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In this paper, two different cost-effective cooling techniques with new designs are proposed and experimentally evaluated to enhance the performance of solar PV system. The first technique is the direct active cooling with water whereas the second one is a passive cooling that uses fins mounted on the backside of the PV module. Besides, an extra PV module is employed without any cooling system as a reference margin for comparison purposes. The experimental measurements for three individuals PV modules have been collected and compared. The results indicated that the temperature of the PV module surface had been reduced using two cooling techniques compared with the non-cooling module. The maximum temperature values are 38, 55, and 58 °C for water-cooling, fins cooling, and non-cooling module, respectively. This reduction in the temperature with cooling systems improves the performance of the PV module. It was found that the harvested energy per day is increased by 10.2% and 7% for backwater cooling and fins cooling modules, respectively, compared with the non-cooling module. Besides, the performance ratio was enhanced up to 84% and 81% for the water-cooling module and fins cooling-module, respectively. While at the same time, it was 77% for the non-cooling module.

Photovoltaic (PV) panels provide a suitable way for the direct conversion of solar energy into electricity. The electrical output and efficiency of PV modules are dependent on working temperature. The present study contributes to investigate the efficiency of utilizing a flat plate closed-loop pulsating heat pipe (CLPHP) to cool down a PV panel in both thermal and economic aspects. Accordingly, a numerical investigation is employed to obtain the surface temperature and electrical gain of the PV panel through four scenarios, including natural cooling without additional equipment, CLPHP-based passive cooling, CLPHP-based active cooling, and a conventional flat plate cooling methods. The efficiency of the cooling approaches is investigated in three different solar radiations and ambient temperatures according to the climatic condition of the considered location, Kerman, Iran. The improvement rate function is established to elaborate on the electrical gain efficiency of each scenario. Furthermore, each scenario is economically compared in terms of the payback period of the different cooling approaches. It is concluded that applying CLPHP-based passive, and active cooling approaches increase the improvement rate by 23% and 35% at the solar radiation of 1235 W / m 2 , respectively. In addition, the results demonstrated that while the 4th scenario, conventional approach, induces higher improvement rate, it requires more operational cost, so increases the payback period by about 10% compared to the 3rd scenario. Accordingly, it is concluded that utilizing CLPHP for cooling the PV panel is an appropriate and cost-effective approach to increase the efficiency of the PV panel.

In recent years, researchers are fascinated to counter problem of PV-efficiency decline arising from high operating temperatures, especially in hot climates. This article conducts a comprehensive review of research activities performed in last 5 years, on cooling techniques with phase-change materials (PCMs), nanofluids and their combined use, leading to efficiency enhancement. By passive cooling approach with PCMs, it is found that maximum enhancement up to 20% in PV-efficiency can be achieved. Effectiveness of PCM for PV is more prominent in summer than in winter. Incorporations of fins inside PCM container at PV rear, results in much improved heat conduction within PCM. Now-a-days, researchers have grown interest in composite PCMs for PV cooling due to their enhanced thermal conductivity. Moreover, better heat regulation as well as PV-surface temperature uniformity can be achieved with two PCMs at a time having different melting points. Studies suggest that combination of passive & active cooling techniques helps in further lowering of PV-cell temperature, leading to enhancement in PV-efficiency with additional thermal power generation. PV-efficiency of water-based hybrid PV/T systems can be improved by 32% by integration with PCM. Although nanofluid-based PV/T systems have been proved to enhance PV-efficiency by more than 60%, but combined use of PCM & nanofluid is more effective approach for PV cooling than individual use of PCM or nanofluid. If combination is made between nanofluid & nano-PCM, electrical power & efficiency can further be enhanced. Nanofluids can also be considered a good spectral filter alternative as they require small thickness and are able to be tuned by varying nanoparticles conc. Finally, environmental impacts & economic viability of mentioned cooling techniques, were discussed. Studies show that PV/PCM systems become expensive & less feasible when operated in single junction due to long payback period up to 20 years. Economic feasibility can be increased by combining passive & active cooling techniques which can increase system compactness and lower its cost.

