• coal, oil, natural gas

2. Hydrogen

3. Biomass

• wood, alcohol, paper, sweet sorghum, corn

4. Direct Solar

• passive (solar home, no moving parts)
  
• active (pumps, fans)
• photovoltaic

5. Wind

6. Nuclear

7. Tidal, wave

8. Geothermal

9. Ocean temperature gradient

10. Hydropower