Four million households in the UK are not connected to the mains gas grid and people in this situation generally have very little choice in their source of heating fuel.

BBC: Winter Fuel Allowance Payments Bill

In December 1995 the space probe Galileo showed that Europa probably has an ocean beneath its icy crust, with tidal heating providing a likely energy source.

FORBES: We've Got Company

Dr Cooper and Julien Reboud, also from the University of Glasgow, have now developed a way to carry out the entire PCR process mixing, heating and cooling, as well as analysis using a single piezoelectric source, without the need for separate heating elements or detection equipment.

ECONOMIST: Acoustic microfluidics

"Our vision is that one of these plants would be the core element of a community energy center" that could provide a local, sustainable source of both transportation and heating fuel.

FORBES: Ethanol