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1 Jul 2011

Volume 3, Issue 4, Articles (04xxxx)

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Editorial: Should we develop a sense of urgency in science and technology development?

Michael Kintner-Meyer

J. Renewable Sustainable Energy 3, 040401 (2011); http://dx.doi.org/10.1063/1.3634041 (2 pages)

Online Publication Date: 30 August 2011

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Abstract Unavailable
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89.20.Bb Industrial and technological research and development
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Prospects for electricity from renewable resources in the United States

K. John Holmes and Larry Papay

J. Renewable Sustainable Energy 3, 042701 (2011); http://dx.doi.org/10.1063/1.3613947 (14 pages) | Cited 1 time

Online Publication Date: 26 July 2011

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In 2009, the National Research Council issued Electricity from Renewables: Status, Prospects, and Impediments the study report of the Panel on Electricity from Renewable Sources. As part of the larger America’s Energy Future study undertaken by the National Academies, the panel was asked to examine the technical potential for development and deployment of renewable electricity technologies. This paper summarizes the report by this panel. The panel noted that renewable electricity generation technologies represent a tremendous opportunity to provide low net carbon dioxide (CO2)-emitting electricity generation from domestic resources and to generate new economic opportunities for the United States. The panel found that there are sufficient domestic renewable resources and technologies to allow renewable electricity to play a significant role in future electricity generation. However, although wind and solar electricity in particular have exhibited very large growth rates, non-hydropower renewables still provide a small percentage of total US electricity generation. The study considered the size and distribution of the resource base; the status of renewable electricity technologies; the economics of renewable electricity in light of various policy options; the environmental impacts of electricity from renewable resources; and the issues related to scaling up deployment. The panel concluded that an aggressive but achievable future for renewables could have non-hydroelectric renewables contributing 10% of the nation’s electricity generation by 2020 and 20% or more by 2035. To reach these levels, significant and sustained actions, involving a combination and coordination of policy, technology, and capital, will be essential. The panel emphasizes policy, technology, and capital equally because the scale of the effort required to reach such levels brings significant challenges beyond simple resource availability or technical capabilities.
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88.80.-q Energy delivery and storage
88.05.Np Environmental aspects
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Commentary: Building bridges—Towards a new energy/science partnership between Europe and Middle East and North Africa

Frank Lehner

J. Renewable Sustainable Energy 3, 042801 (2011); http://dx.doi.org/10.1063/1.3631794 (3 pages)

Online Publication Date: 30 August 2011

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Abstract Unavailable
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
88.40.-j Solar energy
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An integrated energy storage scheme for a dispatchable solar and wind powered energy system

Jared B. Garrison and Michael E. Webber

J. Renewable Sustainable Energy 3, 043101 (2011); http://dx.doi.org/10.1063/1.3599839 (12 pages)

Online Publication Date: 5 July 2011

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This research analyzed an integrated energy system that includes a novel configuration of wind and solar coupled with two storage methods to make both wind and solar sources dispatchable during peak demand, thereby enabling their broader use. Named DSWiSS for Dispatchable Solar and Wind Storage System, the proposed system utilizes compressed air energy storage (CAES) that is driven from wind energy and thermal storage supplied by concentrating solar thermal power (CSP) in order to achieve firm power from intermittent, renewable sources. Although DSWiSS mimics the operation of a typical CAES facility, the replacement of energy derived from fossil fuels with energy generated from renewable resources makes this system unique. West Texas is a useful geographical testbed for this system because it has abundant co-located wind and solar resources; it has competitive electricity markets, which give producers an economic incentive to store night-time wind energy in order to be sold during peak price times; and it has a significant number of locations with geological formations suitable for CAES. Through a thermodynamic and a levelized lifetime cost analysis, the power system performance and the cost of energy are estimated for this integrated wind-solar-storage system. We calculate that the combination of these components yields an energy efficiency of 46% for the CAES main power block, and the overall system cost is only slightly more expensive per unit of electricity generated than the current technologies employed today.
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84.60.Ve Energy storage systems, including capacitor banks
88.40.-j Solar energy
88.50.-k Wind energy

Numerical-simulation and experimental-validation of the largest Egyptian solar process-heat system

