Sustainable energy is the provision of energy such that it meets the needs of the present without compromising the ability of future generations to meet their needs. A broader interpretation may allow inclusion of fossil fuels as transitional sources while technology develops, as long as new sources are developed for future generations to use. A narrower interpretation includes only energy sources which are not expected to be depleted in a time frame relevant to the human race, which can potentially also include nuclear power if it is utilized differently from the current manner.
Hydroelectric power may be unsustainable if it involves damming a river and thus disrupting the river's ecosystem, including nutrient flows via silt and fish migration. This impact can be reduced through measures such as fish ladders, but not easily eliminated. Microhydro and any run-of-the-river hydroelectric scheme potentially has a very much smaller environmental impact.
The broader concept "sustainable energy technology" can be used to include improvements to energy efficiency.
 Types of sustainable energy and harvesting methods
Sustainable energy includes:
- Wind power; can be harvested using Wind energy conversion systems
- Hydropower; can be harvested using Hydro energy conversion systems
- Solar energy; can be harvested using Solar energy conversion systems
- Biomass; can be harvested using ?
- Muscle energy; can be harvested using ?
- Geothermal energy
Other types of energy may be relatively sustainable compared to conventional sources - for example:
- Biofuels, depending on the type and source.
- Nuclear energy - thorium reactors appear to offer many benefits and have much lower risk and environmental impact than uranium-derived nuclear power, but are not commercially viable at this stage.
- Other types of stored energy (ie coal, fossil fuel, can be converted using fossil fuel power plants. If carbon capture and storage is used, the greenhouse impact will be slashed by 80-90%. This has not yet been applied at commercial scale to electric power stations, but all the component technologies are proven in other contexts, and carbon capture and storage is already applied commercially in the gas extraction industry (separating carbon dioxide from natural gas and burying it, and in crude oil extraction ("enhanced oil recovery" involving injecting carbon dioxide into reservoirs to force out more oil).
 See also
- Renewables Interactive Map by REN21