Experimental results of two different solar hot water systems using transparent insulation

As part of the Institute's work on transparent insulation, two different solar hot water systems have been investigated on the outdoor testfield in Freiburg during summer 1990. The results of performance tests of a transparently insulated collector storage were used for long term predictions. An annual system efficiency of 0.35 with a yearly solar fraction of 0.51 was calculated, assuming an absorber surface of 4.2 m2. Additional measurements showed, that the efficiency of a supplementary continous-flow gas heater varied between 0.6 and 0.8 according to the working mode of the burner. First experiments with a newly designed multi-effect solar still show the possibility of increasing the system's productive capacity by the use of transparent insulation. A higher system temperature and the efficient recovery of latent heat lead to a high production rate of desalinated water.