Wiki Home   >   energy return over energy invested

energy return over energy invested

Understanding energy is a key to understanding our current global crisis. Energy sources can be ranked in terms of their EROEI which simply means the amount of energy which you can get out of them (ER) divided by the amount of energy that you need to invest in bringing them to this usable form (EI).

The Industrial Revolution has been dependent on energy produced by fossil fuels. Fossil fuels are a once only resource laid down in the earth many millions years ago in the Jurassic and Carboniferous periods. In the last fifty years the UK and many other countries have become dependent on oil.

Oil is a highly concentrated form of energy and has a massive energy return as compared to the energy required in drilling and refining etc. Its EROEI has been as high as 100. With the decline in the world’s oilfields this ratio has been gradually declining as it has become necessary to access more difficult oilfields or unconventional oil like that bound up in tar sands. Oil may be currently working with an EROEI of around 10 or 20. This decline means that for the world to go on consuming energy at the same rate requires more and more energy input. It is easy to see that an impossible scenario is rapidly reached.

The recent focus on biofuels as an alternative to oil is a dubious process. Estimates of EROEI for Brazilian sugar cane are quoted as 8 but such figures only count fossil fuel inputs to the EROEI. If other sustainable sources of energy are counted then the EROEI falls to 2.

Some researchers suggest that EROEI for the US maize-derived ethanol is actually less than 1 - that is you actually lose energy in producing this fuel.

for moreon the theory

for a discussion of EROEI as it relates to passive houses, hydroelectricity, photovoltaic cells and wind power click here