Indicative appraisal of clustered micro-generators for a low-carbon transition in the UK building sector

Building ‘zero carbon’ homes will be essential for achieving the carbon reductions within industrialised countries required to meet their commitments under the 2015 Paris Agreement on climate change. Such high performance buildings may need a combination or ‘cluster’ of micro-generators to be installed, such as a heat pump to provide heating and a solar photovoltaic (PV) array to produce electricity. When sized and installed appropriately, these technologies have lower emissions than the conventional systems they displace (centralised grid electricity and gas-fired boilers). However, if the ‘embodied’ energy and carbon is not recouped from that saved during the lifetime of the micro-generator, then there is no net saving overall. This study therefore assesses a range of clustered micro-generators using an ‘integrated approach’ that combines energy analysis, environmental life-cycle assessment, and an indicative financial appraisal. Eight clusters of micro-generators were designated to meet the heat and electricity requirements of five different dwelling types, each one specified to two different UK performance standards (2006 building regulations and a zero-carbon specification). For these 80 scenarios, various combinations of heat pumps with solar hot water and/or PV systems yield the most attractive performance metrics with all of the clusters having energy and carbon paybacks (4.5–5.5 and 5.0–7.0 years respectively) within their operational lifetimes, and would hence create net savings overall. But the clusters were generally found to have unattractive financial payback periods (50–80 years), although this result will be sensitive to the discount rate and prevailing energy prices and support mechanisms. The focus is on the use of clustered micro-generators in the context of UK transition pathways to a low-carbon economy out to 2050, but the lessons learned are applicable to many industrialised countries.