Slightly of-topic: compressed air is the preferred source of power for the tools of Amish people, since their religion doesn't allow them to use electricity or internal combustion engines.<p><a href="https://www.cottagecraftworks.com/home-goods/self-sufficient-living/off-grid-power-tools" rel="nofollow">https://www.cottagecraftworks.com/home-goods/self-sufficient...</a>
Compressed air storage really begins to make sense when the tank is deep underground, or deep underwater, so you don't need an overbuilt pressure vessel.<p>The very good idea of floating solar panels on a reservoir (cool panels are more efficient, and keeping them clean is cheap!) raises the question of what to do with excess power generated in the daytime. One alternative would be to pump water up out of another reservoir downstream, but there might not be one. So, just put a big air bladder on the bottom of the reservoir and pump air in.<p>Same applies for offshore wind power.<p>About half the energy you put into a pressure vessel becomes heat that you would not get back, under water. (But rock is an excellent insulator.) With enough spare water, you can draw almost the same amount of heat back in on discharge. Or, you might have a use for cold air.
While I'm a pretty big fan of low tech solutions, I'd just like to point out that electrochemical hydrogen compressors can basically already do this, but better. 80% round trip compression efficiency, up to 700 bar compression, no moving parts, and massively long lifetimes (in the 30-50 year range). The fact that the compression medium (hydrogen) is also an energy storage medium is just a cherry on top. It's just a matter of price coming down for 700 bar pressure vessels.
For fixed-site applications of sufficient land area and scale, it's difficult to beat pumped-storage hydroelectricity (PSH). The round-trip efficiency is around or above 70%, the same or better than CAES. CAES is probably best used in applications similar to flywheel (FES), away from occupied areas.
The system they like, the near-isothermal compressor with a "liquid piston", is described here.[1] They wrote up a description of a small prototype, but don't seem to have built one. The University of Arizona lab from which that paper came does not seem to be doing anything with energy storage any more.<p>[1] <a href="http://www.u.arizona.edu/~deymier/deymier_group/refs/CAES.pdf" rel="nofollow">http://www.u.arizona.edu/~deymier/deymier_group/refs/CAES.pd...</a>
Another cool energy storage technique is using subterranean flywheels. They'd probably require less maintenance than other similar energy storage mechanisms.
Some guys I know built a full-sized car, with the engine built with Lego and powered by compressed air.<p><a href="https://www.youtube.com/watch?v=_ObE4_nMCjE" rel="nofollow">https://www.youtube.com/watch?v=_ObE4_nMCjE</a>
I'm not a fan of this personally. Compressed air is dangerous. A full tank is basically a bomb. While we have the technology to make this safe, it has to be regularly inspected. If your homeowner slacks on the inspections they could come home one day to discover their energy storage has turned itself into a crater and flattened all nearby structures.<p>One thing to consider is that the heat generated by compressing the air could be vented into the home to warm it up in the winter, or simply allowed to escape outside in the summer. When discharging the cool air would either be released outside or inside of the home, depending on if you want to cool it off.
360 Wh for 18 cubic meters? Is this a joke? That is indeed the volume of a small room. You need nearly 40 of them, the volume of a large house, to give the equivalent energy storage of one 13.5 kWh Tesla Powerwall.
I would like somebody to explain his "replace batteries every 2-3 years" comment. I think this is true of small scale Lead-Acid based UPS, but Neoen scale Li-Ion stacks come with a battery management system which I believe offers better than 80% effective battery energy density over a longer life: 5+ years. Certainly the assumptive economics behind grid-scale battery models from Tesla is, a far longer working life than this. And, the evidence of full cycle life on Tesla car batteries and even Prius, is better than 2-3 years of useful life.<p>This may be because they over-provision so "rated" energy is met by replacement from a 110% sold capacity-type model.<p>I think the rest of the article is great. Fascinating.<p>Grid scale compressed air storage is a thing, and may have low energy efficiency, but so does PHES. The thing is, they can be huge, and they can sustain power for long periods. The heat loss story, I am confused by because usually this gets better with scale: you can exploit a lot of lower grade energy in heat/cool cycles, either to retain it in system eg heat transfer to another form of heat energy storage, or, for adjunct purpose like building heating or cooling.<p>Fan, not expert, experts can put me right!
There was a company called LightSail Energy [1] that tried to (unsuccessfully) commercialize this technology. Does anyone know what happened to it? Some searches online show that they had some founder problems. IIRC, they had great investors, but unfortunately it didn't work out.<p>[1] - <a href="https://en.wikipedia.org/wiki/LightSail_Energy" rel="nofollow">https://en.wikipedia.org/wiki/LightSail_Energy</a>
The efficiency loss compressed air suffers is mostly at the hands of the ideal gas law. Storing energy by pressurizing the container heats up the gas which increases the pressure requiring even more energy to store additional gas. When retrieving energy it depressurizes the container which cools the gas down which reduces the pressure which gives you even less energy. What if they could cancel out?<p>Say you have two separate pressure vessels where to charge the system you pump air out of one into the other. Well the depressurizing vessel will cool down, but the pressurizing vessel will heat up. If they came to thermal equilibrium with each other their net temperature change would cancel out somewhat. This is great because it would restore the pressure on both sides to have more favorable conditions for energy storage and extraction.<p>So I wonder if you could design a pressure battery that would exhibit <i>no</i> change in temperature on the exterior throughout the charge/discharge cycle.
This article seems to assume we'd convert the compressed air to electricity, but I could think of a bunch of applications that could use mechanical air power instead.<p>Blenders, washers, dryers, dish washers, garage door openers. Basically anything that uses a motor.
I'll admit this article describes a much less bad system than what I envision when someone mentions compressed air energy storage.<p>On a side note, I wonder what the state of research is on reducing the embodied energy in li-ion battery production. The mentioned figure in the article is surprisingly high (2-10 times the total energy the battery will store - presumably they mean over its lifetime), which now that I think aboute it, squares with what I have seen elsewhere on the embodied energy of electric car manufacture.
The last example, using multiple small pressure containers, seems to get a hugely better energy density than the other examples, and starts to seem realistic for domestic storage.<p>Are the figures correct, I couldn't find much follow up to that study?<p>I can imagine small-scale CAES being ideal where there is also a cooling load (eg humid tropics), since the expanding air will be cool and dry.
Generally I don't like this as an idea given the likelihood of failure of metals after a certain number of stress cycles (why planes have a lifespan)