The active cooling, latent thermal storage and advanced energy conversions are effective solutions to high-efficiently utilise renewable energy for building applications, whereas the electricity consumption of active facilities for the thermal performance enhancement needs to be considered. In this study, the exergy analysis of a hybrid renewable system, with on-site thermal and electric energy forms, sensible and latent heat storages, was investigated, in terms of technical feasibility of proposed active cooling solutions. The contradiction between the increased electricity consumption of active cooling facilities and the enhancement of renewable generations has been presented, discussed, together with effective solutions, from the perspective of exergy. A machine-learning based optimisation methodology was proposed and used, to address the contradiction and to maximise the overall exergy, with the integration of an advanced optimisation algorithm. The results showed that, in regard to the contradiction, effective solutions include the active water-based cooling and the optimal design of the geometric and operating parameters. Furthermore, with the adoption of optimal parameters through the machine-learning based optimisation, the overall exergy of the hybrid renewable system is 872.06 kWh, which is 2.6% higher than the maximum overall exergy through the Taguchi standard orthogonal array (849.9 kWh). This study demonstrates an effective solution to the contradiction of an active renewable system, together with a machine-learning based optimisation methodology, which can promote the practical feasibility and applicability of active renewable systems in renewable and sustainable buildings.

This paper details a field study and a theoretical model of a PhotoVoltaic-Thermal (PV-T) system consisting of a solar PV panel with a thermally insulated water reservoir underneath. Unlike conventional PV-T systems, water is in direct contact with the glass solar PV panel. Thus, metallic tubular heat exchangers are omitted in this design. During operation, the PV-T panel is tilted, and cold water is pumped into the reservoir from the side closest to the ground. This achieves an active cooling of the PV panel maintaining an optimal electrical efficiency. Generated electricity is used to operate pumps and run the control system, while excess electricity is stored in a battery to be utilised as desired. The system and the inlet water absorb solar thermal energy and as a result they increase in temperature. In our field study, we explore the viability of this system as a self-powered, off-grid, solar collector and find that it can provide enough hot water of approximately 80 °C for a household of four in areas where average daily solar irradiance is > 4.5 kWh/m2. We varied (1) the exposure angle, (2) PV panel type and (3) reservoir depth and found that in the limited ranges covered by our experiments the optimised configuration is with (1) an exposure angle of 14.7°, (2) a bifacial mono-crystalline solar PV panel and (3) a reservoir depth of 12 mm (given a fixed inlet water flow rate). The theoretical model of the device that is built, tracks energy losses with time and outputs the average reservoir temperature at each five-minute time-step. We validated this model with the obtained data during the field study. Then, this model is used to perform a sensitivity analysis on the parameters in testing and beyond (such as primarily insulation types and thicknesses), to provide a direction for further development and improvement.

The article describes a control architecture for solar furnaces where active cooling is employed to improve the tracking of a time-varying temperature reference. This capability is important during the decreasing phase of the temperature reference where heat loss must be increased. The results of two different control methodologies, exact linearization and model predictive control with integral action, are shown with active cooling that is done in coordination with the command of the shutter which adjusts the solar incident power. The controller parameters are computed from the temperature dynamics which is identified off-line from collected process data. This approach is used to avoid online adaptation mechanisms of the controller parameters, that may cause stability problems during the controller startup, and may melt the testing material sample. The novelty of the present work is to present a control architecture that coordinates the operations of the shutter together with the application of active cooling. This methodology improves temperature reference tracking and increases the usability and the operation of solar furnaces.

A spectrum splitting, transmissive concentrating photovoltaic (tCPV) module is proposed and designed for a hybrid photovoltaic-solar thermal (PV/T) system. By utilizing III–V triple junction solar cells with bandgaps of 2.1 eV/1.7 eV/1.4 eV, ultraviolet (UV) and visible light will be absorbed and converted to electricity, while infrared (IR) light will pass through and be captured by a solar thermal receiver and stored as heat. The stored thermal energy may be dispatched as electricity or process heat, as needed. According to the numerical analysis, the tCPV module can perform with overall power conversion efficiency exceeding 43.5% for above bandgap (in-band) light under a standard AM1.5D solar spectrum, under an average concentration ratio of 400 suns. Passive and active cooling methods, keeping cells below 110 °C, are also investigated and discussed, indicating that a transparent active cooling design could improve the CPV module efficiency by around 1% (absolute), relative to a passive design, by reducing the maximum cell working temperature by around 16 °C. Furthermore, cost analysis shows that installation cost of around $1.9/W–$2.2/W could be reached for the tCPV based PV/T system, which shows a competitive economic advantage compared to a more conventional PV with battery system.

