Explaining the energy cliff

19 03 2016

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…?






13 responses

19 03 2016
Chris Harries

A while ago I read an economists interpretation of the EroEI concept and it went something like this. If you are an investor and you invested $1 and in return you got $100 return, that is a truly fantastic investment and you would have no bones about investing at that rate of return.

But then he went on to argue that if you invested $1 and got $10 return, that was not as good of course, but in business investment terms it was still a bonanza.

Many small businesses thrive on a doubling on their investment – receiving just $2 for every $1 invested. This requires the business those very low overheads. With high overheads you need in most cases a minimum return of $3 per dollar, but you are probably still on shaky ground.

Much of this is true, but if you are receiving just $2 or $3 in return whilst some of your competitors are achieving, $30, then you are out of business. That’s why it has been hard for alternative energy projects to succeed without subsidy.

The ERoEI factor that is needed to keep our high flying, energy-dense society going without disruption (the bottom line ERoEI that you need to keep the train on the rails) is estimated to be approximately 12:1. This has presented competing alternative energy enthusiasts with a challenge because most alternative energy forms (including traditional nuclear power, solar pv and thermal solar) have ERoEI values well below that level. This has resulted in there various advocates inflating return rates based on wherever they can find nice big figures. The nuke blokes do this and so too do the solar blokes, so we see ERoEI figures that are pure fiction.

This faking of ERoEI figures has flummoxed the ERoEI debate a fair bit in recent times for it is rather hard to nut out who to believe. In the main its probably best to go to the works of Charles Hall and his academic associates in the US who have been the pioneers in ERoEI concepts and calculations. His team’s ERoEI calculations are probably the best general unbiassed guide.

Here’s an interview with him: http://www.scientificamerican.com/article/eroi-charles-hall-will-fossil-fuels-maintain-economic-growth/

And some precise data here: http://www.sciencedirect.com/science/article/pii/S0301421513003856

I must add here that though ERoEI is a bottom line that determines viability of an energy enterprise, there are other bottom lines too. As we know in Tasmania, hydro has a nice high ERoEI but every energy source has a range of other limits on top of the ERoEI barrier. The energy return on investment for hydro-electricity in South Australia is almost nil.

And even the best ERoEI figures are somewhat rubbery. If you included all of the energy required to totally remediate the end of life of most energy technologies (clean up the mess and restore natural environments) the ERoEI would have to be reduced substantially. This factor is what largely cripples the economics of traditional nuclear energy.

19 03 2016

The thinking and the math are not flawed, but you forgot that that the new style fission/fusion reactors are only 10 years away from full production and will give us the promised too cheap to meter power. They will run flawlessly for hundreds of years without any issues, there will be no waste and they are clean.
There will be units small enough to power your house if you want to live remote.

But from memory, that has been the promise since the late 40s, and every time it is mentioned it is still 10 years away. The same as the hydrogen economy where the hydrogen gas is produced using natural gas.

Maybe a larger block, out of the way with an independent power system will survive the first crash wave, and if remote enough it may also survive the second one. Pity my shoulder can not handle the cold or I would join you.

19 03 2016

Well, I didn’t know about the energy efficiency multiplication thing, so I’ve learned something at least, but I think it’s still way too complex when people don’t even understand energy. Even if you tell them the standard physics definition….the ability to do work….they still want THAT explained before you can go on!

I still think EROEI is the best way to get some understanding into thick brains, but getting people to understand the energy in/energy out/net energy bit can be damned hard! Especially when they WANT to believe in a golden renewables-type future and you’re only squashing that for them with blinding science. EROEI shows up renewables for what they are…pie-in-the-sky alternatives which may or may not be sustainable and which certainly won’t allow us to continue our present lifestyles.

And there’s another concept that few people really understand…sustainability. I could go on….

19 03 2016
Daniel Koeppel

I subscribe to the notion that physical labour provides fertile soil both for plants and thoughts.
This post explains the faultiness of the general backslapping post Paris in December :’ lets switch to 100% RE asap, and all will be fine!”
Your repeated EROEI approach is challenging the linear and easy transition, everyone wants to be true. Because no one wants to start cutting “perceived comfort” and their way of life/consumption, they have worked so hard to ingest & build up, since WWII.
To point this out is starting to hold very sidelining effect on ones reputation. Hence your easy math is rather helpful to enforce the argument…. for all other eventualities i continue to train in Aikido.

19 03 2016

Applying ERoEI to free energy, such as a solar array, makes no sense. So, presuming 2.45 for this metric is just wrong. The fuel is free (solar power), so the ultimate result is that your solar-powered array could last far longer than anticipated and thus give you an .ERoEI which approaches infinity over time. Now, in practice, anything in the system can break down, especially if it’s an inverter, the least reliable component of the system. Ideally, you would use pure DC appliances in your solar system, eliminating the need for an inverter in the first place. In this way, you would have a sustainable source of energy that lasts a very long time. Using NiFe batteries allows you to extend the working life of the system as well.

