Today when people are talking more and more about alternative energy sources especially for the cars we have many different products coming out e.g. Hybrid cars that run on gasoline and electricity, pure electric cars etc. Hydrogen vehicles are using hydrogen as the energy carrier not the energy source so people would need some large scale hydrogen plants or home hydrogen stations to power their cars. Hydrogen can be produced by many thermo-chemical methods using coal (coal gasification), natural gas, biomass, liquefied petroleum gas, biohydrogen.

Hydrogen can also be produced from water by electrolysis. However, this process takes a lot of energy and it should be renewable energy sources to call it ecologically clean fuel. It would take humanity a few decades to create a low cost hydrogen production as all these methods are very expensive. However, the only emission you have is water and that is a very good deal. There are two ways of using hydrogen to run the vehicle:

However in both of these ways of powering the car hydrogen is not that efficient because it has low volumetric energy.

This means that it can store less energy than some substances we use today. For example: even if we keep hydrogen in liquid form its volumetric energy density will be only few mega joules per liter, which is much smaller than that of gasoline. Using hydrogen as the electricity carrier is even less efficient than using Li-Ion batteries in the cars.

As you can see on this chart you lose 7% of energy you get from the plant for charging the batteries and 7% of the remaining amount is lost in the battery itself. However if you want to use hydrogen to store that energy this is what you get: 30% of energy from the windmill for example is lost during the process called electrolysis, the other bad thing is that you need to compress the gas in order to use it and this is where you lose another 10%, finally fuels cells are not that efficient and you lose up to 60% of remaining energy there. See for yourself which method is more efficient. Taking in consideration all these hydrogen fuel is one of the most expensive to produce and one of the least efficient energy carriers out there. Maybe we will be able to produce hydrogen fuel but we surely need to lower the cost of its production dramatically.