Photovoltaic (PV) systems operate in a paradox; sunlight is the essential input to generate electricity with PV, but they suffer a digression in performance as the operating temperature goes higher. This work is a comprehensive compilation and review of the latest literature regarding research works rendered to achieve improved efficiency through appropriate cooling systems. Most of the research goals were twofold, that is to enhance the efficiency of the solar PV systems and to ensure a longer life at the same time. The passive cooling systems are found to achieve a reduction in PV module temperature in the range of 6–20 °C with an improvement in electrical efficiency up to 15.5% maximum. On the other side, active cooling systems’ performance are better, as may expected, with a reduction in PV module temperature as high as 30 °C with an improvement in electrical efficiency up to 22% maximum along with additional thermal energy output with efficiency reaching as high as 60%. Based on the wide-ranging review, it may be predicted that with the swelling growth of solar PV electricity worldwide, the compatible cooling system is becoming obligatory in order to ensure better energy harvest and utilization.

International audience; Densely packed concentrated photovoltaic (CPV) receivers require efficient active cooling in order to maintain the photovoltaic cells within their nominal operating temperature range. The cooling device must have low thermal resistance coefficients and also provide good cell temperature uniformity in order to maximize the efficiency and the reliability of the whole system. A hybrid jet impingement/microchannel cooling device designed for CPV receivers is experimentally tested under real sun in outdoor conditions. The measurements include the irradiation profile at the outlet of the secondary optics and the temperature distribution of the receiver. The experimental results show that the thermal resistance coefficient and the temperature uniformity provided by the cooling device met the requirements for CPV receivers. This work also emphasizes that the internal geometry of the cooling device must be tailored, at the design stage, to the irradiation profile provided by the optics, which is generally nonperfectly uniform in CPV systems based on densely packed receivers. The impact of the solar concentration ratio and flow rate on the electrical output of the receiver is also assessed.

Performance of the absorption cooling system is still a challenge due to the coefficient of performance (COP) that is generally poor when compared with the conventional vapor compression cycle. High solar radiation in hot climates is usually associated with high ambient temperature and consequently peak cooling demand. Absorption cooling cycles can be powered by solar but the performance is limited by heat source temperature (solar collector) and high ambient temperature that can affect the condensation process. Efficiency enhancement of the system components is essential to increase the COP of the system. A modification in the combined absorption–ejector cooling system is adopted. Adding a removable flash tank between the condenser and evaporator could improve entrainment ratio of the ejector, along with improving the cooling effect inside the evaporator. A computer simulation program is developed to evaluate the performance of the modified combined cycle using aqua-ammonia (NH3–H2O) refrigerant. The performance of the proposed combined cooling cycle is compared with basic absorption, and combined absorption–ejector cooling cycles. Results showed a significant improvement in the COP of the modified cycle at different operating conditions. Cooling effect and capacity of the evaporator is enhanced due to the reduction of flash gas delivered to the evaporator. Furthermore, the flash tank optimized the ejector entertainment ratio and consequently increasing the condenser pressure. This optimization will enable the system to perform well in hot climates where the condenser efficiency is limited by ambient temperature.

In this paper, a solar hybrid desiccant air conditioning system, which combines the technologies of two-stage desiccant cooling (TSDC) and air-source vapor compression air-conditioning (VAC) together, has been configured, experimentally investigated and theoretically analyzed. The system mainly includes a TSDC unit with design cooling capacity for 10 kW, an air-source VAC unit with 20 kW in nominal cooling capacity, a flat plate solar collector array for 90 m 2 , a hot water storage tank and a cooling tower. Performance model of the system has been created in TRNSYS simulation studio. The objective of this paper is to report the test result of the solar hybrid air conditioning system and evaluate the energy saving potential, thereby providing useful data for practical application. Experimental results show that, under typical weather condition, the solar driven desiccant cooling unit can achieve an average cooling capacity of 10.9 kW, which contributes 35.7% of the cooling capacity provided by the hybrid system. Corresponding average thermal COP is over 1.0, electric COP is up to 11.48. Under Beijing (temperate), Shanghai (humid) and Hong Kong (extreme humid) weather conditions, the solar TSDC unit can remove about 57%, 69% and 55% of the seasonal moisture load, thereby reducing electric power consumption by about 31%, 34% and 22%, respectively. These suggest that the solar hybrid system is feasible for a wide range of operating conditions.

