% higher exergy efficiency relative to water based system.
Chapter
The perovskite-based flexible solar cells are a novel group of photovoltaic devices that have drawn interest because of their considerable opto-electrical features with the inclusion of high carrier motions, tunable bandgaps, good absorption coefficients, long-range porter diffusion lengths, easy manufacturing, and low expense. The perovskite-based flexible solar cells have achieved performances of 18.36% and 22.70% on rigid with poly substrates and fluorine tin-oxide, respectively. These can be compared to those of copper-indium-gallium-selenium and single-crystal silicon solar cells. During a duration of more than 8 years, the perovskite-based flexible solar cells’ photo transformation performance has been developed through adjustments in the device-architecture, and optimization of the absorber and electron/hole transport sheet. In the market, there is a wide range of photovoltaic cells. In the last years, new generation photovoltaic cells from diverse materials have taken their place in the market. In a photovoltaic cell, the primary operating characteristics are efficacy, area, and density characteristics. For perovskite-based flexible solar cells, this study aims to determine the photovoltaic effectiveness and compare the photovoltaic cells manufactured in various kinds with respect to primary operating characteristics. The main contributions of the study are the assessment of the collection of parameters needed in the assessment of solar concentrator cells, definition of their comparative priorities based on expert opinions, and the provision of a straightforward quantitative investigation.
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Solar selective absorbers (SSAs) possess high sunlight absorption (300–2500 nm) and low infrared thermal radiative losses (2.5–25 μm), which are undoubtedly the best choice for photothermal conversion process, and SSAs have been widely used in concentrating solar power, solar water heating, and solar drying. Recently, to promote the realization of “double carbon” goal, SSAs have received widespread attentions, many emerging sustainable applications have been developed. In this review, the recent developments of SSAs and their latest sustainable applications in solar‐driven seawater desalination, multistage solar desalination, atmospheric water harvesting (AWH), wastewater treatment, solar thermophotovoltaics (STPVs), hybrid photovoltaic‐thermal (HPVT), solar‐thermoelectric generators (STEG), personal thermal management (PTM), photothermal catalysis, photothermal deicing, and photothermal sterilization, etc. are systematically summarized. Also, the challenges as well as future opportunities of SSAs are discussion. It is expected that this review will effectively complement the published comments on SSAs and provide more inspirations on sustainable applications of SSAs in the future. The latest developments of solar selective absorbers (SSAs) and their latest sustainable applications in solar‐driven seawater desalination, multistage solar desalination, atmospheric water harvesting, wastewater treatment, solar thermophotovoltaics, hybrid photovoltaic‐thermal, solar‐thermoelectric generators, personal thermal management, photothermal catalysis, photothermal deicing, and photothermal sterilization, etc. are systematically summarized. The challenges as well as future opportunities of SSAs are also discussed.
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One of the current problems is the use of energy obtained from fossil fuels, especially due to the emission of greenhouse gases. An option to replace fossil fuels is the use of alternative energies such as solar or wind energy. The objective of this work is to carry out a thermal and energy analysis of an indirect air heating system that receives energy through solar collectors that operate with water as the thermal fluid used in a food dehydration system, in order to know the efficiency of the system and therefore, make improvements to the circuit, in addition to the characterization of the water storage tank of the system, obtain the amount of energy that can be provided and the behavior of temperatures at different operating flows. According to the methodology, the temperature profile was obtained inside the hot water tank in two modes of operation (heating and energy extraction) reaching temperatures of 50 to 70 ° C, where the optimum temperature for drying is found and in turn reaching an efficiency 84%, compared to a conventional drying system that uses LP gas.
Conference Paper
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The load on a solar water heating system does not usually coincide with the resource availability, hence a means to store collected energy for later use is essential. To avoid problems of freezing in the collector and blockage of the tubes by calcium deposits in hard water areas, various indirect techniques have been devised to connect the collector and the store. A type of indirect system which is common in Australia utilises a concentric heat exchanger between the collector and the storage tank. In this paper, the flow behaviour and heat transfer characteristics in the annulus of a concentric heat exchanger are investigated for a stratified inner cylinder with various inlet conditions using Fluent CFD code. The results are in qualitative agreement with the flow visualization results obtained using dye injection. For the sake of a simpler model for future experimental investigations, computations are also performed for a vertical cavity in order to examine the extent to which the two flows are similar in terms of flow patterns and heat transfer characteristics.
