Design and simulation of a prototype of a small-scale solar CHP system based on evacuated flat-plate solar collectors and Organic Rankine Cycle

This paper presents a dynamic simulation model of a novel prototype of a 6 kWe solar power plant. The system is based on innovative solar thermal collectors and a small Organic Rankine Cycle (ORC), simultaneously producing electric energy and low temperature heat. The novelty of the proposed system lies in the solar collector field, which is based on stationary evacuated flat-plate solar thermal collectors capable to achieve the operating temperatures typical of the concentrating ones. The ORC was simulated in Engineering Equation Solver (EES), using zero-dimensional energy and mass balances. The ORC model was subsequently implemented in a more general TRNSYS model. The model was used to evaluate the energy and economic performance of the solar CHP system under analysis, in different climatic conditions. The results show that the efficiency of the ORC does not significantly vary during the year, being close to 10%. On the other hand, the efficiency of the solar collectors is very high in summer (>50%) and significantly lower during the coldest winter days (down to 20%). Pay-back periods are extremely attractive in case of feed-in tariffs (about 5 years), whereas the profitability of the system is scarce when no public funding is available.