Performance evaluation of low concentrating photovoltaic/thermal systems: A case study from Sweden[edit | edit source]
Abstract: Some of the main bottlenecks for the development and commercialization of photovoltaic/thermal hybrids are the lack of an internationally recognized standard testing procedure as well as a method to compare different hybrids with each other and with conventional alternatives. A complete methodology to characterize, simulate and evaluate concentrating photovoltaic/thermal hybrids has been proposed and exemplified in a particular case study. By using the suggested testing method, the hybrid parameters were experimentally determined. These were used in a validated simulation model that estimates the hybrid outputs in different geographic locations. Furthermore, the method includes a comparison of the hybrid performance with conventional collectors and photovoltaic modules working side-by-side. The measurements show that the hybrid electrical efficiency is 6.4% while the optical efficiency is 0.45 and the U-value 1.9 W/m2 °C. These values are poor when compared with the parameters of standard PV modules and flat plate collectors. Also, the beam irradiation incident on a north–south axis tracking surface is 20–40% lower than the global irradiation incident on a fixed surface at optimal tilt. There is margin of improvement for the studied hybrid but this combination makes it difficult for concentrating hybrids to compete with conventional PV modules and flat plate collectors.
- Propose a testing method to characterize concentrating photovoltaic/thermal hybrids.
- Suggest a series of simulations and performance analysis for different latitudes based on the results from the testing method.
- Compare the hybrid performance with conventional PV modules and solar collectors.
- Electrical & thermal performance of of PV/T hybrid model
- Two hybrid areas were defined: total glazed area and active glazed area
Abstract: PV modules show temperature increase during their operation due to the absorption of solar radiation, as most of it is converted into heat and not into electricity. Hybrid Photovoltaic/Thermal (PV/T) solar systems combine a simultaneous conversion of solar radiation in electricity and heat. These devices consist of PV modules and heat extraction units mounted together, by which a circulating fluid of lower temperature than that of PV modules is heated by cooling them. An extensive study on water and air cooled PV/T solar systems has been conducted at the University of Patras, where hybrid prototypes have been experimentally studied. The water cooled PV/T systems consist of metallic heat exchanger placed at PV module rear surface, by which water circulating through pipes is heated. The methodology of Life Cycle Assessment (LCA) has been used to do an energetic and environmental assessment of the heat recovery system. The goal of this study, carried out at the University of Rome " La Sapienza", was to verify the benefits of heat recovery, implemented by a specific software for LCA, SimaPro 5.0. In this work Author(s) present the design, performance and aspects of improved PV/T systems based on the LCA results, giving guidelines for their application.
- Natural or forced air circulation is a simple and low-cost method to remove heat from PV modules, but it is less effective if the ambient air temperature is over 20*C
- PV/T systems with and without glazing cover are presented, suggesting also the concept of using a stationary diffuse reflector, instead of the specular reflector, to increase the total energy output.
- Description of PV/T module with reflection & its application
- To increase the system operating temperature, an additional glazing cover is necessary (like that of the usual solar thermal collectors), but it has as result the decrease of the PV module electrical output from the additional absorption of the solar radiation
[A dynamic model of hybrid photovoltaic/thermal panel][edit | edit source]
Abstract: In this paper, a dynamic simulation model of a photovoltaic and water heating system (PV/T) is developed. The model consists of a set of mathematical equations governing the main components of the system; namely: transparent cover, solar cell, absorber plate, operating fluid and storage tank. The model is based on the analysis of the energy balance which includes the photo electric conversion and the thermal conduction, convection and radiation. The model gathers all components equations so as to reflect the electrical and thermal behaviour of the PV/T system. It delivers the state equation of the system function of the climatic parameters and the fluid flow rate. The investigation of the effect of water mass flow rate through the collector on PV/T outputs have been carried out.
- A hybrid system, the PV/T collector can simultaneously produce thermal and electric energy.
- Utilization of a copolymer for the total design of the solar collector has numerous advantages as reducing the weight, facilitating the manufacturing, and reducing the cost.
- The hybrid photovoltaic thermal system is basically constructed by pasting photovoltaic solar cells directly over the absorber plate of the solar collector in a conventional forced circulation type solar water heater.
- The energy and fluid flow equations are developed on the basis of the four nodes. All sub-parts in each node are considered lumping together in proportion to give the average properties of the representing major component.
