Many people point to hydrogen as the new clean fuel.
While it is true that using hydrogen in a fuel cell results in the ultimately clean water and carbon dioxide, there remains this vitally important question: where does the hydrogen come from?
Hydrogen can come from two types of source: one results in a true fuel, while the other amounts to a type of energy storage.
Hydrogen can be derived from organic sources such as methane or natural gas.
In the case of natural gas, the hydrogen cell is burning fossil fuels, and is not different from a gas turbine in that it transforms a fossil fuel into electricity. There may be advantages to using a fuel cell instead of a gas turbine, but in the end, it is consuming fossil fuels and causing a net increase in carbon dioxide, a greenhouse gas.
In the case of methane, the hydrogen cell can become part of the natural cycle for hydrogen, oxygen and carbon. This depends very much on how the methane is produced.
Methane is a product of natural gas fields, and in this form is yet another fossil fuel.
Methane can also be produced from biomass, for example waste products from farms (both plant and animal based).
Now we are getting much closer to a natural cycle, but with one caveat, and its a big one.
With the exception of the small but growing organic sector (in the Western world), the majority of farming depends on chemical fertilizers, which gets us back to fossil fuels again.
Most of the developing world (India, Africa etc.) still uses old fashioned (sensible) farming methods which are truly a cycle and do not use chemical fertilizers.
Biomass from sources that do not depend on chemical fertilizers tap in to the natural energy/element cycle where by plants raise the energy level of CO2 by converting it into other compounds with the aid of sunlight. The resulting biomass can eventually be converted into methane, which can supply truly clean hydrogen with a zero net gain of carbon dioxide in the atmosphere.
Hydrogen works very well as a form of energy storage.
For example, if electricity is produced using intermittent energy sources such as wind or solar, the energy can be converted into hydrogen and stored until it is needed. If the wind isn't blowing or the sun isn't shining at the time when the energy is required, the hydrogen can be converted back into electricity using a hydrogen cell.
Never the less, our current energy requirements far outstrip our production of electricity by alternative energy sources such as solar or wind.
More likely, the bulk of hydrogen will be produced for conventional electrical generation methods such as coal.
Hydrogen is not necessarily clean. It depends very much on its source.
In most cases it is not truly a fuel, and even when it is, it can not be considered an alternative energy source if it comes from fossil fuels.
You have to know what the source of hydrogen is before you can know if you have a truly clean and alternative source of energy or not.