From energy-saving refrigerators, low-consumption automobiles, and intelligent building management systems to resource-saving production processes in industry, energy efficiency is a versatile topic that is - and will remain - of great importance in all areas of our everyday lives. Solar technologies are characterized as either passive or active depending on the way they capture, convert and distribute sunlight and enable solar energy to be harnessed at different levels around the world, mostly depending on the distance from the equator.

51 Plug-in hybrids also have increased battery capacity, which makes it possible to drive for limited distances without burning any gasoline; in this case, energy efficiency definition simple is dictated by whatever process (such as coal-burning, hydroelectric, or renewable source) created the power.

Solar panels convert solar energy into usable electricity through a process known as the photovoltaic effect Incoming sunlight strikes a semiconductor material (typically silicon) in solar cells and knocks electrons loose, setting them in motion and generating an electric current that can be captured with wiring.

Similarly, investing in energy efficiency is almost always cheaper and cleaner for utilities than new generation resources—or even the fuel costs of existing generation—but such investments lead to reduced earnings potential under the traditional utility business model.