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The advantage of PV–thermal hybrid systems is their high total efficiency. By using concentrating hybrid systems, the cost per energy produced is reduced due to simultaneous heat and electricity production and a reduced PV cell area. In this article, the optical efficiency of a water-cooled PV–thermal hybrid system with low concentrating aluminium compound parabolic concentrators is discussed. The system was built in 1999 in Alvkarleby, Sweden (60.5° N, 17.4° E) with a geometric concentration ratio of C=4 and 0.5 kWp electric power. The yearly output is 250 kWh of electricity per square metre solar cell area and 800 kWh of heat at low temperatures per square metre solar cell area. By using numerical data from optical measurements of the components (glazing, reflectors, and PV cells) the optical efficiency, ηopt, of the PV–CPC system has been determined to be 0.71, which is in agreement with the optical efficiency as determined from thermal and electrical measurements. Calculations show that optimised antireflection-treated glazing and reflectors could further increase the electric power yield. |
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