Ever since Jeff Gibbs, Ozzie Zehner and Michael Moore released the new documentary ‘Planet of the Humans’ on Earth day 2020 it has been mired in controversy. Accusations of inaccuracies and misinformation have been lobbed against Moore and his associates. The film’s main contention is that the Green Energy Technology that has been proclaimed as the panacea to the Climate doomsday is not at all what it is cracked up to be. The film in particular focuses on alternative energy sources of Solar, Wind and Biomass and the film very poignantly illustrates that these so called Green technologies are using more fossil fuel energy in their creation or in the case of Biomass generating more Carbon than they are able to offset. The Green Technology proponents have not taken this criticism well. They view this film as seriously misinformed and that it undermines years of effort invested by the Green Technology buffs in attempting to do something to mitigate Climate change. GreenTech proponents have gone to great lengths to get this film banned and have successfully lobbied Youtube to do so using a somewhat specious Copyright violation claim.
The accusations of inaccuracies appear to focus on clips of Solar panels in the film from a decade ago and other such factors that the GreenTech proponents claim, doesn’t take into account state of the art technology and the improvements that have been made. In particular, what they take offense to is that the film appears to endorse a view that energy spent in the creation of alternative energy technology is never offset by the energy generated by that equipment. I see this view being summarily refuted in many an FAQ on the internet about Solar Panels, Wind Turbines etc. So, it seems valid for the GreenTech proponents to ask: why is Michael Moore endorsing an obvious canard that they have refuted many, many times before.
But is the claim that a Solar panel never offsets the energy spent in it’s creation really a canard?
I decided to put my engineer’s hat on and investigate.
Energy Offset
With some Googling you can easily find reference material that tells you the amount of energy consumed in the manufacture of a Solar panel. Here is one such source: https://www.researchgate.net/publication/282206521_Comparison_between_the_Energy_Required_for_Production_of_PV_Module_and_the_Output_Energy_Througout_the_Product_Life_Time
According to the above source the energy consumed in the process of manufacturing a Solar panel is 1373 kWh. Other sources on the internet confirm that the number is in the 1200 kWh to 1400 kWh range. Let us go with this number 1373 kWh.
It is also equally easy to find facts about the state of the art Solar panels with regards to their power output, lifetime etc. So armed with such numbers we can easily calculate the lifetime energy output of a Solar panel and see for ourselves if it can generate more energy over it’s lifetime than spent in it’s creation.
Typical values:
Energy consumed in manufacture (Emanuf)= 1373 kWh
Panel power output = 300W
Lifetime of panel = 25 to 30 years
Hours of power generation per day = 6 hours
Total energy (Epanel) = 25years x 365days x 6hours x 300W = 16,425 kWh
Epanel 16,425 kWh is handily greater than the 1373 kWh Emanuf invested in manufacture of the Solar panel. So that’s it. We just proved that the claim is indeed a canard. Done!
Not so fast. Did we look at the right metric if we are really interested in sustainability? What is sustainability anyway? Is it enough to simply be able to offset the energy consumed in manufacture? Or do we need a different way to compute for sustainability?
Sustainability
For true sustainability we really want the alternative energy equipment to mitigate the harm done to the environment in it’s original creation. Because, as the ‘Planet of the Humans’ vividly illustrates, there is a lot of fossil fuel energy used in the manufacturing process of alternative energy equipment and that does create a significant harm to the environment. So we need to be able to produce enough energy to mitigate some if not most of that harm. Secondly, to be sustainable we need to be able to generate additional energy to be able to replace the equipment at the end of it’s useful life.
So for a Solar panel for example, we need the panel to generate enough energy that it can mitigate the harm suffered in it’s creation as well as additional energy to create replacement panel. Unfortunately, the rate at which a Solar panel generates energy is low and variable, hence in order to be able to use it for high intensity work activities such as harm mitigation and production of replacement panels we must introduce additional energy storage equipment such as a battery. The battery allows us to slowly capture the Solar energy and use it in bursts of high power to work on mitigation and manufacturing processes. If we put all of these things in our model then things become somewhat more complex as shown in Fig 2.
