How do hydrogen fuel cells compare to solar or wind energy as an alternative energy source?
The overall “hydrogen economy” is quite complex.
The overall “hydrogen economy” is quite complex. Many “easy” options are not really very economical at all. MOST IMPORTANTLY – remember that ALL energy tends towards increased entropy (disorder), so changing the form of an energy source always includes losses of the original energy potential. As with all energy production and usage, a truly sustainable approach must include the energy and materials that must go into the infrastructure and production requirements. “Solar energy” isn’t free! It takes additional energy and material resources to build the equipment necessary to collect solar energy. The same is true with hydrogen.
There are many ways to produce elemental hydrogen for use as a fuel. All of them require more energy than can be recovered from the use of the hydrogen as a fuel. The utility is in terms of accessibility, storage, transport, use, and residues (pollution).
Generation of hydrogen gas by electrolysis of water is energy-intensive. The same is true for the full cycle of hydrogen production from hydrocarbon cracking. Production by catalytic decomposition of water by solar thermal systems is the most sustainable, but again for the overall economy you need to include the cost and energy of system construction, and the collection, storage and transport of the hydrogen. Production of liquid hydrogen from the gas requires huge amounts of energy.
Energy can be neither created nor destroyed, only changed in form. Entropy (disorder) is always increasing, so even the change of energy from one form to another also “loses” energy to the surroundings. Knowing how “efficient” an energy conversion process is helps us to select processes that use the least amount of source energy for the desired final form or use.
For example, a vehicle engine makes several energy conversions. The first is from chemical (potential) energy into thermal energy (heat) in the combustion of the fuel. The second is from that thermal energy to mechanical energy through the engine design. That mechanical energy goes through several other mechanical energy changes from the initial pistons to the final drive of the wheel axles. Some of the mechanical energy is converted to electrical energy by generators. EVERY time the energy is changed in form or application, SOME of it is lost to the surroundings as thermal (heat) energy.
Thus, we NEVER get “100%” of the available energy from a source into useful work. In this example, we may only end up using 15-30% of the chemical energy contained in the fuel!
See also: https://www.fueleconomy.gov/feg/atv.shtml for automotive details.
This is also true for power generation, whether from coal, oil, hydro, nuclear or solar. To really understand environmental impacts it is necessary to look at the TOTAL cost of energy production, not just the final stage! Construction materials, costs, environmental impacts (pollution), land and water use, operating costs, waste materials, AND production and distribution efficiencies all need to be evaluated carefully before we can really decide what is a “better” energy technology.