PVT dispatch strategy literature review

From Appropedia
Jump to: navigation, search

Sunhusky.png Developed by Michigan Tech's Open Sustainability Technology Lab. For more see MOST's Appropedia Hub.

Wanted: Grad students interested in making a solar-powered open-source 3-D printing and distributed manufacturing future. Apply now.
Contact: Professor Joshua Pearce

OSL.jpg

Open-pv.png This page is part of an MTU graduate course MY5490/EE5490: Solar Photovoltaic Science and Engineering. Both the course documentation and the course generated content is open source. However, the course runs over Spring semesters during this time it is not open edit. Please leave comments using the discussion tab.


Contribute to this Literature Review Although this page is hosted by MOST it is open edit. Please feel free to add sources and summaries. If you are new to Appropedia, you can start contributing after you create an account or log in if you have an existing account.

Contents

[edit] This page describes selected literature on combined photovoltaic solar thermal systems

[edit] The effect of hybrid photovoltaic thermal device operating conditions on intrinsic layer thickness optimization of hydrogenated amorphous silicon solar cells[1]

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 oC (STC), 50 oC (representative PV operating conditions), and 90 oC (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 oC, 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

[edit] Effects on amorphous silicon photovoltaic performance from high-temperature annealing pulses in photovoltaic thermal hybrid devices [2]

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
  • 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 oC 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 oC whereas the power reaches its maximum at temperatures lower than 50 oC
  • 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

[edit] A review of solar photovoltaic levelized cost of electricity[3]

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.

[edit] A review on photovoltaic/thermal hybrid solar technology[4]

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

[edit] Improved PV/T solar collectors with heat extraction by forced or natural air circulation[5]

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.

[edit] Hybrid photovoltaic/thermal solar systems[6]

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.

[edit] Performance evaluation of solar photovoltaic/thermal systems[7]

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.

[edit] Optimizing design of household scale hybrid solar photovoltaic + combined heat and power systems for Ontario[8]

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.

[edit] Study of a new concept of photovoltaic–thermal hybrid collector[9]

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.

[edit] Analysis of Potential Conversion Efficiency of a Solar Hybrid System With High-Temperature Stage[10]

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).

[edit] Hybrid PV/T solar systems for domestic hot water and electricity production[11]

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.

[edit] Combined Photovoltaic / Thermal Energy System for Stand-alone Operation[12]

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.

[edit] Hybrid collectors using thin-film technology[13]

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

[edit] Hybrid Solar: A Review on Photovoltaic and Thermal Power Integration[14]

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.

[edit] Parametric analysis of a coupled photovoltaic/thermal concentrating solar collector for electricity generation[15]

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.

[edit] Band-Gap Tuned Direct Absorption for a Hybrid Concentrating Solar Photovoltaic/Thermal System[16]

Abstract: Two methods often proposed for harnessing renewable energy, photovoltaics and solar thermal, both utilize the power of the sun. Each of these systems independently presents unique engineering challenges but when coupled together the challenge intensifies due to competing operating requirements. Recent research has demonstrated these hybrid systems for low-temperature applications but there exists limited studies at higher concentration ratios, and thus higher temperatures. What these studies have shown is that keeping the photovoltaic (PV) cell temperature low keeps the overall system efficiency relatively high but results in low efficiencies from the thermal system. This study presents a unique design strategy for a hybrid PV/thermal system that only has mild thermal coupling which can lead to enhanced efficiency. By creating a fluid filter that absorbs energy directly in the fluid below the band-gap and a PV cell with an active cooling strategy combined efficiencies greater than 38% can be achieved.

[edit] Thermal-photovoltaic solar hybrid system for efficient solar energy conversion[17]

Abstract: A hybrid solar system with high temperature stage is described. The system contains a radiation concentrator, a photovoltaic solar cell and a heat engine or thermoelectric generator. Two options are discussed, one with a special PV cell construction, which uses the heat energy from the part of solar spectrum not absorbed in the semiconductor material of the cell; the other with concentration of the whole solar radiation on the PV cell working at high temperature and coupled to the high temperature stage. The possibilities of using semiconductor materials with different band gap values are analyzed, as well as of the different thermoelectric materials. The calculations made show that the proposed hybrid system could be practical and efficient.

