Geothermal: can only make a % of today's demand, risk of earthquakes, cold water pumped down and steam/got water pumped up for electricity
Hydroelectric: falling water turns generator turbine (kinetic energy to electric power) renewable and not pollution but lose landscape, impact aquatic life, few areas for it..
Bio Fuels: corn ethanol used as fuel/fuel additive. Need to use crops and immerse emissions of N2O canceling the CO2 savings. worsens air quality from combusting organic material
Wind energy: propelloer connected to generator, no heat/pollution, not attractive, need storage when no wind.
Solar energy: rooftop heat collectors, solar thermal power plants, photovoltaic cells (solar panels)
can power US with alternative energy if we combine them and use them at different times of day! first hydroelectric, the photovoltaic, then wind!