The diagram above shows the harm generated in the manufacturing processes of the Solar panel and Battery as Harm1 and Harm2 respectively. There are additional harms that occur during the material extraction and refining processes even before the manufacturing steps begin, but for the sake of simplicity we shall ignore those harms shown in the Gray box in the figure.
We will use the energy consumed in the manufacturing process of the Solar panel as 1373 kWh as before. For the manufacturing process of the Battery we will use the estimate of 55 kWh for every 1kWh of battery capacity based on this recent paper: Energy use for GWh-scale lithium-ion battery production https://iopscience.iop.org/article/10.1088/2515-7620/ab5e1e/pdf. For an example battery I will use the Tesla PowerWall2 specs:
Battery Capacity = 14.5 kWh
Battery usable capacity = 13.5 kWh
Ebatt = 14.5 x 55 = 797 kWh
How do we account for the harms in the manufacturing processes? Harm is the wasted energy and material spent in the manufacturing process. It is related to the efficiency of the process. Basic thermodynamics tells us that such efficiencies are well below 50%, probably closer to 30%. So the wasted energy and material is roughly 3x the actual work of manufacturing itself. But for simplicity’s sake I will assume Harm done is equal to the energy consumed in the manufacturing process. Hence:
Harm1 = Epanel and, Harm2 = Ebatt
Total Harm to be mitigated = Harm1 + Harm2 = Totalharm
Energy required for Harm mitigation = Eharm = Totalharm/Efficiency
Panel replacement energy = Erepl = Epanel/Efficiency
Plugging the earlier results and using efficiency of 33%,
Totalharm = 1373 kWh + 797 kWh = 2170 kWh
Eharm = 2170/0.33 = 6575 kWh
Erepl = 1373/0.33 = 4160 kWh
Hence, total energy to be supplied to repay the sustainability debt using the battery for mitigation and replacement will be Eharm + Erepl = Esustain
From above, Esustain = 6575 + 4160 = 10735 kWh
Esustain is the energy debt that must be repaid by collecting the energy in the battery and then discharging it for the mitigation and replacement activities as required. But since the battery can only store 13.5 kWh, this debt can only be repaid by charging/discharging the battery over many months or years. Of course we want the panel to generate more energy than required to pay the debt so we must use part of the energy generated by the panel for debt service and part for other productive use. If we split that power evenly 50/50 how long does it take to repay the debt?
If we use 50% of the panel power of 300W to charge the battery to 13.5 kWh capacity with 6 hours of power per day then days required to charge the battery can be calculated as:
Charge time = 13500Wh/(50% of Wdaily) = 13500/900 = 15 days
If we discharge at the end of 15 days and start over then in one year there are 365/15 = 24 cycles.
So total energy accumulated and spent per year for sustainability debt payment can be calculated as:
13.5 kWh x 24 cycles = 324 kWh
This amount 324 kWh can be spent each year for for sustainability debt service. We know Esustain = 10735 kWh, hence the years required to repay the sustainability debt is:
Esustain/324 kWh = 10735/324 = 33 years
33 years!!
Lifetime of the panel is anywhere between 25 to 30 years. Sustainability debt takes 33 years to pay. This simple analysis ignores that the battery itself may not last 33 years of repeated cycles. But the fact that debt repayment is longer than the life of the panel itself begs the question can we ever hope to achieve a better outcome? Or is it a law of nature like the second law of thermodynamics that is insurmountable?
Maybe Michael Moore is right after all. Perhaps it is true that it is impossible to clear the environmental debt created by technology with even more technology. The inconvenient truth may be that there is no way to sustain our ever increasing hunger for energy. We must simply reduce our needs down to a level that the earth can clean up after us.
Part II addresses some comments and questions raised on Part I.