The current-voltage characteristics of solar cells, under
illumination and in the dark, represent a very important tool for
characterizing the performance of the solar cell. The PC-ID computer
program has been used to analyze the deviation of the dark
current-voltage characteristics of p-n junction silicon solar cells from
the ideal two-diode model behavior of the cell, namely the appearance of
“humps” in the I-V characteristics. The effects of the
surface recombination velocity, the minority carrier lifetimes in the
base and emitter regions of the solar cell, as well as the temperature
dependence of the I-V characteristics have been modeled using PC-ID. It
is shown that the “humps” in the I-V characteristics arise
as a result of recombination within the space-charge region of the solar
cell, and occur when conditions for recombination are different from the
simple assumptions of the Shockley-Read-Hall theory
A computer model and a methodology has been developed to perform
value analysis for small, low-temperature binary geothermal power
plants. The value analysis method allows for incremental changes in the
levelized energy cost (LEC) to be determined between a baseline plant
and a modified plant. Thermodynamic cycle analyses and component sizing
are carried out in the model followed by economic analysis which
provides LEC results. The emphasis of the work has been on evaluating
different types of heat rejection systems
Computer simulation is an increasingly popular tool for determining the most suitable hybrid energy system type, design and control for an isolated community or a cluster of villages. This paper presents the development of the optimum control algorithm based on combined dispatch strategies, to achieve the optimal cost of battery incorporated hybrid energy system for electricity generation, during a period of time by solving the mathematical model, which was developed in Part I. The main purpose of the control system proposed here is to reduce, as much as possible, the participation of the diesel generator in the electricity generation process, taking the maximum advantage of the renewable sources available. The overall load dispatch scenario is controlled by the availability of renewable power, total system load demand, diesel generator operational constraints and the proper management of the battery bank. The incorporation of a battery bank makes the control operation more practical and relatively easier.
Wind energy conversion systems have become a focal point in the research of renewable energy sources. This is in no small part due to the rapid advances in the size of wind generators as well as the development of power electronics and their applicability in wind energy extraction. This paper provides a comprehensive review of past and present converter topologies applicable to permanent magnet generators, induction generators, synchronous generators and doubly fed induction generators. The many different generator-converter combinations are compared on the basis of topology, cost, efficiency, power consumption and control complexity. The features of each generator-converter configuration are considered in the context of wind turbine systems
In this paper indium is examined for use as an electrical and optical dopant with the n-type silicon wafer to fabricate the In-doped silicon (n) structure. The subgap response of the resulting structure is particularly strong and extends to wavelengths up to 1100 nm, and more. While the response of the structure is very poor at the visible region. The structure has a maximum external and internal quantum efficiency at wavelength equal to 1100 nm
To date, many traditional solar home systems (SHS) have consisted of separate components which required assembly by trained individuals and were also more susceptible to failure and maintenance. As a result, many SHSs in remote areas have not fulfilled their expected lifecycles or simply have not functioned at all. Thankfully, a solution to these problems has arrived - the newly developed integrated solar home system (I-SHS). Within this new system all components such as the support structure, foundation, PV modules, charge controller, DC-AC converter and wiring are pre-assembled by the manufacturer. This eases installation and maintenance resulting in a reduction of cost and failure. Additionally, electrical yield was increased by 9% by a significant reduction of operating cell temperature. This was achieved by an integrated water tank, serving as a cooling unit and also providing the system's foundation. This measure is neither expensive nor energy intensive, improves output of the system in an unproblematic way, and also allows use of the heated water.
The BMFT and the State governments jointly started a
“Thousand Roofs Programme” in September 1990. At first, this
programme was limited to the territory of the former West Germany. In
July 1991, the extension to the new Federal States was announced. In the
programme the installation of 2250 small (1-5 kWp) grid-connected PV
systems on the roofs of one or two-family houses is being sponsored.
Federal and State grants were provided for the actual system costs to an
upper limit of DM 27000 per kWp. The grant proportion was 70%, 50% of
the system costs from Federal and 20% from State funds
Direct conversion of biomass-derived syngas (bio-syngas) to dimethyl ether (DME) at pilot-scale (100 t/a) was carried out via pyrolysis/gasification of corncob. The yield rate of raw bio-syngas was 40–45 Nm3/h with less than 20 mg/Nm3 of tar content when the feedrate of dried corncob was 45–50 kg/h. After absorption of O2, S, Cl by a series of absorbers and partial removal of CO2 by the pressure-swing adsorption (PSA) unit sequentially, the obtained bio-syngas (H2/CO≈1) was directly synthesized to DME over Cu/Zn/Al/HZSM-5 catalyst in the fixed-bed tubular reactor. CO conversion and DME space-time yield (STY) were 67.7% and 281.2 kg/mcat3/h respectively at 260 °C, 4.3 MPa and 3000 h−1(GHSV, syngas hourly space velocity). Synthesis performance would be increased if the tail gas (H2/CO > 2) was recycled to the reactor when GHSV was 650–3000 h−1.