Adel M. Abdel-Dayem

J. Renewable Sustainable Energy 3, 043102 (2011); http://dx.doi.org/10.1063/1.3584836 (17 pages)

Online Publication Date: 7 July 2011

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El-Nasr pharmaceutical solar process heat project is considered as the largest industrial system installed and working in east Cairo, Egypt 30°N. It was simply constructed from a one-axis tracking parabolic-trough collector that can produce about 1.3 ton/h saturated steam to feed the industrial processes in the company. Twenty-three bar compressed water is heated inside 1958.4 m2 collectors, and later on it is flashed in a steam flash-drum to produce saturated steam at 8 bars and 175 °C that is fed to the process heat. A mathematical model was developed for the system components to simulate annual performance of the system. The simulation results were verified successfully by the measured data that are monitoring the system performance. First, each component of the mathematical model was experimentally validated separately. Accordingly, the whole mathematical model was validated under different weather conditions along the year. The validated numerical model was optimized. The optimal number of collectors connected in series was obtained as three collectors not 36 as installed. An economical study of the installed system was provided. The optimal design of the system was economically estimated. The optimal collector area is less than that installed, it equals about 538 m2. Annual performance of the system is presented indicating the seasonal variation. It was found that the optimized system can produce about 2 ton/h in average. Moreover, that value is more than that was proposed by the system design.
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88.40.-j Solar energy
02.60.-x Numerical approximation and analysis
42.79.Ek Solar collectors and concentrators

Control of noise and exhaust emissions from dual fuel engines

Salah B. Al-Omari, Mohamed Y. E. Selim, and A. A. J. Al-Aseery

J. Renewable Sustainable Energy 3, 043103 (2011); http://dx.doi.org/10.1063/1.3596170 (26 pages)

Online Publication Date: 12 July 2011

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An experimental investigation has been carried out to examine the effects of adding water vapor to the intake air of a dual fuel engine on the performance, combustion noise, and emission of CO, HC gases, and smoke opacity. Dual fuel engine is a diesel engine using a small amount (5%) of liquid diesel fuel as a pilot fuel and burns a liquefied petroleum gas as the main fuel. The addition of water vapor to the combustion chamber of a diesel engine has known effects on reducing the dangerous emission of nitrogen oxides. Yet it is not currently clear for the dual fuel engine how much the sacrifice is of engine performance, noise, and other exhaust emissions. Experimental procedures conducted using a Ricardo diesel version variable compression research engine are discussed. Results from testing dual fuel engine with varying the added water vapor to fuel ratios and other design and operating parameters are presented and discussed. The addition of water vapor to the intake air affected the performance, combustion noise, and exhaust emissions.
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89.20.Kk Engineering
82.33.Vx Reactions in flames, combustion, and explosions

Potential order-of-magnitude enhancement of wind farm power density via counter-rotating vertical-axis wind turbine arrays

John O. Dabiri

J. Renewable Sustainable Energy 3, 043104 (2011); http://dx.doi.org/10.1063/1.3608170 (12 pages)

Online Publication Date: 19 July 2011

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Modern wind farms comprised of horizontal-axis wind turbines (HAWTs) require significant land resources to separate each wind turbine from the adjacent turbine wakes. This aerodynamic constraint limits the amount of power that can be extracted from a given wind farm footprint. The resulting inefficiency of HAWT farms is currently compensated by using taller wind turbines to access greater wind resources at high altitudes, but this solution comes at the expense of higher engineering costs and greater visual, acoustic, radar, and environmental impacts. We investigated the use of counter-rotating vertical-axis wind turbines (VAWTs) in order to achieve higher power output per unit land area than existing wind farms consisting of HAWTs. Full-scale field tests of 10-m tall VAWTs in various counter-rotating configurations were conducted under natural wind conditions during summer 2010. Whereas modern wind farms consisting of HAWTs produce 2–3 W of power per square meter of land area, these field tests indicate that power densities an order of magnitude greater can potentially be achieved by arranging VAWTs in layouts that enable them to extract energy from adjacent wakes and from above the wind farm. Moreover, this improved performance does not require higher individual wind turbine efficiency, only closer wind turbine spacing and a sufficient vertical flux of turbulence kinetic energy from the atmospheric surface layer. The results suggest an alternative approach to wind farming that has the potential to concurrently reduce the cost, size, and environmental impacts of wind farms.
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88.50.J- Wind farms
88.50.G- Wind turbines
89.60.-k Environmental studies