Conference Paper
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The performance of water-in-glass evacuated tube solar water heaters is evaluated using experimental measurements of optical and heat loss characteristics and a simulation model of the thermosiphon circulation in single-ended tubes. The performance of water-in-glass evacuated tube solar collector systems are compared with flat plate solar collectors in a range of locations. The performance of a typical 30 tube evacuated tube array was found to be lower than a typical 2 panel flat plate array for domestic water heating in Sydney.
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The high capital costs associated with heat-pipe evacuated tube solar water heating systems can be reduced by replacing forced circulation with thermosyphon circulation. Currently research on thermosyphon heat-pipe evacuated tube solar water heaters is limited. An experimental investigation of the natural convective heat exchange regime that exists within the manifold chamber of a proprietary heat-pipe evacuated tube solar water was undertaken. This paper presents experimental data from a heat-pipe Evacuated Tube Solar Water Heater (ETSWH) subjected to the Northern Maritime Climate at the University of Ulster’s outdoor solar testing facility located at the Jordanstown campus. The thermal performance of this across solar noon (±30min) was experimentally determined to be comparable to two physical laboratory 10 pin-fin model manifolds constructed to the same dimensions and geometry as the manifold chamber of the heat-pipe ETSWH when operated under steady laboratory conditions. When the surface temperatures of the pin-fins (simulated condensers) in the model manifold were normalised with respect to the lowest most pin-fin in the array the influence of buoyant flow was observed. Similarly to related studies in this field it was found that normalised surface temperatures on downstream pin-fins do not increase monotonically as would be expected if no interactions occur. It was found that at the pin-fin diameter to pitch used in the model manifold that normalised surface temperatures decrease at certain points in the array due to the action of buoyant flow generated from upstream pin-fins which increased heat transfer. Two-dimensional Particle Imaging Velocimetry (2D-PIV) was used to visualise the thermosyphon fluid flow regime. It was observed that the fluid flow regime varied across the model due to interactions between the fluid, chamber walls and pin-fins.
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The flow structure inside the inner tank and inside the mantle of a vertical mantle heat exchanger was investigated using a full-scale tank designed to facilitate flow visualisation. The flow structure and velocities in the inner tank and in the mantle were measured using a Particle Image Velocimetry (PIV) system. A Computational Fluid Dynamics (CFD) model of the vertical mantle heat exchanger was also developed for a detailed evaluation of the heat flux at the mantle wall and at the tank wall. The flow structure was evaluated for both high and low temperature incoming flows and for both initially mixed and initially stratified inner tank and mantle. The analysis of the heat transfer showed that the flow in the mantle near the inlet is mixed convection flow and that the heat transfer is dependent on the mantle inlet temperature relative to the core tank temperature at the mantle level.
Chapter
A model of the two phase flow and heat transfer in a solar collector with fluid undergoing phase change is presented. The model is verified using experimental data published in the literature, and good agreement is found. It is then used to investigate the effects of varying the collector pressure, mass flow rate of the heat removal fluid and liquid level in the collector tubes on the collector efficency.
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This investigation presents a new. design of solar water heater as a pyramid shaped frustum. The proposed design is a compact system in which collectors and a water storage tank are integrated together into one unit. The concept of using the frustum of pyramid as an external shape for collecting the solar radiation and as a container for hot water storage tank are presented. The frustum of pyramid solar water heater has five surfaces, four surfaces represent liquid flat-plate collectors as roof and three sides which received all the solar radiation incident on them. The roof and one of the sides face the south direction but the other sides face the south-east and south-west directions, repectively. The three sides tilted the horizontal plane to 30 degrees while the roof tilted to 15 degrees. The total surface area of the collectors is about of 1.68 m(2) and the capacity of the water storage tank is about 150 litres. The absorber consists of copper tubes formed in a serpentine shape which are connected to the tank by;two openings (inlet and outlet). A regulator is connected to the piping line to control the hot water consumption and the reverse flow after sunset. The thermal analysis of the liquid flat-plate collector and the performance of the solar water heater are derived based on the steady state analysis. A comparison between the compact unit and another type which has an elevated tank is done. The results show that the proposed salar water heater gives good performance and can provide a quantity of hot water of about 175 litres/day at an average temperature range from 40 degrees-60 degrees C depending on the weathering conditions and solar intensity.