A high-performance solar ejector cooling system using R141b as the working fluid was developed. We obtain experimentally a COP of 0.5 for a single-stage ejector cooling system at a generating temperature of 90°C, condensing temperature of 28°C, and an evaporating temperature 8°C. For solar cooling application, an optimum overall COP can be obtained around 0.22 at a generating temperature of 95°C, evaporating temperature of 8°C and solar radiation at 700 W m −2 .

Passive cooling techniques applied to thermostatically controlled buildings can contribute to reducing their cooling load significantly. Ground and night ventilation techniques appear to be the more promising among the proposed dissipation techniques. Calculation of the specific contribution of night ventilation and ground cooling techniques requires appropriate algorithms to account for the coupling of the passive with the active cooling system. The present article deals with the development of a new, integrated method to calculate the energy contribution of ground and night ventilation dissipation techniques to the cooling load of thermostatically controlled buildings. The method is based on the principle of “balance point temperature” and succeeds in estimating the hourly value of the balance temperature of a building. In addition, it calculates the cooling load of the building as well as the global contribution of the ground and night ventilation techniques. An extensive validation procedure has been followed using data from an extended version of TRNSYS including detailed algorithms to simulate dynamically the thermal performance of night ventilation and earth-to-air heat exchangers. Very good agreement between the results predicted by TRNSYS and the present method is found.

Battery lifetime in a photovoltaic (PV) system is important in determining life-cycle costs and servicing requirements. Unfortunately, this is often not calculated with any certainty. We present a simple model for estimating PV battery lifetimes which are application- and battery-specific, using data normally available (or easily estimated) at the time of system design. In a correctly designed and operated PV system, one of two properties will limit the ultimate lifetime of the battery: the cycle life or the battery's resistance to internal corrosion. The cycle life is more or less independent of ambient temperature, but the resistance to internal corrosion falls rapidly at higher ambient temperatures. Whether the cycle life or the temperature-dependent corrosion is the limiting factor on battery life depends on the particular details of the photovoltaic system, especially the type of battery used, the daily depth of discharge and the average ambient temperature experienced. Illustrations are given of the particular circumstances for a variety of PV systems with open (vented) lead-acid batteries, ranging from rural lighting systems and vaccine refrigerators to large telecommunications systems. Where possible, the predicted lifetime is compared to actual field experience. In PV systems using tubular plate vented batteries, it is nearly always the temperature-dependent corrosion process that limits the battery lifetime, and not the cycle life. In larger PV systems in hot climates, active cooling of the battery enclosure (powered by photovoltaics) can sometimes increase battery lifetime, and a suitable battery-cooling system under development is described briefly.

Recently, the photovoltaic (PV) power generation system has attracted attention as one of clean energies. Especially, residential roofing PV system connected with power grids has been popularized as a result of increasing concerns over global warming and continuing decline in PV manufacturing costs. The power generated by the PV module increases with irradiance, but it decreases as PV module temperature becomes high. The PV temperature depends on ambient temperature, and becomes more than 60°C in summer. Therefore, the power generated does not necessarily increase even if the irradiance increases in summer. However, if the PV modules were cooled under such a high PV temperature condition, more electrical power would be obtained from PV modules. In this study, a PV power generating system equipped with a cooling device has been developed. The major components of the system are an array of PV modules and cooling panels attached to the backside of the PV modules. The respective PV module is cooled with cooling water flowing through a narrow gap in each cooling panel. Hot water discharged from the cooling panel is delivered to a storage tank and can be reused in anywhere. In order to save energy for introducing cooling water into the panel, a siphonage from an upper level of a building to the ground level is utilized. A siphon tube is connected to a discharge port of the cooling panel, thus the pressure at the discharge port becomes negative. Cooling water enters into the bottom end of the cooling panel at atmospheric pressure and goes up to the top, discharge side. By adopting this cooling water system, we could spread the cooling water evenly over the entire backside of the PV module and thus realized an effective cooling device. In addition, we could make the cooling device light and smaller because no auxiliary pumping system is needed for introducing cooling water. To provide field performance data for the present PV power generation system equipped with the special cooling device mentioned above, long-term monitoring tests in a natural environment were conducted in summer for a test facility constructed at the Yatsushiro National College of Technology (YNCT), Japan. As a result, it was confirmed that the cooling of the PV modules increases the electric power and that the reuse of hot water from the cooling panel contributes very much for saving energy consumed for heating water.Copyright © 2004 by ASME

