Domestic flat-panel collector from the 80 's market dominance gradually declined to about 12%, there are many factors caused by: 1) direct system of flat water heaters in winter can not be antifreeze, must be emptied, so winter can not be used and maintain complex; 2) full glass vacuum tube water heater can be used throughout the year in most areas 3) Full glass vacuum tube as a result of technological innovation, the cost is greatly reduced, the production enterprises rapidly increase, and promote the rapid expansion of the solar water heater market.
Therefore, the current domestic market pattern of household water heaters is due to the characteristics of products and prices and other factors formed, it can be foreseen in the domestic water heater in the low-block market will still be the whole glass vacuum tube water heater mainly. Foreign solar market has always been based on flat plate collector, because of the foreign solar system design concept is different. Foreign systems generally use indirect systems, split systems and closed pressure systems, which generally have high initial investment, but reliable systems, low maintenance costs, no pollution of water quality and long system life. For this kind of system, the flat panel collector embodies its own technical advantages :1) Flat plate collector is most suitable for pressure system; 2) is best suited for double cycle solar water heater; 3) is most conducive to the realization of solar water heater and building combination; 4) long system life, low maintenance cost ; 5) More domestic hot water can be provided in most cases; 6) Flat panel collector can be used in solar heating system to solve the problem of system overheating in non-heating season more easily.
Therefore, in the solar energy system engineering, split solar water heater and the integration of solar energy and building requirements of the site, plate collector than the full glass vacuum tube collector in the system life, system maintenance and other aspects have obvious advantages. At present, there is still a certain gap between domestic flat-panel solar collectors and foreign advanced level. The comparison between the test results and some SPF test reports of domestic manufacturers can be seen : The instantaneous efficiency of solar collectors in China is slightly lower than that of foreign products, and the thermal loss coefficient is quite different. This indicates that there is still a gap between the existing products in the glass transmittance, high-efficiency selective coating and overall structural design, so domestic manufacturers need to strive to improve the performance of flat panel solar collectors, the development of high-efficiency flat-panel solar collectors. Especially in cold areas or solar heating and other occasions, the thermal performance of collector has a particularly significant impact on the earnings of solar systems.