Sure Leonardo DiCaprio loves his Prius and Paris Hilton has embraced the new GMC Yukon hybrid, but what about eco-friendly vehicles in the real world? Celebrities have jumped on the bandwagon, but most of us regular folk can't afford to add one to a small - or in some cases, large (Tom Cruise, I'm looking at you) - fleet of vehicles. When you have a budget, purchasing a new vehicle requires a lot of research and analysis to find the best fit for one's lifestyle and falls within a reasonable price range. There are still many questions regarding alternative vehicles since the concept is still relatively new to most. Here are some of the common questions (and answers of course!) about hydrogen fuel cells, biofuels, hybrids and the elusive electric car.

What's so good about hydrogen?
Hydrogen is green at the point of use. Hydrogen-fuel-cell vehicles emit no carbon dioxide, nitrous oxide or carcinogenic particles. All that emerges from the exhaust is water vapour. The hydrogen fuel, stored in pressurised tanks, is used to create a chemical reaction using catalysts. That is converted into electric power and drives a motor which moves the vehicle along. It is quiet, and performance is acceptable for many purposes; in any case it is early days yet.

So what's the snag?
The greenness of hydrogen does depend on how much energy is inefficiently expended in generating it and moving it around. If, at one extreme, a much more efficient method of making hydrogen could be discovered, and if the energy used in it s manufacture and transport was sustainable (like from a power station using solar energy), then it might well be the greenest option. At worst there isn't much advance on fossil fuels. Storing hydrogen requires pressurisation or cooling, which can be troublesome. Hydrogen also tends to vaporise, so there can be losses in transit. Some, with the tragedy of the Hindenburg airship in mind, wonder whether this highly combustible fuel can ever be safe.

Are biofuels any use?
Biofuel versions of Saabs and Fords can be bought now, though there are few filling stations. This technology is also controversial. In theory, biofuels are carbon neutral, as the carbon dioxide used in producing them is "absorbed" by the plants grown to make create the biofuel. So-called first generation biofuels do suffer from drawbacks. First, they can displace food crops. Biofuels, even their best friends would agree, have had some effect on rising food prices. The EU wants to see monitoring systems to assure consumers that biofuels are not damaging the environment or food supplies, but those safeguards are yet to be implemented . Second, they can reduce biodiversity, as witnessed in the Indonesian rain forest, where palm oil crops for biodiesel have done much damage.

Third, critics point to the energy expended in producing and transporting the biofuels, the artificial fertilisers used, the western subsidies to grow them in Europe and the US, and so on. More defensible are second, third and fourth generation biofuels, which become progressively greener, though none are commercially available. The next stage will be to find ways to use the waste product of crops rather than the nutritionally valuable seeds and grains in biofuel production. One day, the scientists promise "carbon positive" biofuels – enzymes that can save the planet.

Why aren't there more hybrids?
Toyota's Prius leads the field, although Honda and Ford and General Motors in America are also on the scene. Using power wasted, for example in braking, and recycling that via an electric motor to supplement a petrol engine is a clever one. But many manufacturers say small, efficient diesels engines are just as effective and a lot cheaper to make, with no problematic batteries to dispose of. Japanese and US makers tend to favour petrol/electric hybrids because their main markets have very little appetite for diesel; European makes such as Mercedes and Peugeot are more traditionally committed to diesel. "Plug-in hybrids", where energy direct from the mains can add to the cars' range, are a step forward.

What happened to the electric car?
Nothing especially, though GM did can one of its more promising projects on the grounds of cost. However, the motor-show concept Chevrolet Volt (a "plug-in" hybrid) promises much, and GM are committed to making it. Electric cars can be extremely green, but again much crucially depends on how their power is generated. They used to be slow and fragile; mainstream makers are working on that. The Modec van is a fine example of a practical vehicle.

Hit the jump to read more about the pros and cons of the various eco-friendly vehicle options.

» The Independent