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The choice of refrigerant for water chillers used in district cooling plants is subject to some trade-offs because not one of the several leading candidates possesses all the advantages with no disadvantages found in the others. Four different refrigerants are analyzed in this paper for their suitability in large water chillers: R-22 and R-123 (both HCFCs), R-134a (an HFC), and ammonia (R-717). R-22 is a proven refrigerant, but because it will be phased out in the near future, its choice is questionable. R-123 is efficient but its permitted concentration is of the same order of magnitude as ammonia. R-134a is probably the most accepted of the CFC substitutes and is a strong candidate for small and moderate-sized water chillers; however, for large chillers its current high cost and its somewhat lower efficiency than the other refrigerants are disadvantages. Ammonia is a proven refrigerant in the industrial scene and has no damaging effect on the ozone layer nor does it contribute to global warming. While it is efficient and has a very low cost, its major disadvantage is that low concentrations are considered toxic. New approaches to the design of chillers using ammonia are addressing this disadvantage.
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A general procedure is presented for estimating the seasonal performance of solar-assisted heat pumps with refrigerant-filled collectors. The procedure accounts for variations in collector design and orientation and also for heat pump capacity and efficiency. The results from this design procedure for space heating applications are compared against those for both conventional heat pumps and liquid solar systems. The effects of collector area and design, heat pump size and degradation due to cycling, and energy storage are discussed. For space heating, uncovered collector heat pump systems have better performance than both conventional air-source heat pumps and covered collector heat pump systems over a wide range of collector areas. The cooling performance of a collector heat pump system is inferior to that of conventional heat pumps.
Conference Paper
The utilization of renewable energy sources is receiving considerable attention as a non-resource-depleting approach that reduces the emissions of pollutants and green-house gases to the atmosphere. Solar thermal systems have the capability to provide heat in a sustainable way for a variety of applications due to the relatively large range of temperatures that different collector configurations can attain. Most evacuated-tube solar collectors currently found on the market consist of a u-shaped round tube, concentric round tubes in counter flow regime, or a heat-pipe. The external surface in these designs is welded to a thin absorber fin that is covered with a selective coating. This paper analyzes the performance of an evacuated-tube solar collector that contains a U-shaped mini-channel tube. Comparisons of performance with respect to standard u-shaped round-tube solar collector are made. The design of a mini-channel based solar collector without absorber fin is also analyzed and its performance optimized with respect to its geometrical parameters.
Conference Paper
The thermal performance of a Thermosyphon Domestic Solar Water Heater (DSWH) with a vertical storage tank is investigated experimentally. The system is installed on a roof - top of a four person family house and its thermal characteristics is evaluated by means of carefully measuring the temperature distribution of water inside the storage tank, solar collector flow rate and its inlet and outlet temperatures as well as load/consumption outlet and inlet temperatures and the corresponding water flow rate under a realistic operating conditions. The measurements are conducted every hour starting from morning until late night on a daily basis and continued for about 120 days during August until November 2004. It is seen that thermal stratification is well established inside the tank from 11 AM until 10 PM especially during August to September enabling the tank to provide the necessary amount of hot water at an acceptable temperature. However, thermal stratification is observed to start degrading from mid-night until morning when there is no hot water supply from the collector and due to the diffusion of heat from the top hot water layers to the bottom cold region and conduction through tank’s wall. The thermal behavior of the storage tank is also assessed based on both energy and exergy analysis and its first and second law efficiencies are calculated. It is observed that the storage tank under study has an average first law efficiency of 47.8% and is able to supply the required amount of hot water at a proper temperature. The average second law efficiency of the storage tank is observed to be 28.7% and, although is less than its first low efficiency, but is high enough to ensure that the quality of the hot water supply is well preserved. The proper level of second law efficiency is due to the preservation of the thermal stratification inside the storage tank, leading to supply of hot water at highest possible temperature and hence highest possible energy potential. Experiments are also done for no-load conditions when the storage tank only interacts with the collector, without hot water withdrawal from the tank. It is seen that for no-load condition, thermal stratification continuously develops from morning until around 16 PM after which no noticeable changes in the temperature distribution inside the tank is observed.
