While doing mindless tasks on the Fanny Farm, like dragging Macrocarpa branches around to clear the deck for the house building and stacking it on the back of the ute for removal, I tend to do a lot of thinking to keep the brain engaged…… and it occurred to me that very few people ‘get it’ when it comes to the predicament we here at DTM know as the Energy Cliff.
Now I expect nearly all my readers would know what I’m talking about, but likely have the same problem whenever trying to get people to understand what we are on about. So I came up with a metaphor that hopefully simplifies the concept for the masses.
I’m going to break some rules here, but the idea of this metaphor is not to come up with an accurate mathematical and/or physical model, rather a simple way to explain why we are fast running out of energy, even as we extract ever more oil and coal out of the ground.
It’s generally accepted that way back in the 1930’s the ERoEI of oil was 100:1; which means that for every unit of energy invested in finding, extracting, and refining this oil, 100 units were available to do work. You know……. stuff like build the 20th Century!
This is where I start breaking rules. I know that ERoEI is not an efficiency number, but I’m going to use it that way because in many ways it is like efficiency. And for ease of using numbers, I’m going to say that that 1930’s oil had an energy efficiency of 100% – and yes, I know nothing has an efficiency of 100%. Just bear with me….. this isn’t an exercise in maths and science, it’s a thought provoking process.
If you are unfamiliar with the energy efficiency calculations for a whole system, rather than a single part of that system, then the way it’s done is that you multiply the efficiency factors together (where 90% is 0.9, 75% is 0.75, and so on)
So if you have an energy source that is 90% efficient, running a motor that is 90% efficient, running a generator that is 90% efficient, and distributing electricity through a grid that is 75% efficient, then by the time the energy arrives at its destination, the efficiency of the system is 0.9 x 0.9 x 0.9 x 0.75 = 0.54675 or 54.675% efficient. Three decimal places here is largely irrelevant.
This, by the way, demonstrates that complex systems made up of even very efficient components are not efficient! And this is one of the dilemmas we face as we make our systems ever more complex….. even now.
This is not a problem when, like in the 1930’s, the system was not complex, and it was small, and the primary energy, oil, had an unbelievably high ERoEI to boot. So, to mine coal with an ERoEI of 90 in the US in the 1930’s had an ERoEI efficiency of 1.0 x 0.9 = 0.9.
Today, mining coal with an ERoEI of 50 with 12:1 oil gives us 0.12 x 0.5 = 0.06.
The nett energy efficiency available from coal has therefore dropped by a factor of 15!
Then consider this…… to use the above primary energies to make PVs with an ERoEI of 2.45:1 gives us nett energy efficiency of 0.0147.
And people out there actually want to power the world like this?
I know the maths are flawed, but is my thinking…?