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Jan Steinman


Excellent introduction to the topic, that makes me want to go out and build one!

All your examples appear to use photovoltaic panels, which have the two inefficiencies of photon-to-electricity and then electricity to motion. Do you know of any efforts to harness solar thermal for this purpose, perhaps through Stirling engines?

kris de decker



These ideas are dealt with in the other article: http://www.lowtechmagazine.com/2018/05/history-and-future-of-the-compressed-air-economy.html

Here are the paragraphs & the references:

Some proposed designs follow other approaches to deal with the heat of compression, and these could work for both large-scale and small-scale CAES systems. One interesting idea is a compressed air energy storage system that runs on wind energy as well as solar energy. [24]

Wind energy is stored in the form of compressed air by compressor chain, as in the other CAES plants. However, solar energy from a parabolic dish is stored in an insulated solar thermal tank and used to reheat the compressed air prior to expansion. Because the heat from the compression process is no longer needed to warm the air upon expansion, it is used to produce hot water.

A similar concept for a hybrid thermal and compressed air energy storage design uses electric heating instead of solar thermal power. [25] Because the workload in these systems is shifted from pure conversion to investing partially in thermal storage, energy densities well in excess of traditional CAES can be achieved, and the size of the air storage can be reduced.

[24] Ji, Wei, et al. "Thermodynamic analysis of a novel hybrid wind-solar-compressed air energy storage system." Energy Conversion and Management 142 (2017): 176-187.

[25] Houssainy, Sammy, et al. "Thermodynamic analysis of a high temperature hybrid compressed air energy storage (HTH-CAES) system." Renewable Energy 115 (2018): 1043-1054.



Compressed air is still popular for powering tools. Most powered tools are available in compressed air, battery, or AC variant, therefore I really see this CAES idea ideal for the hobbyist.

My garage for example is not connected to the grid, so no electricity. Battery tools were so far the solution, and I was even thinking to add PV to charge them, but to go all compressed air seems way more intelligent.

Just need to invent micro-expander to light the garage now. LEDs need very little power, and need to be cooled for maximum efficiency and durability anyway ;-)

Israel Walker


An article you and your readers might find interesting on this subject:


Also interesting is the comments which reveal the commenters and to a lesser degree the author, do not understand that Amish are not against electricity: they are against community networks controlled by members outside the community, they are localists not luddites. They have little problem with technology as long as it doesn't make the user dependent on those outside the community.

Also this: https://en.wikipedia.org/wiki/Fireless_locomotive

Fireless locos generally proved themselves more useful than compressed air locomotives, at least in part because of a mixing valve mixed air into the steam jet to create a larger volume of working fluid. If you are already designing a heat pump running on water vapor, water vapor/liquid phase shift, and running high pressures, I suspect some applications would be benefit from steam, rather than compressed air.

Mackey McLelland


Maybe you could do a small series on battery storage of energy - gravity, thermal etc.

I once visited the island of AEro in Denmark. They have a district heating system which is based on a huge insulated tank full of molten salt. They heat it up through the summer with excess electricity from their PV and wind generators and then use it to heat the town's houses and water through the winter. Extremely effective...

Chris harries


For a while I contemplated this as an energy source for a bicycle, the idea being that the (modified) bike frame would act as the containment vessel for compressed air. This all looked good and easy to do and would have higher energy performance than a battery electric-assist bike. The stumbling block, though, is safety. Any highly compressed gas needs a very robust containment vessel. A sudden rupturing of any containment vessel or lines can be disastrous. Weight becomes a problem.

But the idea of using compressed air as a stationery energy storage needs to be pursued further. As it almost certainly will be.



Amish use compressed air systems and have for years. Their Wells and washing machines run on air. It's great and been over 20 years that I've known of it...



Thanks for the article, as always inspiring.
One remark:
At the end it says... Build it Yourself?

In conclusion, .... Simply getting hold of the right components and fittings is a headache, as these come in a bewildering variety and... are only sold to industries....?

Entering "electric air valve" in Ebay seems to give a list of possible valves... Fittings, storage and pipes can be had from a local plumbing store or scrap dump?
Arduinos etc. are fairly simple to program and take very little power.

Bryan H.


Is there any reason why compressed air storage systems aren't kept underwater (i'm thinking a pond, lake or undersea)? It seems like the continuous water pressure may take care of some of the problems related to pressure in the chamber dropping as the air is used (assuming the storage chamber walls are flexible).



