J. Renewable Sustainable Energy - Journal of Renewable and Sustainable Energy

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Solar energy potential in Pakistan

Shahzada Adnan, Azmat Hayat Khan, Sajjad Haider, and Rashed Mahmood

J. Renewable Sustainable Energy 4, 032701 (2012); http://dx.doi.org/10.1063/1.4712051 (7 pages)

Online Publication Date: 7 May 2012

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In view of the growing needs of energy in Pakistan, the efficient use and development of renewable energy sources has become a major issue in the country. This has brought the intention of several national and multinational companies to design and implement a major work plan for energy conservation and construction of renewable energy sources like wind mills and solar panels. Fortunately, Pakistan is among those countries in which sun warms the surface throughout the year and therefore has a strong potential for solar power generation. This study was conducted to explore those areas which are most suitable for solar energy potential using fifty eight meteorological stations covering the whole country. Angstrom equation and Hargreaves formula was used to calculate monthly solar energy potential by utilizing monthly climatical data of bright sunshine hours, mean maximum and minimum temperatures. The lowest solar radiation intensity 76.49 W/m² observed at Cherat during December and highest 339.25 W/m² at Gilgit. The average monthly solar radiation intensity remains 136.05 to 287.36 W/m² in the country. The results indicate that the values of solar radiation intensity greater than 200 W/m² were observed in the months: February to October in Sindh, March to October in almost all regions of Balochistan, April to September in NWFP, Northern Areas and Kashmir regions while March to October in Punjab. For 10 h a day, average solar radiation intensity ranges from 1500 W/m²/day to 2750 W/m²/day in Pakistan especially in southern Punjab, Sindh and Balochistan regions throughout the year. In an area of 100 m², 45 MW to 83 MW power per month may be generated in the above mentioned regions.

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88.40.-j	Solar energy
88.05.Gh	Energy conservation; electricity demand reduction

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OCCAM: On-line cost-function based control algorithm for microgrids

Eduardo Alvarez Alvarez, Antonio M. Campos López, and Antonio J. Gutiérrez-Trashorras

J. Renewable Sustainable Energy 4, 033101 (2012); http://dx.doi.org/10.1063/1.4712048 (17 pages)

Online Publication Date: 7 May 2012

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This paper presents the active power dispatching of microsources, as an on-line minimization problem, including electrical and heat generation costs. The use of a new algorithm: on-line cost-function based control algorithm for microgrids (OCCAM), makes it possible to obtain similar or even better solutions than those obtained using other state of the art methods like MADS and SQP. Moreover, its execution time is about one hundred times lower than the time needed by other algorithms and it can run efficiently on-line. OCCAM is based on the same principle as the famous William Occam’s razor: “the simplest explanation is most likely the correct one”; its simplicity is the reason for its low execution time. It uses costs functions of microsources and heat savings (obtained by recovering heat from microsources in cogeneration installations) to determine the optimal solution.

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84.70.+p

High-current and high-voltage technology: power systems; power transmission lines and cables

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Sustainable heat extraction from abandoned mine tunnels: A numerical model

S. A. Ghoreishi Madiseh, Mory M. Ghomshei, F. P. Hassani, and F. Abbasy

J. Renewable Sustainable Energy 4, 033102 (2012); http://dx.doi.org/10.1063/1.4712055 (16 pages)

Online Publication Date: 8 May 2012

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Abandoned mines are often associated with enduring liabilities, which involve significant costs for decades after the decommissioning of the mine. Using a decommissioned mine as a geothermal resource can offset the environmental costs by supplying green heat to the communities living in and around the mine area. In this paper, a numerical assessment of geothermal heat extraction from underground mine workings using an open loop geothermal system is carried out. In this study, our focus is on fully flooded mines where the heat flow from the rock mass to the mine cavities is dominantly controlled by conduction in the rock mass. The sustainable heat flux into the mine workings is assessed using a transient two-dimensional axisymmetric heat transfer model. Finite volume method is applied to solve the model and simulate the transient temperature fields in the rock mass and within the water (flowing through cavities). The model is capable of controlling the rate of heat extraction through continuous adjustment of the rate of water flow through the mine. Sustainable rate of heat extraction is calculated for seasonally varied heat loads and for different project life cycles. It is shown that, with proper resource management, each kilometre of a typical deep underground mine tunnel, can produce about 150 kW of usable heat in a sustainable manner. The model is validated by comparing its results with other published models and realistic data available from Springhill mine, Nova Scotia, Canada. It is found that the sustainable heat extraction is controlled dominantly by virgin rock temperature, thermal conductivity of the rock mass, and seasonal heat load variations.

