Snippets on Energy #7

Wide range of uses

6 min readJan 11, 2022
The Solar furnace of Odeillo, in Font-Romeu-Odeillo-Via (Pyrénées-Orientales, France). Image source: Wikipedia

When people talk about renewables, they mostly talk about electricity. True, it is very important to our comfortable western lifestyle, however it is but a tiny fraction of our total energy consumption. Where does the rest come from? Residential heating, industrial processes (mining, smelting, chemical feed-stock and fertilizer production, agriculture etc.) and of course transportation. There are a multitude of difficulties however when it comes to electrifying these processes: each one has a special, mostly technological reason why it remained a primary consumer of fossil energy. Can “renewables” take over their role one day, providing a wide range of uses?

It is one thing to have an “economic” alternative to fossil fuels when it comes to electric power generation, this does not imply however, that everything can be electrified, or manufactured using solely “renewable” or nuclear sources of electricity and heat. Let’s take glass melting furnaces for example — producing a critical component to solar panels: plate glass. If we are to believe in a 100% “renewable” green economy (or an economy at all after fossil fuels are depleted or left in the ground), then we should be able to manufacture glass using renewable sources of energy, right?

The good news is, that in a controlled environment (i.e: using artificial light) you can melt glass in solar furnaces, as they are capable of reaching (and exceeding) 1,500 °C (2,732 °F) (1). The bad news is that this method was never put to practice — and for a good reason. In the real world, temperatures in a solar furnace are subject to rapid changes and are very hard to maintain. If a cloud blocks the Sun, temperatures start to fall quickly, only to return in the form of a thermal shock once it starts to shine again. Also, the Sun as a source of heat is only available around midday when it is shining strong enough — and of course mostly on lower latitudes, where you don’t have to deal with a low angle, weak winter sunlight and all that persistent cloud cover.

The problem with this is, that in order to melt and form glass efficiently, you have to run your furnaces around the clock without interruption or fluctuations in temperature. Why? Because if you let glass solidify in a furnace, then the only way to get it out is to blast it with jackhammer. And there goes your million dollar furnace with it. This leaves us with the option of producing glass only in small batches: heat it up in the morning, pour all of the molten glass out around midday, then let the furnace cool down in the evening. Out of 24 hours you get maybe (and I’m wildly guessing here) 2–4 hours of manufacturing time (when you have molten glass to work with)… All this for an investment in material resources much larger than a regular gas furnace… Which, on the other hand, can work around the clock, paying back its cost within a couple of years.

This is also not an insignificant factor, when calculating the EROEI of solar panels. If you were to manufacture glass via solar furnaces (presuming you can overcome thermal shocks and other difficulties) you would have to invest a lot of materials and energy into an equipment capable of producing glass a few hours a day only, and standing idle (heating up, or cooling down) during the rest of the time. I’m not risking too much by betting that this would push the energy return of solar panels into a net negative territory.

Chances are that the energy and one-time mineral resources invested in manufacturing panels this way would never make a payback: you would be loosing energy all the way through mining, building, maintaining all this equipment, and not generating enough electricity from the panels to compensate your losses.

I might be underestimating human ingenuity here, but consider this. If melting glass in solar furnaces were such a great idea, wouldn’t be someone doing it already…? We have solar furnaces for half a century now — the world’s largest is about to turn 53 next year. Why don’t we see it producing useful material outputs?

Economics of fossil fuels (24/7 service for a dirt cheap price) surely played a role. With rising prices for fossil fuels since 2005 however we did have an incentive to develop such technologies for more than a decade now — at least in theory. For some reason it is still not happening in real life. Maybe it’s due to the net negative return on the energy invested…? The world is still yet to see a “renewable” energy site built and manufactured using “renewable” sources of energy only (2).

Time is ticking fast however. We don’t have another five decades to figure out how to melt glass using solar furnaces, or how to make fusion work.

When extraction of fossil fuels will finally stop growing during this decade due to perfectly natural causes (depletion), economies around the world will be struggling to keep up with a continuous and permanent loss of energy — barrel by barrel, kilowatt by kilowatt. Not to mention the resulting ups and downs in prices, rendering long term investments ever more impossible to repay.

Remember: energy is everything. Attempting to repeat the feat of the post WWII recovery, or at least maintaining this level of consumption on ever decreasing energy returns is equal to fighting a losing battle.

Current “renewable” technologies are fully dependent on fossil fuels due to energetic reasons, and are as transitory as their polluting counterparts. They are capable to produce intermittent electricity and low diffuse heat only, and are wholly inadequate to power their own reproduction, let alone powering a world economy. The only thing they can do for us, is to soften the landing into a post-industrial, low-tech world, then to be left behind as unreproducible relics of a long lost age.

Image credit: Patrick Hendry via Unsplash

Having this in mind would result in a whole different set of policies: aimed at working towards true sustainability and reducing overshoot — not trying to maintain rabid consumption. This is a story for another day however.

Until next time,



(1) This temperature range (needed for many applications, like smelting for e.g.) is completely out of range for nuclear power, as even the most advanced molten salt reactors are capable to maintain a “mere” 750–1000°C range only. The same goes for electric heating via resistance coils. Arc heating has higher temperatures but come also with a limited usability.

(2) The same goes for mining minerals for low-carbon technologies. As I’ve mentioned multiple times before, mining will require ever greater energy inputs to maintain (let alone to grow) current levels of “production”. There are some processes (mostly large, stationery machines doing the grinding and sorting of minerals) which can be electrified — although intermittency can be a problem here too. The bulk of the load however will continue to fall on huge dump trucks like the Caterpillar 797F powered by a 3,550 hp (2,647 kW) diesel engine and carrying a 363 metric ton payload. Replacing them with battery powered dump trucks (which are available, albeit in a much smaller size, in the 120–150 ton range) would require an even higher energy investment (batteries) per ton of mineral “produced”. These new trucks would then have to carry many tons of dead weight in form of batteries, and as a result would have to travel more frequently between the mining pit and the mill — damaging energy returns even further…




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