Indicative Appraisal of Clustered Micro-generators in the Home

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In 2007 the UK Government announced its intention to require all new homes to be ‘Zero Carbon Homes’ from 2016, which would necessitate an improvement in the energy efficiency of the building fabric, together with low-carbon micro-generation technologies installed in the building. This national policy was abandoned in 2015, amongst some controversy, but the Mayor of London has nevertheless implemented a city-wide zero-carbon homes policy. In addition, given the difficulty of decarbonising some sectors of the economy, it is likely zero-carbon buildings will ultimately be needed to meet the UK’s Climate Change Act 2008 (revised in 2019 to a net-zero emissions target) and commitments under the 2015 Paris Agreement. In order to achieve zero-carbon homes, it is envisaged that micro-generation will be required to offset the carbon emissions associated with energy use in the home. However, to produce a micro-generator, energy is required and carbon is emitted ‘upstream’ of the building itself. This energy and carbon associated with the production and installation of a micro-generator is known as the ‘embodied energy’ and ‘embodied carbon’ respectively. Such data is determined using methods like energy analysis and environmental life-cycle assessment (LCA). If the embodied energy and carbon is not recouped from energy and carbon saved throughout the lifetime of the micro-generator, there is no net benefit in terms of saving energy and carbon. The time that is required for the cumulative amount of energy saved to equal the amount of embodied energy is known as the Energy Payback Period (EPP). Similarly, the Carbon Payback Period (CPP) is the time taken for carbon savings to offset the amount of embodied carbon in construction. Much research has recently been undertaken on the net energy and carbon performance of individual micro-generators {e.g. micro-wind turbines, solar hot water [SHW] systems, and solar photovoltaic [PV] cell arrays}. But clusters of micro-generators may be required to achieve zero-carbon homes: perhaps, for example, an air source heat pump (ASHP) to provide heating and a solar PV panel to deliver electricity. Indeed, the performance of heat generating technologies (e.g., ASHP, ground source heat pumps (GSHP), micro-combined heat and power [mCHP] plants, or SHW systems) is strongly related to demand as well as the interaction with other such heat generating technologies. Consequently, rather than evaluating individual devices, it is important to analyse the operation of the whole cluster.

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