Flat solar collector

The flat type solar collector mainly comprises a heat absorbing plate, a transparent cover plate, a heat insulation layer and an outer casing. A water heater composed of a flat type solar collector is a flat solar water heater.

When the flat type solar collector works, the solar radiation passes through the transparent cover, is projected on the heat absorption plate, is absorbed by the heat absorption plate and converted into heat energy, and then transmitted to the heat transfer medium in the heat absorption plate, so that The temperature of the heat transfer medium rises as a useful energy output of the collector; at the same time, the heat absorbing plate after the temperature rise is inevitably radiated to the surroundings by conduction, convection and radiation, and becomes a collector. The heat loss.

The flat type solar collector is one of the most basic types of solar collectors. It has simple structure, reliable operation and reasonable cost. It also has the characteristics of strong pressure bearing capacity and large heat absorption area. It is the most integrated solar energy and building. One of the best collector types to choose from.

According to the IEA report, as of the end of 2004, flat-plate collectors accounted for 35% of the total market share, and vacuum tube collectors accounted for 41%. If you do not count solar collectors without cover, Europe, Japan and Israel are mainly flat-plate collectors, accounting for about 90% of the market share; the domestic market is dominated by vacuum tubes, which accounted for about 2005. 87% of the share, flat-plate collectors only accounted for 12%.

The domestic flat collector has gradually declined from the market dominance in the 1980s to about 12%. There are many factors: 1) The direct system flat water heater can not be frozen in winter and must be drained, so it cannot be used and maintained in winter. 2) All-glass vacuum tube water heaters can be used throughout the year in most areas; 3) All-glass vacuum tubes are greatly reduced in cost due to technological innovations, and production companies are rapidly increasing, which promotes the rapid expansion of the solar water heater market. Therefore, the current domestic market pattern of domestic water heaters is formed by factors such as product characteristics and price. It can be foreseen that in the low-end market of domestic water heaters, all-glass vacuum tube water heaters will still be the mainstay.

The foreign solar energy market has always been dominated by flat panel collectors because of the different design concepts of foreign solar systems. Foreign systems generally use indirect systems, split systems, and closed pressure systems. These systems generally have high initial investment, but the system is reliable, the maintenance cost is low, the water quality is not polluted, and the system has a long service life. For such systems, flat panel collectors have their own technical advantages [4][5]: 1) flat collectors are best suited for pressure systems; 2) solar water heaters are best suited for dual cycles; 3) It is most beneficial to realize the combination of solar water heater and building; 4) long system life and low maintenance cost; 5) more domestic hot water can be provided in most cases; 6) flat collector can be more conveniently solved when used in solar heating system System overheating during non-heating seasons. Therefore, in solar energy system engineering, split solar water heaters and places where solar energy and building integration are required, flat panel collectors have obvious advantages in system life and system maintenance than all-glass vacuum tube collectors.

At present, there is still a certain gap between the domestic flat-panel solar collectors and the advanced level in foreign countries. The comparison between the domestic manufacturers' test results and some SPF test reports can be seen [6]: the interceptivity of the instantaneous efficiency of solar collectors in China is slightly lower than that of foreign products, and the heat loss coefficient is quite different. This indicates that there are still gaps in glass transmittance, high-efficiency selective coating and overall structural design of existing products. Therefore, domestic manufacturers need to work hard to improve the performance of flat-plate solar collectors and develop high-efficiency flat-plate solar collectors. Especially in cold areas or solar heating, the thermal performance of the collector has a particularly significant impact on the revenue of the solar system.