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

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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) | Cited 1 time

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) | Cited 2 times

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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84.60.-h	Direct energy conversion and storage
88.05.Lg	Economic issues; sustainability; cost trends
88.60.nj	Marine thermal gradients

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Core loss behavior in high frequency high power transformers—I: Effect of core topology

M. A. Bahmani, E. Agheb, T. Thiringer, H. K. Høidalen, and Y. Serdyuk

J. Renewable Sustainable Energy 4, 033112 (2012); http://dx.doi.org/10.1063/1.4727910 (17 pages)

Online Publication Date: 6 June 2012

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This two-part paper presents an overview of core loss computations performed in both time and frequency domains in order to evaluate their behavior in single phase transformers with different core topologies. Moreover, the effects of non-sinusoidal waveforms on well-known core loss calculation methods are investigated with both analytically and finite element calculations. Three well-known configurations of transformers utilized in high frequency high power applications are investigated, namely, the core type, the shell type, and the matrix transformer. Based on the results obtained from a large number of FEM simulations for different operating conditions, the efficiencies of the transformers are compared in terms of distribution of magnetic flux density, loss density, total core loss, and weight. The analysis shows that for lower range of frequency and power, the shell type core could be the favorable option, and on the other hand, core type seems to be an appropriate solution for higher values of the operating frequency and nominal power.

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84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables
02.70.Dh	Finite-element and Galerkin methods

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Core loss behavior in high frequency high power transformers—II: Arbitrary excitation

E. Agheb, M. A. Bahmani, H. K. Høidalen, and T. Thiringer

J. Renewable Sustainable Energy 4, 033113 (2012); http://dx.doi.org/10.1063/1.4727917 (11 pages) | Cited 1 time

Online Publication Date: 6 June 2012

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High frequency high power transformers used in power electronic converters are frequently subjected to non-sinusoidal excitations. The main purpose of this paper is to study the effects of some general arbitrary waveforms on magnetic core loss in these transformers. First, using well-known empirical equations, general expressions were derived based on the parameters of the waveforms. Second, the impacts of different orders of voltage harmonics were investigated. Finally, capabilities of nanocrystalline and amorphous magnetic materials were compared. It is shown that the loss inside the core is highly sensitive to the rise time and duty cycle of trapezoidal and rectangular waveforms, respectively. Furthermore, although amorphous materials have higher saturation flux density, the total core loss inside the transformer designed using nanocrystalline material is considerably lower than the similar transformer with amorphous materials.

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84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables
75.50.Kj	Amorphous and quasicrystalline magnetic materials

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(LiFePO₄-AC)/Li₄Ti₅O₁₂ hybrid supercapacitor: The effect of LiFePO₄ content on its performance

Shuli Chen, Huachong Hu, Changqing Wang, Guiling Wang, Jinling Yin, and Dianxue Cao

J. Renewable Sustainable Energy 4, 033114 (2012); http://dx.doi.org/10.1063/1.4727929 (7 pages)

Online Publication Date: 6 June 2012

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Composites of LiFePO₄ and activated carbon (LFP-AC) were prepared by a ball milling method. Their morphologies were investigated by scanning electronic microscopy and energy dispersive spectroscopy. Hybrid supercapacitors were assembled using the LFP-AC composites as the positive electrode and Li₄Ti₅O₁₂ as the negative electrode (LFP-AC/Li₄Ti₅O₁₂). Effects of the positive electrode composition (ratio of LiFePO₄ to AC) on the performance of LFP-AC/Li₄Ti₅O₁₂ were investigated via constant current charge-discharge tests. The results demonstrated that the specific capacity and the specific power of the LFP-AC/Li₄Ti₅O₁₂ hybrid supercapacitor significantly depend upon the content of LiFePO₄ in the LFP-AC positive electrode. At 0.5 A g⁻¹ charge-discharge current, the specific capacity of the LFP-AC/Li₄Ti₅O₁₂ with 30 wt. % LiFePO₄ and 70 wt. % AC in the positive electrode is 42% higher than that of AC/Li₄Ti₅O₁₂, and the two supercapacitors have the same specific power. After 500 charge-discharge cycles at 1.0 A g⁻¹, the specific capacity of the LFP-AC/Li₄Ti₅O₁₂ with 80 wt. % LiFePO₄ and 20 wt. % AC in the positive electrode is 53% higher than that of AC/Li₄Ti₅O₁₂. The hybrid device stores electric energy via both the double-layer electrostatic adsorption and the intercalation/deintercalation of lithium ions.