Article
A 13.6 m2 east-west aligned CPC-collector (compound parabolic concentrator) with flat absorbers, proposed for use in large-area applications, has been built and tested and compared with a flat plate collector. The performance of the CPC at a working temperature of 50°C over ambient can be described by F′ηO = 0.75 and F′UL = 2.5 W m−2 K−1 while the flat plate collector is described by F′ηO = 0.80, and F′UL = 3.3 W m−2 K−1. The large difference in heat loss coefficient is to a large degree explained by absorption of solar radiation in the reflectors in the CPC-collector. The incidence angle dependence of the optical performance of the two collectors showed a similar appearance. Both collector constructions are based on the LGB (long ground based) technology, which allows them to be built in large modules up to 170 m2.
Article
The thermal behaviour of a horizontal cylindrical storage tank has been investigated both experimentally and numerically. Four sets of experiments have been carried out where cold water is injected into the bottom of the tank with three different initial thermal fields. The first one is the tank with initial thermal stratification with bottom temperature the same as the inflow temperature. The second set is the tank with the initial thermal stratification, the bottom being at a relatively higher temperature than the inflow temperature. The third set is an initially heated isothermal tank and the fourth is the same as the first set of experiments except that the straight tube inlet nozzle is replaced by a 30 degrees downward bent divergent conical tube. The above experiments show that better thermal stratification can be obtained using the divergent conical tube as the inlet nozzle due to the diffusion effect of the nozzle. Also a slight improvement in the tank performance has been achieved in the second set of experiments when the initial bottom temperature of the tank is higher than the injected cold water temperature. To check the accuracy of the experimental results two different types of one-dimensional numerical models, namely Turbulent Mixing Model and Displacement Mixing Model have been developed and the results are compared with the experiments. This comparison indicates that the numerical results are in good agreement with the experiments especially at the top of the tank.
Article
A rigid stratifier is investigated theoretically with Computational Fluid Dynamics and experimentally with Particle Image Velocimetry and temperature measurements. The stratifier consists of a main tube with three circular openings. The stratifier is mounted inside a 144 l water tank.During a tank charge test, the investigations show that cold tank water is sucked into the stratifier through the lowest opening. The mixed fluid enters the tank through the top opening.To illustrate the influence of mounting flaps working as “non-return valves” at the stratifier openings, the experiment is repeated with the stratifier with flaps. The results show that the “non-return valves” reduce the unwanted flows into the lowest opening.To quantify how well the stratifier with the flaps works for other flow rates more tank charge tests are carried out. Based on a stratifier efficiency it is found that the stratifier is most efficient for flow rates between 5 l/min and 8 l/min.
Article
There are various types of solar water heater system available in the commercial market to fulfill different customers’ demand, such as flat plate collector, concentrating collector, evacuated tube collector and integrated collector storage. A cost effective cum easy fabricated V-trough solar water heater system using forced circulation system is proposed. Integrating the solar absorber with the easily fabricated V-trough reflector can improve the performance of solar water heater system. In this paper, optical analysis, experimental study and cost analysis of the stationary V-trough solar water heater system are presented in details. The experimental result has shown very promising results in both optical efficiency of V-trough reflector and the overall thermal performance of the solar water heater.
Article
Water heating by utilizing solar energy for domestic use is a well established technique. However, most systems consist of the solar collector and storage tank as separate units and require piping and extra thermal insulation for both. This work considers an integrated system, which is easy to manufacture or to modify the storage tank to operate as a solar collector as well as a storage tank. The system contains a thermal diode to prevent reverse circulation at night-time. A prototype is constructed and a mathematical model is developed to study the thermal performance of the integrated system. It is found that the thermal efficiency of the suggested system is comparable with conventional systems. Also, simulation indicated that the thermal diode significantly reduces heat losses at night-time.
Article
A theoretical and experimental analysis of water jets entering a solar storage tank is performed. CFD calculations of three inlet designs with different inlet flow rates were carried out to illustrate the varying behaviour of the thermal conditions in a solar store. The results showed the impact of the inlet design on the flow patterns in the tank and thus how the energy quality in a hot water tank is reduced with a poor inlet design. The numerical investigations were followed by experiments. A test solar store, similar to the store investigated by numerical modelling was constructed with cylindrical transparent walls so that the flow structures due to the inlet jets could be visualized. With the three inlets, nine draw-off tests with different inlet flow rates were carried out and the temperature stratification in the tank was measured during the draw-offs. The experimental results were used in an analysis using the first and second law of thermodynamics. The results showed how the entropy changes and the exergy changes in the storage during the draw-offs influenced by the Richardson number, the volume draw-off and the initial tank conditions.