An automatic global and direct solar spectral irradiance system has been designed based on two LICOR spectroradiometers equipped with fibre optics and remote cosine sensors. To measure direct irradiance a sun tracker based on step motors has been developed. The whole system is autonomous and works continuously. From the measurements provided by this system a spectral irradiance database in the 330–1100 nm range has been created. This database contains normal direct and global horizontal irradiances as well as diffuse irradiance on a horizontal plane, together with total atmospheric optical thickness and aerosol optical depth.
ISO 14000 has attracted interest from industry, international organizations and governments around the globe. Policy-makers and industry both appear to be looking to the standards as a key component of a new paradigm for cooperation between regulators and industry. This realization seems to have resulted from a growing awareness that the fragmented, reactive approach to environmental management in the past has not produced optimal results. Businesses are realizing the value of integrating their compliance procedures for each regulation into a broader system. Compliance problems can often be linked to system problems such as inadequate training, lack of responsibility at the right level, inadequate data, and other related causes. An effective Environmental Management System (EMS) eliminates these pitfalls. The evolution of the EMS is being shaped by market forces, ISO 9000, regulatory shifts, public awareness, and cost implications for ISO certifications. The transformation of these management practices is not limited to industrialized countries. In anticipation of the non-tariff trade barriers that could be erected as a result of these standards, many developing countries are seeking avenues of compliance with ISO 14000's requirements. Egypt should be concerned with the implementation of this system, for firms in countries of the European Community (EC) have been given explicit instructions by the three prevalent European standard-setting organizations to “familiarize” themselves with the requirements of ISO 14000. This paper will focus primarily on the expected effects of ISO 14001
The achievement of the proposed bioenergy objectives and targets for the E.U. (210 M. TOE/year ≈ 12% total gross energy consumption by the year 2010) are indeed very challenging.At present, the contribution of bioenergy is 44 M. TOE/year (∼ 3% of the total consumption). Furthermore, a significant export volume of E.U. bioenergy technology is expected as high as 6 billion ECU/year (year 2010) with the creation of many new industrial manufacturing SMEs (150–200) and about 200,000 direct and indirect new jobs. The recommended high level of bioenergy activity in the E.U. will also open many additional job opportunities (∼ 2 million in a longer term) with specific investment of about 150,000 – 230,000 ECU/job. The consequent CO2 reduction is estimated at 255 million ton/year in the year 2010.The most promising markets are: •■ the heat, with a contribution of 75 M. TOE/year is estimated•■ the power generation, with a contribution of 230 TWh/y•■ bioethanol/biomethanol (∼7 million TOE/year).
India's Renewable Energy Programme is the largest and the most extensive among the developing countries of the World. The increased use of renewable energy technologies has been facilitated by a variety of policy and support measures from the Government of India (GoI). The programme is administered by the Ministry of Non-Conventional Energy Sources (MNES) - the nodal ministry of the GoI, entrusted with the responsibility of policy making, planning, promotion and coordination of various aspects of renewable energy.The need to optimize utilization of India's vast potential for energy generation from renewables and to alleviate the severe power crunch faced by the country requires the integration of renewable energy into the national energy planning thereby enabling the creation of a balanced energy-mix. This in turn calls for taking renewable energy technologies beyond the stage of research, development and demonstration to commercialization through appropriate financing mechanisms. It was to this end that the MNES set up the Indian Renewable Energy Development Agency Ltd. (IREDA) in 1987.IREDA's mandate is to develop, promote, support and extend financial assistance to renewable energy projects. In its first decade of operation, IREDA has committed financial assistance to the tune of US$ 397 million for renewable energy projects and is the recipient of several multi-lateral and bi-lateral assistance's.The presentation will discuss the accomplishments of IREDA and the barriers faced in its efforts to support and catalyze the commercialization of renewable energy technologies through innovative and well structured programmes.
In this paper numerical simulation has been used to predict the effect of the thickness and aluminium (Al) mole fraction of an AlGaAs layer, used as a window for a p+–n–n+ GaAs solar cell under AM0 illumination and exposed to 1 MeV electron irradiation. Such solar cells are used in satellites and undergo severe degradation in their performance due to induced structural defects. The irradiation-induced defects are modelled as energy levels in the energy gap of GaAs. To predict this effect, the spectral response is evaluated for different electron irradiation fluences for two types of cells. In the first a narrow Al0.31Ga0.69As window is a small part of the p+ layer while in the second type the whole window is an AlxGa1−xAs layer with a gradual Al mole fraction. The obtained results show that the AlxGa1−xAs window with a gradual Al mole fraction improves the resistance of the solar cell to electron irradiation especially in the short wavelengths range.
