Energy and carbon payback times for solid oxide fuel cell based domestic CHP

Fuel cells already provide heat and power to people’s homes with lower direct CO2 emissions and fuel consumption than traditional methods. However, their whole life cycle, including manufacture and disposal, must be considered to verify that these environmental impacts are actually reduced and not merely shifted elsewhere. The total carbon footprint and energy payback times have been widely reported for other emerging microgeneration technologies, but have not previously been calculated for fuel cell systems.This paper presents a life cycle assessment comparing solid oxide fuel cell (SOFC) based domestic CHP with the current embedded technologies in the UK. An inventory is given for the construction of a 1 kW stack and then its operation is simulated in detail using measured energy demands from hundreds of UK houses. Producing a 1 kW planar SOFC micro-CHP system was estimated to require 12–17 GJ of energy input and emit 700–950 kg of CO2, although these impacts triple when including the production of replacement stacks needed over the 10 year system life.The carbon intensity of electricity generation from an SOFC was estimated to be 325–375 g/kWh, and is primarily determined by the operating efficiency as manufacturing only adds 10% to this. By displacing electricity generation in less efficient centralised power stations, operating an SOFC in UK homes would reclaim the energy and carbon from its manufacture in under 2 years; however, payback may not be possible if only high efficiency CCGT units are displaced.

► We present primary data on the construction of an SOFC micro-CHP system.
► Construction of a 1 kW system requires 12–17 GJ and emits 700–950 kg of CO2.
► The carbon intensity of electricity generation is 325–375 g/kWh.
► Construction of the stack and system adds 26–46 g/kWh to this.
► Carbon and energy payback times are 0.75–4.7 years in UK houses.