[edit] Intrinsic and light induced gap states in a-Si:H materials and solar cells—effects of microstructure[18]

Abstract: The effects of microstructure on the gap states of hydrogen diluted and undiluted hydrogenated amorphous silicon (a-Si:H) thin film materials and their solar cells have been investigated. In characterizing the films the commonly used methodology of relating just the magnitudes of photocurrents and subgap absorption, α(E), was expanded to take into account states other than those due to dangling bond defects. The electron mobility-lifetime products were characterized as a function of carrier generation rates and analysis was carried out of the entire α(E) spectra and their evolution with light induced degradation. Two distinctly different defect states at 1.0 and 1.2 eV from the conduction band and their contributions to carrier recombination were identified and their respective evolution under 1 sun illumination characterized. Direct correlations were obtained between the recombination in thin films with that of corresponding solar cells. The effects of the difference in microstructure on the changes in these two gap states in films and solar cells were also identified. It is found that improved stability of protocrystalline Si:H can in part be attributed to the reduction of the 1.2 eV defects. It is also shown that ignoring the presence of multiple defects leads to erroneous conclusions being drawn about the stability of a-Si:H and SWE.

[edit] Reversible conductivity changes in discharge‐produced amorphous Si[19]

Abstract: A new reversible photoelectronic effect is reported for amorphous Si produced by glow discharge of SiH4. Long exposure to light decreases both the photoconductivity and the dark conductivity, the latter by nearly four orders of magnitude. Annealing above 150 °C reverses the process. A model involving optically induced changes in gap states is proposed. The results have strong implications for both the physical nature of the material and for its applications in thin‐film solar cells, as well as the reproducibility of measurements on discharge‐produced Si.

[edit] Carrier recombination and differential diode quality factors in the dark forward bias current-voltage characteristics of a‐Si:H solar cells[20]

Abstract: A careful study has been carried out on dark forward bias current-voltage characteristics in high-quality well-controlled a‐Si:H solar cell structures. Contributions of potential barriers in the intrinsic layers adjacent to the p and n contacts on carrier injection have been clearly identified and carrier recombination in the p/i regions systematically controlled and clearly separated from that in the bulk of the intrinsic layers. It is found that the recombination in the p/i regions results in voltage-independent diode quality factor, n, with values very close to 1 whereas recombination in the bulk results in bias-dependent differential diode quality factors, n(V). These n(V) characteristics are consistent with Shockley-Read-Hall recombination through a continuous distribution of gap states in the intrinsic layers which have spatially uniform distributions of gap states and electric field. Based on an analytical model the n(V) characteristics are interpreted in terms of Gaussian-like energy distributions of gap states in both undiluted and diluted protocrystalline a‐Si:H intrinsic layers. Gaussian-like distributions are identified centered around as well as ∼ 0.3 eV away from midgap with differences in their distributions for the two materials in the annealed states and their evolution upon introducing light-induced defects. These results demonstrate that forward bias dark currents and, in particular, n(V) characteristics offer a reliable probe for characterizing the gap states of the native- and light-induced defect states in a‐Si:H solar cells as well as mechanisms limiting their performance.

[edit] Modeling of light-induced degradation of amorphous silicon solar cells[21]

Abstract: Light-induced degradation of hydrogenated amorphous silicon (a-Si:H) solar cells has been modeled using computer simulations. In the computer model, the creation of light-induced defects as a function of position in the solar cell was calculated using the recombination profile. In this way, a new defect profile in the solar cell was obtained and the performance was calculated again. The results of computer simulations were compared to experimental results obtained on a-Si:H solar cell with different intrinsic layer thickness. These experimental solar cells were degraded under both open- and short-circuit conditions, because the recombination profile in the solar cells could then be altered significantly. A reasonable match was obtained between the experimental and simulation results if only the mid-gap defect density was increased. To our knowledge, it is the first time that light-induced degradation of the performance and the quantum efficiency of a thickness series of a-Si:H solar cells has been modeled at once using computer simulations.

[edit] Room temperature annealing of fast state from 1 sun illumination in protocrystalline Si:H materials and solar cells[22]

Abstract: In order to obtain more insight into the nature of the recovery in the light induced changes at room temperature in hydrogenated amorphous silicon (a-Si:H) solar cells the relaxation of the photocurrents in the light induced changes in protocrystalline a-Si:H thin films were investigated. Immediately upon the removal of 1 sun illumination recoveries in the photocurrents are found like those present in the currents in the dark current-voltage characteristics in corresponding p-i-n solar cells. The striking similarity between the results on thin films and the corresponding dark forward bias current-voltage characteristics of solar cells suggest that the recoveries obtained with low generation rates (5×1015cm-3s-1) in the films are a measure of annealing kinetics of the defect states around midgap in the bulk of the films. The rates of recoveries decrease with higher carrier generation rates and the length of the light induced degradation. Results are presented which indicate that the history of creation and annealing of light induced defect states is important in determining subsequent creation and annealing kinetics.

