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4 - Renewable energy systems
Abstract
The increasing interest in renewable energy sources originates from the negative impacts of overexploitation and the use of fossil fuels with their damaging influence on climate change. Besides, the continuous population growth requires higher energy provision or related energy services (e.g., heated living spaces, electricity, information, mobility) with increasing environmental impacts. Consequently, the “energy supply problem” in conjunction with the underlying “environmental problem” is a major topic in resource assessment, technology development, as well as in the energy and environmental worldwide policies.
Renewable energies originate in the movement and gravitation of the planet (i.e., tidal energy, wind energy), heat stored and released by the Earth (i.e., geothermal energy), and in particular energy radiated by the Sun (i.e., solar radiation). The main renewable energy sources, without the consideration of heating systems, are presented in this chapter. The resource estimation available from different sources as well as the measurement and resource assessment techniques is illustrated.
The main renewable sources are classified and characterized in a particular location, describing the renewable energy flows and considering the spatial and time variations. The focus is on the principal variables that need to be known for the hybrid renewable energy systems design and project development.
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Many studies have investigated the influence of hydropower stations on macroinvertebrate communities, but few have clarified the influence of different types of hydropower stations. A total of 133 samples obtained from seven rivers, on which 45 hydropower stations are located, with the rivers distributed across four provinces (Yunnan, Jiangxi, Fujian, and Hubei) were investigated to study the influence of different types of small hydropower stations on macroinvertebrate communities. Samples were collected during 2011–2012. Results showed that 126 taxa of macroinvertebrates were collected, of which 68.3% were insects. The average macroinvertebrate density and biomass were 966 ± 112 ind/m2 and 17.31 ± 1.54 g/m2, respectively. For dam-type hydropower stations, the intercepting effect of the dam was the main factor affecting macroinvertebrate populations, whereas the influence of hydrological period was nonsignificant. Macroinvertebrate taxa richness exhibited a gradual increase from reservoir reaches to down-dam reaches and then to natural reaches (4.4, 6.5, and 9.5, respectively). The Shannon–Wiener index showed a similar increasing trend (1.06, 1.48, and 1.58, respectively), whereas biomass levels exhibited a decreasing trend (56.3, 25.2, and 6.0 g/m2, respectively). For the diversion-type hydropower stations, hydrological period was the main influential factor, whereas the intercepting effect of the dam was nonsignificant. From wet to dry seasons, increases were observed in macroinvertebrate abundance (5.2 to 8.3), density (322.2 to 1170.5 ind/m2), biomass (24.6 to 40.1 g/m2), and Shannon–Wiener index (1.23 to 2.08).
Hydrokinetic energy conversion devices provide the facility to capture energy from water flow without the need of large dams, impoundments, channels or deviation of the water as in conventional hydroelectric centrals. Hydrokinetic systems are intended to be used in streams, either natural (rivers, estuaries, marine currents) or artificially built channels. This article reviews the advances made over the last 10–15 years regarding the three-dimensional computational fluid dynamics modeling and simulation of this type of turbines. Technical aspects of model design, employed boundary conditions, solution of the governing equations of the water flow through the hydrokinetic turbine and assumptions made during the simulations are thoroughly described. We hope that this review will encourage new computational investigations about hydrokinetic turbines that contribute to their continuous improvement, development and implementation aimed to sustainable use of water resources and addressed to solve the problem of lack of electricity supply in small, isolated populations.
One of the challenges in solar engineering is that the availability of the solar resource varies with time and location. An important engineering task is to design solar energy systems that are able to collect as much solar radiation as possible under these constraints. This book introduces the basic properties of solar radiation that are required to understand how the solar resource can be converted into useful heat and electricity, and what the limitations are. It also shows how solar radiation on planar surfaces can be modeled mathematically. This is useful when optimizing the orientation of collecting surfaces and predicting the performance of different system designs. The book builds upon lecture notes from solar engineering courses at Uppsala University, carefully edited to suit a wider scientific and engineering audience. The two authors have, together, more than two decades' experience of teaching, research and development in the field of solar irradiance modeling.
