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Ditch the Batteries: Off-Grid Compressed Air Energy Storage

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Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#91

Post by beat »

adrianN wrote: post #43
harperlee wrote: post #38

Earlier quoted context omitted.

It would be great if there was a (safe, efficient) way to store electricity in ethanol - but it seems that the process is not very efficient and requires carbon monoxide as input, which is not very safe at offgrid-home scale. That is, unless electricity is used to light corn crops. Still not very efficient.

It's not really efficient, but you can create short chain hydrocarbons to store fuel for your fuel cell. Methanol for example is a lot easier to handle than hydrogen and there are fuel cells that consume it.

Methanol is avoided in a lot of non-industrial situations because it's so incredibly toxic. Very dangerous to children and animals and idiots.

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#92

Post by bdamm »

3pt14159 wrote: post #85
throwaway5752 wrote: post #82

Earlier quoted context omitted.

There's a video somewhere of a failing flywheel, it's a fairly energetic explosion. I follow the energy space, also, and ... while I didn't expect Li batteries to have grid scale roles, I didn't think flywheels were going to succeed there. They have properties more like ultracapacitors (discharge rate suitable for continuous backup, clean up messy grid sine waves). I thought pumped air/pumped water was more likely be…

The core insight for me was when Musk talked about how little the cost of Li mattered in the unit economics of Li batteries. It was something like 3% of the cost. The rest of it was mostly manufacturing costs. With so much room for improvements at scale and so many potential applications, it seemed like a sure winner.

That's a very useful insight. My "aha" moment came during a lecture given by DARPA at PARC about 5 years ago, outlining how wasteful current battery technology is in terms of density entirely because of safety requirements. They had at the time over a dozen different research projects on ways to improve density by changing how safety is achieved. It is only a matter of time until some of them get to market, and in fact I believe one of them has. They were all 2x-10x improvements.

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#93

Post by saosebastiao »

ajuc wrote: post #74
jandrese wrote: post #62

Earlier quoted context omitted.

For home use you also have to consider that you're basically making a bomb every time you store energy in the thing.

Any kind of high-density energy storage is basically a bomb. If you charge or discharge Lithium polymer or lithuium ion batteries "wrong" they explode too. I wouldn't want to be near a flywheel that stores 360 Wh of energy when it breaks.

360Wh of flywheel is tiny. You could easily bury it and never have to worry about the danger of a failure. Grid scale flywheels are the ones that are scary.

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#94

Post by IkmoIkmo »

evan_ wrote: post #59
beat wrote: post #51

Earlier quoted context omitted.

You probably keep multiple gallons of gasoline nearby, tho.

Not to mention the giant propane tanks that many houses in rural areas already have

Or the LPG tanks hundreds of millions of people have in their homes outside the developed world. e.g. India, Brazil, much of North Africa etc. They're considered quite safe, though.

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#95

Post by Diederich »

joncrane wrote: post #75
drizzle87 wrote: post #24

I was quite excited by compressed air storage when Lightsail came into the picture almost 5-7 years ago. Sadly, they could not make the economics work and ended up pivoting into a company that sells carbon fibre tanks for high-pressure storage. As someone who follows the energy space closely, Lithium ion batteries now have so much momentum and $$$ pumped into them via R&D work, it's going to be hard for competing ene…

Aren't flywheels used in datacenters to cover the split second between when the power goes out and the generators kick on?

The various datacenters I've had such in-depth knowledge of over the years all used a big battery for that.

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#96

Post by jandrese »

Cthulhu_ wrote: post #84
jandrese wrote: post #62

Earlier quoted context omitted.

For home use you also have to consider that you're basically making a bomb every time you store energy in the thing.

Eh, at least air isn't as dangerous as e.g. water would be, the tank can be / is designed to fail gracefully and there's overpressure valves.

Huh? Compressed air is way way more dangerous than pumped water. A pumped water disaster is a flood. A compressed air disaster completely obliterates the containment vessel and surrounding room and the overpressure wave and shrapnel are also fatal. I'm not sure how you would design a high pressure air tank to fail gracefully. The air is like a gigantic spring, and once it starts to go it's going to tear the containment vessel to shreds.

There are things you can do to make it safer, like installing the tank at the bottom of a pool or buried under a few feet of dirt, but they add complications and expense.

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#97

Post by bdamm »

sandworm101 wrote: post #41
mabbo wrote: post #31

> However, to store 360 Wh of potential electrical energy, the system requires a storage reservoir of 18 m3, the size of a small room measuring 3x3x2 metres. The authors note that “although the tank size appears very large, it still makes sense for applications in rural areas”. This would light a home for an hour, with LED bulbs and careful usage. And all it requires is a room-sized storage tank. So if I wanted somet…

Or you could liquify the air. That would make the storage much more energy-dense but introduces all sorts of practical/heat issues. People have played around with running cars on liquified nitrogen. The air conditioners probably worked well.

Steam power, in a sense. Now I kind of want to build one, although the crash scenario is just as terrifying as with a hot car. Hmm.

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#98

Post by jandrese »

agumonkey wrote: post #66
jandrese wrote: post #62

Earlier quoted context omitted.

For home use you also have to consider that you're basically making a bomb every time you store energy in the thing.

few mechanical engineer~ youtubers said so many times; compressed gas seems less dangerous than water but compression is terribly dangerous

This doesn't make sense at all. High pressure water can be dangerous for sure, but water based energy storage doesn't use high pressure... It's all about pumping the water uphill and then letting the water flow back down through the pump to recover the energy. At worst your house gets flooded because the containment vessel failed.

Worst case with compressed air is a total disintegration of the tank, the room it's in, and the rest of the house along with the occupants.

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#99

Post by djrogers »

JohnJamesRambo wrote: post #44

I'm surprised no one is talking about how scary it is that you are basically making a high powered bomb at your house any time you have one of these. Anyone that has watched Mystbusters understands the incredible destructive power stored in compressed air. I'll stick with batteries, thanks.

There are literally tens of millions of compressed air tanks in use every day in this country, and many of hem are kept full for long periods of time. That part is a solved problem and has been for ages...

Re: Ditch the Batteries: Off-Grid Compressed Air Energy Storage

#100

Post by hedora »

juliangoldsmith wrote: post #35
Uhrheber wrote: post #19

When compressing air, a lot of heat is generated, and in most cases wasted. When the air is released, it cools down, and has to take heat from the surroundings. Which doesn't work very fast without additional heat exchangers, and especially not in cold environments. Compressed air storage is only efficient with additional heat storage, which is something that promoters of compressed air storage often "forget" to tell…

I wonder how well it would work to have a compressed air storage system where the tank is in a loop with a solar water heating system. The heat from the loop could be used to provide heated water, or maybe drive something like a Stirling engine. You could use the output of the Stirling engine to compress a bit more air using the waste heat.

They talk about this in the middle bit. Some high pressure small scale systems report 70% efficiency when used for heating + refrigeration + electricity, even though the electricity part is only ~11% efficient.
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