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Test results and evaluation of integrated collector storage systems with transparent insulation

: Schmidt, C.; Goetzberger, A.; Schmid, J.

Solar energy 41 (1988), Nr.5, S.487-494
ISSN: 0038-092X
ISSN: 0375-9865
Fraunhofer ISE ()

Two integrated collector storage (ICS) prototypes with about 1 qm absorber surface each have been installed and investigated at the Institut für Solare Energiesysteme (ISE). Each consists of a water tank with an integrated collector, which is covered with a highly transparent insulating material and is very well insulated on the sides and at the back. During the test period from November 1986 to October 1987 one of them was operated at water-main pressure, and 40 liters corresponding to the hot water consumption of one person, were withdrawn every day. The solar fraction was 58% (68%) with a system efficiency of 28% (36%) (the values in parentheses also take the surplus energy in summer into account, see "Results"). The second one has been installed to study the stagnation (no water flow) performance during the same period. Detailed computer simulation programs have been developed and compared with the experimental results. Based on the u value and the transmittance-absorptance product (Tau alpha), the annual performance can be predicted with an accuracy of 4%. The influence of various parameters such as specific water withdrawal, angle of inclination, profile of water withdrawal, required hot water temperature etc. on the yearly solar fraction and yearly efficiency of the ICS can be studied. Some of the results are presented here.