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88.10.-g	Geothermal energy
84.60.-h	Direct energy conversion and storage
91.60.Ki	Thermal properties

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Heat transfer and friction factor of solar air heater having duct roughened artificially with discrete multiple v-ribs

Anil Kumar, R. P. Saini, and J. S. Saini

J. Renewable Sustainable Energy 4, 033103 (2012); http://dx.doi.org/10.1063/1.4717511 (16 pages)

Online Publication Date: 11 May 2012

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In this paper, results of an experimental investigation on heat transfer and friction in a rectangular duct roughened with discrete multi v-shaped rib on one of its broad wall are presented. The discretizing of multi v-shaped rib is done by providing small symmetrical gap equal to rib height in both legs of multi v-rib. The artificially roughened duct was investigated having width to height ratio (W/H) of 12, relative width ratio (W/w) of 6, relative roughness pitch (P/e) of 10, relative roughness height (e/D_h) of 0.0433, angle of attack (α) of 60°, and relative gap distance (Gd/Lv) of 0.55. The relative gap width (g/e) was varied from 0.5 to 1.5. The heat transfer and friction factor results obtained experimentally were compared with those of smooth duct under similar experimental conditions. It is seen that there is a significant change in Nusselt number and friction factor as a result of providing discrete multi v-shape ribs. The enhancement in Nusselt number is found to be 6.32 times (that of smooth surface) for discrete multi v-shaped rib with relative gap width of 1.0. It is also found that the duct having this roughness geometry results in best thermo-hydraulic performance in comparison to other geometries under similar operating conditions.

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88.40.-j	Solar energy
42.79.Ek	Solar collectors and concentrators
47.85.Dh	Hydrodynamics, hydraulics, hydrostatics
47.60.Dx	Flows in ducts and channels

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Spectrally selective ultra-high temperature ceramic absorbers for high-temperature solar plants

Elisa Sani, Luca Mercatelli, Paola Sansoni, Laura Silvestroni, and Diletta Sciti

J. Renewable Sustainable Energy 4, 033104 (2012); http://dx.doi.org/10.1063/1.4717515 (13 pages)

Online Publication Date: 11 May 2012

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Ultra-high temperature ceramics are the ideal materials for extreme conditions owing to their very high melting points and good thermo-mechanical properties at high temperatures. For these reasons, they are widely known as materials for aerospace applications. This paper presents a comparative spectral characterization of zirconium, hafnium, and tantalum carbides ultra-high temperature ceramics for concentrating solar power applications. Room-temperature reflectance spectra have been measured from the ultraviolet wavelength region to the mid-infrared band. Using these spectral properties, the ceramics were evaluated as sunlight absorbers in receivers for high-temperature thermodynamic solar plants.

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42.79.Ek	Solar collectors and concentrators
88.40.-j	Solar energy

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Effect of oxygen ambient during phosphorous diffusion on silicon solar cell

Dinesh Kumar, S. Saravanan, and Prakash Suratkar

J. Renewable Sustainable Energy 4, 033105 (2012); http://dx.doi.org/10.1063/1.4717513 (8 pages)

Online Publication Date: 16 May 2012

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Phosphorous (P) diffusion is the most important and crucial process in the fabrication of silicon (Si) solar cells from p-type Si substrates. P-diffusion using phosphorous-oxycholoride (POCl₃) as a precursor in a tube furnace had shown the best cell performance over the belt diffusion because of uniform dopant concentration all over the Si surface and gettering of metallic impurities present in the substrate. The emitter formation by using POCl₃ is a complex and advanced process which provides the gettering and forming the unwanted dead layer on the front surface due to inactive phosphorous. Along with temperature, the ambient conditions during the diffusion process, such as gas flow rates and their composition, flow kinetics also have an impact on the emitter properties. In the present paper, the impact of oxygen (O₂) flow during the diffusion process on the emitter formation and the solar cell performance were studied. It has been found that, the presence of oxygen during the diffusion process influences the concentration of inactive phosphorous over the surface and the gettering process as well. The optimized oxygen flow shows an improvement in the effective minority carrier lifetime of ∼24 μs after diffusion and an absolute efficiency gain of 0.2% at pilot production.

