http://en.wikipedia.org/wiki/Biological_hydrogen_productionhttp://www1.eere.energy.gov/biomass/pdfs/34726.pdfMost of what we think of as fuel is chemical energy .
Chemicals store energy in the forming of bonds or the breaking of bonds , either way potential energy is stored as if you were winding a spring.
Fossil fuels have hydrocarbons whose bonds represent springs wound long ago by sunlight that fell on anchient plants.
Sunlight falling on earth today winds the hydrocarbons of the processes of life , potentially enough to replace fossil fuels totally with currently harvested solar power , if we can make the process efficient enough and devote enough real estate to collection .
I like algae for hydrogen production , also for hydrocarbon production, they are already pretty efficient naturally , and a little tweaking can make them even moreso.
I imagine tubes and glass panels installed on the faces of downtown buildings flowing with nutritious slurry extracted from sewage and turned bright green , red or blue by cultivar algae , produceing H2 and oil suitable for operating deisel or turbine engines.
Not only would the city harvest a lot of fuel right on the site where it would be used , the City would take on a glittering emerald apperance as though Frank Baum had engineered it.