Based on a theoretical analysis of small-scale experiments, a 57 m earth contact cooling tube was designed, constructed, and tested to provide cooling for residential buildings and related applications. Warm outside air is drawn through the tube and its heat is absorbed through the tube walls into the surrounding soil. The cooled air then enters the building. Our study investigated cooling performances at different air velocities and soil saturation in test run durations up to 30 days. Experiment results demonstrated that this system could provide up to 1.5 tons of cooling at a flow rate of 1600 cubic meter/hour during hot summer days. This study concluded that earth-cooling tubes are a feasible air-conditioning option for cooling demands in the Midwest, U.S.A. This system requires very little energy. Thus its use is especially interesting in areas where energy generation or supply is problematic. This paper presents the earth contact tube system, structure details of the system, and experiments.

In this experimental study, several solar-assisted heating and cooling configurations have beenconsidered for a basic system comprised of a two-speed heat pump, photovoltaic (PV) arrays, solar thermal collectors, and thermal storage. The objective of the study was to determine the performance of the PV arrays at decreased insolation, the effects of air preheat by solar thermal energy on heat pump operation, and cooling system performance under two different configurations. During the entire operation, the PV arrays converted 4.7 per cent (9.5 MWh) of the incident solar insolation to d.c. power, of which 54.6 per cent was used by the residence. This contributed 23.4 per cent of the total house electrical demand. The remaining 45.4 per cent of the output was fed to the utility, indicating the arrays and the heat pump were not properly sized with each other. Based on results from the winter heating operation, it is shown that for the particular heating system consdered, the best performance is attained when the solar heating is used alone. By using the heat pump as a booster, the remaining available solar energy left in the storage tank can be used with good seasonal performance factor. Summer cooling operation consisted of two sequential cooling configurations. In the first cooling test, the heat pump was operated to either the house or storage when the PV array generation level was greater than the energy demand of the heat pump and associated equipment. When the array output level was less than the cooling system demand, the operating strategy was that of an off-peak cooling operation to chill the water storage. Utilization of chilled water storage was not realized in the first cooling test because of the inherent inefficient design of the Tri-X coil. The capacity at low-speed heat pump operation was too small to effect significant cooling of the water loop; whereas high-speed heat pump operation in attempting to chill water (fan operation absent) caused frosting of the coil. The heat pump was utilized only to maintain chilled water storage in the second cooling test, without heat transfer through the Tri-X coil. Cooling system performance obtained in cooling test 2 using the Ametex exchanger was considerably improved over the test 2 performance with the Tri-X coil.

The relative advantages of a single-stage, lithium bromide-water absorption air conditioner heated from a flat-plate solar collector are compared theoretically to those for an ammonia-water system, and the lithium bromide system is selected as the preferred one. Double-stage absorption systems with their improved performance are described and are shown theoretically to require generator temperatures that are too great to make them attractive for use with flat-plate collectors. Dual, series-connected systems which require no cooling tower for heat rejection are shown by analysis to have a low coefficient of performance. Systems utilizing refrigerant storage and a heat rejection buffer between a cooling tower and the absorber and condenser are discussed along with the computer simulation describing them. They are shown to require smaller cooling towers than conventional units. Operation with an air heat exchanger rather than the cooling tower in such a system is shown to yield acceptable system performance with a small reduction in the fraction of the cooling load which can be met with solar energy.