This article is assuming the use of compressed air for conversion to electricity...given that premise, is there any way to convert the temperature differential directly into electricity as well, either through modified Peltier coolers or (as a Low-Tech method) a Stirling Engine sensitive enough to run off of the ambient temp changes?

Jim Baerg


Bryan: I think that is perfectly possible IF you have quite deep water close to shore. It takes 10 m water depth to give 1 bar of extra pressure, so for 10 bar pressure you need a water depth of 100 m. For 100 bar 1 km water depth is needed. An exercise for the student is to determine where these conditions are available.

I'm a bit surprised that the technology from this company (http://www.lightsail.com/ ) wasn't mentioned in this article or the previous one. The trick of spraying water into the air being compressed or expanded to absorb or release heat & so keep the compression/expansion near isothermal sounds like a good way to increase the efficiency of CAES. I recall that the claimed efficiency was at least as good as pumped hydro, but I can't find the efficiency figure on that website now.

Energy storage as good as claimed by the Lightsail company, would greatly reduce my skepticism about the worth of wind energy. Since energy demand is higher during daylight hours, solar is still of considerable use without storage in the large part of the world where seasonal variation in sunlight is modest.

kris de decker


@ Bryan

So-called "Underwater CAES" is a research topic. The advantage is a steady pressure, but anything that's built underwater, especially in salt water, is going to have a shorter lifespan. And it makes CAES dependent on geography again.

@ order99

Sounds possible to me. The Stirling engine is a way to convert solar energy to mechanical energy, allowing to drive the compressor directly.

@ Wim

That's not my experience, but it may be different depending on where you live. Maybe I was looking in the wrong places.

@ Jim

I did not mention LightSail because quite a lot has been written about them already, and because they seem to have advanced little recently. By the way, there are other approaches I did not write about. There is so much research going on at the moment that I had to make a selection.



I was left thinking that a passive solar approach to heating tanks (and thereby increasing the pressure) could be used as a way to boost output if the energy usage was cyclical. Day and night temperature variances would seem to be a natural component of any rural design along with direct solar heating.

Oliver Evans


wind powered air compressors are built by the Amish in Maine. I have seen them at an Amish cabinet shop in Choteau Oklahoma. They pump air into a large propane tank that is used to power the air tools in the shop. They work great!



I can't access the original paper [27] but 410Wh energy from 570l of stored air is higher than I would expect. It is about 6.5x what the formula at the Wikipedia page on Compressed Air Energy Storage says is the theoretical maximum in the case of isothermal storage.

Why is that not an appropriate formula to apply in this case? What am I misunderstanding?

Here's my units session, with the Wikipedia formula giving the maximum as being 63Wh:

You have: 5 bar 570 l ln(1 atmosphere / 5 bar) + ((5 bar - 1 atmosphere) 570 l)
You want: watt hour
* -63.248223
/ -0.015810721

Cristián Lávaque



Great article, again!

About heat during compression/decompression, this could be used directly, avoiding the need of electricity later for those same uses. Most homes would have a water heater and a refrigerator.

The compression part could have a heat exchanger to heat up a water tank, and the decompression part have one to cool an insulated box/room. They'd avoid energy losses and improve the overall efficiency of the system.

But that's assuming that the home would have used electricity for cooling and heating, for which there are other efficient approaches.

kris de decker


@ Karl (#15)

I have sent you my copy of the paper you can't access.

In short, a higher energy density is obtained by using multiple interconnected storage tanks instead of one large tank. This allows more effective heat transfer to take place, because every air tank acts as an additional heat exchanger. Also, discharging the vessels sequentially allows longer discharge times and solves the problem of pressure drops. These factors are not taken into account in the Wikipedia formula.

kris de decker


@ Oliver Evans (#14)

Great link, thanks !

This link goes straight to the product page: http://windcompressor.com/html/compressors.html

And here is another wind-powered compressor: https://www.cottagecraftworks.com/wind-compressor-wind-driven-air-compressor-alt-energy

The same website has several air powered kitchen tools for sale, as well as fans:



If a windmill compresses air directly, without converting it to electricity, and the devices are powered directly by compressed air, a small-scale CAES system can become even more energy efficient than the articles states. This strategy, which also works on a larger scale, is explained in the other article: http://www.lowtechmagazine.com/2018/05/history-and-future-of-the-compressed-air-economy.html

Additional links found via Hackernews: https://news.ycombinator.com/item?id=17143163

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