Civilization has embraced a highly refined essence of culture for well over 2,000 years. Commerce and quality of life have danced in a delicate and at times bold interplay throughout the evolution of humankind. Yet, never so precariously as it does, today.The earth with its abundant blessings and resources sway on a pendulum in orbit between the drive for survival and the corruptibility of commerce. Decisions regarding global resources are now - more than ever - entwined with the very essence of global survival. We must put responsible energy products in reach and within budget, today.Sound market deployment of building-integrated photovoltaics are focused within core industrialized nations where the technology and related systems may be proven on a broad scale with closely monitored installations primarily self-financed with Solar Bond incentives. The 100 Headrick Solar-Voltaic Dome Power Stations By 2000 Program advances a unique mid-size 2,100 m2 (21,000 SF) solar array increasing peak output on an acre four times from 60 kWp to 262 kWp (at 1 kWp per 8m2) with 3,400 m2 leasable.Formal ceremonial signing of this commitment by leaders of the United States, the European Commission and Japan is an important step to encourage the commercial real estate industries of these industrialized nations to advance this Program assuring photovoltaics timely achieves status as a World Trade Commodity of the 21st Century.
EOLE 2005 has been launched in July 1996 by the French Ministry of Industry, Electricité de France and ADEME (Agency for Environment and Energy Management). The Ministries of Research and Environment are participating also in this programme. The purpose is to create an initial market in France for wind power generation in order to evaluate the cost-effectiveness and the competitiveness of the wind energy compared to other energy sources by 2005. The installed capacity will reach at least 250 MW and possibly 500 MW.
Cyprus is a small island situated in the north-eastern Mediterranean with no indigenous conventional energy sources, away from interconnected networks of electricity and gas. Recently, Cyprus won the prestigious World Renewable Energy Congress Trophy for its remarkable efforts and initiatives to increase the contribution of renewable energy sources (RES) to the county's energy mix. This paper presents the energy system of Cyprus, analyses and reviews the energy policy and the various measures taken by the government for the development and support on the use of RES in the island, which had a decisive role on the judges’ decision for the nomination of the award.
The 1993 world shipments increased only 6.7% from 57.9MW in 1992 to 60.69MW in 1993. European shipments increased 1% from 16.4MW in 1992 to 16.55MW in 1993. U..S. shipments increased 24.0% to 22.44MW and Japanese shipments decreased 8% to 17.3MW. The status of all major PV module producers will be summarized. New entrants in the thin film area include: Golden Photon (CdTe), Solar Cells Inc. (CdTe), United Solar Systems (triple-stack amorphous silicon), and B.P. Solar (CdTe). In the silicon crystal area, plant expansions have been made by Siemens Solar Industries, B.P. Solar, and Solec. New crystal silicon entrants include: Astropower, Texas Instruments, Nukem, and Gallivare. Potential capacity increases by 1996 of 75–100MW are described. Module performance (efficiency and warranty), and manufacturing costs will be summarized and forecast to 2010. In the limit, the sliced silicon product tends to approach profitable prices of $2.00 per watt, while several thin-film options and concentrators can be manufactured with profitable prices less than $1.50 per watt. The world market for PV modules is summarized by market sector and forecast to 2010 under two scenarios -- “Business as Usual” and “Accelerated“. Under the Business as Usual assumptions, world PV module shipments are forecast to be 195 MW in 2000 and 800MW in 2010. The Accelerated scenario forecasts world module shipments in 2000 to be 440 MW and 4000 MW in 2010. Module shipments for the last four years have been growing at a rate .
This paper considers biodiesel production from residues; tallow and used cooking oil (UCO). The tallow system is more complex involving two processes. The first process is rendering in which tallow (animal fat) and Meat and Bone Meal (MBM) are produced from the slaughter of cattle. MBM is assumed as a thermal energy source for cement manufacture and thus is not used for biodiesel production. The second process is biodiesel production from tallow. Three methodologies are employed to examine sustainability of the biodiesel. The no allocation approach assigns all the parasitic demands to the tallow; thus all energies required to make both MBM and tallow are associated with the tallow biodiesel. The resulting energy balance is negative. The substitution approach allocates the energy in MBM (used to produce cement) to tallow biodiesel. This results in the net energy being greater than the gross energy. The allocation by energy content method divides the parasitic demands of the rendering process between tallow and MBM by energy content. The parasitic demands of the biodiesel process are divided by energy content of the biodiesel, glycerol and K-fertiliser. For tallow biodiesel this yielded a net energy value of 38.6% of gross energy. The same method generated a net energy value of 67% for UCO biodiesel. More importantly the recommended method (allocation by energy content) generated a value of 54% greenhouse gas (GHG) emission savings for tallow and a value of 69% for UCO. Plants commencing after 2017, need to have a 60% GHG emission savings, to be considered sustainable. Thus a facility treating both feedstocks would need to treat a maximum of 60% tallow to be considered sustainable after 2017.
A great number of daylighting research activities including investigations of innovative daylighting systems, lighting controls, and development of daylighting design tools are being conducted in Australia, North America, and Europe. There is a strong need for coordination and sharing of the experience from these activities, and for transformation of the achievements into practical building design guidance. International collaboration is necessary for the establishment of procedures for the characterization and evaluation of daylighting and lighting control system performance under the very diverse nature of sky conditions throughout the world, and it was on this basis that IEA Task 21 started in 1995. Task 21 is a comprehensive collaborative research effort, involving more than 40 institutions from 16 IEA countries, under the Solar Heating & Cooling Programme of the International Energy Agency. The paper reports on the work of this huge international daylighting Task, with only 12 months to go of its four-year duration, describing how the work hopefully will influence on future building design.
