A comparison of five solar systems for heating greenhouses
Five greenhouses equipped with different solar heating systems have been built in Bonn. Performance of the systems has been monitored for about two years to establish energy balances for the houses. The systems considered are groundwater heat pump, rock bed storage and the greenhouse itself acting as collector, concentrating collectors with water storage, venetian blind air collectors with rock bed storage, flat plate collectors consisting of rotating lamellas with stratified water storage and a heat pump. The payback periods of the air systems are about 20 years and have been calculated on the basis of estimated costs for rock bed storage and climatic data of Hamburg and Bonn.