19 03 2016

Read the link…… oil is free too!

20 03 2016

You’re thinking that fuel is the only energy input. There’s also the manufacturing energy. In the case of PV, the energy input is the original fossil fuel energy that goes into making them.

19 03 2016
Geoff Pearce

Hi Mike,
I think you have made a mistake in relating eroei and efficiency.
If the eroei on oil is 100 units recovered for 1 unit spent, then it means you have turned 1 unit of energy into 100 units.

According to The Oil Drum site, coal has an eroei of 80. This means 1 unit spent recovers 80 units of energy. So if you used 1 unit of oil and recovered 100 units, then used all of those units mining coal, then effectively for 1 unit spent, you recover 100 x 80 which equals 8000 units total.

Now is where the efficiency factor comes in. If you burn 8000 units of coal in a power plant that is 90% efficient, then you have converted it to 7600. units of energy in the form of electricity.

Regarding solar panels with an eroei of just 2.45, if we didn’t use fossil fuels to mine, transport and process the minerals that make them, then you would need huge banks of solar panels and batteries to produce and store the energy required to create the finished panels. We all know that fossil fuels are finite resources but I haven’t heard about mining machinery or manufacturing processes being converted to run on renewable energy.

Then with solar panels there is longevity to consider. If panels last 25 years and inverters and batteries need replacing every x and y years, then one would have to work out the kilowatt hours available during the system’s lifetime and compare the cost of the energy created, to the cost of using grid electricity and hope you dont have too many cloudy days!

20 03 2016

“I know the maths are flawed, but is my thinking…?”

I’m not sure. But a lower-than-unity EROEI (bad) would make your final number get better, wouldn’t it?

It might make more sense to invert everything.

If I can expend a unit of energy and get 15 units of energy out, that’s a 1:15 ratio. Or a multiplication of 15x.

If I take each of those 15 output units and make PV out of it, I get another multiplication of (only) 2.45. We should multiply those two numbers, since I have 15 units to spend on PV.

So for PV, the ratio of input to output energy is 1:37. Not a loser, but not as good as using that oil energy for something with a better ratio.

21 03 2016
David Barnes

Thanks for that analysis. For me it’s an extension of the work I’ve been reading by Dr. Tim Morgan. As has been said, getting folks to understand this basic stuff is difficult. I’m mostly met with anger and/ or denial which isn’t surprising. I can’t ever recall anything on this in the MSM. No wonder the public is clueless. Denial of facts doesn’t mean they go away.
Something else that really worries me is the rubbish about renewables being put about by equally clueless politicians such as Shorten with his ” we’ll run the whole show with 50 % renewables by 2030 ( or 2050.. I can’t remember the details). I also recall hearing the new chief scientist sprouting the same line,on the ABC radio. If this is the best we can expect from our ” leaders” then we are in serious trouble. Unprepared for the future it’s going to smack us hard.
Keep up the good fight.
David Barnes, Sydney.

21 03 2016
Chris Harries

One question that I’ve been asking of late is ‘with the price of solar power dropping every year, is there any relationship between this trend and its Net Energy Return?’ Put more succinctly, “Is the ERoEI of solar increasing as its price drops?’

Intuitively expect that it would be to a degree, because they are being made with lighter and lighter materials, requiring less aluminium framing and being incorporated onto surfaces such as roofing panes, rather than add-ons… so one would expect a better energy return on energy inputs.

Nobody seems to be able to answer this riddle. I expect there is a ceiling, perhaps around 7:1, if the ultimate technology can be developed. It is after all, and will always be, a very dilute energy source.

21 03 2016

Energy density is another factor to consider.

14 05 2016

Yes, your thinking is very flawed…but in my opinion EROI just shows the flaws of EROI as a metric.

Coal with a 100:1 EROI would need 1J of energy input for each 100J of coal produced, so the efficiency is (100-1)/100 = 99%

Oil with a 12:1 EROI would need 8.33J (1/12) to produce 100J of oil, so the efficiency would be (100-8.33)/100 = 91.67%… not as good as the coal, but still pretty good, and nowhere near the 12% you claim.

Mining coal with an ERoEI of 50 with 12:1 oil should instead be 0.98×0.9167 = 0.90. So its still a very efficient process.

The effects of EROI do however become more pronounced at low values. So using oil to produce coal to then produce solar it would drop considerably to 53%, but nowhere in the realms of the tiny percentage you calculate.

Of course a 53% efficiency isn’t good news, but not quite a doomsday scenario. Mainly means we are going to have to improve the efficiency of the end-use of energy, and/or adapt to less energy intensive lifestyles.

The real problem is the climate change from all that fossil fuel use!

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