The keystone of the green economy is a drastic increase in energy efficiency. Increasing our societies energy efficiency is the single most vital and important thing we need to do in order to have a green economy or in fact any kind of economy at all. It is also vitally important to throttle back the amounts of fossil fuel we burn in order to mitigate and diminish the rapid and potentially catastrophic climate change that is being driven by our fossil fuel habit.
Without much more energy efficient buildings and transportation systems nothing we do will be able to prevent an economic collapse brought about by the inevitable and rapidly approaching decline in the recoverable supplies of all forms of fossil energy. We cannot build out wind, geothermal, biofuel, or solar energy fast enough to sustain our civilization in the face of rapidly shrinking recoverable fossil energy reserves; unless we embark on an urgent and sustained drive to use energy (and other resources) with much higher efficiency.
Energy Returned on Energy Invested (ERoEI) – also sometimes referred to as EROI — is a key energy accounting metric that measures the net usable energy that can be obtained from some potential energy source after all of the various energy costs necessary to produce usable energy from the potential energy source have been subtracted from the estimated life time energy production of the potential source.
It is rapidly becoming a rather widely quoted statistic, but remains poorly understood by many people who are starting to use it or are becoming exposed to it for the first time. ERoEI is deceptively simple and seems very straightforward, but it masks a complex underlying computation that is subject to some important and arbitrary decisions. These underlying assumptions and boundary decisions have profound effects on the resulting ERoEI figure. For this reason, if for no other, it is important that as wide an audience as possible become more educated about what ERoEI means and how the many assumptions that go into a particular ERoEI calculation can lead to significantly different ERoEI figures for the same energy system.
