Solar photovoltaic power generation and solar hot water utilization have always been divided into two different fields of solar energy utilization: solar photovoltaic utilization and solar thermal utilization. For a long time, there has been a strict division of labor and a self-contained system from scientific research to production. Therefore, there is no technology or product that combines the two into one comprehensive utilization in China and abroad. In fact, the combination of solar photovoltaic and photothermal is an important development direction for the comprehensive application of solar energy. Because the solar radiation energy used by photovoltaics is mainly taken from the short-wave ultraviolet band of sunlight, and the solar thermal utilization mainly collects the infrared band of solar radiation energy, the two do not conflict. Theoretically, only through the comprehensive utilization of photovoltaic-photothermal composite system, can the maximum utilization efficiency of solar radiation energy be obtained under the same area of equipment.
As we all know, the electricity produced by a solar cell is proportional to the intensity of solar radiation and the area of the cell. Photoelectric conversion efficiency is directly related to the wavelength of sunlight, radiation intensity and battery temperature, but not directly related to the size of the battery area: the output power of the solar cell has a negative temperature coefficient, and the output power increases with the increase of the ambient temperature. Reduced; with the increase of the temperature of the crystalline silicon panel under the sun, the photovoltaic conversion efficiency will drop significantly; for the crystalline silicon panel with a normal conversion efficiency of only ten percent, every percentage point is extremely valuable .
Therefore, when the intensity of solar radiation cannot be controlled, how to maintain the stable photoelectric conversion efficiency of photovoltaic cells, the remaining alternative is how to effectively cool the photovoltaic cells under sunlight to reduce the operation of photovoltaic cells. temperature. For a long time, in order to ensure that photovoltaic cells can operate in a low temperature state all year round under strong solar radiation, it has become a hot spot, difficulty and focus that the international photovoltaic building distributed power station has been concerned about and strived to overcome for a long time. In order to reduce the operating temperature of photovoltaic cells, people usually use radiation or convection heat dissipation to cool photovoltaic cell modules. For example: installing metal heat sinks on the back of photovoltaic cells; adding air cooling channels; or laying forced water cooling systems; and coating surface coatings with high emissivity, etc.
The key to the long-term failure of the above-mentioned measures to be popularized and utilized is the high cost and the energy consumption that cannot make ends meet. In order to reduce the loss of photoelectric conversion heating efficiency by 2-3 percentage points behind a photovoltaic cell of a unit area, installing a forced air cooling or water cooling cooling system will increase the cost of construction and the consumption required to maintain the operation of the system. Electricity, compared with the efficiency loss caused by the heating of the photovoltaic cell system, is completely worth the loss. This is true for small distributed power plants, and even more so for large photovoltaic power plants. In a word, the above methods seem to be feasible in principle, but in fact they do not have the feasibility of obtaining the necessary technical and economic benefits in practical production applications.
To solve the above problems, it is theoretically very simple, that is, as long as a way is found: on the premise of not consuming auxiliary energy to provide circulating power, the “waste heat” generated by photovoltaic cells under sunlight can be effectively replaced. And while maintaining long-term low-temperature operation of photovoltaic cells, it can also convert the collected “waste heat” into useful heat energy for recycling, and make it available to the entire system (photoelectric conversion is not decayed and effective heat recovery and utilization) The technical and economic benefits are sufficient to compensate for the increased investment in materials and equipment. Obviously, the method may not be the only one; but as long as who can achieve the above goal in the simplest, safest and most reliable way, we can determine who can best solve this “worldwide problem”.
In 2003, Kunming Nankai Energy Research Institute took the lead in the research and development of natural circulation system integration technology for solar water heaters, and took the lead in breaking through the scope of a flat solar collector with a total thickness of no more than 68mm, realizing the efficient conversion of the entire natural circulation. Thermal mechanism, the system is integrated in a thinner flat box core, thus finding a new breakthrough for effectively solving the problem of natural circulating water cooling and heat dissipation of photovoltaic cells.
During the “Eleventh Five-Year Plan” period, Kunming Nankai Energy Research Institute and Yunnan Tianda Sunshine jointly applied to the Ministry of Science and Technology and the Yunnan Provincial Department of Science and Technology to declare the “Engineering Design and Demonstration of the Combination of Solar Cells and Buildings – Solar Photovoltaic Buildings with Yunnan Characteristics” National Key projects; the technologies that need to be broken through to complete this project are: first, to develop a set of standardized production of solar photovoltaic power generation-water heater composite components; to realize the passive natural circulation function of silicon solar cells synchronously passing water during photovoltaic power generation, The waste heat generated by it is effectively replaced to maintain the long-term optimal working environment temperature of the photovoltaic cell; to ensure that the output power of the photovoltaic cell does not decrease due to the increase of the negative effect of the battery temperature. Secondly, the solar cell waste heat collected by the module through the natural circulation system must be automatically transferred out in real time, and further raised to the standard temperature of 45°C or higher set by the domestic hot water, and finally automatically entered into the thermal insulation hot water storage tank. stored for use. Thirdly, as a solar photovoltaic distributed power station, it must also have the function of grid-connected operation with the national power supply system. Finally, in the construction and installation of distributed power stations, it is necessary to realize four major problems, such as the coordinated installation of solar photovoltaic power generation and water heater composite components, and the coordinated installation of building integration with ethnic residential buildings, especially Chinese-style rural tile roof buildings with civil structure.
After continuous hard work, Kunming Nankai Energy Research Institute finally independently obtained “Solar Photovoltaic Power Generation-Water Heater Composite Components and System “Flat Box System Integrated Solar Water Heater”; and other two invention patents and five utility model patents “Degassing Stopper” The research and development results of water valve “multi-functional flat plate collector frame profile tube plate system integrated solar water heater” special locking bracket for solar tile sloping roof “flat plate system integrated household solar water heater” and Yunnan Tianda Sunshine completed the project. , and successfully passed the project acceptance of the Ministry of Science and Technology.