The Energy Return on Energy Investment of various energy sources from the year 1930 to 2005. Energy Return on Investment indicates the yield of a type of energy over a particular period. This graph allows comparison of the various energy sources and their EROI historical trend. Clearly the world is moving towards an era of lower energy yields and higher energy costs. No environmental costs are taken into account here. If the energy cost of scrubbing coal clean of carbon emissions were included, the EROI of coal would be very close to that of PV Solar.
EROI: Energy return on energy investment. Example: If the energy from one barrel of oil is used to find, drill for and pump more oil with a yield of 50 barrels, then that source has and EROI of 50:1.
Net Energy: In the above example 1 unit of input produces an output of 50 so the net energy is 49 units.