[edit] Thin-film Si:H-based solar cells[23]

Abstract: Recent developments in the photovoltaic (PV) industry, driven by a shortage of solar grade Si feedstock to grow Si wafers or ribbons, have stimulated a strong renewed interest in thin-film technologies and in particular in solar cells based on protocrystalline hydrogenated amorphous silicon (a-Si:H) or nanocrystalline/microcrystalline (nc/μc)-Si:H. There are a number of institutions around the world developing protocrystalline thin-film Si:H technologies as well as those based on tandem and triple junction cells consisting of a-Si:H, a-Si:Ge:H and nc/μc-Si:H. There are also several large commercial companies actively marketing large production-scale plasma-enhanced chemical vapor deposition (PECVD) deposition equipment for the production of such modules. Reduction in the cost of the modules can be achieved by increasing their stabilized efficiencies and the deposition rates of the Si:H materials. In this paper, recent results are presented which provide insights into the nature of protocrystalline Si:H materials, optimization of cell structures and their light-induced degradation that are helpful in addressing these issues. The activities in these areas that are being carried out in the United States are also briefly reviewed.

[edit] Light-induced recovery of a-Si solar cells[24]

Abstract: The light-induced recovery in efficiency of amorphous silicon (a-Si) solar cells has been studied. The recovery of solar cells degraded by a concentrated light-soaking was accelerated under 1 sun illumination as compared with that in the dark. A similar phenomenon has been observed under current injection. The kinetics of light-induced annealing has been discussed on the basis of a series of the experiments.

[edit] Phase engineering of a-Si:H solar cells for optimized performance[25]

Abstract: Until recently, the advances in hydrogenated amorphous silicon (a-Si:H) solar cell performance and stability have been achieved materials prepared with hydrogen dilution following primarily empirical approaches. This paper discusses the recently obtained insights into the growth, microstructure and nature of these materials. Such protocrystalline Si:H materials are more ordered than the a-Si:H obtained without dilution and evolve with thickness from an amorphous phase into first a mixed amorphous–microcrystalline and subsequently into a single microcrystalline phase. The development of deposition phase diagrams, characterize their microstructural evolution during growth which can be used to guide the fabrication of solar cell structures in a controlled way. Examples are presented and discussed of their application in solar cell fabrication to obtain a fundamental understanding of the properties of the phase transitions as well as the systematic optimization of cell performance.

[edit] Light-induced defect states in hydrogenated amorphous silicon centered around 1.0 and 1.2 eV from the conduction band edge[26]

Abstract: To take into account the presence of multiple light-induced defect states in hydrogenated amorphous silicon (a-Si:H) the evolution of the entire spectra of photoconductive subgap absorption, α(hν), has been analyzed. Using this approach two distinctly different light-induced defect states centered around 1.0 and 1.2 eV from the conduction band edge are clearly identified. Results are presented on their evolution and respective effects on carrier recombination that clearly point to the importance of these states in evaluating the stability of different a-Si:H solar cell materials, as well as elucidating the origin of the Staebler–Wronski effect.

[edit] Performance test of amorphous silicon modules in different climates - year three: higher minimum operating temperatures lead to higher performance levels[27]

Abstract: This paper presents third year results of a round robin exposure experiment designed to assess the performance of thin-film amorphous silicon (a-Si) solar modules operating in different climatic conditions. Three identical sets of commercially available a-Si PV modules from five different manufacturers were simultaneously deployed outdoors in three sites with distinct climates (Arizona -USA, Colorado - USA and Florianopolis - Brazil). Every year all PV module sets were sent to the National Renewable Energy Laboratory (NREL) for standard testing conditions measurements under a SPIRE simulator. The four-year experiment aims to determine the light-induced degradation and stabilization characteristics of a-Si regarding specific history of exposure, and to monitor and compare degradation rates in different climates. We present results from the first three years of measurements, showing that while most of the manufacturers underrate their products by 20 to 25% to account for the light-induced degradation, outdoor exposure temperature seems to be what will ultimately determine the stabilized performance level of a-Si.

[edit] The potential of solar industrial process heat applications[28]

Abstract: The temperature requirements of solar industrial process heat applications range from 60 °C to 260 °C. The characteristics of medium to medium-high temperature solar collectors are given and an overview of efficiency and cost of existing technologies is presented. Five collector types have been considered in this study varying from the simple stationary flat-plate to movable parabolic trough ones. Based on TRNSYS simulations, an estimation of the system efficiency of solar process heat plants operating in the Mediterranean climate are given for the different collector technologies. The annual energy gains of such systems are from 550 to 1100 kWh/m2 a. The resulting energy costs obtained for solar heat are from 0.015 to 0.028 C£/kWh depending on the collector type applied. The viabilities of the systems depend on their initial cost and the fuel price. None of these costs however is stable but change continuously depending on international market trends and oil production rates. The costs will turn out to be more favourable when the solar collectors become cheaper and subsidisation of fuel is removed. Therefore the optimisation procedure suggested in this paper should be followed in order to select the most appropriate system in each case.

