Solar Thermal Technologies for Domestic Hot Water Applications: an Energy and Economic Investigation Comparing Flat Plate and Evacuated Tube Type Collectors

In this computational study, extensive simulations where conducted to quantify the performance of several solar thermal hot water systems consisting of flat plate and evacuated tube collectors operating under four climates in Australia. The results showed that solar fractions and payback periods can vary considerably, ranging from 58 to 100 per cent and between 3.8 and 10.1 years respectively. It was found, in this work that, although the evacuated tube collector generally operates with a marginally higher annual thermal efficiency over the selective surface flat plate collector, the overall performance of a system comprising of two selective surface collectors, is greater than a 30 tube evacuated tube system due to its larger absorber area despite taking less roof area. Due to the ratio of absorber to gross collector area, the selective surface flat plate collector was shown, in this study, to yield a higher thermal output per unit area of roof over the evacuated collector making it an ideal choice for domestic hot water projects where roofing area is limited relative to the thermal load. Furthermore, for the regions of high solar irradiance in Australia (Rockhampton and Alice Springs) the cheaper, lower performance flat plate collector was found in this study to operate with very high solar fractions while lowering the stagnation temperature over the selective surface flat plate and evacuated tube collector alternatives and is therefore the preferred solution.