Comparative greenhouse emissions analysis of domestic solar hot water systems

It is commonly assumed that solar hot water systems save energy and reduce greenhouse emissions relative to conventional fossil fuel-powered systems. Very rarely has the life-cycle greenhouse emissions (including the embodied greenhouse emissions of manufacture) of solar hot water systems been analysed. The extent to which solar hot water systems can reduce emissions compared with conventional systems can be shown through a comparative life-cycle greenhouse emissions analysis. This method determined the time it takes for these net greenhouse emissions savings to occur, or the 'emissions payback period'. This paper presents the results of a life-cycle greenhouse emissions analysis of solar hot water systems in comparison with conventional hot water systems for a southern (Melbourne) and a northern (Brisbane) Australian city. The life-cycle costs of these hot water systems were also analysed to determine the financial payback period. The fuel source and solar fraction determined the emissions resulting from the energy used for operating hot water systems. The solar systems provide net emissions savings compared with the conventional systems after 2.5-5 years in Melbourne and after 2.5 years in Brisbane, depending on the auxiliary fuel. The life-cycle cost analysis also revealed that the financial payback period for solar hot water systems is more than 10 years in Melbourne and around 10 years for an electric-boosted system in Brisbane. This suggests the need for greater subsidies to increase market take-up for solar systems, especially where electricity is the only available fuel.