Comparison of two techniques for wind speed forecasting in the South Coast of the state of Oaxaca, Mexico is presented in this paper. The Autoregressive Integrated Moving Average (ARIMA) and the Artificial Neural Networks (ANN) methods are applied to a time series conformed by 7 years of wind speed measurements. Six years were used in the formulation of the models and the last year was used to validate and compare the effectiveness of the generated prediction by the techniques mentioned above. Seasonal ARIMA models present a better sensitivity to the adjustment and prediction of the wind speed for this case in particular. Nevertheless, it was shown both developed models can be used to predict in a reasonable way, the monthly electricity production of the wind power stations in La Venta, Oaxaca, Mexico to support the operators of the Electric Utility Control Centre.
Energy is a vital input for economic and social development of any country. With increasing industrial and agricultural activities in the country, the demand for energy is also rising. Solar, wind and biomass are accepted as dependable and widely available renewable sources of energy. Development of an energy model will help in the proper allocation of these renewables in meeting the future demand of energy in India. The present work deals with the development of an Optimal Renewable Energy Model (OREM) for the effective utilisation of renewable energy sources in India for the year-2020-21. The objective of the Optimal Renewable Energy Model (OREM) was minimising cost/efficiency ratio based on social acceptance, reliability, demand and potential constraints. The OREM model allocated renewable energy sources for different end-uses such as lighting, cooking, pumping, heating, cooling and transportation for the year 2020-21.
The UNESCO Engineering Education and Training Programme is currently focusing its priorities on training of engineering students (although much of the output is suitable for advanced undergraduates) and working engineers requiring retraining or updating. To meet the needs especially for educational materials for developing countries and for distance-learning purposes, a multi-media “Learning Package” is in preparation which consists of a textbook, multi-media products and software for self-training and distance learning. It is intended to train students in the field of renewable energies with some dozen packages in preparation or for which half of the textbooks have already been published.
A preliminary solar–hydrogen energy system for the United Arab Emirates (UAE) has been proposed to bridge the gap between oil and natural gas demand and supply in the 21st century, and to meet the country's share in the energy market. In our study, we quantitatively consider the benefits of such an energy system on the overall energy situation in the UAE. The variables considered include population, energy demand, energy production, income from sales of fossil fuels and hydrogen energy, photovoltaics area, and total land area required for installing such a system. Our study indicated that the UAE would fail to meet its share in the oil market demand by the year 2015, while in the case of natural gas it will be by the year 2042. In order to maintain its share in the world energy market, we propose that hydrogen be gradually introduced to meet the demand. The income generated by hydrogen energy would account for 90% of the nation's total income if such a system were utilized. Our analysis could be greatly influenced by several factors such as future government projects related to fossil fuel production and increasing diversification in the economy of the country.
In most developing countries more than 25% of total energy use comes from biofuels. In Ghana, the figure is between 70–80%. Bioenergy is mainly used for cooking and heating, and is also important in rural or cottage industries. As a developing country, Ghana's economic growth remains coupled to the availability and supply of energy. About 29% of this energy is obtained through hydropower and imported petroleum. The two hydropower installations generate about 1102 MW annually mainly for domestic and industrial uses. At the current 3.0% average annual population growth rate, a population of about 35 million is expected by 2025. Coupled with the country's efforts to promote industrialisation, future energy demand is expected to increase severalfold. This paper provides an overview of Ghana's current energy situation and discusses the role of bioenergy in the future energy demand of the country. The paper concludes with a recommendation for a major shift in energy policy to accommodate the conversion of biofuels into versatile energy carriers in a decentralised system to meet the energy requirements of the people and to provide a basis for rural development and employment.
“Solar Chemistry and Solar Materials Research” is one important task of the “Solar Energy Association North Rhine–Westphalia, Germany”. Numerous individual projects have been carried out which address the construction and operation of a high-flux solar furnace, solar chemical engineering, and solar materials research. Almost 10 years of research and development have led to significant progress. This paper reviews the scope of work in solar chemistry and summarizes the results. The authors present perspectives for commercialization and address open questions and needs for further research and development.
Current approaches to energy are unsustainable and non-renewable. Implementing sustainable energy strategies is one of the most important levers humankind has for creating a sustainable world. Future energy policies should put more emphasis on developing the potential of energy sources, which should form the foundation of future global energy structure. The FAO, in support of the Sustainable Rural Environment and Energy Network (SREN), is developing a concept for the optimisation, evaluation and implementation of integrated renewable energy sources for rural communities.
