After realizing that there is not enough mining capacity to “produce” the necessary amount of metals to build enough batteries (not only lithium, but copper, nickel and much more), a mad scramble to find an alternative electricity storage solution began. Last time I revisited the problem, the hype was all about using aluminum waste to convert its embedded chemical energy into hydrogen and heat. Now its time for thermal batteries to receive their fare share of criticism.
Thermal storage is touted as a “clean and sustainable alternative” to Lithium-Ion Batteries. According to media reports: “The thermal batteries industry is in the nascent stage of development, but it is gaining increasing attention, as governments and companies worldwide look for alternative green solutions. These batteries work by heating a substance to store thermal energy, which can be converted into heat or electricity. Energy from renewable sources, such as solar and wind farms, can be stored to use when energy is not being produced on-site, to ensure a stable flow of electricity to the grid.”
Well, where to start? It is one thing to store excess electricity generated by wind and solar as heat, it is quite another to convert that heat back into electricity… A “problem” grossly overlooked by the technutopists pushing this idea. You see, the efficiency of such an energy storage system is still ruled by physics, and thinking that this is just another “problem” to be solved, well, is magical thinking at best. As discovered by Nicolas Léonard Sadi Carnot in 1824, not even an ideal, frictionless engine can convert 100% of its input heat into work: that nasty second law of thermodynamics puts a fundamental limit on the thermal efficiency of all heat engines. Do they teach that as part of the Master’s program in International Development? I guess you know the answer… Nevertheless, the idea did gain traction:
According to Pitchbook Venture Capital, thermal battery startups have seen a substantial increase in their median post-money valuation over the past year, as well as growth in capital investment. In the U.S., this has been aided by greater government funding into clean technology, supported by tax breaks and other financial incentives for private investors.
Sounds promising? Well, let’s take one concrete example from the article: using vertical tanks filled with salt, holding heat generated with electricity at temperatures up to 500 °C. Now, could this stored heat be used to generate electricity, as touted by the author of the article? Without going too much into the details, the limiting factors of such a system are the temperature at which the heat enters the engine, and the temperature of the environment into which the engine exhausts its waste heat. Using Carnot’s formula, converting that heat into useful work (like driving an electric generator) in a 20 °C environment comes at a mere 62% efficiency. The rest of the energy is lost as waste heat. Forever. And mind you this is the theoretical maximum, for a frictionless, perfect engine.
Now consider also, that as such a thermal battery gets “discharged”, it’s heat content keeps reducing: resulting in an ever lower temperature difference between the storage medium and the environment. So, as the core of such an energy storage device cools to 250 °C for example, the thermal efficiency of the engine harnessing it falls to 44%, and so on… Till at a mere 30 °C inner temperature the generator driven by the battery barely works at a 3% efficiency. (In practice internal friction would eventually stop any motion at such a low temperature difference.) No room for negotiations, improvements, or human ingenuity. It is what it is.
That means, without doing some complex math here, that we are down to a twentyish percent average efficiency during the complete discharge of such a thermal battery. Adding insult to injury heat also tends to dissipate during storage, or the time spent between “loading” the heat battery and “discharging” it. (Oh, that damned second law of thermodynamics, again…) Thus the longer heat needs to be stored, the lower the starting efficiency will be. And again, we are talking about a frictionless, ideal heat engine harnessing that thermal potential, and converting it back into electricity without any waste whatsoever.
Now factor in some usual real life energy losses during conversion and power generation, and you are getting closer to a 10% average efficiency during a round-trip of charging and discharging a thermal battery (starting and ending with electricity). Folks, we are talking about a 90% energy loss here... How come this “idea” hasn’t received a Nobel-prize yet…? With that tremendous technical and economic performance in mind, try to make sense of the closing statement from the article above:
Greater investment in the sector will likely spur more innovations and lead to the wider global rollout of the technology in the coming years.
Yeah. Sure.
My sarcastic quibbles aside, this terrible energy efficiency is one of the many reasons why concentrated solar power stations like the Ivanpah have failed to become the wonder solution to our energy predicament (and has ended up being a “subsidy dumpster” as John Michael Greer likes to call these).
Looking at the bigger picture I also have to ask, how does wasting 90% of stored energy helps with our technological civilization’s biggest and most immediate, yet wholly unrecognized problem: the increasing energy cost of energy? Contrary to modern beliefs, our energy efficiency as a global superorganism is actually getting lower and lower. As the fossil fuel industry is forced to tap ever lower quality reserves and spend ever more energy to access them, the rest of the economy is getting less and less energy for the same investment, and has to spend more just to stay in place.
The ever increasing energy cost of accessing energy is already killing us, even without wasting 90% of it during storage… And before anyone cries foul: materials needed to build “renewables” — as well as nuclear and hydro — are all mined, transported and often manufactured using fossil fuels. So, as the energy efficiency of the oil industry flounders, so will the efficiency of the entire industrial civilization. Sorry folks, there is no such thing as an “energy transition” — except a transition back to burning trash, wood and biomass as fossil fuels and mineral resources deplete.
So, even if you manage to hold onto the belief that “renewables” made by “renewables” in a clean and green way is possible, then the energy losses during and after storage will certainly make you think twice. Batteries are the most efficient way of storing electricity, but their material demand puts them out of reach — not to mention the immense amount of poisonous chemicals released during mining, manufacturing and recycling.
Other “solutions” like pumped hydro is limited by the number of sites available for building a dam, and the amount of freshwater needed to fill those (not to mention the megatons of concrete needed, made by burning a comparable amount of fossil carbon). Hydrogen is an energy hog, and a potent amplifier of the greenhouse effect (by preventing the breakdown of methane in the atmosphere). And now these heat batteries, wasting 90% of the hard earned “renewable” energy, which often comes at an EROEI of 10 or lower in higher latitudes… What remains after a full discharge cycle then? An EROEI of 1? Or below one, considering all the energy needed to build the supporting infrastructure? Just how feasible is it to maintain civilization with that?
Where thermal storage could actually make sense is residential and small scale commercial use— but only when talking about heating, hot water or process heat (to cook food, make paper pulp, distill liqueur etc.). In practice however, nothing needs to be “invented” here: small scale solar heaters are already widely available, what’s more: such devices can be also made at home. Just take a long enough black plastic tube, wind it up and place it on your roof to make hot water. Or use a black metal barrel, or a polished parabolic mirror. Anything more just needlessly over-complicates things.
I get it that there is not enough metal to electrify everything, and to provide adequate power storage needed to iron out intermittencies of “renewables”. But then resorting to outright scams boosted by magical thinking — like using thermal batteries “to ensure a stable flow of electricity to the grid” — is not a strategy either. It is mere tactics. Strategic thinking would involve actively planning and preparing for a post-industrial, low energy, low-tech world, not throwing spaghetti at the wall until something sticks. As Sun Tzu wisely observed two and a half millennia ago:
“Strategy without Tactics is the slowest route to victory. Tactics without strategy is the noise before defeat.”
Until next time,
B
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