Almost all energy comes from fusion either directly or indirectly:
|
RENEWABLE |
|
Sunlight |
Directly from fusion |
|
Photovoltaic |
Directly from sunlight |
|
Solar heating |
Directly from sunlight |
|
Wind |
From solar heating |
|
OTEC* |
From solar heating |
|
Hydro |
From rain cycle driven by solar heating |
|
Photosynthesis |
Directly from sunlight |
|
Biomass |
From photosynthesis |
|
*OTEC = Ocean Thermal Energy Conversion
|
|
NONRENEWABLE |
|
Petrochemical |
From biomass |
|
Coal |
From biomass |
|
Nuclear Fission |
From end products of fusion |
Exceptions:
Geothermal and Tidal
Renewable resources do the least harm to the environment, but are not always available when and where we need them. We need ways to to store the energy we can get from renewable sources.
For some applications we need storage as potential chemical energy. This can come in many forms, including:
batteries
gasoline or other combustible fuel
hydrogen for either fuel cells or combustion
For other applications, we can use potential kinetic energy (e.g., water pumped up a hill to be released and come back down to run a turbine when needed).
NOTE:
Electricity is not a source of energy, it is a use of energy. Most of the electricity used in the U.S. comes from non-renewable fossil fuels (coal, natural gas and fuel oil).
Also note that hydrogen is not a source of energy, but a way to store energy. Hydrogen can either be produced from hydrocarbons (mostly fossil fuels), or by using electricity to split it from water. In either case, it is not necessarily a clean alternative.