New and renewable fuels are the major alternatives to conventional fossil fuels. Biomass in the form of agricultural residues is becoming popular among new renewable energy sources, especially given its wide potential and abundant usage. Pyrolysis is the most important process among the thermal conversion processes of biomass. In this study, the production of bio-oil and biochar from rapeseed cake obtained by cold extraction pressing was investigated and the various characteristics of biochar and bio-oil acquired under static atmospheric conditions were identified. The biochar obtained are carbon rich, with high heating value and relatively pollution-free potential solid biofuel. The bio-oil product was presented as an environmentally friendly green biofuel candidate.
In the present work, the aerodynamic performance prediction of a unique 30 kW counter-rotating (C/R) wind turbine system, which consists of the main rotor and the auxiliary rotor, has been investigated by using the quasi-steady strip theory. The near wake behavior of the auxiliary rotor that is located upwind of the main rotor is taken into consideration in the performance analysis of the turbine system by using the wind tunnel test data obtained for scaled model rotors. The relative size and the optimum placement of the two rotors are investigated through use of the momentum theory combined with the experimental wake model. In addition, the performance prediction results along with the full-scale field test data obtained for C/R wind turbine system are compared with those of the conventional single rotor system and demonstrated the effectiveness of the current C/R turbine system.
Urban form, i.e., the layout, density, shape and orientation of buildings within the street grid of a city, affects greatly the potential of using renewable energy sources such as sun and wind for electricity production and climatisation of buildings. This paper outlines the framework of the European research Project PRECis (assessing the Potential for Renewable Energy in Cities) and, in particular, the role of the Polytechnic University of Turin in that Project.
The conventional module has many deficiencies during its long-term operation on environmental conditions. Examples of such deficiencies are cracked cells, interconnection failure and degradation of the electrical output power. Also, the module is not repairable, once one cell is degraded the module needs to be replaced. In this work the fabrication and testing of the 3FPT module is presented. The 3FPT module is a newly developed photovoltaic module structure, which overcomes the drawbacks of the conventially existing modules and uses commercially available materials in Egypt. The 3FPT module consists of three plates; the front cover, cells adhered to substrate and the back cover. A 0.065 m2 photovoltaic module is fabricated using four single crystal cells each of 0.102 m diameter. The tests carried out on the 3FPT module after fabrication are X-ray radiography examination, illumination measurements, dark measurements, electrical isolation test, electrical performance test, non-destructive tests, environmental test, thermal cyclic test, humidity test, thermal shock test and cyclic pressure loading test. An experimental setup was arranged to gather actual temperature measurement data for the different 3FPT module encapsulation layers of interest. The temperature measurement data were recorded every half hour from 10 a.m. to 3 p.m. during November and December of 1997 in the Cairo area. Also, an experimental setup is arranged to measure the transmissivity and reflectivity behavior for different front cover materials. The results of those tests and measurements leads to the optimum design criteria of the 3FPT module with simple fabrication technique and good performance.
Interest in renewable and clean energies such as hydrogen has increased because of the high level of polluting emissions, increasing costs associated with petroleum and the escalating problems of global climate change. In the presence of a light source, a microbial photosynthetic process provides a system for the conversion of some organic compounds into biomass and hydrogen. Using Rhodopseudomonas palustris as a cell-factory, hydrogen photo-evolution was investigated in a photobioreactor (PBR) irradiated either from one or two opposite sides. Irradiating the photobioreactor from only one side, in the presence of malic acid, a reactor hydrogen production of 2.786 l(H2) PBR−1 was achieved. When the PBR was irradiated from two opposite sides, hydrogen photo-evolution increased to 3.162 l(H2) PBR−1. Experiments were carried out using inoculum from either the retardation or the exponential growth phases. Using the latter, the highest hydrogen photo-evolution rate based on the bacteriochlorophyll (Bchl) concentration was achieved (3295 μl(H2) mg (Bchl−1 h−1). The hydrogen to biomass ratio (rg) was 1.91 l g−1 in the medium containing malic acid and 1.07 l g−1 in that containing acetic acid. It was found that the hydrogen production rate was higher with malic than with acetic acid. Although photobiological hydrogen production cannot furnish alone the greater and greater world requirements of clean renewable energy, it is desirable that photobiological hydrogen technology will grow, in the near future, because photobioreactors for bio-hydrogen production can be positioned in fringe areas without competition with agricultural lands.
A detailed technical cost analysis has been conducted on a generic 45-m wind turbine blade manufactured using the vacuum infusion (VI) process, in order to isolate areas of significant cost savings. The analysis has focused on a high labour cost environment such as the UK and investigates the influence of varying labour costs, programme life, component area, deposition time, cure time and reinforcement price with respect to production volume. A split of the cost centres showed the dominance of material and labour costs at approximately 51% and 41%, respectively. Due to the dominance of materials, it was shown that fluctuations in reinforcement costs can easily increase or decrease the cost of a turbine blade by up to 14%. Similarly, improving material deposition time by 2 h can save approximately 5% on the total blade cost. However, saving 4 h on the cure cycle only has the potential to provide a 2% cost saving.