[edit] Industrial application of PV/T solar energy systems[29]

Abstract: Hybrid photovoltaic/thermal (PV/T) systems consist of PV modules and heat extraction units mounted together. These systems can simultaneously provide electrical and thermal energy, thus achieving a higher energy conversion rate of the absorbed solar radiation than plain photovoltaics. Industries show high demand of energy for both heat and electricity and the hybrid PV/T systems could be used in order to meet this requirement. In this paper the application aspects in the industry of PV/T systems with water heat extraction is presented. The systems are analyzed with TRNSYS program for three locations Nicosia, Athens and Madison that are located at different latitudes. The system comprises 300 m2 of hybrid PV/T collectors producing both electricity and thermal energy and a 10 m3 water storage tank. The work includes the study of an industrial process heat system operated at two load supply temperatures of 60 °C and 80 °C. The results show that the electrical production of the system, employing polycrystalline solar cells, is more than the amorphous ones but the solar thermal contribution is slightly lower. A non-hybrid PV system produces about 25% more electrical energy but the present system covers also, depending on the location, a large percentage of the thermal energy requirement of the industry considered. The economic viability of the systems is proven, as positive life cycle savings are obtained in the case of hybrid systems and the savings are increased for higher load temperature applications. Additionally, although amorphous silicon panels are much less efficient than the polycrystalline ones, better economic figures are obtained due to their lower initial cost, i.e., they have better cost/benefit ratio.

[edit] Temperature coefficients for PV modules and arrays: measurement methods, difficulties, and results[30]

Abstract: The term “temperature coefficient” has been applied to several different photovoltaic performance parameters, including voltage, current and power. The procedures for measuring the coefficient(s) for modules and arrays are not yet standardized and systematic influences are common in the test methods used to measure them. There are also misconceptions regarding their application. Yet, temperature coefficients, however obtained, play an important role in PV power system design and sizing, where often the worst case operating condition dictates the array size. This paper: describes effective methods for determining temperature coefficients for cells, modules and arrays; identifies sources of systematic errors in measurements; gives typical measured values for modules; and provides guidance for their application in system engineering

[edit] Dispatch strategy and model for hybrid photovoltaic and trigeneration power systems[31]

Abstract: The advent of small scale combined heat and power (CHP) systems has provided the opportunity for in-house power backup of residential-scale photovoltaic (PV) arrays. These hybrid systems enjoy a symbiotic relationship between components, but have large thermal energy wastes when operated to provide 100% of the electric load. In a novel hybrid system is proposed here of PV-trigeneration. In order to reduce waste from excess heat, an absorption chiller has been proposed to utilize the CHP-produced thermal energy for cooling of PV-CHP system. This complexity has brought forth entirely new levels of system dynamics and interaction that require numerical simulation in order to optimize system design. This paper introduces a dispatch strategy for such a system that accounts for electric, domestic hot water, space heating, and space cooling load categories. The dispatch strategy was simulated for a typical home in Vancouver and the results indicate an improvement in performance of over 50% available when a PV-CHP system also accounts for cooling. The dispatch strategy and simulation are to be used as a foundation for an optimization algorithm of such systems.

[edit] Energy performance of water hybrid PV/T collectors applied to combisystems of Direct Solar Floor type[32]

Abstract: The integration of photovoltaic (PV) modules in buildings allows one to consider a multifunctional frame and then to reduce the cost by substitution of components. In order to limit the rise of the cell operating temperature, a photovoltaics/thermal (PV/T) collector combines a solar water heating collector and PV cells. The recovered heat energy can be used for heating systems and domestic hot water. A combination with a Direct Solar Floor is studied. Its low operating temperature level is appropriate for the operating conditions of the mono- or poly-crystalline photovoltaic modules which are selected in that study. However, for a system including a glass covered collector and localised in Mâcon area in France, we show that the annual photovoltaic cell efficiency is 6.8% which represents a decrease of 28% in comparison with a conventional non-integrated PV module of 9.4% annual efficiency. This is obviously due to a temperature increase related to the cover. On the other hand, we show that without a glass cover, the efficiency is 10% which is 6% better than a standard module due to the cooling effect.