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84.60.Ve	Energy storage systems, including capacitor banks
88.80.fh	Supercapacitors
81.20.Ev	Powder processing: powder metallurgy, compaction, sintering, mechanical alloying, and granulation
82.45.Fk	Electrodes

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Exploring energy consumption and CO₂ emission of cotton production in Iran

S.H. Pishgar-Komleh, P. Sefeedpari, and M. Ghahderijani

J. Renewable Sustainable Energy 4, 033115 (2012); http://dx.doi.org/10.1063/1.4727906 (14 pages)

Online Publication Date: 11 June 2012

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This study examined the energy use, greenhouse gas (GHG) emission and the relationship between energy inputs and yield of cotton production in Iran. Data were collected randomly from 57 cotton farms using a face to face questionnaire. The results revealed the total energy of 31 237 MJ ha⁻¹ which fertilizer, diesel fuel, and machinery were the main energy consuming inputs. Total GHG emission was 1195 kg CO_2eq ha⁻¹, and machinery, diesel fuel, and irrigation had the highest emissions. Energy ratio and energy productivity were 1.85 and 0.11 kg MJ⁻¹, respectively. In order to explore the relationship between inputs and outputs, the Cobb-Douglas production function was applied and it was deduced that machinery, fertilizer, diesel fuel, and biocide energies had significant effect on cotton yield. Also, the results of marginal physical productivity technique indicated that an additional use of 1 MJ ha⁻¹ from each of the biocide, machinery, and diesel fuel would lead to an increase in production by 1.68, 0.45, and 0.38 kg ha⁻¹, respectively. The share of direct, indirect, renewable, and non-renewable energies was 40%, 60%, 29%, and 71%, respectively.

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89.20.Kk	Engineering
88.05.Qr	Energy use in agriculture
92.40.Xx	Irrigation; dams
88.05.Np	Environmental aspects

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Constant voltage ultracapacitor

Ezzat G. Bakhoum

J. Renewable Sustainable Energy 4, 033116 (2012); http://dx.doi.org/10.1063/1.4729585 (13 pages)

Online Publication Date: 13 June 2012

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Ultracapacitors have attracted lots of attention recently due to their growing use in hybrid vehicles and in energy storage applications for the smart grid. A very undesirable feature of ultracapacitors is the fact that the voltage drops as the capacitor is discharged. DC-DC converters are employed at present to convert the voltage of the ultracapacitor to constant voltage; however, these converters typically do not operate if the voltage of the ultracapacitor drops below 1 V. In addition, DC-DC converters suffer from well-known size/efficiency tradeoffs. This paper introduces a novel new ultracapacitor that is characterized by constant voltage. The new ultracapacitor does not utilize familiar energy conversion principles. Rather, operation depends on an embedded electromechanical system that actually alters the capacitance of the ultracapacitor as the device is discharged. Due to a simple proportionality relationship between charge, capacitance and voltage, the voltage remains constant. Theoretical and experimental investigations have shown that the embedded mechanism for altering the capacitance has an efficiency of 99% or higher.

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84.60.Ve

Energy storage systems, including capacitor banks

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Design of a new linear generator for wave energy conversion based on analytical and numerical analyses

M. R. A. Calado, P. M. C. Godinho, and S. J. P. S. Mariano

J. Renewable Sustainable Energy 4, 033117 (2012); http://dx.doi.org/10.1063/1.4729569 (11 pages)

Online Publication Date: 18 June 2012

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This paper addresses the problem of the sea wave energy conversion. The power delivery at low speeds is one of the barriers imposed by the irregular movement of sea waves, requiring the use of electric machines that can produce large amounts of force to compensate the low speeds of that motion. The main concern is the proposal of a new linear switched reluctance generator. The proposed generator has high power density, robustness, and easy modeling and construction. Its analytical design and optimization based on finite element method are presented. Results and design challenges are discussed.

