Efficient Energy Use
Efficient energy use, sometimes simply called energy efficiency, is using less energy to provide the same level of energy service. An example would be insulating a home to use less heating and cooling energy to achieve the same temperature. Another example would be installing fluorescent lights and/or skylights instead of incandescent lights to attain the same level of illumination. So efficient energy use is achieved primarily by means of a more efficient technology or process rather than by changes in invidual behaviour.
Energy efficient buildings or Green building, industrial processes and transportation could reduce the world’s energy needs in 2050 by one third, and be crucial in controlling global emissions of greenhouse gases, according to the International Energy Agency.
Energy efficiency and renewable energy are said to be the “twin pillars†of sustainable energy policy.
Energy conservation
Energy conservation is different to energy efficiency in that it involves using less energy to achieve a lesser energy service, and usually requires behavioural change. Examples would be heating a room less in winter, or driving less, or working in a less brightly lit room. As with other definitions, the boundary between efficient energy use and energy conservation can be fuzzy, but both are important in environmental and economic terms. This is especially the case when actions are directed at the saving of fossil fuels.
Sustainable energy
Energy efficiency and renewable energy are said to be the “twin pillars†of a sustainable energy policy. Both strategies must be developed concurrently in order to stabilize and reduce carbon dioxide emissions in our lifetimes. Efficient energy use is essential to slowing the energy demand growth so that rising clean energy supplies can make deep cuts in fossil fuel use. If energy use grows too rapidly, renewable energy development will chase a receding target. Likewise, unless clean energy supplies come online rapidly, slowing demand growth will only begin to reduce total carbon emissions; a reduction in the carbon content of energy sources is also needed. A sustainable energy economy thus requires major commitments to both efficiency and renewables.
Sources:http://en.wikipedia.org/wiki/Efficient_energy_use