Article
This paper extends the current techniques used in the prediction of flat plate solar collector performance for use in the analysis of non-metallic collectors. An analytical model was developed to study the characteristics of these solar collctors which eliminate the need for metals, glass, and special coatings. Using this model, plate efficiency factors are presented for various common non-metallic absorber plate configurations. A parametric study was conducted with emphasis placed on collector plate thermal conductivity and partial transmittance of glazings to long-wave radiation. From the results of this study, it was shown that it is possible to meet or exceed performance levels of conventional metal tube and fin collectors through the use of non-metallic collectors in the low- to medium-temperature range.
Article
The experimental set up for evaluating the performance of a solar collector with a fluid undergoing phase change is described. The effect of insolation and the liquid level on the collector performance has been studied with acetone and petroleum ether 40–60°C. The Hottel-Whillier equation, when modified to include the fraction of liquid level, correlates the experimental data. The collector efficiency increases linearly with liquid level.
Article
In this brief note, we have experimentally measured the temperature stratification in a solar hot water storage tank resulting from a simulated solar heating load. Various modifications using a double chimney device that acts as a thermal diode were examined with the intent of maximizing temperature stratification. The greatest stratification was seen with a unique thermal diode arrangement named the express-elevator design, so-called for the direct hot water path from the bottom third of the tank to the top third. (author)
Article
This paper presents recent developments and state of the art for transcritical CO2 cycle technology in various refrigeration, air-conditioning and heat pump applications. The focus will be on fundamental process and system design issues, including discussions of properties and characteristics of CO2, cycle fundamentals, methods of high-side pressure control, thermodynamic losses, cycle modifications, component/system design, safety factors, and promising application areas. The article provides a critical review of literature, and discusses important trends and characteristics in the development of CO2 technology in refrigeration, air-conditioning and heat pump applications. Advanced cycle design options are also introduced suggesting possible performance improvements of the basic cycle.
Article
Refrigerant-charged passive solar domestic hot water (SDHW) systems, which can be installed even in freezing climates, may achieve the high performance and reliability of direct thermosyphon systems. The prototype was installed in a single-family residence using a stabilized R-11 as the heat transfer fluid. A system analysis was performed based on measured data. The analysis method and preliminary results, which indicate that there is reason to be optimistic about this type of system are discussed.
Article
In this paper the results of the influence of position of the flat plate reflectors made of Al sheet on thermal efficiency of solar thermal collector with spectrally selective absorber are presented. Analytical and experimental results on determination of the optimal position of flat plate solar reflectors during the day time over the whole year period are shown. Both numerical calculation and experimental measurements indicate that optimal angle position of the bottom reflector is the lowest (5°) in December and the highest (38°) in June for collector fixed at β=45oposition. The thermal efficiency of thermal collector without reflectors and with reflectors in optimal position has been determined. Though the thermal efficiency of thermal collector decreases slightly with the solar radiation intensity, the total thermal energy generated by thermal collector with reflectors in optimal position is significantly higher than total thermal energy generated by thermal collector without reflectors. These results show the positive effect of reflectors made of Al sheet and there is an energy gain in the range 35-44% in the summer period for thermal collector with reflectors, which is expected to reduce the cost pay back time.
Article
CO2 is one of the few non-toxic and non-flammable working fluids that do not contribute to ozone depletion or global warming, if leaked to the atmosphere. Tap water heating is one promising application for a trans-critical CO2 process. The temperature glide at heat rejection contributes to a very good temperature adaptation when heating tap water, which inherits a large temperature glide. This, together with efficient compression and good heat transfer characteristics of CO2, makes it possible to design very efficient systems. A heating-COP of 4.3 is achieved for the prototype when heating tap water from 9°C to 60°C, at an evaporation temperature of 0°C. The results lead to a seasonal performance factor of about 4 for an Oslo climate, using ambient air as heat source. Thus, the primary energy consumption can be reduced with more than 75% compared with electrical or gas fired systems. Another significant advantage of this system, compared with conventional heat pump water heaters, is that hot water with temperatures up to 90°C can be produced without operational difficulties.
