Planning and operation of two small SDH plants as test site: Comparison between flat plate and vacuum collectors

A small solar district heating plant has been built to provide heat to an existing district heating system supplied by natural gas CHP units. This test site, located at 1,600 m a.s.l., allows comparing the performances of evacuated solar collectors (ETC) with flat plate double glazed ones (FPC) in a mountain environment. The preliminary results of the first months of operation show a better performance of ETC than FPC. The daily heat production shows a good correlation with available radiation, with the FPC having a slightly larger variability. Moreover, while ETC system efficiency is comparable with the theoretic curve, the FPC system efficiency show lower values. The monitoring of the SDH is still ongoing, and some control logics of the system are being performed in order to optimize the heat production from FPC. The specific electricity consumption for pumping is in the range 5 – 20 kWhel/MWhth, in accordance with usual literature values. The specific pumping consumption decreases with increasing daily heat production, and no significant difference arises from the trends of the two systems.