Optimal sizing of distributed resources in micro grid with loss of power supply probability technology by using breeding particle swarm optimization

S. M. Moghaddas-Tafreshi, H. A. Zamani, and S. M. Hakimi

J. Renewable Sustainable Energy 3, 043105 (2011); http://dx.doi.org/10.1063/1.3610979 (17 pages) | Cited 2 times

Online Publication Date: 19 July 2011

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The deregulated energy environment, among other effects, has favored a gradual transition from centralized power generation to distributed generation sources connected at the medium voltage or low voltage side of the distribution network. Interconnection of small, modular generations and energy storages of low or medium voltage distribution systems forms a new type of power system, which called the micro grid (MG). This paper has developed a methodology of performing the optimal unit sizing for distributed energy resources in MG. The methodology aims at finding the configuration, among a set of systems components, which meets the desired system reliability requirements, with the minimum cost of energy (COE). Other than solar and wind energies, in this study the biogas power plant and the use of urban waste for producing electricity power are considered. The size of biogas power plant is calculated according to available municipal waste. The micro grid system is connected to the utility and can sale its extra produced power to utility. In first step, accurate mathematical models for characterizing standalone photovoltaic module, wind generator, biogas plant, and battery bank are proposed. In second step, based on a breeding particle swarm optimization algorithm, one optimal sizing method is developed to calculate the optimum system configuration that can achieve the customers required loss of power supply probability with a minimum COE. By this methodology, we can analyze MG
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
88.20.F- Renewable alternative fuels from biomass energy
02.60.Pn Numerical optimization

Layered mesoporous nanostructures for enhanced light harvesting in dye-sensitized solar cells

Bin Liu and Eray S. Aydil

J. Renewable Sustainable Energy 3, 043106 (2011); http://dx.doi.org/10.1063/1.3615641 (10 pages) | Cited 1 time

Online Publication Date: 25 July 2011

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Incident-photon-to-current-conversion efficiency of TiO2 photoanodes is increased significantly in the visible and near infrared range of the electromagnetic spectrum by assembling films that are structured on both micrometer and nanometer length scales. Photoanodes assembled from alternating layers of TiO2 nanoparticles and mesoporous TiO2 microspheres increase the overall power conversion efficiencies of dye-sensitized solar cells by as much as 26%. This increase is due to enhanced light scattering by porous TiO2 microspheres and is achieved without sacrificing the specific surface area.
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88.40.J- Types of solar cells

Temperature and methanol concentration dependences of direct methanol fuel cell performance measured by single cell having reference electrode

Minoru Umeda, Kazuya Sayama, and Mitsuhiro Inoue

J. Renewable Sustainable Energy 3, 043107 (2011); http://dx.doi.org/10.1063/1.3608911 (9 pages)

Online Publication Date: 26 July 2011

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In this study, we measured the cell temperature and methanol concentration dependences of direct methanol fuel cell (DMFC) performances and its polarization characteristics using a single cell with a Ag/Ag2SO4 reference electrode, which has been developed for the DMFC research in our laboratory. The membrane electrode assembly composed of carbon-supported Pt-Ru and Pt catalysts and the Nafion membrane was used for the measurements. As a result, the power densities obtained while feeding 1 and 5 mol dm−3 methanol solutions increase in the order of 26, 40, and 60 °C. For the 10 mol dm−3 methanol, the power density at 60 °C is lower than those at 26 and 40 °C. In these cases, the polarization curves to investigate the details of the relationship between the DMFC performance and temperature indicate that for the 1 and 5 mol dm−3 methanol, the current densities measured at the same anode and cathode potentials are enhanced with the increasing temperature. As for the 10 mol dm−3 methanol, the current densities at the anode and cathode decrease at 60 °C. To clarify a reason for the particular results of the 10 mol dm−3 methanol, the DMFC performances and the polarization curves at 40 and 60 °C were compared as a function of the methanol concentration. These results demonstrate that the decrease in the DMFC performance at 60 °C by feeding 10 mol dm−3 methanol is attributed to the simultaneous appearance of the O2 crossleak and methanol crossover causing the decline in the methanol oxidation performance at the anode and O2 reduction performance at the cathode.
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88.30.pf Direct methanol fuel cells
82.45.Fk Electrodes

