By Karen Pirie
You and Yours, BBC Radio 4
As oil price and duty rises threaten to push diesel prices beyond the £1-a-litre mark, more of us are finding inventive ways to save money on our transport costs.
Thousands of people in the UK are now making their own biofuel
Since the law changed in July, it is now legal to make up to 2,500 litres of your own biodiesel, enough to run the average family car, without having to pay tax.
"Home brewers" convert chip fat from pubs and restaurants, which would otherwise go straight to landfill. Companies who make the kits needed to convert this unwanted oil are reporting a steady rise in sales.
Thousands of enthusiasts are also expected to attend a biofuels trade fare in Nottinghamshire on 17 and 18 October.
Dan Purkis, a consultant engineer, puts home-brewed fuel into the tanks of his 4x4, even though he is based in Aberdeen - the oil capital of the UK.
He admits that messing about with old chip fat is not for everyone but adds: "It's interesting and fun and it reduces my impact on the environment?
"When I looked at my lifestyle I realised that fuel was the greatest energy user in my life."
You can buy conversion kits from £700 but Mr Purkis has made his own.
He told the BBC's You and Yours programme: "No special tools were required and nothing was beyond the ability of a typical DIY enthusiast. Most of the parts were bought second hand or salvaged from scrap yards.
"I recycle used vegetable oil from a local hotel. They throw away between 50 and 100 litres a week which would otherwise go to landfill."
Once he gets it home, he puts the oil through a series of refinements:
The waste product from this process is glycerin, which has to be washed out of the biodiesel with soap and half-water to half-fuel. He then composts the glycerin.
- Allows sediment in the oil to settle to the bottom of the bottle
- Pumps and filters the top 70% of the oil; it is pure enough to put straight into his car
- Treats the remaining sludge and converts it into biodiesel by adding methanol and caustic soda
- Heats the oil, causing it to react with the caustic soda
Mr Purkis says his car runs better on biodiesel: "It's smoother - better lubricated."
Even though he is a qualified engineer, he insists that it is not a difficult process.
"If you can follow a recipe, you can make biodiesel," he explains. "There's lots of information out there on websites and forums and in books."
Motoring agencies, however, suggest a more cautious approach.
Rising pump prices make home-made fuels more appealing
Vanessa Guyll of the AA says using clean vegetable oil is possible in cars with older pumps. But she adds: "Because it's thicker it can affect the injector.
"Some diesel pumps are more vulnerable than others, and if your pump goes it could cost up to £1,200 to replace it."
Mr Purkis reckons you can get round this by modifying your vehicle to warm the oil up which makes it less viscous.
He says you can adapt your car so that the fuel pipe is near the car's heater: "You can do this yourself if you know a bit about cars or you can buy a conversion kit."
But the AA has another word of caution.
"Using a small amount mixed with regular fuel is okay but a higher concentrate can block filters," explains Vanessa Guyll. "If you're in any doubt about putting biofuels in your car, contact the manufacturer of your vehicle."
And Christopher McGowan, chief executive of the Society of Motoring Manufacturers and Traders (SMMT), adds: "You have to be very careful in the manufacturing process. There are some tricky chemicals."
He also warns anyone with a new car under warranty against using their own biofuel. "If you buy a brand new car, you would want to be very certain that it was approved by the dealer."
A discussion on biofuel with Dan Purkis and two other biofuel experts is available at the Radio 4 You and Yours website.