PVT dispatch strategy literature review/Band-Gap Tuned Direct Absorption for a Hybrid Concentrating Solar Photovoltaic

Band-Gap Tuned Direct Absorption for a Hybrid Concentrating Solar Photovoltaic/Thermal System[1][1][1][1][edit | edit source]

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.

Thermal-photovoltaic solar hybrid system for efficient solar energy conversion[2][2][2][2][edit | edit source]

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.

Intrinsic and light induced gap states in a-Si:H materials and solar cells—effects of microstructure[3][3][3][3][edit | edit source]

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.

Reversible conductivity changes in discharge‐produced amorphous Si[4][4][4][4][edit | edit source]

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.

Carrier recombination and differential diode quality factors in the dark forward bias current-voltage characteristics of a‐Si:H solar cells[5][5][5][5][edit | edit source]

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.

Modeling of light-induced degradation of amorphous silicon solar cells[6][6][6][6][edit | edit source]

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.

Room temperature annealing of fast state from 1 sun illumination in protocrystalline Si:H materials and solar cells[7][7][7][7][edit | edit source]

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.

Thin-film Si:H-based solar cells[8][8][8][8][edit | edit source]

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.

Light-induced recovery of a-Si solar cells[9][9][9][9][edit | edit source]

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.

Phase engineering of a-Si:H solar cells for optimized performance[10][10][10][10][edit | edit source]

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.

Light-induced defect states in hydrogenated amorphous silicon centered around 1.0 and 1.2 eV from the conduction band edge[11][11][11][11][edit | edit source]

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.

Performance test of amorphous silicon modules in different climates - year three: higher minimum operating temperatures lead to higher performance levels[12][12][12][12][edit | edit source]

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.

The potential of solar industrial process heat applications[13][13][13][13][edit | edit source]

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.

Industrial application of PV/T solar energy systems[14][14][14][14][edit | edit source]

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.

Temperature coefficients for PV modules and arrays: measurement methods, difficulties, and results[15][15][15][15][edit | edit source]

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

Dispatch strategy and model for hybrid photovoltaic and trigeneration power systems[16][16][16][16][edit | edit source]

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.

Energy performance of water hybrid PV/T collectors applied to combisystems of Direct Solar Floor type[17][17][17][17][edit | edit source]

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.

Reversible conductivity changes in discharge‐produced amorphous Si[18][18][18][18][edit | edit source]

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.

Development in understanding and controlling the Staebler-Wronski effect in a-Si:H[19][19][19][19][edit | edit source]

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.

The influence of operation temperature on the output properties of amorphous silicon-related solar cells[20][20][20][20][edit | edit source]

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.

Correlation of light-induced changes in a-Si:H films with characteristics of corresponding solar cells[21][21][21][21][edit | edit source]

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.

Photovoltaic thermal (PV/T) collectors: A review[22][22][22][22][edit | edit source]

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.

Hybrid photovoltaic and thermal solar-collector designed for natural circulation of water[23][23][23][23][edit | edit source]

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.

Photovoltaic modules and their applications: A review on thermal modelling[24][24][24][24][edit | edit source]

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.

Optimization of the photovoltaic thermal (PV/T) collector absorber[25][25][25][25][edit | edit source]

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.

Analytical expression for electrical efficiency of PV/T hybrid air collector[26][26][26][26][edit | edit source]

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.

Comparative Study on Hybrid PV/T Heat Pump Systems Using Different PV Panels[27][27][27][27][edit | edit source]

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.

References[edit | edit source]