Simply put, energy efficiency means using less energy to get the same job done - and in the process, cutting energy bills and reducing pollution. Declines in energy intensity are a proxy for efficiency improvements, provided a) energy intensity is represented at an appropriate level of disaggregation to provide meaningful interpretation, and b) other explanatory and behavioral factors are isolated and accounted for.

Typically these two technologies are used separately (or only placing them in parallel) to produce hot water 133 In this system the solar energy efficiency definition biology thermal panel performs the function of the low temperature heat source and the heat produced is used to feed the heat pump's evaporator.

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.