Once the plates are stacked and connected to a power supply - typically a domestic gas boiler - it becomes what the energy boffins call a 'micro-CHP' - a small combined heat and power appliance. Bance prefers to call it a 'mini-power station'.

Last week, Bance was a member of a top-level delegation of energy giants, including British Gas and BP, that visited Downing Street to advise the government on energy policy as part of its wide-ranging review of energy needs. 'It's a recognition that our product is commercially viable and that we have a contribution to make on this crucial issue,' said Bance.

Ceres, which makes the plates for the micro-CHP, grew out of research initiated 15 years ago by Imperial College London. 'We have been in stealth mode for a decade,' says Canadian-born Bance, a physics PhD. 'We didn't want to let the Japanese and the Chinese know. If you have a technological breakthrough, you keep silent until you can shout about it.'

Ceres listed on the Alternative Investment Market in 2004, and has raised more than £25m for development and marketing of the micro-CHP. It now has a broad list of blue-chip shareholders such as Fidelity International, while Imperial still holds 9 per cent of the shares. Bance's key markets are homeowners and industrial users. He has signed deals with British Gas, giving him access to its 15 million domestic customers, and with BOC, which has a host of big industry customers. 'We prefer to do single deals with significant industrial partners,' he says.

The micro-CHP retails for about £3,000 but should pay for itself in a few years' time, says Bance. It attracts carbon credits under the Kyoto accords.