Article
Solar liquid collectors are potential candidates for enhanced heat transfer, but there are just a few studies focused on this topic. However, enhancement techniques can be applied to thermal solar collectors to produce more compact and efficient designs. This work presents the study of heat transfer enhancement in a tube-on-sheet solar panel with wire-coil inserts, using TRNSYS as the simulating tool. The numerical simulation methodology predicts the thermohydraulic flow behaviour of enhanced and standard tube-on-sheet solar collectors, evaluating the local losses, friction coefficients and Nusselt numbers as functions of the operating parameters. The standard and the enhanced collectors have been simulated under the same ambient, radiant and operating conditions. The standardized efficiency curves according to the standard UNE-EN 12975-2 are provided. The enhanced collector increases the thermal efficiency values by 4.5%. A parametric study was performed to relate the fluid and flow characteristics with the heat transfer enhancement by wire-coil inserts. The simulations were performed for different working fluids (water and propylene glycol/water mixtures) in a mass flow rate range from 15 to 120l/hm2.
Article
The filled-type evacuated tube with U-tube, in which the filled layer is used to transfer energy absorbed by the working fluid flowing in the U-tube, is proposed to eliminate the influence of thermal resistance between the absorber tube and the copper fin of the conventional evacuated solar collector. In this paper, the thermal performance of the filled-type evacuated tube with U-tube was researched by means of theoretical analysis and experimental study. The temperature of the working fluid in the flow direction was obtained, and the efficiency of the evacuated tube was also calculated, based on the energy balance equations for the working fluid in the U-tube. The effects of the heat loss coefficient and the thermal conductivity of the filled layer on the thermal performance of the evacuated tube were studied. In addition, the test setup of the thermal performance of the filled-type evacuated tube with U-tube was established. The evacuated tube considered in this study was a two-layered glass evacuated tube, and the absorber film was deposited in the outer surface of the absorber tube. The results show that the filled-type evacuated tube with U-tube has a favourable thermal performance. When the thermal conductivity of the heat transmission component is λc=100, the efficiency of the filled-type evacuated tube with U-tube is 12% higher than that of the U-tube evacuated tube with a copper fin. The modelling predictions were validated using experimental data which show that there is a good concurrence between the measured and predicted results.
Article
A novel multiple curved surfaces compound concentrator is developed in this paper. It is composed of a parabolic and a flat contour. This new concentrator has a focus at the backside which is extremely useful and convenient for some applications. The reflected rays here are transmitted forward instead of backward as in the conventional parabolic concentrators. The design method of the concentrator is introduced. Some of important parameters are discussed and the value rang of them is determined. Simple comparisons between proposed concentrators and traditional paraboloid and CPC are made. Light rays tracing are carried out in the concentrator.
Article
This paper reports experimental data from, and numerical modelling of, plastic solar collectors fabricated from a novel thermoplastic extrudate. The extrudate, termed as microcapillary film (MCF), consists of an extruded flexible, plastic, film with a parallel array of hollow capillaries running along the film’s length. Experimental investigations were carried out on two laboratory scale solar collectors, illuminated with an infrared lamp, to determine the effects that different process fluids, glazing layers and collector backgrounds had on the overall heat recovery of the collector. The experiments also examined the effects that fluid flow rate, collector length and capillary wall thickness had on the heat recovery. Heat recovery of a similar order of magnitude to commercially available collectors was attained. A finite difference model was developed to calculate the temperature gain and the heat recovery of these solar collectors as a function of design and operating parameters. This model was successfully validated against experimental data, and was able to quantitatively predict the performance of these devices. Results from this investigation suggest that MCFs perform heat exchange duties of this type well, with the potential to make a low-cost, lightweight, mechanically flexible, solar collector.