This paper summarises the first eight months of monitoring of the PHA BONG photovoltaic generation project, a 500 kWp photovoltaic pilot plant, in Mae Hong Son province, Thailand. The local grid in this remote area in the North West of Thailand is very limited in its capacity and cannot be enlarged. It has been in operation since 20 March 2004 by feeding into 400 VAC, 22 kV medium voltage grid. The system consist of a photovoltaic array 1680 modules (140 strings, 12 modules/string; 300 W/module), power conditioning units and battery converter system. During the first eight months of this system's operation, the PV system generated about 383,274 kWh. The average of generating electricity production per day was 1695.9 kWh. It ranged from 1452.3 to 2042.3 kWh. The efficiency of the PV array system ranged from 9 to 12%. The efficiency of the power conditioning units (PCU) is in the range from 92 to 98%. The final yield (YF) ranged from 2.91 to 3.98 h/d and the performance ratio (PR) range from 0.7 to 0.9.
The aim of this article is to describe how closely PV grid-connected inverters (of around 5 kW) operate at the actual maximum power point. These inverters could be installed at any low voltage, PV grid-connected systems. To carry this study out, twelve 50 Hz single-phase inverters were selected from the European market. Each one of them was put into an outdoor grid-connected system installed in Spain. PV power generation with respect to irradiance, ambient temperature and local time was measured under different meteorological conditions. DC voltage and maximum power point tracking efficiency were analyzed. From the results obtained it has been possible to see that the MPPT algorithms used in some inverters do not bring the optimum utilisation of the PV array.
A new approach for hybrid metal–insulator–semiconductor (MIS) Si solar cells is adopted by Institute of Fundamental Problems for High Technology, Ukrainian Academy of Sciences. In order to interpret the effect of illumination and 60Co γ-ray radiation dose on the electrical characteristics of solar cells are studied at room temperature. Before the solar cells are subjected to stressed irradiation six different illumination levels of forward and reverse bias I–V measurements are carried out at room temperature. The solar cells are irradiated with 60Co γ-ray source irradiation, with a dose rate of 2.12 kGy/h and an over dose range from 0 to 500 kGy. Experimental results shows that both the values of capacitance and conductance increase with increasing illumination levels and give the peaks at high illumination levels. γ-ray irradiation induces an increase in the barrier heights Φb(C–V) which are obtained from reverse-bias C–V measurements, whereas barrier heights Φb(I–V) which are deducted from forward-bias I–V measurements remain essentially constant. This negligible change of Φb(I–V) is attributed to the low barrier height (BH) in regions associated with the surface termination of dislocations. Both the I–V and C–V characteristics indicate that the total-dose radiation hardness of the Si solar cells cannot be neglected according to illumination levels.
Experimental study on 75 kWth, downdraft (biomass) gasifier system has been carried out to obtain temperature profile, gas composition, calorific value and trends for pressure drop across the porous gasifier bed, cooling–cleaning train and across the system as a whole in both firing as well as non-firing mode. Some issues related to re-fabrication of damaged components/parts have been discussed in order to avoid any kind of leakage. In firing mode, the pressure drop across the porous bed, cooling–cleaning train, bed temperature profile, gas composition and gas calorific value are found to be sensitive to the gas flow rate. The rise in the bed temperature due to chemical reactions strongly influences the pressure drop through the porous gasifier bed. In non-firing mode, the extinguished gasifier bed arrangement (progressively decreasing particle size distribution) gives much higher resistance to flow as compared to a freshly charged gasifier bed (uniformly distributed particle size). The influence of ash deposition in fired-gasifier bed and tar deposition in sand filters is also examined on the pressure drop through them. The experimental data generated in this article may be useful for validation of any simulation codes for gasifiers and the pressure drop characteristics may be useful towards the coupling of a gasifier to the gas engine for motive power generation or decentralized electrification applications.
An experimental investigation has been carried out to study the heat transfer coefficient by using 90° broken transverse ribs on absorber plate of a solar air heater; the roughened wall being heated while the remaining three walls are insulated. The roughened wall has roughness with pitch (P), ranging from 10–30 mm, height of the rib of 1.5 mm and duct aspect ratio of 8. The air flow rate corresponds to Reynolds number between 3000–12,000. The heat transfer results have been compared with those for smooth ducts under similar flow and thermal boundary condition to determine the thermal efficiency of solar air heater.
Wind speed forecasts are important for the operation and maintenance of wind farms and their profitable integration into power grids, as well as many important applications in shipping, aviation, and the environment. Modern machine learning techniques including neural networks have been used for this purpose, but it has proved hard to make significant improvements on the performance of the simple persistence model. As an alternative approach, we propose here the use of abductive networks, which offer the advantages of simplified and more automated model synthesis and transparent analytical input–output models. Various abductive models for predicting the mean hourly wind speed 1 h ahead have been developed using wind speed data at Dhahran, Saudi Arabia during the month of May over the years 1994–2005. The models were evaluated on the data for May 2006. Models described include a single generic model to forecast next-hour speed from the previous 24 hourly measurements and an hour index, which give an overall mean absolute error (MAE) of 0.85 m/s and a correlation coefficient of 0.83 between actual and predicted values. The model achieves an improvement of 8.2% reduction in MAE compared to hourly persistence. The above model was used iteratively to forecast the hourly wind speed 6 h and 24 h ahead at the end of a given day, with MAEs of 1.20 m/s and 1.42 m/s which are lower than forecasting errors based on day-to-day persistence by 14.6% and 13.7%. Relative improvements on persistence exceed those reported for several machine learning approaches reported in the literature.
