Efficient Home Energy, belonging to the Mondragón group, manufactures the Stirling energy microgeneration boiler. This is a normal-sized domestic boiler with a combined heat and electricity microgenerating system, running on gas, which besides covering domestic heating and hot water needs also generates electricity. Its impellers are capable of reducing home energy bills by over 20%, and cutting CO2 emissions by up to a tonne a year per household.
The Stirling principle comes from an invention in 1816 by a Scottish religious minister of that name. Basically it is a motor which runs on hot air. The expansion induced within a gas moves a working piston which drives a dynamo.
With domestic heating boilers, use is made of the combustion exhaust gases which are lost up the flue. The movement of the pistons is converted into electricity generation which is fed into the grid. It is therefore an "energy saving" system which means energy can be saved in every home.