The idea of having a central heating boiler which generates electricity for the home may sound far-fetched - but just such an energy-saving boiler is coming on to the market. Powergen is looking for hundreds of customers prepared to buy these personal power stations in a limited launch this winter. When the electricity isn't needed in the home, it is fed back on to the National Grid, reducing the owner's bills. Richard Tait from Suffolk has had an experimental version in his garage for the last eight months. He's convinced the unit has saved money. "I reckon it's contributing quite a lot to the electricity I use during the day and I think it's also using less gas than a normal boiler," he says. Richard is starting up a catering company specialising in Mexican food. So he is at home a lot, and that means using more electricity. It might be for his electric guitar, for standard electrical appliances or for his personal computer, which he never dared to leave on for long periods before because of the cost. "With this generating electricity as it heats the house I can have the PC on and not pay for it, if you like," he explains. The boiler fits under the kitchen counter. It makes a slight humming noise and has an LCD display showing that Richard's water has been heated to 65 degrees Celsius and that he's generating 850 watts of electricity. That's enough to run the guitar, and a few lights and appliances. But once a power-hungry device is turned on - the electric kettle, for instance - electricity has to be taken in from the mains supply. The boiler is based on the Stirling engine, dreamed up by the Scottish inventor Robert Stirling in 1816. [BBC News]