Renewable energies can play an important role to provide electricity to
rural communities .This work study the design optimization of a hybrid
hydro-wind , micro-power system in a rural area . Six case studies, including
the impact of hydro head, flow rate ,efficiency, and head loss for micro
hydropower with wind turbine hub height were implemented based on
HOMER software. The simulation results show the importance of using
HOMER to assist system designers for assigning the optimum design of
hybrid system components.
Wind-deformed trees can be good bioindicators of the mean wind speed and prevailing wind directions. The current research used bioindicators, computational fluid dynamics (CFD), and linear models to assess the wind fields in the windy coastal area of Cascais/Portugal. The main objectives of this research are to assess mean speed and directions of winds by using bioindicators and modeling techniques and to correlate both results in order to assess the best methods. The results obtained with the bioindicators showed that carpeting, the most severe deformation, was observed near the shoreline showing that the highest wind speeds are felt in this sector. Inland, where the winds have lower mean speeds, flagging forms are more frequent. When correlated with the bioindicators, the linear model gave better results than CFD models. We can conclude that in areas with good wind potential, the use of bioindicators can be a good alternative in the absence of wind data.
In this paper, a comparison of total entropy generation between a suggested design and a constant chord Wells turbine is presented. A variable chord rotor Wells turbine design is suggested in order to have a more uniform axial velocity distribution at blades leading edge in comparing conventional design to improve turbine efficiency. Each model is analysed numerically with respect to the total entropy generation due to viscous dissipation around rotor blades. Simulations have been performed by numerical solving of the steady, incompressible, three-dimensional Reynolds-averaged Navier–Stokes together with RNG k–ε turbulence model equations in a non-inertial reference frame rotating with the turbine rotor. A comparison of the computed results with the available experimental data exhibits agreement in terms of efficiency, torque and input coefficients at different flow rates. Finally, the detailed comparisons of the results are done between the suggested design and the conventional Wells turbine, demonstrating a 26.02 % average decrease in entropy generation throughout the full operating range, hence supporting the superiority of the new design.
The energy in flowing river streams, tidal currents or other artificial water channels is being considered as viable source of renewable power. Hydrokinetic conversion systems, albeit mostly at its early stage of development, may appear suitable in harnessing energy from such renewable resources. A number of resource quantization and demonstrations have been conducted throughout the world and it is believed that both in-land water resources and offshore ocean energy sector will benefit from this technology. In this paper, starting with a set of basic definitions pertaining to this technology, a review of the existing and upcoming conversion schemes, and their fields of applications are outlined. Based on a comprehensive survey of various hydrokinetic systems reported to date, general trends in system design, duct augmentation, and placement methods are deduced. A detailed assessment of various turbine systems (horizontal and vertical axis), along with their classification and qualitative comparison, is presented. In addition, the progression of technological advancements tracing several decades of R&D efforts are highlighted.
This review article aims to provide an overview and insight into the most relevant aspects of wind energy development and current state-of-the-art. The industry is in a very mature stage, so it seems to be the right time to take stock of the relevant areas of wind energy use for power generation. For this review, the authors considered the essential aspects of the development of wind energy technology: research, modeling, and prediction of wind speed as an energy source, the technology development of the plants divided into the mechanical and electrical systems and the plant control, and finally the optimal plant operation including the maintenance strategies. The focus is on the development in Europe, with a partial focus on Germany. The authors are employees of the Fraunhofer Institutes, Institute for Energy Economics and Energy Systems Technology and Institute for Wind Energy Systems, who have contributed to the development of this technology for decades.