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84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables
88.60.nf	Energy from ocean waves
84.50.+d	Electric motors
02.70.Dh	Finite-element and Galerkin methods

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Optimization of enzymatic hydrolysis of prairie cordgrass for improved ethanol production

Vasudeo P. Zambare, Archana V. Zambare, Debmalya Barh, and Lew P. Christopher

J. Renewable Sustainable Energy 4, 033118 (2012); http://dx.doi.org/10.1063/1.4729587 (8 pages)

Online Publication Date: 18 June 2012

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Prairie cordgrass (PCG), Spartina pectinata, is considered an energy crop with potential for bioethanol production in North America. The focus of this study was to optimize enzymatic hydrolysis of PCG at higher solids loadings using a thermostable cellulase of a mutant Penicillium pinophilum ATCC 200401. A three variable, five-level central composite design of response surface methodology (RSM) was employed in a total of 20 experiments to model and evaluate the impact of pH (4.1–6.0), solids loadings (6.6%–23.4%), and enzyme loadings (6.6–23.4 FPU/g dry matter, DM) on glucose yield from a thermo-mechanically extruded PCG. The extruded PCG was first hydrolyzed with the crude P. pinophilum cellulase and then fermented to ethanol with Saccharomyces cerevisiae ATCC 24860. Although all three variables had a significant impact, the enzyme loadings proved the most significant parameter for maximizing the glucose yield. A partial cubic equation could accurately model the response surface of enzymatic hydrolysis as the analysis of variance showed a coefficient of determination (R²) of 0.89. At the optimal conditions of pH of 4.5, solids loadings of 10% and enzyme loadings of 20 FPU/g DM, the enzymatic hydrolysis of pretreated PCG produced a glucose yield of 76.1% from the maximum yield which represents an increase of 15% over the non-optimized controls at the zero-level central points. The predicted results based on the RSM regression model were in good agreement with the actual experimental values. The model can present a rapid means for estimating lignocellulose conversion yields within the selected ranges. Furthermore, statistical optimization of solids and enzyme loadings of enzymatic hydrolysis of biomass may have important implications for reduced capital and operating costs of ethanol production.

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88.20.F-	Renewable alternative fuels from biomass energy
02.60.Pn	Numerical optimization
46.55.+d	Tribology and mechanical contacts

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A comparison of biomass gasification and pyrolysis in three kinds of reactors using corn stalk pellets

Zhiwei Wang, Tingzhou Lei, Zenghe Yue, Xiaoyu Yan, Xiaofeng He, Jianjun Hu, and Jinling Zhu

J. Renewable Sustainable Energy 4, 033119 (2012); http://dx.doi.org/10.1063/1.4729594 (8 pages) | Cited 1 time

Online Publication Date: 18 June 2012

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Biomass resources are abundant in China, the cultivation of which is encouraged as it could provide energy for future social and economic development. Utilization of biomass pellets for energy through gasification could help ease critical problems such as energy shortage and environmental deterioration in China. In this paper, the performance of three types of gasification and pyrolysis reactors—downdraft, bubbling, and pyrolysis—were evaluated in terms of thermal output using the same corn stalk pellets. The three reactors were connected in parallel with a common control system, condenser, root blower, gas tank, and gas chromatography (GC) system. Gas composition was analysed using two GC columns. The lower heating values (LHVs) of the pellets, pellets charcoal, and bio-oil were analysed using a rapid screening device. Analyses of the properties of the pellets and pellets charcoal were carried out using an automatic proximate analyser. In the downdraft reactor, gas with an LHV of 3.91–4.44 MJ/Nm³ was obtained at a reduction zone temperature (RZT) of 660–760 °C. In the bubbling reactor, gas with an LHV of 8.48–9.38 MJ/Nm³ was obtained at an RZT of 575–750 °C. In the pyrolysis reactor, gas with an LHV of 14.51–16.49 MJ/Nm³ was obtained at a pyrolysis temperature of 380–530 °C, and pellets charcoal and bio-oil were formed in the pyrolysis reactor as gas-assisted products.

