Henry Hobhouse, 52, who lives near Castle Cary, packs two underground tanks full of apples and collects the methane gas produced as they rot.
The 3.0-litre XJ6 saloon now runs on methane and costs around 40p a litre.
Hobhouse says the car still returns around 28mpg.
Hobhouse said: “Methane has so many benefits over other alternative fuels we should be looking at expanding its use.
“I can drive from the north of Sweden down to the toe of Italy on methane – but it is not available in the UK.
“Using methane makes total sense. Our reliance on North Sea oil has made us complacent. Other countries are far ahead of us in terms of independent energy production.”
The rotting process is speeded up by adding bacteria from cows’ intestines to the tanks.
The gas is then bubbled through an alkaline and water solution to remove carbon dioxide and sulphur – leaving pure methane.