Sustainable low temperature desalination: A case for renewable energy

Veera Gnaneswar Gude, Nagamany Nirmalakhandan, and Shuguang Deng

J. Renewable Sustainable Energy 3, 043108 (2011); http://dx.doi.org/10.1063/1.3608910 (25 pages)

Online Publication Date: 27 July 2011

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In this paper, different configurations for running a low temperature desalination process at a production capacity of 100 liters/day are presented. Renewable energy sources such as solar and geothermal energy sources are evaluated as renewable, reliable, and suitable energy sources for driving the low temperature desalination process round the clock. A case study is presented to evaluate the feasibility of sustainable recovery of potable water from the effluent streams of wastewater treatment plant. Results obtained from theoretical and experimental studies demonstrate that the low temperature desalination unit has the potential for large scale applications using renewable energy sources to produce freshwater in a sustainable manner. The following renewable energy/waste heat recovery configurations may produce around 100 liters/day of desalinated water: (1) solar collector area of 18 m2 with a thermal energy storage (TES) volume of 3 m3; (2) photovoltaic thermal collector area of 30 m2 to provide 14–18 kW electricity and 120 liters/day freshwater with an optimum mass flow rate of the circulating fluid around 40–50 kg/h m2; (3) A geothermal source at 60 °C with a flow rate of 320 kg/h; and (4) waste heat rejected from the condenser of an absorption refrigeration system rated at 3.25 kW (0.95 tons refrigeration), supported by 25 m2 solar collector area and 10 m3 TES volume. Additionally, the secondary effluent of local wastewater treatment plant was processed to recover potable quality water. Experimental results showed that >95% of all the water contaminants such as biological oxygen demand (BOD), total dissolved solids (TDS), total suspended solids (TSS), ammonia, chlorides, nitrates, and coliform bacteria can be removed to provide clean water for many beneficial uses.
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88.05.-b Energy analysis
89.60.-k Environmental studies
42.79.Ek Solar collectors and concentrators
84.60.-h Direct energy conversion and storage

Modeling of optimum inclination angles of solar systems for Amman, Jordan

Abdulrahman I. Tamimi

J. Renewable Sustainable Energy 3, 043109 (2011); http://dx.doi.org/10.1063/1.3610974 (6 pages) | Cited 1 time

Online Publication Date: 27 July 2011

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A generalized analytical model was developed to determine the optimum inclination angle of flat-plate solar collector for any location worldwide. The developed analytical model was found to be directly related to the latitude φ of the location under consideration, the declination angle δ of the earth axis, and the day hour angle at sunset ωs at any day throughout the year. The optimum inclination angle βopt was expressed by a generalized mathematical model. This model was applied to Amman, Jordan. The results were compared with those calculated by NASA and showed very good agreement.
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42.79.Ek Solar collectors and concentrators

Performance analysis of W-shaped rib roughened solar air heater

Atul Manikrao Lanjewar, Jiwan Lal Bhagoria, and Rishindra Mohan Sarviya

J. Renewable Sustainable Energy 3, 043110 (2011); http://dx.doi.org/10.1063/1.3595740 (10 pages)

Online Publication Date: 29 July 2011

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Artificial rib roughness is a convenient method for enhancing thermal performance of solar air heater. An experimental investigation has been carried out to study the thermo-hydraulic performance of solar air heater using W-shaped ribs on absorber plate, the roughened wall being heated while the remaining three walls being insulated. W-shaped ribs have been tested both pointing downstream (W-down) and upstream (W-up) to the flow. The roughened wall has relative roughness height (e/Dh) of 0.03375, relative roughness pitch (p/e) of 10 and duct aspect ratio (B/H) of 8. The airflow rate corresponds to Reynolds number between 2300 and 14 000. The heat transfer results have been compared with those for smooth duct under similar flow and thermal boundary condition. Thermo-hydraulic performance ratio of roughened absorber plate by providing W-shape roughness is in the range of 1.46–1.95 for W-down and 1.21–1.73 for W-up ribs. Friction factor and heat transfer coefficient correlations have been developed based on the law of wall similarity and heat-momentum transfer analogy.
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88.40.-j Solar energy
42.79.Ek Solar collectors and concentrators
46.55.+d Tribology and mechanical contacts
47.27.te Turbulent convective heat transfer
47.85.Dh Hydrodynamics, hydraulics, hydrostatics

