| With the development of renewable energy and low carbon economy, new energy technologies have become the consensuses about dealing with sustainable energy and environmental issues. Solar photovoltaic is the most attractive and promising technology in all kinds of renewable energy technology. The global solar photovoltaic power generation will account for 15% to 20% of the number as one of the basic energy in the world in middle of 21st century. Improvement efficiency of solar cell and reduction cost of photovoltaic power generation are the keys to develop solar photovoltaic technology and increase its proportion in the whole energy resources gradually.When solar cells work, part of solar energy not converted into electricity are transformed into heat and reserved in photovoltaic module. That will result in linear reduction of conversion efficiency with raise of temperature of module. The researches of PV's cooling technology spring up in order to improve photovoltaic conversion efficiency of solar cells. Although a large number of researches proved that reduction temperature of solar cells can increase its efficiency, few of them concerned with the detailed mechanism. The current solar cell cooling technologies include two categories: water cooling and air cooling both using air as the low temperature heat source which results in final temperature higher than the transient air temperature. Therefore, as the transient air temperature increase with the solar radiation intensity, the intense solar radiation will lead to decrease of the efficiency. This problem has become a bottleneck in improving the cooling performance.According to the background of solar cells'cooling research and the defects of traditional cooling technology, and based on the review of extensive literature and analysis for latest solar cells'cooling technology, the solar cooling mechanism, the course of the system's enhanced heat transfer process and working performance of solar cell is researched in-depth by uniting material science and Engineering Thermophysics, microparticle dynamics and macrosystem, theoretical analysis and experimental and numeral simulation. The main research works and conclusions are as followings:1. Mechanism of temperature effect on the solar cells' efficiencyBased on the internal electronic process between sunlight and the material in cells, the mechanism of temperature effects and its specific acting forms are defined in the processes of electron-hole pair formation, electron transport and collection occuring in silicon solar cells. The method in analysis the contribution rate of temperature decrease which brings about the increase in efficiency of solar cell is also cleared. Due to the performances of solar cell is strongly sensitive to temperature, mechanism analysis mainly includes the following three parts:the effects of temperature on forbidden energy gap; the effects of temperature on carriers' velocity and the effects of temperature on scattering. Two important conclusions are drawn:(1) Increase in solar cells' conversion efficiency is mainly due to the energy loss decrease in carriers' transport process when the temperature drops, so carriers'output proportion and solar cells' conversion efficiency are both improved in the same solar radiation intensity. (2) The efficiency and output of solar cell linearly increase when the temperature decrease, but it is effective for system efficiency only in case of no energy consumed or less energy consumed.2. Thermodynamics and heat transfer analysis of the solar photovoltaic modulesThe energy conservation law in the heat system formed by the sun, solar photovoltaic module and atmosphere are used to analyze the specific light-heat-power process. The temperature distributions in module, its influence factors and principle of factors'changes were determined, and these effects on photoelectric conversion are also obtained. When material of a solar cell and module structure were confirmed, the solar cell's temperature and conversion efficiency almost changes linearly with solar radiation and air temperature's variation, and the change rate depends not only on the physical and thermodynamic performance parameters of the materials and its structure configuration, but also on the surface shape and surface heat transfer coefficient. For the conventional flat-plate modules, the highest temperature appears in solar cell, and its lowest temperature equals to the air temperature only observes when solar radiation is zero. It was found that under present material and structure of solar photovoltaic module the interior thermal resistance was extremely large that lowered the effect of exterior convective heat transfer coefficient on the heat transfer rate. Therefor both decreasing material thermal resistance of the module and increasing temperature difference in cooling become very important.3. Research on solar photovoltaic module's metallic backplaneAimed at decreasing material thermal resistance of the module, the effects of various backplane materials on the solar photovoltaic module's performances have been investigated. Based on the studies of the selection principles and methods, metal material was utilized as backplan Material to substitute high Polymer material through comprehensive match from optical, mechanical, thermal, chemical, electrical and the economical aspects. The material type and size, mechanical strength, corrosion resistance, insulation, heat transfer properties, surface properties and thermal elongation are analyzed and determined. A innovative mechanical method is proposed to reduce effects on the stress of cells caused by mismatch of material extension length, which not only guaranteed insulativity but also lowered the effect of high Polymer Material on heat conduction. A new type of solar modules used aluminum alloy backplane was developed and a convention patent has been authorized. The experimental studies confirm that the backplane temperature of the solar modules with aluminum alloy may decrease 2～8℃compared to TPT backplane solar modules in the same environmental condition of Guangzhou. The maximum power may also increase up to 2% while the effects would strengthen as the solar radiation increase.4. Researches on Cool-Sstorage Mode Solar Photovoltaic ModuleAimed at increasing cooling temperature difference based on no energy consumed or less energy consumed, a innovational concept and method were presented that atmosphere's temperature difference and solar energy will be combined together to alter the low temperature heat release surrounding and create multi-source, and its influences on solar module's performance was analyzed. Through the studies of atmospheric temperature variation and optimization both parameters of energy transfer and conversion and structures of enhanced heat transfer, a composite system named the Cool-Storage Mode Solar Photovoltaic Module(abbreviated as CSSM) was constructed, which diverts the atmosphere's cold energy to day-time so as to lower the Photovoltaic module's temperature. The principle and design method of CSSM are proposed, which breaks the temperature bottleneck of conventional cooling method, and greatly reduces the temperature of solar modules. This method also accesses to the authorized patents. The experiment studies confirmed that backplane's temperature of CSSM may reduce the temperature by 26.5℃compared with TPT backplane Photovoltaic modules in the same environmental conditions at Guangzhou. A maximum output power increase up to 14%～18% were achieved.
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