Moreover, in the case of a glazed PV/T collector with a conventional control system for Direct Solar Floor, the maximum temperature reached at the level of the PV modules is higher than 100 °C. This is due to the oversize of the collectors during the summer when the heating needs are null, i.e. without a heated swimming pool for example. This temperature level does not allow the use of EVA resin (ethylene vinyl acetate) in PV modules due to strong risks of degradation. The current solution consists of using amorphous cells or, if we do not enhance the thermal production, uncovered PV/T collector. Further research led to water hybrid PV/T solar collectors as a one-piece component, both reliable and efficient, and including the thermal absorber, the heat exchanger and the photovoltaic functions.

[edit] Reversible conductivity changes in discharge‐produced amorphous Si[33]

Abstract: A new reversible photoelectronic effect is reported for amorphous Si produced by glow discharge of SiH4. Long exposure to light decreases both the photoconductivity and the dark conductivity, the latter by nearly four orders of magnitude. Annealing above 150 °C reverses the process. A model involving optically induced changes in gap states is proposed. The results have strong implications for both the physical nature of the material and for its applications in thin‐film solar cells, as well as the reproducibility of measurements on discharge‐produced Si.

[edit] Development in understanding and controlling the Staebler-Wronski effect in a-Si:H[34]

Abstract: Hydrogenated amorphous silicon (a-Si:H) exhibits a metastable light induced degradation of its optoelectronic properties that is called the Staebler-Wronski effect, after its discoverers. This degradation effect is associated with the relatively high diffusion coefficient of hydrogen and the changes in local bonding coordination promoted by hydrogen. Reviewed are the fundamental aspects of the interplay between hydrogen and electronic energy states that form the basis of competing microscopic models for explaining the degradation effect. These models are tested against the latest experimental observations, and material and preparation parameters that reduce the Staebler-Wronski effect are discussed.

[edit] The influence of operation temperature on the output properties of amorphous silicon-related solar cells[35]

Abstract: The influence of the operation temperature on the output properties of solar cells with hydrogenated amorphous silicon (a-Si:H) and hydrogenated amorphous silicon germanium (a-SiGe:H) photovoltaic layers was investigated. The output power after longtime operation of an a-Si:H single junction, an a-Si:H/a-Si:H tandem, and an a-Si:H/a-SiGe:H tandem solar cell was calculated based on the experimental results of two types of temperature dependence for both conversion efficiency and light-induced degradation. It was found that the a-Si:H/a-SiGe:H tandem solar cell maintained a higher output power than the others even after longtime operation during which a temperature range of 25°C to 80°C. These results confirm the advantages of the a-Si:H/a-SiGe:H tandem solar cell for practical use, especially in high-temperature regions.

[edit] Correlation of light-induced changes in a-Si:H films with characteristics of corresponding solar cells[36]

Abstract: For the first time direct correlations are obtained between the light induced changes under 1 sun illumination in the properties of a-Si:H and those in the characteristics of p-i-n cells incorporating identically-prepared i-layers. These correlations were obtained after account was taken of the effects that the location of the electron and hole quasi-Fermi levels have on the carrier recombination that occurs through the different gap states. The changes in midgap state density, as measured on the films and reflected in the subgap absorption at 1.2 eV, are directly correlated with changes in the dark I-V characteristics under low forward bias. In this case small quasi-Fermi level splitting is present so the recombination of the injected carriers is determined by the midgap states in the bulk of the i-layer. In addition, the changes in the electron mobility-lifetime products as measured on the films are correlated with changes in the fill factor measured on cells under the same conditions as long as large quasi-Fermi level splitting is present and recombination occurs through states spanning a wide region of the gap, such as occurs under 1 sun illumination. The results explain (i) the failure of numerous attempts to correlate the degradation of solar cells reliably with the creation of dangling bond defects and (ii) the inadequacy of the large number of modeling results that assume such a correlation.

[edit] Photovoltaic thermal (PV/T) collectors: A review[37]

Abstract: This paper presents a review of the available literature on PV/T collectors. The review is presented in a thematic way, in order to enable an easier comparison of the findings obtained by various researchers, especially on parameters affecting PV/T performance (electrical and thermal). The review covers the description of flat plate and concentrating, water and air PV/T collector types, analytical and numerical models, simulation and experimental work and qualitative evaluation of thermal/electrical output. The parameters affecting PV/T performance, such as covered versus uncovered PV/T collectors, optimum mass flow rate, absorber plate parameters (i.e. tube spacing, tube diameter, fin thickness), absorber to fluid thermal conductance and configuration design types are extensively discussed. Based on an exergy analysis, it was reported that the coverless PV/T collector produces the largest available total (electrical + thermal) exergy. From the literature review, it is clear that PV/T collectors are very promising devices and further work should be carried out aiming at improving their efficiency and reducing their cost, making them more competitive and thus aid towards global expansion and utilization of this environmentally friendly renewable energy device.

