Financial incentives for solar heating systems. Some aspects on Swedish and German rules for subsidies.

Abstract

Abstract This thesis compares the Swedish and the German way of handling subsidies for solar collectors. While in Sweden subsidy is related to collector performance and refers to aperture area, in Germany gross area determines the amount of subsidy. Both countries require similar tests and certifications for subsidies but the collector performance is calculated in different ways. Five flat-plate and five evacuated tube collectors have been calculated with the Swedish boundary conditions, using the Swedish SED-program and POLYSUN (a publicly available calculation program. Additionally, the German boundary conditions have been used in POLYSUN. Calculations made with SED and the Swedish way of assuming an average operating temperature gives the lowest output for all collectors. POLYSUN gives higher outputs at the same average operating temperature which is mainly due to the fact that the programs are using different climate files. Transferring the Swedish climate file into POLYSUN still leads to different results. For flat-plate collectors this relative deviation is the same but it varies a lot for the evacuated tube collectors. That is due to the incident angle modifier (IAM) which is handled in different ways in both programs. Calculating with the in Germany required boundary conditions leads to the highest collector performance. That is due to the fact that these boundary conditions do not represent a commonly used system and therefore lead to a lower operating temperature level. Calculating with representative parameters leads to nearly the same results as those at the average operating temperature. Thus, assuming this average operating temperature instead of regarding the whole system is appropriate. All calculations refer to aperture area. But due to the fact that the gross area is the area actually needed on the roof and it is the only area defined in the same way for all collectors, it is logical that subsidies refer to this area, as they do in Germany. Furthermore, in order to promote efficient solar collectors, a combination of relating subsidy to performance and requiring a minimum output could be a good solution to displace low efficient collectors from the market. A European environmental certificate would additionally avoid the production of collectors, having detrimental effects on the environment.