- This paper shows details mathematical model for hybrid photovoltaic/thermal panel and corresponding theoretical output.
Abstract: This paper presents a general energetic and entropic analysis of ideal photovoltaic and solar-thermal converters. Its purpose is to determine the efficiency limit when both types of converters operate together (hybrid converters). It has been found that, while in practical cases hybrid converters may give very high efficiency (61.7% vs. 40.0% of the solar thermal at 500 K and 40.7% of the photovoltaic at 300 K), in the limiting case of a system formed by an infinite number of band gaps, the efficiency of hybrid converters, 86.8%, is strictly equivalent to photovoltaic or solar thermal converters. Conversely, hybrid systems operating with one gap give efficiency of 86.7%, very close to the previous one and higher than the top efficiency achievable with a single temperature solar thermal, 85.4%.
- Theoretical analysis of maximum efficiency of a PV cell
- In a hybrid system, the escaping radiation will be a matter-coupled radiation at a temperature above the ambient and in some cases will be characterized by a zero chemical potential at some wavelengths and by a non-zero chemical potential at others.
- Low pass hybrid converter, the receiver only absorbs photons with energy above the bandgap of the solar cell, leaving the rest of the photons available for further use, for example, in a second solar cell located beneath.
- In case of Opaque hybrid converter, occurs when the photons below the semiconductor bandgap are also absorbed in a perfect sub-band absorber located beneath the cell. This absorber is at the cell temperature and the heat produced is converted reversibly into work in the thermal engine.
Band-Gap Tuned Direct Absorption for a Hybrid Concentrating Solar Photovoltaic/Thermal System[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.
- Thermally decouple the photovoltaic (PV) cell from the heat transfer fluid (HTF)
- The approach to harvesting solar energy is through the use of photovoltaics which directly converts solar energy, specifically solar energy above the band-gap of the solar cell, into electricity.
- In PV systems incoming solar flux below the band-gap and various loss mechanisms for energy above the bandgap result in heat generation, increasing the temperature of the cell and decreasing the cell efficiency.
- Concentrating systems utilize a form of focusing optics, often a Fresnel lens or mirrors, to focus incoming sunlight onto the cell. These systems generate much higher temperatures in the system resulting in excess thermal energy but less electrical energy.
- Two main approaches exist for this method. The first, utilize optical techniques that actually split the incoming irradiance into separate beams of different spectrums which are then directed either to the PV cell or the thermal absorber. The second, approach utilizes an absorption-based filter that is highly absorptive in the thermal regions of interest while transmitting as much light as possible.
- The thermal system and the PV system are only lightly coupled thermally since they are not in direct contact as is typically done in conventional hybrid collectors.
- Result shows that using a coupled thermo-electric model demonstrated that it is possible to increase the efficiency of a hybrid system through utilizing the HTF to remove excess heat as well as by small increases in the fluid absorptance which provided a decrease in PV cell temperature while having limited impact on the thermal efficiency.
Abstract: Hybrid conversion of solar radiation implies simultaneous solar radiation conversion into thermal and electrical energy in the PV/Thermal collector. In order to get more thermal and electrical energy, flat solar radiation reflectors have been mounted on PV/T collector. To obtain higher solar radiation intensity on PV/T collector, the position of reflectors has been changed and the optimal position of reflectors has been determined by both experimental measurements and numerical calculation so as to obtain maximal concentration of solar radiation intensity. The calculated values have been found to be in good agreement with the measured ones, both yielding the optimal position of the flat reflector to be the lowest (5°) in December and the highest (38°) in June. In this paper, the thermal and electrical efficiency of PV/T collector without reflectors and with reflectors in optimal position have been calculated. Using these results, the total efficiency and energy-saving efficiency of PV/T collector have been determined. The energy-saving efficiency for PV/T collectors without reflectors is 60.1%, which is above the conventional solar thermal collector, whereas the energy-saving efficiency for PV/T collector with reflectors in optimal position is 46.7%, which is almost equal to the values for the conventional solar thermal collector. Though the energy-saving efficiency of PV/T collector decreases slightly with the solar radiation intensity concentration factor, i.e. the thermal and electrical efficiency of PV/T collector with reflectors are lower than those of PV/T collector without reflectors, the total thermal and electrical energy generated by PV/T collector with reflectors in optimal position are significantly higher than total thermal and electrical energy generated by PV/T collector without reflectors.