The rapid development of distributed generation in different forms and capacities is transforming the conventional planning of distribution networks. Despite the benefits offered by renewable distributed generation technologies, several economic and technical challenges can result from the inappropriate integration of distributed generation in existing distribution networks. Therefore, the optimal planning of distributed generation is of paramount importance to ensure that the performance of distribution network can meet the expected power quality, voltage stability, power loss reduction, reliability and profitability. In this paper, we firstly discuss several conventional and metaheuristic methodologies to address the optimal distributed generation planning problem. Metaheuristic algorithms are often used as they offer more flexibility, particularly for multi-objective planning problems without the pursuit of globally optimized solution. Analytical techniques are considered suitable for modeling power system mechanisms and validating numerical methods. Then, this paper conducts a comprehensive review and critical discussion of state-of-the-art analytical techniques for optimal planning of renewable distributed generation. The analytical techniques are discussed in detail in six categories, i.e. exact loss formula, loss sensitivity factor, branch current loss formula, branch power flow loss formula, equivalent current injection and phasor feeder current injection. In addition, a comparative analysis of analytical techniques is presented to show their suitability for distributed generation planning in terms of various optimization criteria. Finally, we present conclusive remarks along with a set of recommendations and future challenges for optimal planning of distributed generation in modern power distribution networks.
In this study, wind energy density in the southern and southwestern region of Turkey was investigated by using the Weibull and Rayleigh probability density functions, and the wind atlas analysis and application program (WAsP). Hourly wind speeds and directions collected by the General Directorate of Electrical Power Resources Survey Administration were used. Before the construction of the wind turbine generator in these locations, several fundamental properties of the site such as wind behavior, availability, continuity, and probability should be carried out in order to provide the necessary information to the potential investors about cost and economical aspects of planning the wind energy project. The dominant wind direction, probability distribution, Weibull parameters, mean wind speed and power potential of all stations were determined by the Weibull and Rayleigh models, and the WAsP program. The results obtained with these models were compared with the measured data. Finally, it is found that these regions have a reasonable wind power potential and they are suitable for planting wind energy turbines. However, Belen is the most promising and convenient site for production of electricity from wind power.
Photosynthesis-irradiance response curves and leaf nitrogen contents were measured weekly by destructive sampling over the life cycles of leaves 10, 15, 20 and 25 of sunflower plants (cv. Prosol 35) grown in large pots in the open under optimum conditions of temperature and high irradiance. Individual leaf responses were adequately described by a hyperbola of three parameters, viz. Pmax, the rate of photosynthesis in saturating irradiance; R, the rate of dark respiration adjusted for temperature (30ºC); and ε, the apparent quantum efficiency of photosynthesis at low irradiance. Pmax (range 0-40 μmol CO2 m-2 s-1) and R (0-4 μmol CO2 m-2 s-1) were non-linearly related to nitrogen content per unit leaf area (NL) (range 0.3-2.9 g N m-2) across all leaf positions and for all leaf ages. ε (mean value 0.050 mol mol-1, s.e. 0.001) was independent of NL. The equations for net photosynthesis derived from pot studies were shown to explain (r2 =0.80) leaf photosynthesis in a crop of the same cultivar over a wide range of NL and irradiance.
The impact of managing biomass specifically for the conservation or production of energy can become a significant factor in the global management of atmopsheric CO2 over the next century. This paper evaluates the global potential for: (1) conserving energy by using trees and wood for shading, shelterbelts, windbreaks, and construction material; and (2) increasing the use of biomass and improving its conversion efficiency for producing heat, electricity, and liquid biofuels. The potential reduction in CO2 emissions possible by the anticipated time of atmospheric CO2 doubling was estimated to be up to 50106t C yr–1 for energy conservation and as high as 4109 t C yr–1 for energy production. Of the many opportunities, two stand out. Through afforestation of degraded and deforested lands, biomass energy production offers the potential of 0.36 to 1.9109t C yr–1 emission reduction. Dedicated energy crops, which include short-rotation woody crops, herbaceous energy crops, halophytes, some annual crops, and oilseeds, offer the potential of 0.2 to 1.0109t C yr–1 emission reduction. Also addressed in the paper, but not quantified, were establishment of new forests, increasing the productivity of existing forests, or protecting forests to sequester C as an offset against CO2 emissions from burning fossil fuels or forest destruction. Also addressed are uncertainties, gaps in scientific knowledge about ecosystems and their management, and policy considerations at the international and national levels.
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