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88.40.jj	Silicon solar cells
88.40.hj	Efficiency and performance of solar cells

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Air supply control for maximum efficiency point tracking in fuel cell systems

Jun Lu (路骏) and Ahmad Zahedi

J. Renewable Sustainable Energy 4, 033106 (2012); http://dx.doi.org/10.1063/1.4717516 (14 pages)

Online Publication Date: 16 May 2012

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The efficiency of the fuel cell system nonlinearly depends on operating conditions and the air flow supplied to the fuel cell system is one of the most significant factors in determining the efficiency. The conventional method of controlling the air flow is to stabilize the oxygen supply at a predetermined constant rate for the optimal efficiency. However, in practice, the optimal point can deviate from the pre-set value due to the varying operating conditions, such as the uncontrollable load. Therefore, the maximum efficiency point tracking (MEPT) controller is necessary to maintain the optimal efficiency over a broad range of operating conditions. In this paper, the MEPT controller is designed based on the extremum seeking control algorithm for searching the optimal oxygen excess ratio in real time to maximize the efficiency of the fuel cell system. Simulation was conducted in the matlab/simulink environment and the results demonstrate that the proposed control method is able to track the maximum efficiency point when variations in operating conditions occur.

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88.30.G-	Fuel cell systems
84.30.Jc	Power electronics; power supply circuits
84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables

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Development of a proof-of-concept hybrid electric fuel cell vehicle

Peter Strahs, Jordan Weaver, Luis Breziner, Christophe Garant, Keith Shaffer, Georgiy Diloyan, and Parsaoran Hutapea

J. Renewable Sustainable Energy 4, 033107 (2012); http://dx.doi.org/10.1063/1.4718369 (14 pages)

Online Publication Date: 16 May 2012

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The demand for fuel-efficient vehicles is on the rise due to the rising costs of gasoline and increasing environmental concerns. Zero tailpipe emission vehicles that run on electricity or hydrogen lack infrastructure to have a significant impact, while some successful hybrid electric vehicles achieve little more than eliminating idling time and capturing small percentages of braking energy. One possible solution that addresses these problems is a series hybrid electric powertrain with range extending capabilities using hydrogen and gasoline. The described powertrain was designed and modeled to simulate performance and fuel economy. In order to further prove the concept of this design, a 2000 Audi TT was converted to a plug-in hybrid electric vehicle with a 90 kW AC electric motor, LiFePO₄ batteries, 10 kW internal combustion generator, and 5 kW hydrogen PEM fuel cell. Using the U.S. Environmental Protection Agency’s standard city and highway driving tests, the vehicle has a simulated increase in fuel economy from 20/29 miles per gallon, respectively, to 230/173 miles per gallon gasoline equivalent.

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88.85.Fg	Plug-in hybrid vehicles (HEVs)
88.85.Cd	Fuel cell vehicles (FCVs)
84.50.+d	Electric motors
82.47.Cb	Lead-acid, nickel-metal hydride and other batteries
88.30.pd	Proton exchange membrane fuel cells (PEM)

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Total instantaneous energy transport in polychromatic fluid gravity waves at finite depth

J. Engström, J. Isberg, M. Eriksson, and M. Leijon

J. Renewable Sustainable Energy 4, 033108 (2012); http://dx.doi.org/10.1063/1.4719678 (8 pages)

Online Publication Date: 16 May 2012

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The total instantaneous energy transport can be found for polychromatic waves when using the deep water approximation. Expanding this theory to waves in waters of finite depth, we derive an expression for the total instantaneous energy transport for polychromatic fluid gravity waves based on potential theory with linearized free surface boundary conditions. We present the results for time series of wave elevation measured at the Uppsala University wave energy research test site. We show that a significant proportion of the total instantaneous energy transport is not accounted for when using the deep water theory. This is important since many wave energy conversion devices under development will operate in waters that do not fulfil the deep water criteria.

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88.60.nf	Energy from ocean waves
02.30.Mv	Approximations and expansions
02.50.-r	Probability theory, stochastic processes, and statistics
47.35.Bb	Gravity waves
47.85.Dh	Hydrodynamics, hydraulics, hydrostatics

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Set-up and performance investigation of an innovative solar vehicle