Article
The paper presents the thermal performance of a solar collector with TPNR (thermoplastic natural rubber) tubing as the absorber plate. A commercial blend of TPNR (dynamically vulcanised natural rubber—DVNR 9011) was used as the absorber plate which was of the parallel type and satisfies the test conditions indicated by the standard GB 4271-84. The values of the thermal performance parameters FR(τα) and FRUL were 0.72 and 9.67, respectively. A domestic hot water thermosyphon solar collector system with a vertical tank was used for performance monitoring. The thermosyphon hot water system is capable of producing temperature output up to 65°C for a typical day of 550W/m2. For monitoring purposes, two methods were used. In the first method, the storage tank was filled up with water the night before the test and the temperature readings were recorded for the next day’s test. The end-of-the-day temperature rise in the storage tank and the accumulated total solar radiation values were also noted over the same period. The test were repeated under varied environmental conditions that covers low and high radiation intensities. A temperature rise of 15°C in the storage tank was obtained for this system at an accumulated solar radiation of 4.5kWh/m2. In the second method, the temperature readings without draw-off or draining of the hot water from the storage tank were recorded for 6 days and a temperature of more than 60°C can be achieved by the storage tank. Hence, this system has the potential to be used as domestic thermosyphon hot water system.
Article
The paper presents the steady state performance of two types of commercially available evacuated-tube heat-pipe solar collector that were tested under the meteorological conditions of Singapore. The tests were made in arrays of collectors in contrast with the normal tests performed under controlled laboratory conditions. A theoretical model is also presented to predict the collector efficiency as well as the collectable energy during a steady state test. Within the range of expected coolant temperatures, the efficiency and the heat loss coefficient of collectors are measured and a linear expression can adequately depict their characteristics.
Article
The feasibility of reducing the cost of solar water heating systems by using polymer heat exchangers is illustrated by comparing thermal performance and cost of heat exchangers made of nylon, cross linked polyethylene (PEX), or copper. Both tube-in-shell heat exchangers and immersed tube banks are considered. For the thermal analysis, the tube geometry and the arrangement of tubes are fixed and the heat transfer surface areas required to provide 3000 and 6000 W are determined. Thermal performance is estimated using published heat transfer correlations. The nylon heat exchanger outperforms the PEX design, primarily because nylon is a stronger material. Consequently, the ratio of diameter to wall thickness required to withstand the operating pressure is greater and the conduction resistance across the polymer wall is less. The cost of nonoptimized nylon heat exchangers is about 80 percent of the cost of heat exchangers made of copper. Significant additional work is required to optimize the tube arrangement and geometry and to validate our initial estimates of thermal and economic performance.
Article
Tubular absorbers installed inside evacuated tubes represent an increasingly common design for low-temperature solar collectors. Much work has been done on the subject of solar radiation received by flat-plate collectors; much less has been done for tubular collectors. In this paper we present an algorithm to estimate irradiance impinging on tubular arrays. Key examples are provided to illustrate the difference of energy collected between flat-plate and tubular collectors.
Article
An experimental flat plate solar collector operating in conjunction with a closed-end oscillating heat pipe (CEOHP) offers a reasonably efficient and cost effective alternative to conventional solar collector system that use heat pipes. The CEOHP system described in this study relies on the natural forces of gravity and capillary action and dose not require an external power source. The flat plate collector consisted of a 1mm thick sheet of black zinc covered by a glass enclosure with a collecting area of 2.00×0.97m2 , an evaporator located on the collecting plate, and a condenser inserted into a water tank. A length of 0.003 ID copper tubing was bent into multiple turns at critical points along its path and used to channel the working fluid throughout the system. R134a was used as the working fluid. Efficiency evaluations were conducted during daylight hours over a two month period and included extensive monitoring and recording of temperatures with type-K thermocouples placed at key locations throughout the system. The results confirmed the anticipated fluctuation in collector efficiency dependant on the time of day, solar energy irradiation, ambient temperature and flat plate mean temperature. An efficiency of approximately 62% was achieved, which correlates with the efficiency of the more expensive heat pipe system. The CEOHP system offers the additional benefits of corrosion free operation and absence of freezing during winter months.
