Editing PVT dispatch strategy literature review

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This page describes selected literature on combined photovoltaic solar thermal systems.

== [http://www.sciencedirect.com/science/article/pii/S0038092X12002137 The effect of hybrid photovoltaic thermal device operating conditions on intrinsic layer thickness optimization of hydrogenated amorphous silicon solar cells<ref name="Pathak">M. J. M. Pathak, K. Girotra, S. J. Harrison, and J. M. Pearce, "The effect of hybrid photovoltaic thermal device operating conditions on intrinsic layer thickness optimization of hydrogenated amorphous silicon solar cells," Solar Energy, vol. 86, no. 9, pp. 2673–2677, Sep. 2012.</ref>] ==

'''Abstract''': Historically, the design of hybrid solar photovoltaic thermal (PVT) systems has focused on cooling crystalline silicon (c-Si)-based photovoltaic (PV) devices to avoid temperature-related losses. This approach neglects the associated performance losses in the thermal system and leads to a decrease in the overall exergy of the system. Consequently, this paper explores the use of hydrogenated amorphous silicon (a-Si:H) as an absorber material for PVT in an effort to maintain higher and more favorable operating temperatures for the thermal system. Amorphous silicon not only has a smaller temperature coefficient than c-Si, but also can display improved PV performance over extended periods of higher temperatures by annealing out defect states from the Staebler–Wronski effect. In order to determine the potential improvements in a-Si:H PV performance associated with increased thicknesses of the i-layers made possible by higher operating temperatures, a-Si:H PV cells were tested under 1 sun illumination (AM1.5) at temperatures of 25 <sup>o</sup>C (STC), 50 <sup>o</sup>C (representative PV operating conditions), and 90 <sup>o</sup>C (representative PVT operating conditions). PV cells with an i-layer thicknesses of 420, 630 and 840 nm were evaluated at each temperature. Results show that operating a-Si:H-based PV at 90 <sup>o</sup>C, with thicker i-layers than the cells currently used in commercial production, provided a greater power output compared to the thinner cells operating at either PV or PVT operating temperatures. These results indicate that incorporating a-Si:H as the absorber material in a PVT system can improve the thermal performance, while simultaneously improving the electrical performance of a-Si:H-based PV.

* Amorphous silicon has a smaller temperature coefficient (.1%/oC) than c-Si (.4%/oC) and can display improved PV performance over extended periods of higher temperatures by annealing out defect states from the Staebler–Wronski effect
* a-Si:H can be deposited directly onto the absorber plate making an integral system
* Running the system at optimal thermal conditions would allow for the a-Si:H cells to achieve a higher operating temperature, which would have the added benefit of annealing SWE defects and achieving a higher electrical performance
* The temperatures of the cells are measured at the degradation temperature. The effect of temperature on the power is -0.016 W/oC
* If the thicker cells are degraded at higher temperatures they stabilize at a higher power than the thinner cells degraded at STC
* Choosing the correct thickness for the a-Si:H in a PVT system, the 25 oC DSS from SWE is not the limiting factor and that the operating temperature of the module should also be considered

== [http://www.sciencedirect.com/science/article/pii/S0927024812000165 Effects on amorphous silicon photovoltaic performance from high-temperature annealing pulses in photovoltaic thermal hybrid devices<ref name="Pearce">M. J. M. Pathak, J. M. Pearce, and S. J. Harrison, "Effects on amorphous silicon photovoltaic performance from high-temperature annealing pulses in photovoltaic thermal hybrid devices," Solar Energy Materials and Solar Cells, vol. 100, no. 0, pp. 199–203, May 2012.</ref>] ==

'''Abstract''': There is a renewed interest in photovoltaic solar thermal (PVT) hybrid systems, which harvest solar energy for heat and electricity. Typically, a main focus of a PVT system is to cool the photovoltaic (PV) cells to improve the electrical performance; however, this causes the thermal component to underperform compared to a solar thermal collector. The low temperature coefficients of amorphous silicon (a-Si:H) allow the PV cells to be operated at high temperatures, which are a potential candidate for a more symbiotic PVT system. The fundamental challenge of a-Si:H PV is light-induced degradation known as the Staebler–Wronski effect (SWE). Fortunately, SWE is reversible and the a-Si:H PV efficiency can be returned to its initial state if the cell is annealed. Thus an opportunity exists to deposit a-Si:H directly on the solar thermal absorber plate where the cells could reach the high temperatures required for annealing.
In this study, this opportunity is explored experimentally. First a-Si:H PV cells were annealed for 1 h at 100 1C on a 12 h cycle and for the remaining time the cells were degraded at 50 1C in order to simulate stagnation of a PVT system for 1 h once a day. It was found when comparing the cells after stabilization at normal 50 1C degradation that this annealing sequence resulted in a 10.6% energy gain when compared to a cell that was only degraded at 50 1C.