A simulation model for the liquid desiccant component of a hybrid liquid desiccant cooling system was developed. Seasonal simulations were performed on different operational modes of a hybrid liquid desiccant cooling system including regeneration by solar energy. The seasonal thermal and electrical energy use and operational costs were compared to those of conventional cooling systems. For the system configuration investigated, the study shows that the cooling energy required by the conditioner exceeds the cooling requirements of the load. Although the conditioner cooling water is provided at a higher temperature (and therefore at a higher COP) than required in a conventional system, the additional requirement of regeneration energy cause the operating costs to be comparable to greater than those of a conventional chilled water cooling system. A preferred liquid desiccant configuration from an operating cost standpoint is proposed.

The use of cool storage in conjunction with residential lithium bromide absorption chillers allows for improved operating conditions of the cooling subsystem. Significant performance degradation in the absorption cooling capacity is evident whenever the chiller cycles on and off during periods of low cooling demand. The capability of providing storage for the chiller out-put prevents short-term cycling of the absorption machine and significantly improves the seasonal average coefficient of performance of the cooling system. Cool storage can also be utilized to allow for a lower cooling capacity of the absorption unit (lower tonnage), without decreasing the ability of the subsystem to meet the cooling demands of the building. The size of cool storage can, in fact, be optimized by evaluating the ability of the cool storage component to minimize cycling of the absorption machine and in meeting the cooling demands on a smaller tonnage chiller.

This report develops nominal cost and performance goals for solar photovoltaic conversion devices intended for large-scale electric utility applications. The objective is to provide an improved basis for establishing research and development priorities for photovoltaic devices and conversion concepts. Comparisons are made among a number of generic power plant conceptual designs, with the aid of an array design parameter that is defined to include array-area-related costs, overall power plant efficiency, and average available insolation. The analysis indicates that flat plate approaches without concentration or tracking have good prospects for commercial viability if device conversion efficiencies near 10 per cent can be combined with installed device costs under $20/m2 ($2/ft2) and device lifetimes in excess of 20 years. Thin-film approaches have potential for achieving these cost and performance goals because of low material content and potentially low fabrication costs. Very high efficiency devices coupled with concentrations in excess of about 100:1 represent a viable alternative if sufficiently high conversion efficiencies (25% or more) can be achieved. Such devices are likely to be expensive, but high concentration may make their costs acceptable. Several device types and converter approaches exist or have been proposed that have potential for reaching these efficiencies. In contrast to flat plate approaches, however, high-concentration approaches may have the disadvantage of requiring active cooling. Approaches employing low-to-medium concentration appear to have limited potential for large-scale applications. Required effieciencies are likely to be comparable to those needed for high-concentration approaches, but the concentration ratios are not likely to be high enough to make the photovoltaic device costs tolerable.

This paper describes the design of a solar air heating and night/day exchange cooling system with emphasis on the operational modes. In this type of system the collector absorbs solar energy and converts it to heat for space heating and domestic water heating. Cooling is accomplished by using the cool night air available in dry climates) to cool a pebble-bed storage unit and subsequently using the cool pebbles to lower the air temperature in the building during the day. Circulation is from the solar system to the building in the same manner as most modern heating and air conditioning units but uses air as the medium for heat transfer. The air system is particularly suited for climatic regions where heating loads are high and cooling requirements are moderate. The system utilized in Solar House II operates in either the heating or cooling mode as selected through a seasonable change-over switch. Solar preheated hot water is furnished for domestic use in either mode.

India is the first major tropical country which has set out to widen her industrial dimensions. The prevailing wet bulb temperatures in many parts of the country vary between 80–85°F. In this process the scientists and engineers have to face the problem of the heat of the process added to the heat of the atmosphere. This often results in working conditions beyond the limits of human endurance and a considerable drop in productivity of operators. The high wet bulb temperatures rule out the possibility of using evaporative cooling and the high cost of maintenance and operation eliminate the use of airconditioning with refrigeration. The object of this study is to explore the possibilities of the utilization of solar energy in conjunction with different systems for the dehydration and cooling of air, and to endeavour to establish one which will be most suited under the Indian conditions. An adsorption or absorption system of dehumidi-fication with sensible and evaporative cooling of air appears to show promise.