The Reason Why EROI can’t be applied to Solar Energy
Explaining a Mathematical Impossibility
“Energy Return on Investment (EROI), a ratio that measures the amount of usable energy delivered from an energy source versus the amount of energy used to get that energy resource”
— Corporate Finance Institute website, 2022:
I will avoid going into all of the reasons why this makes no sense in terms of solar, as I’ve labored the various points in many other stories in Medium.
For this analysis of EROI, we’ll just go straight to the jugular; the maths.
The Maths
A ratio is obtained by dividing one finite quantity by another.
In the case of oil, we might estimate how much oil can be extracted from a particular drilling installation, knowing approximately how much oil can be extracted from the well. So there we can put a figure on the amount of oil to be extracted. It is then a simple Engineering task to estimate the amount of drilling hardware and labor required to extract the oil, and therefore the amount of energy required to extract the oil.
The EROI then is calculated as follows:
Total Energy of Oil to be Extracted ÷Estimated Energy Cost of Drilling Program
But in the case of solar, it is not possible to put an upper limit on the amount of solar energy received, because it is inexhaustible, the sun will continue to shine as long as we exist, for the foreseeable future.
So there is no practical limit to the amount of time we can continue to draw solar energy, as long as our hardware holds out.
If the hardware comprises many elements put together as an assembly to collect the solar energy, like the leaves of a tree, as is usual in solar installations, then the facility to collect can be maintained indefinitely by replacing the elements one by one, as they fail, just like the tree, to obtain a continuous flow of energy from the installation, forever, for all practical intents and purposes.
So the energy returned is infinite, no matter how small the rate of Joules per second received, it is forever, therefore the energy received is infinite.
Dividing infinity by any finite number, even trillions, is still infinity.
So the EROI of solar is always infinity.
Any attempt to base an argument on the EROI for solar, including unfortunately the information on the source reference of the corporate finance institute, is actually invalid.
Any limit applied to the solar energy received, is an unnecessary, seemingly arbitrarily chosen limit, in order perhaps to obtain a figure for EROI which does not look like infinity, so as to perhaps try to raise finance.
So EROI can’t honestly be used for solar, unless investors like to hear that the EROI for solar is actually infinity.
“Payback period”, on the other hand is something which can be sensibly computed.
I will cover that in another story soon, unless someone beats me to it (Please do!).