* PVT hybrid systems have been shown to be more efficient at solar energy collection on the basis of exergy, energy and cost
* SWE is reversible and the a-Si:H PV cell efficiency can be returned to its initial state if the cell is heated to 150 oC for 4 h as the defect states are annealed
* In a solar thermal flat plate collector the temperature can easily reach over 100 oC and even climb higher than 200 oC if the system is stagnated
* a-Si:H PV when degraded at higher temperatures will stabilize at higher efficiencies

== [http://www.sciencedirect.com/science/article/pii/S1364032111003492 A review of solar photovoltaic levelized cost of electricity<ref name="Branker">K. Branker, M. J. M. Pathak, and J. M. Pearce, "A review of solar photovoltaic levelized cost of electricity," Renewable and Sustainable Energy Reviews, vol. 15, no. 9, pp. 4470–4482, Dec. 2011.</ref>] ==

'''Abstract''': As the solar photovoltaic (PV) matures, the economic feasibility of PV projects is increasingly being evaluated using the levelized cost of electricity (LCOE) generation in order to be compared to other electricity generation technologies. Unfortunately, there is lack of clarity of reporting assumptions, justifications and degree of completeness in LCOE calculations, which produces widely varying and contradictory results. This paper reviews the methodology of properly calculating the LCOE for solar PV, correcting the misconceptions made in the assumptions found throughout the literature. Then a template is provided for better reporting of LCOE results for PV needed to influence policy mandates or make invest decisions. A numerical example is provided with variable ranges to test sensitivity, allowing for conclusions to be drawn on the most important variables. Grid parity is considered when the LCOE of solar PV is comparable with grid electrical prices of conventional technologies and is the industry target for cost-effectiveness. Given the state of the art in the technology and favourable financing terms it is clear that PV has already obtained grid parity in specific locations and as installed costs continue to decline, grid electricity prices continue to escalate, and industry experience increases, PV will become an increasingly economically advantageous source of electricity over expanding geographical regions.

== [http://www.sciencedirect.com/science/article/pii/S0306261909002761# A review on photovoltaic/thermal hybrid solar technology<ref name="Chow">T. T. Chow, "A review on photovoltaic/thermal hybrid solar technology," Applied Energy, vol. 87, no. 2, pp. 365–379, Feb. 2010.</ref>] ==

'''Abstract''': A significant amount of research and development work on the photovoltaic/thermal (PVT) technology has been done since the 1970s. Many innovative systems and products have been put forward and their quality evaluated by academics and professionals. A range of theoretical models has been introduced and their appropriateness validated by experimental data. Important design parameters are identified. Collaborations have been underway amongst institutions or countries, helping to sort out the suitable products and systems with the best marketing potential. This article gives a review of the trend of development of the technology, in particular the advancements in recent years and the future work required.

* A common PV module converts 4–17% of the incoming solar radiation into electricity and more than 50% of the incident solar energy is converted as heat
* The double glass configuration is better than the single-glass option for conventional PVT/a collectors
* The parametric study showed that the thermal and electrical outputs increase with increased absorber length, air mass flow rate and packing factor, but decrease with increased duct depth
* The thermal efficiency depends on the packing factor, but this is not the case for cell efficiency

== [http://www.sciencedirect.com/science/article/pii/S0960148106000784# Improved PV/T solar collectors with heat extraction by forced or natural air circulation<ref name="Tonui">J. K. Tonui and Y. Tripanagnostopoulos, "Improved PV/T solar collectors with heat extraction by forced or natural air circulation," Renewable Energy, vol. 32, no. 4, pp. 623–637, Apr. 2007.</ref>] ==