[edit] Hybrid photovoltaic and thermal solar-collector designed for natural circulation of water[38]

Abstract: The electricity conversion-efficiency of a solar cell for commercial application is about 6–15%. More than 85% of the incoming solar energy is either reflected or absorbed as heat energy. Consequently, the working temperature of the solar cells increases considerably after prolonged operations and the cell’s efficiency drops significantly. The hybrid photovoltaic and thermal (PVT) collector technology using water as the coolant has been seen as a solution for improving the energy performance. Through good thermal-contact between the thermal absorber and the PV module, both the electrical efficiency and the thermal efficiency can be raised. Fin performance of the heat exchanger is one crucial factor in achieving a high overall energy yield. In this paper, the design developments of the PVT collectors are briefly reviewed. Our observation is that very few studies have been done on the PVT system adopting a flat-box absorber design. Accordingly, an aluminum-alloy flat-box type hybrid solar collector functioned as a thermosyphon system was constructed. While the system efficiencies did vary with the operating conditions, the test results indicated that the daily thermal efficiency could reach around 40% when the initial water-temperature in the system is the same as the daily mean ambient temperature.

[edit] Photovoltaic modules and their applications: A review on thermal modelling[39]

Abstract: Renewable energy (RE) resources have enormous potential and can meet the present world energy demand by using the locally available RE resources. One of the most promising RE technologies is photovoltaic (PV) technology. This paper presents a review of the available literature covering the various types of up and coming PV modules based on generation of solar cell and their applications in terms of electrical as well thermal outputs. The review covers detailed description and thermal model of PV and hybrid photovoltaic thermal (HPVT) systems, using water and air as the working fluid. Numerical model analysis and qualitative evaluation of thermal and electrical output in terms of an overall thermal energy and exergy has been carried out. Based on the thorough review, it is clear that PVT modules are very promising devices and there exists a lot of scope to further improve their performances particularly if integrated to roof top. Appropriate recommendations are made which will aid PVT systems to improve their overall thermal and electrical efficiency and reducing their cost, making them more competitive in the present market.

[edit] Optimization of the photovoltaic thermal (PV/T) collector absorber[40]

Abstract: In an effort to reduce the cost of conventional fin and tube photovoltaic thermal (PV/T) collectors a novel mathematical analysis was developed which determines the optimum absorber plate configuration having the least material content and thus cost, whilst maintaining high collection efficiency.

The analysis was based on the “low-flow” concept whose advantages include: improved system performance, smaller pump (less expensive with lower power consumption), smaller diameter tubes requiring lower thickness and thus cost of insulation, less construction power and time for the optimum absorber configuration.

From the optimization methodology developed it was found that very thin fins (typically 50 μm) and small tubes (of 1.65 mm inside diameter for the risers, in the header and riser arrangement and 4.83 mm for the serpentine arrangement), with a tube spacing of 62 mm and 64 mm (both corresponding to 97% fin efficiency) and a mass of 1.185 kg/m2 and 2.140 kg/m2, respectively, can be used. This optimum serpentine absorber plate contains 40.50% less material content and mass, as compared to the serpentine prototype proposed by others. In one such design a mass of 3.596 kg/m2 was used (with 10 mm diameter tubes, 95 mm tube spacing and 200 μm thick absorber).

To predict the performance of the determined optimum configurations, a steady-state model (using the EES code) was developed. To validate the steady-state model two prototypes, one in Header and Riser and the other in Serpentine configuration, were built and tested. It was found from the experiments that there is a good agreement between the computational and the experimental results. Moreover, it was found that optimum PV/T configurations do indeed have thermal and electrical performance comparable to non-optimum ones of greater mass and cost.

[edit] Analytical expression for electrical efficiency of PV/T hybrid air collector[41]

Abstract: The overall electrical efficiency of the photovoltaic (PV) module can be increased by reducing the temperature of the PV module by withdrawing the thermal energy associated with the PV module. In this communication an attempt has been made to develop analytical expression for electrical efficiency of PV module with and without flow as a function of climatic and design parameters. The four different configurations of PV modules are considered for the present study which are defined as; case A (Glass to glass PV module with duct), case B (Glass to glass PV module without duct), case C (Glass to tedlar PV module with duct), case D (Glass to tedlar PV module without duct). Further, experiments were carried out for all configurations under composite climate of New Delhi.