A three-axial acoustic sounder with doppler wind measurements capability has been successfully operated to detect anabatic and katabatic winds in a mountainous and lake-locked region of northern Sweden, Abisko (68°20'N, 18°50'E) between 1 and 2 April 1983. While the flow was predominantly katabatic, two types of anabatic flows were detected: 1.(a) an intermittent type resulting from the action of unsteady wave phenomena and2.(b) a convectively-induced type resulting from the lifting and erosion of nocturnal inversion as the boundary layer deepens following the input of solar radiation by the sun at dawn.Vertical fluxes of zonal and meridional momentum were calculated. The imprint of gravity wave activity was made manifest by these results and spectral analysis of vertical velocities which were in agreement with observed facsimile record signatures. Observed winds closely follow a modified form of Reiher's 1936 model [M. Reiher, Bioklim Beiblatter3, 152–163 (1936)].
Renewable power supply systems have been a natural choice for many of Australia’s small remote aboriginal communities where the costs of diesel fuel are high. The results have been mixed. This is partially due to design factors, but more importantly due to community acceptance of these technologically complex systems and the maintenance arrangements with the community power station operators and local resource agencies. This paper looks at some of the issues to consider in the selection, design, installation and maintenance of appropriate hybrid power stations for smaller remote aboriginal communities.
In medium to large scale wind energy conversion systems (WECS), the control of the pitch angle of the blades is an usual method for power regulation above rated wind speed. However, limitations of the pitch actuator have a marked influence on the regulation performance. In variable-speed mode, the control of the generator torque is able to reduce the effects of the pitch actuator limitations. Nevertheless, in this case the system is multiple-input multiple-output (MIMO) and then the control design results more complex. In this situation advance control techniques, such as optimal control, are an interesting option for a systematic controller design. This work analyzes variable-pitch power regulation above rated wind speed in the context of optimal control. The analysis is approached from a new point of view in order to establish a clear connection between the choice of the optimization criteria and the compromise between power regulation and pitch actuator limitations.
We derive from first principles analytical expressions that give each of the following meteorological parameters in terms of (air) temperature: wind speed, relative humidity, rainfall, absolute humidity, vapour pressure and dew point. The validity of these expressions has been ascertained using past meteorological records. Since air temperature is one of the easiest meteorological parameters to predict [e.g. see E. C. Njau, Nuovo Cimento14C, 473–488 (1991)], the derived analytical expressions are simple and convenient tools by means of which wind speed, absolute humidity, rainfall, relative humidity, vapour pressure and dew point may be predicted. Furthermore, the expressions can be collectively used to make quick assessments of possible influences of man-made effects (e.g. greenhouse warming) upon the different meteorological parameters and hence the environment in general.
An Integrated Collector Storage (ICS) solar water heater was designed, constructed and studied with an emphasis on its optical and thermal performance. The ICS system consists of one cylindrical horizontal tank properly mounted in a stationary symmetrical Compound Parabolic Concentrating (CPC) reflector trough. The main objective was the design and the construction of a low cost solar system with improved thermal performance based on the exploitation of the non-uniform distribution of the absorbed solar radiation on the cylindrical storage tank surface. A ray-tracing model was developed to gauge the distribution of the incoming solar radiation on the absorber surface and the results were compared with those from a theoretical optical model based on the average number of reflections. The variation of the optical efficiency as function of the incident angle of the incoming solar radiation along with its dependence on the month during annual operation of ICS system is presented. The ICS device was experimentally tested outdoors during a whole year in order to correlate the observed temperature rise and stratification of the stored water with the non-uniform distribution of the absorbed solar radiation. The results show that the upper part of the tank surface collects the larger fraction of the total absorbed solar radiation for all incident angles throughout the year. This is found to have a significant effect on the overall thermal performance of the ICS unit. In addition, the presented results can be considered important for the design and the operation of ICS systems consisting of cylindrical tank and CPC reflectors.
A computational analysis of heat transfer augmentation and flow characteristics due to artificial roughness in the form of ribs on a broad, heated wall of a rectangular duct for turbulent flow (Reynolds number range 3000–20,000, which is relevant in solar air heater) has been carried out. Shear stress transport k−ω turbulence model is selected by comparing the predictions of different turbulence models with experimental results available in the literature. A detailed analysis of heat transfer variation within inter rib region is done by using the selected turbulence model. The analysis shows that peak in local heat transfer coefficient occurs at the point of reattachment of the separated flow as observed experimentally. The results predict a significant enhancement of heat transfer in comparison to that for a smooth surface. There is a good matching between the predictions by SST k−ω and experimental results. In this work, nine different shapes of rib are examined using SST k−ω model and compared on the basis of heat transfer enhancement, friction characteristics and performance index considering heat transfer enhancement with the same pumping power.