- Optimal design & inclination angle of reflector for PV/T module
- Comparisons were made between the performances of the two types of combined photovoltaic thermalcollectors, and the results showed that the double-pass photovoltaic thermal collector has superior performance in relation to the single-pass PV/T collector.
- They considered four different configurations of two types of PV modules and carried out experiments for all configurations under composite climate of New Delhi. Agrawal and Tiwari analyzed energy and exergy of building integrated photovoltaic thermal (BIPVT) systems under cold climatic condition in India. This system was used as the roof top of a building to generate higher electrical energy per unit area and to produce necessary thermal energy required for space heating.
- An increase in the power output and in hot water can be obtained. Garg et al. studied the effect of plane booster reflectors on the performance of a solar air heater with solar cells suitable for a solar dryer.
- In order to obtain the highest solar radiation intensity on PV/T collector, position of the bottom and upper reflectors have been changed and optimal positions of reflectors have been determined.
- optimal positions for the upper and bottom reflector are at the angles of 0 degree and 36 degree, respectively. In this study, measurements have been done in the period February-October 2008 for different days.
Design, fabrication and performance evaluation of a hybrid photovoltaic thermal (PVT) double slope active solar still[edit | edit source]
Abstract: A modified photovoltaic thermal (PVT) double slope active solar still was designed and fabricated for remote locations. The system has been installed at the campus of KIET, Ghaziabad (India) and its performance has been experimentally evaluated under field conditions in natural and forced circulation mode (series and parallel). Photovoltaic operated DC water pump has been used between solar still and photovoltaic (PV) integrated flat plate collector to re-circulate the water through the collectors and transfer it to the solar still. The production rate has been accelerated to 1.4 times than the single slope hybrid (PVT) active solar still and obtained highest (7.54 kg/day) for the parallel configuration in forced mode in the month of October, 2010. The daily average energy efficiency of the solar still is obtained as 17.4%. Comparative results have been predicted on annual basis with the single slope hybrid (PVT) active solar still accounting 250, 275 and 300 clear days in a year. Author(s) have found that energy payback time is significantly reduced by almost 30% in present design with less capital investment.
- In this paper, a new simple design of hybrid photovoltaic thermal (PVT) double slope active solar still has been fabricated and its performance is evaluated in field conditions.
- Potable water can be produced at reasonable cost by solar stills.
- The concept behind the hybrid is that a solar cell converts solar radiation to electrical energy with peak efficiency in the range of 9–12%, depending on specific solarcell type and thermal energy dissipated for air or water heating
- The productivity of the solar still can be improved by increasing the temperature of water in the solar still as one of the parameters.The main objective of the work is, to enhance the productivity of the double slope solar still to provide distilled water for isolated communities, facing electricity problems and good quality of water for commercial use.
Abstract: Author(s) 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.
- The electrical and thermal output of hybrid PV/T systems can be increased by using concen-trators of solar radiation of low concentrating ratio as proposed by Al-Baali.
- We include design considerations and experimental results from constructed and tested outdoors hybrid PV/T systems.
- In PV building installation at locations with high solar input and high ambient tempera-tures, liquid PV cooling can be onsidered as the most efficient mode for water preheating all year, most efficient mode for water preheating all year.
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.
- Electric energy is a high-grade form of energy since it is converted from thermal energy.
- The heat-collecting plate adheres directly to the back of the commercial PV module.
- Increasing hot water temperature in order to meet some application requirements would in turn cause the power generation efficiency of solar PV to decrease.
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.
- The experiments provide the collection of weather data from a weather station and experimental values for various operating temperatures
- The advantage of this configuration is that the hot water production function is an option which can be added to the basic solar PV/T air collector, depending on the energy needs of the building.
- There is an air gap between the absorber and an insulation layer. It is in the rib which is originally used for the mechanical rigidity of the sheet steels that the hot water production section is positioned. This rib includes an insulation layer of polystyrene covered by a thin reflective layer as well as a water circulation pipe.
- A parametric study permitted the trends in the variation of the temperature of cells and the fluids as a function of water and air mass flow rates and the collector length to be determined.
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- Application Aspects Of Hybrid PV/T Solar Systems
- A dynamic model of hybrid photovoltaic/thermal panel
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