Green cars can save you money and save the environment. But which technology do you choose?

Petrol
Petrol has been the most popular fuel for cars in the UK for many years; petrol engines are generally quiet and smooth, they are responsive and their performance is good. Unleaded petrol is currently cheaper than diesel. Petrol engines pump out less toxic emissions than diesel but emit around 10% more carbon dioxide. Unfortunately at the moment there is no single source of fuel which can compare with petroleum in terms of its instant bulk availability, energy density and (relative) cheapness. Petrol may be the best option for smaller cars doing low mileages in mixed urban and country driving.

Diesel
Diesel engines are more economical than petrol engines, therefore they also emit less carbon dioxide. However diesels emit more particulates and nitrogen oxides than petrol – although diesel engines with a particulate trap help prevent emissions of sooty particulates. Diesel engine technology has seen some remarkable advances in recent years, giving us diesel engines that are quiet, refined, cleaner and with more instant response. An efficient diesel may be the most economical option for driving long distances in a reasonable sized car with little urban use.

LPG
Over recent years, LPG (liquefied petroleum gas) has been a viable fuel option in the UK. LPG produces fewer emissions than petrol and diesel but fuel consumption is worse. It’s been possible to convert many existing cars to run on LPG by after-market conversions, and some manufacturers have had new cars in their range that are dual-fuel, which are designed to run primarily on LPG with petrol back-up. There is a reasonable network of filling stations. LPG, and natural gas in heavier vehicles, has been an attractive proposition in the past primarily due to its cheaper cost, as it has enjoyed less fuel duty. However there is no guarantee that the Chancellor will maintain this in the future, and although there are some emissions improvements over petrol, LPG is still derived from a fossil fuel and therefore still releases greenhouse gases into the atmosphere. At around half the price of petrol and diesel, LPG could be an attractive option, especially for higher mileages in larger vehicles such as 4x4s, but do the maths to check you get payback on any conversion costs.

CNG
Some vehicles, usually heavier vans or trucks that normally run on diesel, can run on CNG (Compressed Natural Gas), which again results in lower CO2 emissions than standard petrol cars, but the fuel is not as efficient as diesel. Finding CNG for refuelling can be a challenge.

Petrol-Electric Hybrids
Petrol-electric hybrid vehicles run on a combination of a conventional petrol engine and an electric motor powered by an energy storage device such as a battery pack. In simple terms they work on the principle that an electric motor provides the power at low speeds such as in urban driving (but currently only for a short range) and they switch to petrol for driving at higher speeds. The batteries are recharged while driving and hybrids use regenerative braking, which means that energy is put back into the battery when braking, which improves energy efficiency.

Hybrid technologies improve fuel efficiency and therefore provide considerable fuel savings compared with a normal petrol vehicle – as well as carbon emissions savings. While models might cost more than conventional cars, running costs can be two-thirds that of equivalent petrol-fuelled vehicles.

Although the official fuel economy figures for cars such as the Toyota Prius at 65.7mpg sound great, hybrids only really achieve maximum economy benefits in built-up areas. On a motorway run, an efficient diesel is likely to be more economical. Nevertheless hybrids are still one of the best options that the consumer has today to achieve better fuel economy, especially if much driving is done in towns, along with the financial benefits such as lower tax and escaping London’s Congestion Charge. Hybrids are likely to have lower emissions that are bad for local air quality in built-up areas, as well as lower CO2 emissions in this environment.

At the moment there are a limited number of hybrid vehicle choices, and only petrol-electric hybrids are currently available; diesel-electric hybrids will achieve even better fuel consumption – watch out for these appearing in the not-too distant future.

Battery-Electric cars
Electric cars use a battery and electric motor to power the vehicle, meaning they have no emissions at the point of use. Due to the capacity of the battery, their range is normally limited to about 40-60 miles between recharges, which means they are only really suitable for city-based users. Electric vehicles can be recharged by plugging them into an existing electrical socket, and some city councils are installing electric recharging points in car parks or on-street. However, they are only truly ‘green’ if they are recharged with electricity from renewable sources such as windfarms.

Electric cars are not subject to road tax and, as an added bonus for London drivers, they enjoy 100 per cent congestion charge discount. Drivers living in areas where they have to pay for residential parking permits might also find that they get a discount on this cost.

Electric cars are often regarded as the ideal non-polluters, but it’s not quite that simple. They’re obviously good for lack of tailpipe emissions and are near silent, but they need to carry rechargeable batteries. These batteries are not really energy sources, they are energy storers. This creates two issues. Firstly they are heavy and bulky with very low energy densities. Secondly, the original source of energy, for recharging, has to be questioned, because if it’s not renewable, those vehicles will indirectly contribute to climate change. There is a further drawback; if their batteries are lead or cadmium-based, there is a serious pollution problem if they are not properly disposed of at the end of their life.

So electric cars are an option for you if you just do short distance city driving, you don't need a large car, and you can plug the car in to recharge, ideally both overnight and during the day. Viable ‘family-sized’ electric vehicles with a good range and speed are still around the corner, while hybrid vehicles are here now.

Biofuels:

Biodiesel
Biofuel has traditionally been in the form of biodiesel, currently available in various types and qualities, primarily from vegetable oils, such as from recycled cooking oils, and from crops such as rapeseed oil, both of which avoid the carbon emissions of mineral diesel. However there is no wide availability, unless in industrial quantities, and it is more commonly used to blend with normal diesel. There are companies that are currently building up a world-wide biodiesel production and refining capacity but it’s not ready yet. All vehicles should be checked for their compatibility for running on biodiesel, and it should be noted that standards of biodiesel can vary considerably.

Bio-‘petrol’ - Ethanol and Methanol Vehicles
Ethanol and methanol are viable vehicle fuels which are an alternative to petrol in internal combustion engines, giving considerable potential carbon emission benefits. Vehicles usually require adaptation to convert from petrol to ethanol if the concentration exceeds 10% (E10). Recently, biofuels of higher concentrations that can run with petrol have been introduced in the UK. The Saab BioPower range and the Ford Focus Flexi-Fuel range are designed to run on bioethanol (E85).

There has recently been much coverage in the media about biofuels, with many concerns being raised about the environmental impact of biofuels and the food v fuel debate. This has caused the UK government to be more cautious about biofuels, as concluded in the Gallagher Review; for a copy of the Gallagher Review visit: http://www.dft.gov.uk/rfa

Biofuelled cars theoretically have lower CO2 emissions, however they don't offer significant mpg or cost saving advantages, so in practice, without financial incentives in the UK, there are relatively few people running biofuel cars in this country.

Hydrogen
Hydrogen fuel cells are seen by many people as the fuel of the future. Various manufacturers are developing cars powered by hydrogen fuel cells however they still demand much research and development to be commercially viable in vehicles and it will be a number of years before they are widely available at a sensible price, together with the fuel and its necessary infrastructure, in the UK.

Other technologies
Some manufacturers are introducing other new technologies to make their cars more efficient, such as BMW’s EfficientDynamics, Volkswagen’s BlueMotion, SEAT’s EcoMotive, Ford’s ECOnetic and Skoda’s Greenline.

These model ranges have technologies such as auto start-stop, brake energy regeneration, electric power steering, lightweight engineering, improved aerodynamics, reduced rolling resistance tyres, low-friction fluids and optimum gear shift indicator. Such technologies all contribute to improved efficiency, without the engineering expense of a full hybrid system. Some of these vehicles are the most economical cars you can buy in their class.

For more information about green cars you can buy today see our Green-Car-Guide.