A buildings energy consumption can be measured in terms of its fuel use: gallons of fuel oil, kWh of electricity, or therms of gas. Although all of them are in different units, you can ultimately measure them in terms of units of energye.g., How much water can you boil with this energy? For our purposes, energy is commonly measured in Btus (U.S. units) or kWh (metric units); for reference, the definition of a Btu, or British thermal unit, is the energy it takes to heat one pound of water by one degree Fahrenheit. Note that kWh, although it is typically used for electricity, is a unit of energy (not just electricity)and can be applied to any fuel source.

If you add up all the energy (Btus) you are consuming at the meter, this is what is known as site energy. However, this is not the full picture. The problem is that the process of generating electricity incurs substantial lossesenough that for every unit of electricity at the plug, it might have been necessary to burn about 3 times t ...more