Ditch the Batteries: Off-Grid Compressed Air Energy Storage (2018) | Hacker News Reader

Ditch the Batteries: Off-Grid Compressed Air Energy Storage (2018)

lowtechmagazine.com

24 pointsgreesil18 comments

No mention of safety?

I’m barely comfortable with sodastream bottles on my house…

We ditched our air compressor at work because there are strict work safety regulations (like regular maintenance). However, going off grid is probably a bigger risk in itself and realistic risk analysis is a hard task.

I was working on a compressed air energy storage system for a marine application many moons ago. It was a rubber bladder reinforce and shap-constrained externally by Nylon fabric that would assume the load under tension. I can't recall the operating pressure, but what's vividly burned into my memory was the large fear the fabrication shop had of testing the setup (that if a unit ruptured, it would send large/micro projectiles hurtling through the walls of the facility). The solution was to test under water. We never ended up building the design, but storage under water is plausible safety mitigation I think, though that seems a bit unwieldy.

Yah, but heat pumps have compressors too. I'm not sure what failure modes are the most concerning. The pressure vessels probably have some max number of load/unload cycles in them for instance.

Most refrigerators have compressor (exists mostly mobile schemes, powered by heat, but anyway they have pressure inside).

From conditioners installers, I've hear, they mostly have issues with external connections, but near none with what made on big enterprise.

So window conditioners, or mobile conditioners, or heavy duty industrial conditioners with salt water as working liquid, are extremely reliable.

Same thing with heat pumps - if it is possible, to make all pipes with high pressure on enterprise, there will be no problems (reliability 3 Sigmas usually). Only potentially problematic, what done at fields.

I'm less comfortable with lithium batteries in my house.

There are safety mechanisms for pneumatic systems, pressure relief valves are one way to prevent over-pressurizing the system.

You’d want to have a system like this installed by a licensed pipefitter and properly commissioned and tested before operating it, along with regular maintenance.

What kind of maintenance?

Periodic tests of joints and valves to ensure they aren't leaking or stuck, respectively. Servicing the air/water separator so that the stored air is dry rather than moisture laden, causing condensation and rusting inside the piping and storage tanks (see: stuck valves). Changing the compressor oil. Making sure no one stuck a metal blank on the emergency relief, making it useless. Hydrostatic load tests of the storage tanks. Things like that.

It’s curious to see this topic on HN as I just came across an article about the impeding energy crisis in Ontario that sheds light on how the province is leveraging underground compressed air storage[1] as a tactic in their energy storage mitigation strategy.

[1] “Beyond the sprawling nuclear plants and waterfalls that generate most of the province’s electricity sit the batteries, the underground caverns storing compressed air to generate electricity, and the spinning flywheels waiting to store energy at times of low demand and inject it back into the system when needed.” https://toronto.citynews.ca/2022/12/26/ontario-electricity-e...

I've been curious lately about living off grid where I'd have a reasonable amount of land. One concern I had was with battery lifetime and this seems like a way to have a long lived system, at the cost of some efficiency. So I found this article and decided to share.

Given how ludicrous the rest of the article is, I have trouble trusting anything else that they wrote.

Using electric vehicles and reverse chargers to stabilize the grid will never be economically viable; it will always be cheaper to buy dedicated batteries for that purpose because vehicle batteries are limited by charge/discharge cycles, not age.

> vehicle batteries are limited by charge/discharge cycles, not age.

LFP batteries from the last few years are not limited by cycles. If you're charging every few days to weekly, it would take 50 years to hit the 3000-5000 cycle limits. Thermal degradation will happen a lot faster.

Is the amount of thermal degradation a function of use? Or a function of environment (like leaving the car outside in the cold)?

Just a name for the effects of temperature and time. Heavy use contributes, but is mostly accounted for under the 'cycle count at high charge/discharge rate' heading.

It's very hard to wear a new LFP battery with a controller that keeps it in the 20-80% range out now unless you cycle it several times a day or use it in harsh conditions.

We'll probably start seeing manufacturers cost cut and increase cycle depth or decrease cooling.

I am always mystified by assertions that underground CAES systems suffer inefficiency. Earth is a superb insulator, so any heat pumped into an underground reservoir along with the compressed air would be still there when you draw it down later.

If you use water to compress the air as it goes down, you get isothermal compression. The trompe, which originated in the ancient Catalan forges, has been widely used over the centuries. Anecdotally, a trompe in a mine in Switzerland powered a whole bunch of ~1000 horsepower rock drills, provided fresh air to the underground miners, and powered turbines that generated enough electricity to power a town of about 1500 people.

Here's the vid on trompes I always see come up: https://youtu.be/50fJ8Av_g7Q

I know "free energy" devices don't really exist, but a trompe seems pretty darn close, IMO.

https://news.ycombinator.com/item?id=27066295

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