Effect of temperature on structure and water transport of hydrated sulfonated poly(ether ether ketone): A molecular dynamics simulation approach

Giuseppe F. Brunello, William R. Mateker, Seung Geol Lee, Ji Il Choi, and Seung Soon Jang

J. Renewable Sustainable Energy 3, 043111 (2011); http://dx.doi.org/10.1063/1.3608912 (16 pages)

Online Publication Date: 4 August 2011

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The effects of temperature on hydrated sulfonated poly(ether ether ketone) are studied using molecular dynamics. Three different temperature conditions (298 K.15 K, 323.15 K, and 353.15 K) with two different water contents (10 wt. % and 20 wt. %) are simulated. Analyzing the pair correlation functions, it is found that there is limited temperature effect on the distribution and solvation of the sulfonate groups. The structure factor analysis shows that the temperature dependence of the nanophase-segregated morphology is not significant in the simulated temperature range. On the contrary, the structure factors S(q) at ∼30 Å (q = ∼0.2 Å−1) and ∼13 Å (q = ∼0.5 Å−1) clearly increase with water content, indicating that the development of water channels is mostly affected by the water content. Within such water phase in the nanophase-segregated structure, the internal structure of water phase becomes more developed with decreasing temperature and increasing water content. By analyzing the mean square displacement of the water molecules, it is also found that self-diffusion of water is enhanced with the increasing temperature. From the observation that the activation energies calculated from such temperature dependency are very similar (Ea = 25.7 kJ/mol and Ea = 24.9 kJ/mol for 10 wt. % and 20 wt. %, respectively), it is inferred that the extent of the structural change in the water phase as a function of temperature is very similar between the 10 wt. % water content and the 20 wt. % water content. Compared to the bulk water (13.2 kJ/mol) and the water in Nafion (16.7-18.9 kJ/mol), it is confirmed that more nanophase-segregation enhances water transport through the membrane.
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88.30.pd Proton exchange membrane fuel cells (PEM)
82.30.-b Specific chemical reactions; reaction mechanisms
82.45.Yz Nanostructured materials in electrochemistry

Intelligent control of hybrid photo voltaic/fuel cell/energy storage power generation system

Amin Hajizadeh, Samson G. Tesfahunegn, and Tore M. Undeland

J. Renewable Sustainable Energy 3, 043112 (2011); http://dx.doi.org/10.1063/1.3618743 (17 pages)

Online Publication Date: 4 August 2011

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This paper proposes a control strategy for hybrid power generation systems including fuel cell and photovoltaic as the main energy sources and battery energy storage as the auxiliary power source. The overall configuration of the hybrid power generation system is given, dynamic models for the fuel cell, photovoltaic and battery bank and its power electronic interfacing are briefly described, and controller design methodologies for the power conditioning units and power sources to control the power flow from the hybrid power plant to the utility grid are presented. Then, a control strategy is presented for designing the controllers of power sources, DC/DC and DC/AC converters, to manage the power flow both on the DC and AC sides. Simulation results are given to show the overall system performance including load-following and power management of the system.
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84.70.+p High-current and high-voltage technology: power systems; power transmission lines and cables
88.30.G- Fuel cell systems
88.80.ff Batteries
84.60.Jt Photoelectric conversion

Small-signal analysis of a fully rated converter wind turbine

Nolan D. Caliao

J. Renewable Sustainable Energy 3, 043113 (2011); http://dx.doi.org/10.1063/1.3618744 (13 pages)

Online Publication Date: 8 August 2011

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Small signal analysis of the fully rated converter wind turbine connected to a large power system was undertaken. The dynamic behaviour of the fully rated converter wind turbine was investigated using eigenvalue analysis. Eigenvalue analysis was undertaken to determine the influence of the network short circuit level on the networks dominant eigenvalues. It was shown that the strength of the transmission system does not influence the dynamic behaviour of the generator of the fully rated converter wind turbine.
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88.50.G- Wind turbines
02.10.Ud Linear algebra