Adel M. Abdel Dayem

J. Renewable Sustainable Energy 4, 033109 (2012); http://dx.doi.org/10.1063/1.4717512 (17 pages)

Online Publication Date: 23 May 2012

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Solar energy is a regenerative and clean source of energy. In Makkah city (21.4 °N), the solar radiation is relatively high along the year; it is more than 5 KWh/m² a day and it is high enough to be efficiently used. On the other hand, due to high pollution and traffic in “MASHAER” region in Makkah where pilgrimage is developed, a solar vehicle can be considered as smart solution for these problems. Therefore, a gasoline engine is replaced by an electrical drive motor in an old (second hand) vehicle, cargo car. The energy required for this motor is converted from the solar energy to electric power through the installation of solar photovoltaic (PV) modules those produce energy by absorbing incoming sunlight. Then it is stored in batteries that feed the motor by needed energy. Therefore, the vehicle transmission mechanism includes electrical motor with variable speed controller that rotates the vehicle wheels by a chain drive. A simple brake system is installed to control the vehicle speed. The size of photovoltaic cells is determined based on the motor power and volt. It is found that 4 m² PV panel area is enough to feed the car by needed power. Moreover, 6 batteries are seemed enough to move the car for about 6 h daily. The vehicle is efficiently tested carrying six passengers for about 8 h continuously working under different operating and weather conditions. Moreover, a numerical simulation was developed for the solar vehicle system to visualize the annual performance of the system. A mathematical model of the photovoltaic cells, batteries, and controller were established. Annual measured data of Makkah city is used as input parameters to the numerical simulation. The system efficiency is investigated along the year demonstrating a successful utilization of solar energy in that sector. It is found that the considered PV array can move the vehicle for less than 2 h a day in average.

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89.40.Bb	Land transportation
88.40.H-	Solar cells (photovoltaics)
88.85.Hj	Electric vehicles (EVs)
84.50.+d	Electric motors
89.20.Kk	Engineering

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Potential of bioethanol production from Nypa fruticans sap by a newly isolated yeast Lachancea fermentati

Sharmila Dewi Natarajan, Rosfarizan Mohamad, Raha Abdul Rahim, and Nor’ Aini Abdul Rahman

J. Renewable Sustainable Energy 4, 033110 (2012); http://dx.doi.org/10.1063/1.3699621 (9 pages)

Online Publication Date: 23 May 2012

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Four isolated yeast strains from nypa sap: Saccharomyces cerevisiae, Candida tropicalis, Candida parapsilosis, and Lachancea fermentati were screened for their abilities to produce ethanol from Nypa fruticans sap. Fermentation was carried out in shake flasks at 30 °C, 200 rpm utilizing 50 g/l sugar of nypa sap. L. fermentati produced the highest ethanol level (18.7 g/l) with 75% efficiency, thus it was selected for further process optimization. Aiming to obtain high yields of ethanol, orthogonal experiments of ethanol fermentation from nypa sap using L. fermentati were carried out in 250 ml shake flasks to investigate the effects of the main parameters: temperature, pH, substrate concentration, and fermentation time. The results showed that the optimum conditions for bioethanol production were temperature of 30 °C, pH 5.4, substrate concentration of 110 g/l, and fermentation time of 20 h. The model predicted that the maximum concentration of ethanol produced under the above optimum conditions was 46.83 g/l. Verification experiments were carried out at the corresponding parameters, and the results were in close agreement with the model prediction giving 46.4 g/l ethanol production and 82% efficiency close to the theoretical yield. Nypa sap is a good potential substrate as well as a new resource for ethanol production by a local yeast isolate.

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89.20.Kk	Engineering
87.85.M-	Biotechnology
88.20.F-	Renewable alternative fuels from biomass energy
88.20.jm	Hydrolysis and fermentation
89.20.Bb	Industrial and technological research and development

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The feasibility and current estimated capital costs of producing jet fuel at sea using carbon dioxide and hydrogen

Heather D. Willauer, Dennis R. Hardy, Kenneth R. Schultz, and Frederick W. Williams

J. Renewable Sustainable Energy 4, 033111 (2012); http://dx.doi.org/10.1063/1.4719723 (13 pages)

Online Publication Date: 23 May 2012

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A comparative cost/benefit and energy balance analysis addresses the critical scientific and technical challenges that impact the economic feasibility of synthesizing up to 100 000 gal per day of jet fuel at sea using carbon dioxide (CO₂) and hydrogen (H₂) from the sea. Included in this analysis are the capital cost, operation and maintenance, and electrical generation cost for synthesizing jet fuel at sea using either ocean thermal energy conversion or nuclear power processes as the energy source. The results suggest that jet fuel could be produced at sea for $3 to $6/gal. Comparing these costs with current and historical prices of fuel purchased by the Department of Defense provides insight into the economic and operational benefits of a sea-based fuel synthesis process for the Navy.

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