Article
A solar collector using supercritical CO2 as working fluid is proposed in this paper. In order to investigate and estimate the CO2-based solar collector, an experimental set-up was constructed. Of particular interest of this paper are the basic collector characteristics, such as CO2 temperature and pressure in the collector, CO2 flow rate, and collector performances. The collector has been tested under various weather conditions. The results show that the CO2 temperature, CO2 pressure and mass flow rate increase with the solar radiation, which is different from those of traditional solar collector using liquid as working fluid. The solar radiation has influence on the CO2 states, being liquid, liquid-gas or supercritical state in the test, furthermore, affects the CO2 mass flow rate. The annually-averaged collector efficiency is found to be above 60.0% in the case of supercritical CO2 as working fluid, which is much higher than that of water-based solar collector. This study shows the potential of the supercritical CO2-based solar collector in the field of solar thermal utilization.
Article
The thermal performance of a glass evacuated tube solar collector is numerically and experimentally investigated. The solar collector considered in this paper consists of a two-layered glass tube and an absorber tube. Air is used as the working fluid. The length and diameter of this glass tube are 1200 and 37mm, respectively. Four different shapes of absorber tubes are considered, and the performances of the solar collectors are studied to find the best shape of the absorber tube for the solar collector. Beam irradiation, diffuse irradiation, and shade due to adjacent tubes are taken into account for a collector model to obtain a realistic estimation. In addition, a single collector tube with only beam irradiation is studied as a simplified model, and the results of the simplified model are compared to those of the collector model to identify the difference between these two models. The performance of a solar collector is affected by the shape of the absorber, incidence angle of solar irradiation, and arrangement of collector tubes. The results obtained from the simplified model are very different from those from the collector model, which considered not only beam and diffuse irradiation but also shade due to adjacent tubes.
Article
The impact of the optical properties on the annual performance of flat plate collectors in a Swedish climate has been estimated with the MINSUN program. The collector parameters were determined with a theoretically based calculation program verified from laboratory measurements. The importance of changes in solar absorptance and thermal emittance of the absorber, the addition of a teflon film or a teflon honeycomb, antireflection treatment of the cover glazing and combinations of these improvements were investigated. The results show that several improvements can be achieved for solar thermal absorbers. A combined increase in absorptance from 0.95 to 0.97 and a decrease in emittance from 0.10 to 0.05 increase the annual performance with 6.7% at 50 °C operating temperature. The increase in performance by installing a teflon film as second glazing was estimated to 5.6% at 50 °C. If instead a teflon honeycomb is installed, a twice as high performance increase is obtained, 12.1%. Antireflection treatment of the cover glazing increases the annual output with 6.5% at 50 °C. A combination of absorber improvements together with a teflon honeycomb and an antireflection treated glazing results in a total increase of 24.6% at 50 °C. Including external booster reflectors increases the expected annual output at 50 °C to 19.9–29.4% depending on reflector material.
Article
The integration of solar collectors in buildings should be compatible with the architectural design, and solar collectors with colored absorbers would be aesthetically preferable. In our laboratory we constructed and tested flat plate solar collectors with colored absorbers for water heating applications. The study includes collectors in their typical form with the protective glazing, and also collectors without glazing. Unglazed solar collectors are not widely used, although they are cost effective solar devices, suitable for low temperature thermal applications. We tested outdoors the constructed models, glazed and unglazed, with black, blue and red brown absorbers. In order to overcome the high thermal losses of the unglazed collectors and the low optical efficiency of the colored absorbers, we used flat booster reflectors. The additional solar radiation input from the reflectors increases the thermal energy output of the collectors, improving their performance. Theoretical steady state efficiency curves are also given for collectors with or without glazing. The presented experimental and theoretical results determine the range of the effective operation of the proposed solar collector types, which can be used in a variety of applications, instead of glazed or unglazed solar collectors with a black absorber.
Article
The most commonly used absorbers in flat-plate collectors are manufactured as finned tubes. In this article, an alternative design is investigated: the absorber consists of a rectangular, narrow duct, in which the fluid contacts the entire surface. Under the conditions of fully developed laminar flow and negligible heat resistance of the absorber plate material, relations are developed to calculate the temperature distribution within the fluid. These results are used to derive a formula for the collector efficiency factor F' of narrow-duct absorbers, which is then evaluated for water and a commonly used glycol antifreeze liquid as the collector fluid. Finally, the optimisation of narrow-duct absorbers is investigated with consideration of the thermal heat gained by the collector and primary energy consumed by the pump of the solar system due to the pressure drop in the absorber. It is concluded that duct heights in the range of 3–6 mm should be chosen. Collector efficiency factors F' around 0.98 may be expected.