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88.20.mr	Gasification systems; syngas
88.20.F-	Renewable alternative fuels from biomass energy

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Interactive multiobjective daily volt/var control of distribution networks considering wind power and fuel-cell power plants

Taher Niknam, Mohsen Zare, Jamshid Aghaei, and Rasoul Azizipanah-Abarghooee

J. Renewable Sustainable Energy 4, 033120 (2012); http://dx.doi.org/10.1063/1.4727920 (26 pages)

Online Publication Date: 19 June 2012

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This paper deals with a multiobjective daily volt/var control (MDVVC) for radial distribution feeders integrated renewable energy sources (RES) by means of the tap position of the under load tap changer (ULTC) transformers, shunt capacitors, and active and reactive power of RES. The multiple objective functions to be minimized are the electrical energy losses, the voltage deviations, and the total emissions of RES and substations. Discrete behavior of equipments in the distribution systems and nonlinear power flow equations change the VVC problem into a mixed integer non-linear programming (MINLP). Hence, a new optimization method based upon the shuffled frog leaping algorithm (SFLA) is presented to solve the optimization problem. The SFLA is modified for resolving the disadvantages of the original algorithm. Besides of accurately passing local optima, the MSFLA takes less time to achieve the optimal response. Furthermore, the tribe-MSFLA is proposed through using the concept of the tribe. Dealing with the multiobjective optimization problem, an interactive fuzzy satisfying method is used while the objective functions are formulated by a fuzzy set theory. An 85-bus radial distribution system is used to test and assess the performance of the proposed algorithm.

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88.50.J-	Wind farms
88.30.G-	Fuel cell systems
84.70.+p	High-current and high-voltage technology: power systems; power transmission lines and cables
02.60.Pn	Numerical optimization
02.10.Ab	Logic and set theory

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On the optimum sizing of metal hydride tank filled AB₂ type alloy

İsmail Hilali

J. Renewable Sustainable Energy 4, 033121 (2012); http://dx.doi.org/10.1063/1.4732132 (6 pages)

Online Publication Date: 28 June 2012

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When the metal hydride tanks that are used in hydrogen storage are thermally coupled to the fuel cell, thermal management of metal hydride tank is to get importance in the development of the fuel cell performance. Heat transfer has been shown to be the rate limiting process controlling hydrogen uptake or removal. Discharge capacity of the tank has a major impact on the fuel cell efficiency. In this paper, a thermoeconomic optimization analysis is presented yielding a simple algebraic formula for estimating optimum metal hydride tank surface area for heat transfer enhancement. A simple economic method is used in the study, together with thermal analysis. The optimum area of the metal hydride tank filled with commercially available AB₂ type alloy (Ti_0,98Zr_0,02V_0,43Fe_0,09Cr_0,05Mn_1,5) is calculated by this method as 0.16 m². The optimum net savings is about 902.7$ and the value of payback is determined as 1.3 years. Excessive area of the metal hydride tank will not be economical as the optimum tank area.

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88.30.R-	Hydrogen storage
02.60.Pn	Numerical optimization
88.30.P-	Types of fuel cells

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Nusselt number and friction factor correlations for solar air heater duct with broken V-down ribs combined with staggered rib roughness

Anil K. Patil, J. S. Saini, and K. Kumar

J. Renewable Sustainable Energy 4, 033122 (2012); http://dx.doi.org/10.1063/1.4732133 (17 pages)

Online Publication Date: 29 June 2012

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Artificial roughening of a broad wall of solar air heater leads to significant enhancement in heat transfer besides comparable rise in friction losses. This paper presents the outcome of experimental study on heat transfer and fluid friction characteristics of solar air heater duct roughened with broken V-down rib combined with staggered rib piece. Experimental data were collected on a high aspect ratio rectangular duct by varying the Reynolds number from 3000 to 17 000, relative gap position (s′/s) 0.2–0.8, relative staggered rib position (p′/p) 0.2–0.8, relative staggered rib size (r/e) 1–2.5, for the fixed values of relative roughness pitch (p/e) of 10, relative roughness height (e/D_h) of 0.043, relative gap size (g/e) of 1, and angle of attack (α) of 60°. The effect of flow Reynolds number and roughness parameters on Nusselt number and friction factor has been explored and the results are compared with continuous V-down rib roughened duct and smooth duct under similar flow conditions. Correlations for the Nusselt number and friction factor as a function of Reynolds number and roughness parameters have been developed.

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