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.
Richard: Boiler is more efficient
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.
There's a gas burner at the top. It heats up four cylinders, each of which contains nitrogen gas and a piston.
The gas expands as it warms up, pushing the pistons down. The pistons are cooled on the central heating water, which passes underneath, so they go up again.
The result? Pistons which go up and down 1,600 times a minute, turning a generator and producing a constant supply of hot water.
Paul: Savings of 20% are possible
It's known as an external combustion engine. The technical name given to this particular use is Micro Combined Heat and Power or Micro CHP.
Paul Haley, the project manager for Powergen, says that a family-sized home could reduce its carbon dioxide emissions by 1.5 tonnes, or 20%, by using the technology.
"We've seen savings of £150-200 a year on combined gas and electricity bills," he says. "You can see about a 20% reduction."
The easiest way to check whether Richard Tait's system is working is to look at his electricity meter out in the garden.
With not much switched on in the house, the meter wheel turns gently backwards, showing that power is being fed back on to the Grid.
Turn on the kettle and the wheel turns abruptly the other way, as electricity is sucked back into the house from the mains supply.
Powergen wants to sell 400 of the boilers this winter. The company is satisfied from its testing programme that the technology works. Now it wants to test the market.
As the system generates power, the meter goes backwards
The drawback is the cost of the boilers and installation, currently between £2,500 and £3,000 each time.
Paul Haley believes that the price will fall sharply once large-scale production starts, but that's unlikely to happen for a couple a years.
"There are about 1.3 million boilers sold in the UK every year and about 650,000 of those could very well be replaced by the Micro CHP unit," says Paul.
In the meantime, Powergen is suggesting that prospective customers lease the equipment or spread the cost over several years.
The company will be offering an overall monthly package, including installation and maintenance.
Only those in the Ipswich, Nottingham and Manchester areas need apply. The system will not be available elsewhere until next year.
The best savings will be in bigger than average homes, with higher energy needs. So Powergen is looking for three or four bed semi-detached and detached houses.
To find out more, ring Powergen on 0800 107 1366, or send an email to email@example.com
British Gas is testing a rival Micro CHP system which can be mounted on the wall, so personal power stations could soon be big business.