[jillesvangurp]

You stopped reading too soon:

e.g. " By discharging the cylinders sequentially, the discharge time can be greatly increased, making the system comparable to lead-acid batteries in terms of energy density. Based on their experimental set-up, the researchers calculated the efficiencies for different starting pressures and numbers of cylinders. They found that 57 interconnected cylinders of 10 litre each, operating at 5 bar, could fulfill the job of four 24V batteries for 20 consecutive hours, all while having a surprisingly small footprint of just 0.6 m3.

Interestingly, the storage capacity is 410 Wh, which is comparable to the 360 Wh rural system noted earlier, which requires an 18 m3 storage vessel – that’s thirty times larger than the modular storage system. "

Also you missed the points of higher pressure vessels and using the residual heat/cold for things like hot water. Basically you trade off lower electricity efficiencies, space, and heat. Excess heat is not necessarily a bad thing in a domestic situation.

My take aways from this article:

- there are a few scenarios where stuff like this makes sense.

- there's lots of room for innovation and component improvement (e.g. more efficient dynamos are hinted at). This is currently a niche market and people have not put much R&D into this so far (i.e. I'd expect some improvements are entirely feasible).

- sequential vs. monolithic setups have different properties.

It boils down to cost / kwh and whether the requirements make sense. In an industrial setup, having a cheap but enormous vessel might not be the end of the world. In an apartment, you'd want maybe a smaller but higher pressure one.

[jacknews]

This is by far the most efficient example from the article, and seems to make this kind of system viable for domestic use, but I question whether the numbers are true, as I've seem no follow-up studies.

[jillesvangurp]

Too early for that. There are barely any products in the market for this. The ultimate proof will be people installing this in their homes for a certain amount of $ and then getting some measurable ROI (also in $).

But do you have reason to be skeptical about the physics? The premise here is brutally simple centuries old physics and engineering that any high school kid should be able to understand. Simple pressurized vessels holding compressed air. It sounds plausible to me that that ought to be dirt cheap to implement with very low tech solutions for pumping and compressing air and storing it in some kind of vessel.

You see people arguing here for an alternative based on Tesla batteries costing in the order of thousands of dollars even for a modest/small setups. It's kind of easy to see that this could potentially undercut that by orders of magnitudes because there are no special/hard to get materials and it's all based on dirt cheap commodities and technology. Pumps, valves, steel, etc.

[jacknews]

Yes, I question the physics. The last example, where they use multiple fire-extinguishers as the storage vessel appears to me to be able to store far more energy per volume than the other examples cited.

If these numbers are accurate, then such a system seems quite feasible for domestic use. The others, much less so, as the storage vessels to store just a few KW/h are so massive.