1 Department of Buildings and Energy, Technical University of Denmark2 Department of Civil Engineering, Technical University of Denmark
Recently a number of Chinese companies started mass production of evacuated tubular solar collectors. Contrary to Europe, in China the evacuated tubular solar collectors have reached such a low price level that it has become normal to use these high-efficient solar collectors in many different types of solar heating systems.Four different evacuated tubular solar collectors produced by Chinese companies have been tested in a small solar domestic hot water test system. The test system has been tested under realistic conditions in a test facility for solar heating systems at DTU. By means of the tests a simulation model has been developed for each of the four solar collectors.With the developed models calculations of the yearly thermal performance of different Danish solar heating systems were carried out: Small and large solar domestic hot water systems, combined solar domestic hot water and space heating systems and solar heating plants. Calculations were carried out with the four investigated evacuated tubular solar collectors and with ordinary flat plate collectors.The investigations showed that the thermal performance of solar heating systems is increased by using evacuated tubular solar collectors instead of ordinary flat plate collectors and that the solar collector area of a solar heating system with a fixed thermal performance can be reduced considerably by using evacuated tubular solar collectors instead of ordinary flat plate collectors. The higher the solar fraction and the operation temperature are the greater the advantage of using the evacuated tubular solar collectors will be. For solar domestic hot water systems and for combined space heating and domestic hot water systems with typical solar fractions the solar collector area can be reduced about 2-3 times if the best suitable evacuated tubular solar collector is used instead of an ordinary flat plate collector.The price level of the Chinese evacuated tubular solar collectors that are exported to Europe is relatively high. With these prices it will be possible to improve the price/performance-ratios for solar heating plants with high operation temperatures. For the other solar heating systems it is not possible to improve the price/performance-ratios by using evacuated tubular solar collectors instead of flat plate collectors unless the solar fraction of the solar heating system is unusually high.As the prices of the solar collectors sold in China are very low, it is not unthinkable, however, that the prices of exported Chinese solar collectors can be reduced so that they can become attractive in several types of solar heating systems.