Hawkes and Leach [47] consider the environmental impact of energy use in the residential sector for three different types of micro-CHP installations in the UK, and five different types of residential dwelling, as well as three different electricity demand values. The authors calculate the ‘equivalent annual cost’ and CO2 emissions using the CODEGen model, a generalised model of heat and power provision that minimises the present value lifetime cost of meeting a given energy demand. The authors find that the micro-CHP system can reduce CO2 emissions by between 10% and 20% of current CO2 emissions for the residential sector, and generate annual cost savings of between approximately d100 and d500 per tonne of CO2. The authors also note that the cost of the CO2 savings is, in the majority of cases, such that micro-CHP can be an economically efficient instrument for reducing carbon emissions (given the carbon price in the EU ETS).