Geothermal works only in places where there is hot magma near the surface. Iceland has made great use of geothermal power.

Solar is the most promising. Sun is readily available in much of the world (polar regions during their winter being the exception). Biggest drawback is that it isn’t available at night, however power usage surges during the day so it is most available when most needed. The cost is a bit prohibitive, but technology is slowly making solar power competitive. We will see the day where in more tropical latitudes every square inch of rooftop is covered in solar panels.

Wind is unsteady and usually the most available where it is least needed. The high plains have lots of wind potential, and not many people to consume it. This means long distance transmission, with its attendant costs.

Hydroelectric, most of the good rivers in the west already are dammed, though there is plenty of potential in the rest of the world. Tidal and ocean currents have great potential, but the cost and technical challenges are prohibitive.

Biomass, similar problems to coal and oil, puts carbon particulate matter into the air. Waste from crops or garbage is a good use of otherwise unused material, but when we go to corn or cane we are taking food supplies generally from the poorest and diverting it to energy generally for the richer world.

For all these ideas, coal and oil are going to be king for quite some time to come.

Actually the biggest source of untapped energy is in reducing usage, better insulation, telecommuting, smarter homes and appliances for instance.

6. Hydrogen. — pro(s): clean burning, plentiful.

Solar is good definately cheap and all you need is the sun and you have power. however my understanding of solar is you would need a large field of panels to power a city so the wasted land with these panel sitting on them turns me off.

Wind power is very good especially in coastal areas, but you will find you would need huge wind farms to be able to power cities or even contribute reasonably to the national grid.

Hydro- electric is very good, it does however require the land to be valley like and have a gorge present to work effectively but it is the most popular and can power up the entire grid by itself very efficient.

Biomass hmmm, not to keen on bio mass green house gas emissions use of methane to produce power to extract biomass energy is expensive.

How about Nuclear i think though it is dangerous it is the best because of the amount energy it can produce. The smaller nuclear power stations used on US NAVY ships are refuelled or re- serviced once every 20 years how good is that. Good luck