Non-manmade Energy Inputs
The natural or original sources of energy are not usually included in the calculation of energy invested, only the human-applied sources. For example in the case of biofuels the solar insolation driving photosynthesis is not included, and the energy used in the stellar synthesis of fissile elements is not included for nuclear fission. The energy returned includes usable energy and not wastes such as heat.
Because much of the energy required for producing oil from oil or tar sands (bitumen) comes from low value fractions separated out by the upgrading process, there are two ways to calculate EROEI, the higher value given by considering only the external energy inputs and the lower by considering all energy inputs, including self generated. See: Oil sands#Input energy
Read more about this topic: Energy Returned On Energy Invested
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