'''Abstract''': The photovoltaic (PV) cells suffer efficiency drop as their operating temperature increases especially under high insolation levels and cooling is beneficial. Air-cooling, either by forced or natural flow, presents a non-expensive and simple method of PV cooling and the solar preheated air could be utilized in built, industrial and agricultural sectors. However, systems with heat extraction by air circulation are limited in their thermal performance due to the low density, the small volumetric heat capacity and the small thermal conductivity of air and measures for heat transfer augmentation is necessary. This paper presents the use of a suspended thin flat metallic sheet at the middle or fins at the back wall of an air duct as heat transfer augmentations in an air-cooled photovoltaic/thermal (PV/T) solar collector to improve its overall performance. The steady-state thermal efficiencies of the modified systems are compared with those of typical PV/T air system. Daily temperature profiles of the outlet air, the PV rear surface and channel back wall are presented confirming the contribution of the modifications in increasing system electrical and thermal outputs. These techniques are anticipated to contribute towards wider applications of PV systems due to the increased overall efficiency.

== [http://www.sciencedirect.com/science/article/pii/S0038092X01000962# Hybrid photovoltaic/thermal solar systems<ref name="Tripanagnostopoulos">Y. Tripanagnostopoulos, T. Nousia, M. Souliotis, and P. Yianoulis, "Hybrid photovoltaic/thermal solar systems," Solar Energy, vol. 72, no. 3, pp. 217–234, Mar. 2002.</ref>] ==

'''Abstract''': We present test results on hybrid solar systems, consisting of photovoltaic modules and thermal collectors (hybrid PV/T systems). The solar radiation increases the temperature of PV modules, resulting in a drop of their electrical efficiency. By proper circulation of a fluid with low inlet temperature, heat is extracted from the PV modules keeping the electrical efficiency at satisfactory values. The extracted thermal energy can be used in several ways, increasing the total energy output of the system. Hybrid PV/T systems can be applied mainly in buildings for the production of electricity and heat and are suitable for PV applications under high values of solar radiation and ambient temperature. Hybrid PV/T experimental models based on commercial PV modules of typical size are described and outdoor test results of the systems are presented and discussed. The results showed that PV cooling can increase the electrical efficiency of PV modules, increasing the total efficiency of the systems. Improvement of the system performance can be achieved by the use of an additional glazing to increase thermal output, a booster diffuse reflector to increase electrical and thermal output, or both, giving flexibility in system design.

== [http://www.sciencedirect.com/science/article/pii/S0038092X00001535 Performance evaluation of solar photovoltaic/thermal systems<ref name="Huang">B. . Huang, T. . Lin, W. . Hung, and F. . Sun, "Performance evaluation of solar photovoltaic/thermal systems," Solar Energy, vol. 70, no. 5, pp. 443–448, 2001.</ref>] ==

'''Abstract''': The major purpose of the present study is to understand the performance of an integrated photovoltaic and thermal solar system (IPVTS) as compared to a conventional solar water heater and to demonstrate the idea of an IPVTS design. A commercial polycrystalline PV module is used for making a PV/T collector. The PV/T collector is used to build an IPVTS. The test results show that the solar PV/T collector made from a corrugated polycarbonate panel can obtain a good thermal efficiency. The present study introduces the concept of primary-energy saving efficiency for the evaluation of a PV/T system. The primary-energy saving efficiency of the present IPVTS exceeds 0.60. This is higher than for a pure solar hot water heater or a pure PV system. The characteristic daily efficiency ηs* reaches 0.38 which is about 76% of the value for a conventional solar hot water heater using glazed collectors (ηs*=0.50). The performance of a PV/T collector can be improved if the heat-collecting plate, the PV cells and the glass cover are directly packed together to form a glazed collector. The manufacturing cost of the PV/T collector and the system cost of the IPVTS can also be reduced. The present study shows that the idea of IPVTS is economically feasible too.

