Buy any one for £150, get a second for £100, and then a third (or more) for £50

INTEGRATEDSOLAR.co.uk: 114,000 Google. Tons of end user and development possibilities.

HYDROGENTABLETS.CO.UK: The solution to the problem of storing and distributing hydrogen for fuel cell cars? More here.

METHANOLCARS.CO.UK: actually in production - see here.

GSHPS.CO.UK: The accepted acronmy for "Ground Source Heat Pumps", for example, here

MICROCHPSYSTEMS.CO.UK: Here's wikipedia

These next three as a set would corner the market, and at only £300. Many companies are in this market, such as: this one).

ROOFTOPTURBINE.CO.UK
ROOFTOPWINDTURBINE.CO.UK
ROOFTURBINE.CO.UK