As is well known, the heat transfer coefficient of a solar air heater duct can be increased by providing artificial roughness on the heated wall (i.e. the absorber plate). Experiments were performed to collect heat transfer and friction data for forced convection flow of air in solar air heater rectangular duct with one broad wall roughened by wedge shaped transverse integral ribs. The experiment encompassed the Reynolds number range from 3000 to 18000; relative roughness height 0.015 to 0.033; the relative roughness pitch 60.17φ−1.0264<p/e<12.12; and rib wedge angle (φ) of 8, 10, 12 and 15°. The effect of parameters on the heat transfer coefficient and friction factor are compared with the result of smooth duct under similar flow conditions. Statistical correlations for the Nusselt number and friction factor have been developed in terms of geometrical parameters of the roughness elements and the flow Reynolds number.
Mechanically manufactured low-cost selective inhomogeneous rough graphite–aluminium (C/Al2O3/Al) solar absorber surfaces provide, at the current state of development, solar absorptance α=0.90 and thermal emittance ε=0.22. Based on a literature review, significantly lower emittance values could theoretically be achieved by utilization of surface plasmons in rough surfaces with an optimal graphite layer thickness, groove depth and sinusoidal surface profile periodicity. It is possible that an arbitrary form of roughening could produce equally good optical properties. In order to achieve lower emittance manufacturing parameters, the composition of silicon carbide grinding pad and the corresponding grinding pattern are required to be enhanced. The commercially available grinding pads used so far have not yielded optimal results. An antireflection coating could improve α to >0.90. Absorber samples were subjected to 383 days of temperature and irradiance cycling. In total, the samples were exposed to ultraviolet (UV) irradiation equivalent to 5–15 years of normal outdoor use. The results show that the samples are not sensitive to natural levels of UV irradiation or cycling-induced degradation of optical properties. A clear increment in absorptance was observed after the first 50 days of cycling. The elevated temperature of 130 °C is the probable cause for the increase. Reference samples indicated similar aging behaviour both after 4 years of natural exposure and after relatively short constant temperature tests at 120 and 180 °C.
Artificially roughened solar air heaters perform better than the plane ones under the same operating conditions. However, artificial roughness leads to even more fluid pressure thereby increasing the pumping power. The entropy generation in the duct of solar air heater having repeated transverse chamfered rib–groove roughness on one broad wall is studied numerically. Roughness parameters, viz., relative roughness pitch P/e, relative roughness height e/Dh relative groove position g/P, chamfer angle φ and flow Reynolds number Re have a combined effect on the heat transfer as well as fluid friction. The entropy generation is minimized and reasonably optimized designs of roughness are found.
Theoretical efficiencies (η) and thermal behaviour of all-glass Evacuated Tube solar Collectors with an Internal Absorber Film (ETCIAF), i.e. the absorber film deposited in the inner surface of the inner tube, are compared and contrasted with the traditional design of all-glass Evacuated Tube solar Collectors with an External Absorber Film (ETCEAF), using the absorber film on the external surface of the inner tube. The values of η of the ETCIAF are unacceptably lower than that of ETCEAF for any particular value of the heat transfer coefficient (hb) for the annular space, except in the case of a highly leaky ETCEAF, with hb > 2.6 W/m2 K. However, it is shown that the use of a transparent conductive coating with moderately low emittance ∼0.1−0.25 on the outside of the absorber tube of ETCIAF can offer efficiences ∼0.75−0.63, respectively, for f = 0.1 °C m2/K, competing well (η = 0.76) with the ETCEAF design operating under best conditions (α = 0.91, ϵ = 0.05, and hb = 0.026 W/m2 K).
An experimental investigation has been carried out to study the heat transfer and friction characteristics by using a combination of inclined as well as transverse ribs on the absorber plate of a solar air heater. The experimental investigation encompassed the Reynolds number (Re) ranges from 2000 to 14 000, relative roughness pitch (p/e) 3–8 and relative roughness height (e/Dh) 0.030. The effect of these parameters on the heat transfer coefficient and friction factor has been discussed in the present paper and correlations for Nusselt number and friction factor has been developed within the reasonable limits. A procedure to compute the thermal efficiency based on heat transfer processes in the system is also given and the effect of these parameters on thermal efficiency has been discussed.
This paper provides a theoretical investigation on the optimum absorber temperature of a once-reflecting full conical concentrator for maximizing overall efficiency of a solar-powered low temperature differential Stirling engine. A mathematical model for the overall efficiency of the solar-powered Stirling engine is developed. The optimum absorber temperature for maximum overall efficiency for both limiting conditions of maximum possible engine efficiency and maximum possible engine power output is determined. The results indicated that the optimum absorber temperatures calculated from these two limiting cases are not significantly different. For a given concentrated solar intensity, the maximum overall efficiency characterized by the condition of maximum possible engine power output is very close to that of the real engine of 55% Carnot efficiency, approximately.