Dust accumulation effect on efficiency of Si photovoltaic modules

R. E. Cabanillas and H. Munguía

J. Renewable Sustainable Energy 3, 043114 (2011); http://dx.doi.org/10.1063/1.3622609 (8 pages)

Online Publication Date: 9 August 2011

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We experimentally studied the electrical efficiency effects of naturally forming atmospheric dust deposits on commercial photovoltaic panels. The variable considered for measurements was the electric potential for three commercial silicon modules: monocrystalline, polycrystalline, and amorphous. A mathematical model was developed to determine maximum potential as a function of temperature and of total incident radiation. The study presents two essential parts: the naturally deposited dust particles and the variation in maximum electric potential between clean and dirty modules. The results indicate that the maximum reduction in potential is around of 6% for monocrystalline and polycrystalline modules and of 12% for the amorphous silicon.
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88.40.H- Solar cells (photovoltaics)

Performance evaluation of a solar photovoltaic thermal air collector using energy and exergy analysis

F. Sobhnamayan, A. Hamidi, H. R. Monavari, F. Sarhaddi, S. Farahat, and M. A. Alavi

J. Renewable Sustainable Energy 3, 043115 (2011); http://dx.doi.org/10.1063/1.3624760 (16 pages)

Online Publication Date: 10 August 2011

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In this article, a comparative study is carried out between two equations for the exergy efficiency of photovoltaic thermal (PV/T) air collectors; the first equation is based on net output exergy and the second equation is in terms of exergy losses. The exergy efficiency equation parametrically is dependent on thermal and electrical parameters of PV/T air collector; therefore, improved thermal and electrical models are used to calculate them. Developing an exergy balance for PV/T air collector system, the various exergy components in PV/T system are introduced and two equations for the exergy efficiency of PV/T air collector are derived. A computer simulation program is also developed which is based on the used improved thermal and electrical models. In order to validate the simulation results, a typical PV/T air collector has been built and some experiments have been carried out on it. The results of numerical simulation are in good agreement with the experimental results. Finally, parametric studies have been carried out and the effect of design and climatic parameters on two exergy efficiency equations has been investigated. It is observed that the improved exergy efficiency obtained in this paper is in good agreement with the one given by the previous literature and it is better because it shows the portion of each of exergy losses in the exergy efficiency equation, directly.
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88.40.hj Efficiency and performance of solar cells
88.40.me Solar heating and cooling systems
42.79.Ek Solar collectors and concentrators
84.60.Bk Performance characteristics of energy conversion systems; figure of merit
84.60.Jt Photoelectric conversion
88.05.De Thermodynamic constraints on energy production
88.40.M- Residential and commercial buildings

Evaluation of thermal efficiency of oscillating-bed solar dryer through drying of sunflower seeds

S. Shanmugam, P. Kumar, and AR. Veerappan

J. Renewable Sustainable Energy 3, 043116 (2011); http://dx.doi.org/10.1063/1.3618742 (8 pages)

Online Publication Date: 23 August 2011

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Quite a number of solar dryers have been reported for drying of different agricultural produce and products. Few dryers have their bed oscillated. A solar dryer, the bed of which is oscillated at different frequencies is presented in this paper. This paper also explains the drying methodology, variation in relative humidity, and removal of moisture content from sunflower seeds. It is possible to dry 31.36 kg of sunflower seeds to the average moisture level of 7.9% which is in the acceptable level of moisture content of less than 10% in just 8 h. The average thermal efficiency of the solar dryer is 30.1%.
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88.05.Qr Energy use in agriculture
88.40.-j Solar energy

Optimization of energy resources for cooking and heating—A fuzzy goal programming approach

A. M. Jinturkar and S. S. Deshmukh

J. Renewable Sustainable Energy 3, 043117 (2011); http://dx.doi.org/10.1063/1.3625251 (10 pages)

Online Publication Date: 23 August 2011

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A fuzzy goal programming (FGP) approach is used for rural energy resource allocation for heating and cooking. The detail survey has been conducted to determine the potential of biogas and biomass and to find energy consumption pattern in four villages of Buldhana district, Maharashtra, India. Four fuzzy objective functions and six constrains based on the local availability are considered in this model. Four scenarios have been developed such as equal priority, cost priority, emission priority, and local resources priority. Due to vast uncertainty in energy data at micro level, fuzzy goal approach has been found suitable to take into consideration the variation in energy consumption rate. The proposed model can provide the best possible options for micro-level energy planning to the decision maker.
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88.20.F- Renewable alternative fuels from biomass energy
02.60.Pn Numerical optimization
07.05.Mh Neural networks, fuzzy logic, artificial intelligence
88.20.-j Biomass energy