It is found that the glass to glass PV modules with duct gives higher electrical efficiency as well as the higher outlet air temperature amongst the all four cases. The annual effect on electrical efficiency of glass to glass type PV module with and without duct is also evaluated. The annual average efficiency of glass to glass type PV module with and without duct is 10.41% and 9.75%, respectively.

[edit] Comparative Study on Hybrid PV/T Heat Pump Systems Using Different PV Panels[42]

Abstract: Many studies have found that the photovoltaic (PV) cell temperature plays an important impact on the solar-to-electricity conversion efficiency. Different cooling liquids like air and water have been introduced to pass across the PVs to reduce the cell temperature, and thus increase the electrical efficiency. In this paper, the refrigerant R134a is used as the cooling liquid and the PV/thermal (PV/T) panel is coupled with a heat pump system acting as the evaporator, which is expected to achieve a better cooling effect and energy performance due to its low boiling temperature. Two different kinds of PV/T panels, glass vacuum tube (GVT) type and flat plate (FP) type, are proposed for the study on the energy performance comparison. The results show that the GVT PV/T panel has an average thermal efficiency of 0.775 and an average electrical efficiency of 0.089 (based on the reference efficiency of 0.12), which is 73.4% and 1.1% higher than that of the FP PV/T panel respectively, with the solar radiation varying from 200 W/m2 to 1000 W/m2. The GVT PV/T heat pump system has an average COP of 5.6, 9.8% higher the FP PV/T heat pump system. The GVT PV/T heat pump system has a better energy performance than the FP PV/T heat pump system.