== [http://ieeexplore.ieee.org/xpl/articleDetails.jsp?arnumber=5411247 Optimizing design of household scale hybrid solar photovoltaic + combined heat and power systems for Ontario<ref name="Derewonko">P. Derewonko and J. M. Pearce, "Optimizing design of household scale hybrid solar photovoltaic + combined heat and power systems for Ontario," in 2009 34th IEEE Photovoltaic Specialists Conference (PVSC), 2009, pp. 001274 –001279.</ref>] ==

'''Abstract''': This paper investigates the feasibility of implementing a hybrid solar photovoltaic (PV) + combined heat and power (CHP) and battery bank system for a residential application to generate reliable base load power to the grid in Ontario. Deploying PV on a large-scale has a penetration level threshold due to the inherent power supply intermittency associated with the solar resource. By creating a hybrid PV+CHP system there is potential of increasing the PV penetration level. One year of one second resolution pyranometer data is analyzed for Kingston Ontario to determine the total amount of PV energy generation potential, the rate of change of PV power generation due to intermittent cloud cover, and the daily CHP run time required to supply reliable base load power to the grid using this hybrid system. This analysis found that the vast majority of solar energy fluctuations are small in magnitude and the worst case energy fluctuation can be accommodated by relatively inexpensive and simple storage with conventional lead-acid batteries. For systems where the PV power rating is identical to the CHP unit, the CHP unit must run for more than twenty hours a day for the system to meet the base load requirement during the winter months. This provides a fortunate supply of heat, which can be used for the needed home heating. This paper provides analysis for a preliminary base line system.

== [http://www.sciencedirect.com/science/article/pii/S0038092X07000813 Study of a new concept of photovoltaic–thermal hybrid collector<ref name="Assoa">Y. B. Assoa, C. Menezo, G. Fraisse, R. Yezou, and J. Brau, "Study of a new concept of photovoltaic–thermal hybrid collector," Solar Energy, vol. 81, no. 9, pp. 1132–1143, Sep. 2007.</ref>] ==

'''Abstract''': This work represents the second step of the development of a new concept of photovoltaic/thermal (PV/T) collector. This type of collector combines preheating of the air and the production of hot water in addition to the classical electrical function of the solar cells. The alternate positioning of the thermal solar collector section and the PV section permits the production of water at higher mean temperatures than most of existing hybrid collectors. These higher temperatures will allow the coupling of components such as solar cooling devices during the summer and obviously a direct domestic hot water (DHW) system without the need for additional auxiliary heating systems. In this paper, a simplified steady-state two-dimensional mathematical model of a PV/T bi-fluid (air and water) collector with a metal absorber is developed. Then, a parametric study (numerically and experimentally) is undertaken to determine the effect of various factors such as the water mass flow rate on the solar collector thermal performances. Finally, the results from an experimental test bench and the first simulation results obtained on full scale experiments are compared.

== [http://asmedl.org/getabs/servlet/GetabsServlet?prog=normal&id=JSEEDO000128000002000258000001&idtype=cvips&gifs=yes Analysis of Potential Conversion Efficiency of a Solar Hybrid System With High-Temperature Stage<ref name="Vorobiev">Y. V. Vorobiev, J. González-Hernández, and A. Kribus, "Analysis of Potential Conversion Efficiency of a Solar Hybrid System With High-Temperature Stage," Journal of Solar Energy Engineering, vol. 128, no. 2, p. 258, 2006.</ref>] ==

'''Abstract''': The analysis is given of hybrid system of solar energy conversion having a stage operating at high temperature. The system contains a radiation concentrator, a photovoltaic solar cell, and a thermal generator, which could be thermoelectric one or a heat engine. Two options are discussed, one (a) with concentration of the whole solar radiation on the PV cell working at high temperature and coupled to the high-temperature stage, and another (b) with a special PV cell construction, which allows the use of the part of solar spectrum not absorbed in the semiconductor material of the cell ("thermal energy") to drive the high-temperature stage while the cell is working at ambient temperature. The possibilities of using different semiconductor materials are analyzed. It is shown that the demands to the cell material are different in the two cases examined: in system (a) with high temperature of cell operation, the materials providing minimum temperature dependence of the conversion efficiency are necessary, for another system (b) the materials with the larger band gap are profitable. The efficiency of thermal generator is assumed to be proportional to that of the Carnot engine. The optical and thermal energy losses are taken into account, including the losses by convection and radiation in the high-temperature stage. The radiation losses impose restrictions upon the working temperature of the thermal generator in the system (b), thus defining the highest possible concentration ratio. The calculations made show that the hybrid system proposed could be both efficient and practical, promising the total conversion efficiency around 25–30 % for system (a), and 30–40 % for system (b).

