Hydrogen fuel cell car
The hydrogen fuel cell car is what most people mean by "hydrogen car." Fuel cells are like electrochemical batteries, where hydrogen combines with oxygen to create electricity. The sole waste product is water. However, for hydrogen to replace gas, each filling station would need to produce hydrogen in large volumes, but storage is a big issue. So the fuel cell technology currently being used is restricted to prototype cars and is not viable for the mass market yet.

Electric car
An electric car is powered by electric motor. With the advancement in the batteries the range of car has almost doubled in the last ten years. At the recently held 'Frankfurt Motor show' there was a clear shift towards electric and plug-in hybrid cars. However, it will take years before electric technologies become standard, as there are still problems with the batteries, as well as the cost of electric technology.

Hybrid car
Most hybrid cars available today are a combination of petrol and electric engines. The key to a hybrid car is that the petrol engine can be much smaller than the one in a conventional car as most drivers use the peak power of their engines less than one percent of the time. The engine in the hybrid car is powerful enough to move the car along on the freeway, but when it needs to get the car moving in a hurry, it gets help from electric motor. Besides this today's hybrids use many other tricks to increase fuel efficiency.

Compressed air car
A compressed air car is an alternative fuel car that uses a motor powered by compressed air. The compressed air is stored in a tank at very high pressure. Rather than driving engine pistons with an ignited fuel-air mixture, compressed air cars use the expansion of compressed air. So the car can be powered solely by air, or combined as a hybrid. However, since air compression is usually done using electricity, its total environmental impact depends on how clean the source of electricity is.

Solar car
Solar cars combine technology typically used in the aerospace, bicycle, alternative energy and automotive industries. The design of a solar vehicle is severely limited by the energy input into the car, as it depend on photo voltaic cells to convert sunlight into electricity. The battery pack plays the same role in a solar car that a petrol tank plays in a normal car. Interestingly, all solar cars ever built have been for the purpose of solar car races.