Energy efficiency technologies reduce the energy wasted in commercial and residential buildings, industry and transportation. This rubric is large and loosely defined. Conceptually, passive solar architecture falls somewhere between renewable energy and energy efficiency. It involves the use of building techniques and materials that lower the energy required in a building. Many of these techniques are conceptually quite simple, for example orienting a building to take best advantage of the sun's heat, or installing skylights to maximize the use of daylighting.
Fuel cells represent one of the most exciting energy developments of recent years.
Unlike all other fuel-based generation technologies, fuel cells involve no combustion. Microturbines are another generating technology attracting attention at the moment. Able to burn a variety of fuels, most microturbines burn natural gas, with comparatively low noise and emissions-hence their inclusion in the family of sustainable energy technologies. Finally, the category of sustainable energy technologies often includes energy storage such as batteries, ultra-capacitors and flywheels. Such devices are especially important for energy resources such as photovoltaic and wind systems which generate power only intermittently.