CORDIS Archive

June
2000

Tank goodness for gas

Today's motor vehicles depend on petroleum for their fuel. Could a change to natural gas, biofuels or hydrogen give us a cleaner environment and reduce Europe's reliance on oil imports? The International Energy Agency is betting on gas.

The first reason is political. Europe imports most of its oil, and has little control over prices or security of supply. It is therefore not surprising that governments would prefer fuels found closer to home, including gas. And then there's pollution: many alternative fuels produce less pollutants and greenhouse gases than their conventional counterparts. So what is the best fuel? This well-written book, which summarises a much longer IEA report on alternative fuels, sets out the arguments.

There are plenty of alternative fuels to choose from. They include liquefied petroleum gas (LPG), liquefied or compressed natural gas (LNG and CNG), dimethyl ether (DME) and methanol made from natural gas, hydrogen made by electrolysis or from natural gas, 'biodiesel' (RME) from rapeseed oil, ethanol from sugar beet and methanol from straw.

Most alternative fuels contain less energy than petrol or diesel, so they need larger fuel tanks and consume more energy in distribution. Many alternatives are also comparatively costly and energy-intensive to produce.

LPG, LNG, CNG, DME and hydrogen from natural gas avoid most of the sulphur, smog-forming volatiles and carcinogenic chemicals associated with petrol and diesel. These 'clean' fuels are good for cutting urban pollution, though they also produce less carbon dioxide than conventional fuels.

To further reduce greenhouse gases we need biofuels such as biodiesel and plant-derived ethanol and methanol, or hydrogen made by electrolysis using electricity from renewable sources. Even then, biofuels do generate some carbon dioxide in processing and distribution, and biodiesel produces even more airborne particulates than ordinary diesel.

To be significant in a global context, says the IEA, an alternative fuel should be able to replace 10% of the oil now used for automotive purposes. This requires four things: enough feedstock, enough conversion capacity to turn it into fuel, a distribution network, and suitable vehicle engines to burn the fuel. No alternative fuel can meet the target within five years, says the report. With a 25-year horizon things look a little brighter. LNG, LPG, and methanol and DME from natural gas qualify, as does hydrogen produced by electrolysis - the only one of the group that has any claim to being renewable, if the electricity comes from hydro or nuclear sources.

Distressing for advocates of green energy is the IEA's contention that plant-derived fuels are unlikely to meet the 10% substitution target within 25 years. The problem is not the technology, says the report, but simply a shortage of feedstock. To grow enough biofuel we would have to use between 4% (for sugar beet) and 12% (for oilseed rape) of our total arable land. For ethanol from sugar beet or methanol from cellulose we might just manage it, says the IEA, but "the other fuels simply require too much land for any reasonable expectation that they could meet the criterion."

To define the best fuels the IEA adds two more modest criteria to the 10% substitution rule. To reduce local pollution, the fuel should meet California's ULEV (ultra-low-emission vehicle) standards, and to help meet climate change targets, it should have only half of petrol's 'well-to-wheel' greenhouse gas emissions. In addition, it should not cost too much more than petrol.

At the moment the clear winner is DME (dimethyl ether) derived from natural gas. DME meets all three criteria and should become available in the long term at a price comparable to that of petrol.

As to the other possibilities, LPG, CNG and methanol from natural gas currently produce too much carbon dioxide to meet the greenhouse gas criterion, though they may become suitable as engine technology improves. Methanol from cellulose will be a contender if we can find enough land on which to grow the necessary crops, and hydrogen from electrolysis may be an option, though its future cost is unclear.