Cars are known to be one of the biggest producers of greenhouse gases, and the biggest users of fossil fuels; sources of sustainable energy for cars are few and far between, with even the most environmentally friendly car using a combination of solar power and fossil fuel energy. Alternatives to running with fossil fuels do exist, but they tend to cost more than petrol or diesel, and they can cause damage to the car if not monitored carefully.
Solar power is probably the best known resource for sustainable energy. Solar cars are in fact very limited: most of the cars solely powered by solar panels have been built for solar races, or for use as a utility vehicle. Solar power can be used in a hybrid car, along with a typical internal combustion engine.
Solar cars are powered by the sun, which is converted to electricity through the use of solar panels. Once the car is built and paid for, this means that the car will effectively be driven on 'free' energy: although the cost of installing solar panels will be very high. Solar panels also have a limited lifespan.
Solar cars are nowhere near ready for public use. A purely solar-powered scooter has a top speed of around 30mph; and this speed is borne out by experiments with solar cars.
Bio-diesel is fuel made from vegetable or animal fat products. These biofuels is made by reacting the lipids, or fats, with alcohol. It is a good lubricant, and can increase the life of a fuel-injection system used in cars. It produces little to no sulphur, and in areas is subsidised by local governments.
Unmodified engines may work on a blend of 20% biodiesel and 80% petrol; any more than this, and the car will require modifications in order to avoid damage to the engine.
Biodiesel can erode rubber in cars, so this needs to be watched out for, although these parts tend to wear out quickly anyway. Replace these parts with FKM, which can manage biodiesels. You should also examine the inside of the car for fuel residue along the fuel lines; fuel lines and filters can be clogged with lipid fats if too much is used before the engine has been converted.
Biodiesel is a renewable source of fuel for a car, although it can wear down parts more quickly than traditional petrol fuels.
Electricity is the most commonly used sustainable energy source for a car. Combined with a charger which is connected to a solar panel, electric cars have the potential to be an entirely renewable source vehicle. Electric cars can be used to drive to and from work during the day, and then recharged at night from a charger using stored sustainable energy.
Electric cars must be charged for several hours a day: one solution has been to use replaceable battery packs. One battery would be charging during the day, while the other was in use, and then they would be swapped over at night. Electric cars are still in their infancy, and they are at the moment only suitable for short journeys; 25 miles or so is considered to be the maximum for a rechargeable car.