== [http://www.sciencedirect.com/science/article/pii/S0196890406000409# Hybrid PV/T solar systems for domestic hot water and electricity production<ref name="Kalogirou">S. A. Kalogirou and Y. Tripanagnostopoulos, "Hybrid PV/T solar systems for domestic hot water and electricity production," Energy Conversion and Management, vol. 47, no. 18–19, pp. 3368–3382, Nov. 2006.</ref>] ==

'''Abstract''': Hybrid photovoltaic/thermal (PV/T) solar systems can simultaneously provide electricity and heat, achieving a higher conversion rate of the absorbed solar radiation than standard PV modules. When properly designed, PV/T systems can extract heat from PV modules, heating water or air to reduce the operating temperature of the PV modules and keep the electrical efficiency at a sufficient level. In this paper, we present TRNSYS simulation results for hybrid PV/T solar systems for domestic hot water applications both passive (thermosyphonic) and active. Prototype models made from polycrystalline silicon (pc-Si) and amorphous silicon (a-Si) PV module types combined with water heat extraction units were tested with respect to their electrical and thermal efficiencies, and their performance characteristics were evaluated. The TRNSYS simulation results are based on these PV/T systems and were performed for three locations at different latitudes, Nicosia (35°), Athens (38°) and Madison (43°). In this study, we considered a domestic thermosyphonic system and a larger active system suitable for a block of flats or for small office buildings. The results show that a considerable amount of thermal and electrical energy is produced by the PV/T systems, and the economic viability of the systems is improved. Thus, the PVs have better chances of success especially when both electricity and hot water is required as in domestic applications.

== [http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=4374983 Combined Photovoltaic / Thermal Energy System for Stand-alone Operation<ref name="Jardan">R. K. Jardan, I. Nagy, A. Cid-Pastor, R. Leyva, A. El Aroudi, and L. Martinez-Salamero, "Combined Photovoltaic / Thermal Energy System for Stand-alone Operation," in IEEE International Symposium on Industrial Electronics, 2007. ISIE 2007, 2007, pp. 2403 –2408.</ref>] ==

'''Abstract''': The utilization of solar energy can be made by photovoltaic (PV) cells to generate electric power directly and solar thermal (T) panels can be applied to generate heat power. When the utilization of the solar energy is necessary to generate electric power, the option of using T panels in combination with some heat / electric power conversion technology can be a viable solution. The power generated by utilizing the solar energy absorbed by a given area of solar panel can be increased if the two technologies, PV and T cells, are combined in such a way that the resulting unit will be capable of co-generation of heat and electric power. In the present paper combined Photovoltaic / Thermal panels are suggested to generate heat power to produce hot water, while the photovoltaic part is used to obtain electric power mainly for covering the electric power consumption of the system, to supply the electronic control units and to operate pump drives etc. Ac and dc supplies are provided by converters for covering self-consumption and possibly the need of some household appliances. The development and design of the system is made by extensive use of modeling and simulation techniques. In the paper a part of the simulation studies, carried out to determine the energy balance in the electric energy conversion section of the system and the control structure, assuming stand-alone operation is presented.

== [http://ieeexplore.ieee.org/xpls/abs_all.jsp?arnumber=654325 Hybrid collectors using thin-film technology<ref name="Platz">R. Platz, D. Fischer, M.-A. Zufferey, J. A. A. Selvan, A. Haller, and A. Shah, "Hybrid collectors using thin-film technology," in , Conference Record of the Twenty-Sixth IEEE Photovoltaic Specialists Conference, 1997, 1997, pp. 1293 –1296.</ref>] ==

'''Abstract''': Amorphous silicon (a-Si:H) based solar cells are highly interesting in the context of hybrid (i.e. photovoltaic/thermal) solar energy conversion. First, their large area capability and the variety of possible substrate materials permit to apply a-Si:H PV modules directly on the surface of conventional heat collectors at low cost. Further, the low temperature coefficient of a-Si:H cells (0.1%/K) allows operation of a-Si:H solar modules at temperatures as high as 100°C without substantial power loss. The authors focus on the thermal performance of such hybrid collectors based on a-Si:H cells, with emphasis on a ZnO coat on top of the solar cell. ZnO can be "tuned" to absorb the infrared part of sunlight and, at the same time, its emission coefficient for heat-radiation is nearly as low as that of the optimized selective surfaces used in thermal collectors. The authors propose a collector structure with a high potential for thermal conversion efficiency while maintaining high electrical conversion efficiency