Biogas potential on Long Island, New York: A quantification study

Saurabh Patel, David Tonjes, and Devinder Mahajan

J. Renewable Sustainable Energy 3, 043118 (2011); http://dx.doi.org/10.1063/1.3614443 (13 pages)

Online Publication Date: 25 August 2011

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Biogas is the product of anaerobic digestion of waste, whether occurring spontaneously in landfills or under controlled conditions in digesters. Biogas is viewed as an important energy source in current efforts to reduce the use of fossil fuels and dependency on imported resources. Several studies on the assessment of biogas potential have been made at regional, national, and global scales. However, because it is not economically feasible to transport biogas feedstock over long distances, it is more appropriate to consider local waste sources for their potential to produce biogas. An assessment of the biogas potential on Long Island, based on the review of local landfills, wastewater treatment plants, solid waste generation and management, and agricultural waste, found that 234 × 106 m3 of methane (CH4) from biogas might be harvestable, although substantial barriers for complete exploitation exist. This number is equivalent to 2.52 TW-h of electricity, approximately 12% of fossil fuel power generation on Long Island. This work can serve as a template for other areas to rapidly create or approximate biogas potentials, especially for suburban U.S. locations that are not usually thought of as sources of renewable energy
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88.20.F- Renewable alternative fuels from biomass energy
88.20.T- Markets for renewable alternative fuels
89.60.-k Environmental studies

Heat transfer and pressure drop through rectangular helical ducts

Ahmad K. Sleiti

J. Renewable Sustainable Energy 3, 043119 (2011); http://dx.doi.org/10.1063/1.3625252 (11 pages)

Online Publication Date: 26 August 2011

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Optimization of heat transfer and flow in a helical duct of rectangular cross-section used to cool the stators of electric machines is studied using computational fluid dynamics (CFD) techniques. Realizable turbulent model is used with water and oil as working fluids for two different designs (helical continuous (HC) and helical reverse annulus (HRA) designs) and total of five configurations of the helical duct at small pitch size of 0.00254 m. The HRA is a new design proposed by the author. Due to the curvature of the ducts, as fluid flows through curved tubes, a centrifugal force is generated. A secondary flow induced by the centrifugal force has significant ability to enhance the heat transfer rate. Results showed that the HC design provides better heat transfer in terms of lower surface temperatures at the expense of higher pressure drop for the same flow rate of fluid.
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47.85.Np Fluidics
47.27.te Turbulent convective heat transfer
47.27.nf Flows in pipes and nozzles
47.60.Dx Flows in ducts and channels

Simulation of helically wrapped, compact heat exchangers

John Gorman, Ephraim Sparrow, Greg Mowry, and John Abraham

J. Renewable Sustainable Energy 3, 043120 (2011); http://dx.doi.org/10.1063/1.3630953 (11 pages)

Online Publication Date: 30 August 2011

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A new category of heat exchanger has been invented which fulfills the dual requirements of compactness and high thermal efficiency. The underlying principle of the exchanger is the helical intertwining of the tubes which carry the participating fluids. To ensure a thermal bridge of high conductivity between the tubes, silver braze was introduced into the interstitial space. Numerical simulation was used to characterize the performance of this category of heat exchanger. The simulation model is three-dimensional for both fluid flow and heat transfer and is also conjugate in that it encompasses two flow passages, their walls, and the interconnecting silver braze. A fabrication means was also developed. Numerical results were obtained for two general classes of heat exchange situations, one of which dealt with single-phase flows while the other related to two-phase flows. The single-phase situation investigated here is a water-water heat exchanger. The heat exchange effectivenesses evaluated from the numerical simulations demonstrated a level of enhancement of 84% compared to a baseline case consisting of straight flow passages. This level of enhancement is substantially higher than that achieved by other modes of augmentation. The results also showed that further enhancements can be achieved by increasing the number of helical turns per unit length. Experimentation was used to validate the basic computational model. For a given physical situation, the measured relationship between volumetric fluid flow and pressure drop was compared with that predicted by the numerical simulation. The excellence of the agreement lends strong support to the physical principles that underlie the simulation model
Show PACS
89.20.Kk Engineering
02.60.-x Numerical approximation and analysis
47.11.-j Computational methods in fluid dynamics
47.27.te Turbulent convective heat transfer
47.85.-g Applied fluid mechanics
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