Which green car technology is best for you?

If you drive a car, the idea of spending less on fuel and tax while doing your bit for the environment is probably quite attractive. You can do both by switching to a green car but which one?

'Green car' is a massive catch-all term covering a huge range of vehicles that go about delivering improved fuel efficiency and lower emissions in a number of very different ways.

You can't just wander into a random showroom and ask for a green car. They'll take your money but there's no guarantee that the model you'll get will suit your needs. It may not even be particularly green when you use it as you normally would.

We can't all manage with a tiny city car that can be parked in a phone box but needs to charge its batteries for eight hours every 50 miles. People need different green cars for their different lifestyles but which of the many kinds of green car technology is best for yours?

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Petrol cars

It used to be the default fuel choice for motorists but these days petrol is neck and neck with diesel in the battle to be the UK's favourite fuel. Internal combustion engine technology has come on leaps and bounds in recent years but the greenest petrol cars are also assisted by lightweight design, stop-start technology, brake energy regeneration and other green technological advances.

Pros: Many keen drivers prefer the free-revving responsiveness of a good petrol engine. Petrol engines tend to be cheaper than diesel equivalents so they make more sense in smaller, more affordable cars. Emissions of some harmful substances like NOx and hydrocarbons are lower with petrol cars.

Cons: A petrol engine will usually be less fuel efficient than an equivalent diesel and its CO2 emissions will be higher as a result. Petrol engines often don't produce the same mid-range pulling power as diesels, although use of a turbocharger can change that.

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Diesel cars

The popularity of diesel cars has been on the up for well over a decade. This is largely thanks to improvements in engine technology that have allowed diesel engines to shed their noisy, dirty, rattly reputations.

Pros: The attraction of today's best diesel cars lies in their low running costs and their muscular mid-range performance. Diesel engines produce more torque than petrol ones which makes for more relaxed drive too.

Fuel consumption and CO2 emissions are usually very low, making diesels popular with high mileage drivers and company car users.

Cons: Diesel engines tend to be more expensive than petrol ones and heavier too. This makes them harder to justify in smaller cars and for low-mileage drivers who might take years to recoup the extra upfront cost of a diesel in fuel savings.

Although CO2 emissions are low, diesel cars produce higher levels of other exhaust gases and soot. As emissions regulations tighten, the cost of building diesel engines that comply could push prices up further.

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Biofuel cars

An alternative to petrol or diesel, biofuels are derived from plant matter rather than crude oil. Although it's possible to modify a car to run solely on biofuels, they're almost always blended with petrol or diesel to lower costs and emissions.

In fact, we all use biofuels in our cars right now. European regulations require that small quantities are mixed with the petrol and diesel we buy every day.

Pros: Burning biofuels still releases CO2 but the plants that were used to make them absorbed that CO2 from the atmosphere while growing so the net CO2 output is far lower. Prices fluctuate but biofuel blends are usually cheaper than straight petrol or diesel.

Cons: Most cars can't burn biofuel blends without modifications and these can be expensive. Different blends have different concentrations of biofuels so it's important that you use the right blend for your car or you'll damage it.
Although exhaust emissions are low, there are concerns over the environmental cost of growing and refining biofuels.

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Hybrid cars

By using a battery-driven electric motor to take some of the strain off an internal combustion engine, hybrid cars provide a neat halfway house solution to the problems of fuel efficiency and emissions.

There are a number of different kinds of hybrids. Some can run exclusively on electric power for short distances and others can be plugged in to charge their batteries from the mains, but all use some kind of brake energy regeneration system to recapture kinetic energy and keep their batteries topped up.

Pros: A hybrid car's internal combustion engine has an electric helper so it doesn't have to work as hard and uses less fuel. Refinement also tends to be good with the electrics taking a lot of the strain at low speeds. The big advantage over electric cars is even when their batteries are flat, they keep going.

Cons: To work efficiently hybrid cars need to recharge their batteries. That means journeys with braking and coasting where the kinetic energy recovery system can do its thing. On long, high-speed motorway trips hybrids have to rely more on their conventional engines and are less economical.

The batteries and electric motors in hybrids add complexity, which pushes prices up. They're heavy too, which can produce stodgy handling.

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Electric cars

Ditching the internal combustion engine completely and relying on electric power is an idea that's been around almost as long as the motorcar itself. Electric cars have tried and failed to catch on at various points in the past but now the conditions and the technology might be right.

Pros: If the electricity that an electric car is charged with comes from a carbon-neutral source like wind or solar power, there are no emissions whatsoever. In reality, most owners will get theirs from the national grid but that's still pretty green compared to burning fossil fuels. It's cheaper too.

Electric cars are extremely quiet and produce instant torque for performance that's surprisingly brisk off the line. They work a treat in a congested urban setting where noise pollution from conventional cars is a problem.

Cons: Even the best affordable electric cars you can buy today have a best-case-scenario range of less than 100 miles. This means they're only really suitable for short trips around towns and cities where there's a network of charging posts. Range anxiety will probably prevent most people from attempting longer trips because when the battery's flat, you're stuck.

Electric cars are quite expensive although government grants and leasing schemes being operated by some manufacturers bring costs down. There are also doubts over the long-term ownership costs of electric vehicles as the batteries degrade over time and will be very expensive to replace.

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Fuel cell cars

You can't buy a fuel cell car yet but they are out and about on the roads of various cities around the world as manufacturers trial the technology. These vehicles use hydrogen fuel to create a chemical reaction that produces electricity. The only by-product is pure water.

Pros: The fuel cell car driving experience is just like that of an electric car, it's just that power for the batteries is generated on board by the fuel cell. That means there's no problem with range anxiety. You can drive a fuel cell car as far as you like, so long as there's somewhere to fill up with hydrogen.

Cons: We will need a hydrogen refuelling network before fuel cell cars can become commonplace on our roads and that means major investment. The technology needs to get more affordable too, which is one of the main reasons why fuel cell cars have not yet made large-scale production.

Although the use of hydrogen in cars is a zero-emissions process, huge amounts of the gas would need to be produced if lots of fuel cell cars were sold and that could have negative environmental effects.

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