[edit] References

  1. 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.
  2. 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.
  3. 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.
  4. T. T. Chow, “A review on photovoltaic/thermal hybrid solar technology,” Applied Energy, vol. 87, no. 2, pp. 365–379, Feb. 2010.
  5. 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.
  6. 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.
  7. 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.
  8. 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.
  9. 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.
  10. 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.
  11. 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.
  12. 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.
  13. 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.
  14. 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.
  15. 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.
  16. T. P. Otanicar, I. Chowdhury, R. Prasher, and P. E. Phelan, “Band-Gap Tuned Direct Absorption for a Hybrid Concentrating Solar Photovoltaic/Thermal System,” Journal of Solar Energy Engineering, vol. 133, no. 4, p. 041014, 2011.
  17. Y. Vorobiev, J. González-Hernández, P. Vorobiev, and L. Bulat, “Thermal-photovoltaic solar hybrid system for efficient solar energy conversion,” Solar Energy, vol. 80, no. 2, pp. 170–176, Feb. 2006.
  18. [1] C. R. Wronski, J. M. Pearce, J. Deng, V. Vlahos, and R. W. Collins, “Intrinsic and light induced gap states in a-Si:H materials and solar cells—effects of microstructure,” Thin Solid Films, vol. 451–452, no. 0, pp. 470–475, Mar. 2004.
  19. D. L. Staebler and C. R. Wronski, “Reversible conductivity changes in discharge‐produced amorphous Si,” Applied Physics Letters, vol. 31, no. 4, pp. 292–294, Aug. 1977.
  20. J. Deng and C. R. Wronski, “Carrier recombination and differential diode quality factors in the dark forward bias current-voltage characteristics of a‐Si:H solar cells,” Journal of Applied Physics, vol. 98, no. 2, pp. 024509–024509–10, Jul. 2005.
  21. A. Klaver and R. A. C. M. M. van Swaaij, “Modeling of light-induced degradation of amorphous silicon solar cells,” Solar Energy Materials and Solar Cells, vol. 92, no. 1, pp. 50–60, Jan. 2008.
  22. J. M. Pearce, J. Deng, M. L. Albert, C. R. Wronski, and R. W. Collins, “Room temperature annealing of fast state from 1 sun illumination in protocrystalline Si:H materials and solar cells,” in Conference Record of the Thirty-first IEEE Photovoltaic Specialists Conference, 2005, 2005, pp. 1536 – 1539.
  23. C. R. Wronski, B. Von Roedern, and A. Kołodziej, “Thin-film Si:H-based solar cells,” Vacuum, vol. 82, no. 10, pp. 1145–1150, Jun. 2008.
  24. S. Fujikake, H. Ota, M. Ohsawa, T. Hama, Y. Ichikawa, and H. Sakai, “Light-induced recovery of a-Si solar cells,” Solar Energy Materials and Solar Cells, vol. 34, no. 1–4, pp. 449–454, Sep. 1994.
  25. C. R. Wronski and R. W. Collins, “Phase engineering of a-Si:H solar cells for optimized performance,” Solar Energy, vol. 77, no. 6, pp. 877–885, Dec. 2004.
  26. J. M. Pearce, J. Deng, R. W. Collins, and C. R. Wronski, “Light-induced defect states in hydrogenated amorphous silicon centered around 1.0 and 1.2 eV from the conduction band edge,” Applied Physics Letters, vol. 83, no. 18, pp. 3725–3727, Nov. 2003.
  27. R. Ruther, G. Tamizh-Mani, J. del Cueto, J. Adelstein, M. M. Dacoregio, and B. von Roedern, “Performance test of amorphous silicon modules in different climates - year three: higher minimum operating temperatures lead to higher performance levels,” in Conference Record of the Thirty-first IEEE Photovoltaic Specialists Conference, 2005, 2005, pp. 1635 – 1638.
  28. S. Kalogirou, “The potential of solar industrial process heat applications,” Applied Energy, vol. 76, no. 4, pp. 337–361, Dec. 2003.
  29. S. A. Kalogirou and Y. Tripanagnostopoulos, “Industrial application of PV/T solar energy systems,” Applied Thermal Engineering, vol. 27, no. 8–9, pp. 1259–1270, Jun. 2007.
  30. D. L. King, J. A. Kratochvil, and W. E. Boyson, “Temperature coefficients for PV modules and arrays: measurement methods, difficulties, and results,” in , Conference Record of the Twenty-Sixth IEEE Photovoltaic Specialists Conference, 1997, 1997, pp. 1183 –1186.
  31. A. Nosrat and J. M. Pearce, “Dispatch strategy and model for hybrid photovoltaic and trigeneration power systems,” Applied Energy, vol. 88, no. 9, pp. 3270–3276, Sep. 2011.
  32. G. Fraisse, C. Ménézo, and K. Johannes, “Energy performance of water hybrid PV/T collectors applied to combisystems of Direct Solar Floor type,” Solar Energy, vol. 81, no. 11, pp. 1426–1438, Nov. 2007.
  33. D. L. Staebler and C. R. Wronski, “Reversible conductivity changes in discharge‐produced amorphous Si,” Applied Physics Letters, vol. 31, no. 4, pp. 292–294, Aug. 1977.
  34. H. Fritzsche, “DEVELOPMENT IN UNDERSTANDING AND CONTROLLING THE STAEBLER-WRONSKI EFFECT IN a-Si:H,” Annual Review of Materials Research, vol. 31, no. 1, pp. 47–79, 2001.
  35. M. Shima, M. Isomura, K. Wakisaka, K. Murata, and M. Tanaka, “The influence of operation temperature on the output properties of amorphous silicon-related solar cells,” Solar Energy Materials and Solar Cells, vol. 85, no. 2, pp. 167–175, Jan. 2005.
  36. J. M. Pearce, R. J. Koval, R. W. Collins, C. R. Wronski, M. M. Al-Jassim, and K. M. Jones, “Correlation of light-induced changes in a-Si:H films with characteristics of corresponding solar cells,” in Conference Record of the Twenty-Ninth IEEE Photovoltaic Specialists Conference, 2002, 2002, pp. 1098 – 1101.
  37. P. G. Charalambous, G. G. Maidment, S. A. Kalogirou, and K. Yiakoumetti, “Photovoltaic thermal (PV/T) collectors: A review,” Applied Thermal Engineering, vol. 27, no. 2–3, pp. 275–286, Feb. 2007.
  38. W. He, T.-T. Chow, J. Ji, J. Lu, G. Pei, and L. Chan, “Hybrid photovoltaic and thermal solar-collector designed for natural circulation of water,” Applied Energy, vol. 83, no. 3, pp. 199–210, Mar. 2006.
  39. G. N. Tiwari, R. K. Mishra, and S. C. Solanki, “Photovoltaic modules and their applications: A review on thermal modelling,” Applied Energy, vol. 88, no. 7, pp. 2287–2304, Jul. 2011.
  40. P. G. Charalambous, S. A. Kalogirou, G. G. Maidment, and K. Yiakoumetti, “Optimization of the photovoltaic thermal (PV/T) collector absorber,” Solar Energy, vol. 85, no. 5, pp. 871–880, May 2011.
  41. S. Dubey, G. S. Sandhu, and G. N. Tiwari, “Analytical expression for electrical efficiency of PV/T hybrid air collector,” Applied Energy, vol. 86, no. 5, pp. 697–705, May 2009.
  42. H. B. Chen and P. Wei, “Comparative Study on Hybrid PV/T Heat Pump Systems Using Different PV Panels,” Advanced Materials Research, vol. 446–449, pp. 2888–2894, Jan. 2012.