== [http://www.hindawi.com/journals/ijp/2012/307287/ref/ Hybrid Solar: A Review on Photovoltaic and Thermal Power Integration<ref name="T. T. Chow">T. T. Chow, G. N. Tiwari, and C. Menezo, "Hybrid Solar: A Review on Photovoltaic and Thermal Power Integration," International Journal of Photoenergy, vol. 2012, pp. 1–17, 2012.</ref>] ==

'''Abstract''': The market of solar thermal and photovoltaic electricity generation is growing rapidly. New ideas on hybrid solar technology evolve for a wide range of applications, such as in buildings, processing plants, and agriculture. In the building sector in particular, the limited building space for the accommodation of solar devices has driven a demand on the use of hybrid solar technology for the multigeneration of active power and/or passive solar devices. The importance is escalating with the worldwide trend on the development of low-carbon/zero-energy buildings. Hybrid photovoltaic/thermal (PVT) collector systems had been studied theoretically, numerically, and experimentally in depth in the past decades. Together with alternative means, a range of innovative products and systems has been put forward. The final success of the integrative technologies relies on the coexistence of robust product design/construction and reliable system operation/maintenance in the long run to satisfy the user needs. This paper gives a broad review on the published academic works, with an emphasis placed on the research and development activities in the last decade.

== [http://jap.aip.org/resource/1/japiau/v108/i11/p114907_s1 Parametric analysis of a coupled photovoltaic/thermal concentrating solar collector for electricity generation<ref name="Otanicar">T. Otanicar, I. Chowdhury, P. E. Phelan, and R. Prasher, "Parametric analysis of a coupled photovoltaic/thermal concentrating solar collector for electricity generation," Journal of Applied Physics, vol. 108, no. 11, pp. 114907–114907–8, Dec. 2010.</ref>] ==

'''Abstract''': The analysis of the combined efficiencies in a coupled photovoltaic (PV)/thermal concentrating solar collector are presented based on a coupled electrical/thermal model. The calculations take into account the drop in efficiency that accompanies the operation of PV cells at elevated temperatures along with a detailed analysis of the thermal system including losses. An iterative numerical scheme is described that involves a coupled electrothermal simulation of the solar energy conversion process. In the proposed configuration losses in the PV cell due to reduced efficiencies at elevated temperatures and the incident solar energy below the PV bandgap are both harnessed as heat. This thermal energy is then used to drive a thermodynamic power cycle. The simulations show that it is possible to optimize the overall efficiency of the system by variation in key factors such as the solar concentration factor, the band gap of the PV material, and the system thermal design configuration, leading to a maximum combined efficiency of ∼ 32.3% for solar concentrations between 10–50 and a band-gap around 1.5–2.0 eV.

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 * In a solar thermal flat plate collector the temperature can easily reach over 100 oC and even climb higher than 200 oC if the system is stagnated
 * a-Si:H PV when degraded at higher temperatures will stabilize at higher efficiencies
-* a-Si:H PV performs better at high temperatures since the optoelectronic properties of a-Si:H materials stabilize at a higher efficiency
-* During the ramp up in temperature, the power drops initially, but then slowly increases thereafter. This may be because the cell initially suffers from the rapid increase in the temperature during the ramp until it is closer to achieving surface cell temperatures of 100 <sup>o</sup>C required for the annealing process to take a significant effect
-* Although a-Si:H PV do perform better at higher temperatures to a point, cells are also very sensitive to fluctuations in temperature
-* In all three annealing tests, the FF spiked at around 80 <sup>o</sup>C whereas the power reaches its maximum at temperatures lower than 50 <sup>o</sup>C
-* The higher the temperature, the faster the DSS obtained and higher the corresponding Pmax
-* At the lower degraded temperatures, the annealing has a larger effect on the power increase compared to the higher degraded temperature
-* The thicker cells having more material and defect states requires a greater annealing time
 == [http://www.sciencedirect.com/science/article/pii/S1364032111003492 A review of solar photovoltaic levelized cost of electricity<ref name="Branker">K. Branker, M. J. M. Pathak, and J. M. Pearce, "A review of solar photovoltaic levelized cost of electricity," Renewable and Sustainable Energy Reviews, vol. 15, no. 9, pp. 4470–4482, Dec. 2011.</ref>] ==