An Assessment of Solar–Thermal Collector Designs for Small-Scale Combined Heating and Power Applications in the United Kingdom

Abstract

This paper focuses on suitable solar–thermal collectors for use in a combined heat and power system targeted at the UK market, based on an organic Rankine cycle. Concentrating and non-concentrating collector products are compared by way of annual energy and exergy analyses using London climate data. It is found that non-concentrating collectors show a wide range of annual power outputs, up to a highest of 67 kWh m−2 yr−1 attained by the best collector (or an average power of 115 W for a 15-m2 rooftop array, representing 30% of the electrical demand in a typical UK household). The maximum exergy delivered from a parabolic trough collector is 70 kWh m−2 yr−1. The choice of mains (municipal) water or air as the cooling medium makes only a small difference to the annual power output. Importantly, the optimal flow rates for the evacuated tube collectors are far lower than those recommended by the manufacturers, indicating that their application to power generation represents a significant departure from their design and intended mode of operation. New and improved designs would be a key development in this area. The importance of using high-resolution, non-aggregated climate data for predicting total annual work output is also demonstrated.