Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively or changing one's behavior to use less service.   Net energy is the amount of useable energy available from a resource after subtracting the amount of energy needed to make it available. For example, for every five barrels of oil that are made available for use, it requires one barrel for extracting and refining the petroleum. Therefore, the net energy available is only four barrels. The energy needed to obtain an energy resource increases... Show more

Energy conservation is the effort to reduce wasteful energy consumption by using fewer energy services. This can be done by using energy more effectively or changing one's behavior to use less service.
 

Net energy is the amount of useable energy available from a resource after subtracting the amount of energy needed to make it available. For example, for every five barrels of oil that are made available for use, it requires one barrel for extracting and refining the petroleum. Therefore, the net energy available is only four barrels. The energy needed to obtain an energy resource increases when the easy deposits of that resource have already been consumed. For example, if all the near-shore petroleum in a region has been extracted, more costly drilling must take place farther offshore. If the energy cost of obtaining energy increases, the resource will be used even faster because a larger share of the energy obtained is used to obtain it.    
The ratio of energy obtained to the energy needed to obtain it is called the net-energy ratio. For example, if it takes 2  units of energy to make available 10 units of energy, then the net-energy ratio is 10/2 or 5.0. A net-energy ratio larger than 1 means that there is a net gain in usable energy. A net-energy ratio smaller than one means there is an overall energy loss.

Solar energy has a relatively high net-energy ratio of 5.8. For natural gas, the net-energy ratio is 4.9, and for petroleum it is 4.5. Coal has a range of net-energy values, from 2.5 to 5.1, because of differing costs of transporting coal. Solar energy yields more net energy than fossil fuel sources because sunshine is abundant and does not need to be located, extracted, or transported very far.  

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