Hacker News new | past | comments | ask | show | jobs | submit login
Ditch the Batteries: Off-Grid Compressed Air Energy Storage (lowtechmagazine.com)
312 points by helb on May 24, 2018 | hide | past | favorite | 231 comments

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 $$$ pumped into them via R&D work, it's going to be hard for competing energy storage technologies to catch up. Flywheel and hydrogen fuel-cell also often come up but I think we're at a point now where batteries are going to take off simply because of their wide area of applicability. With that economy of scale costs will drive down and even more research and $$$ will flow.

>As someone who follows the energy space closely, Lithium ion batteries now have so much momentum and $$$ pumped into them via R&D work, it's going to be hard for competing energy storage technologies to catch up. Flywheel and hydrogen fuel-cell also often come up but I think we're at a point now where batteries are going to take off simply because of their wide area of applicability. With that economy of scale costs will drive down and even more research and $$$ will flow.

I've been surprised by the development honestly. 15 years ago I assumed heavy industry and automotive would make the big decisions about what energy storage tech we go with and the rest of the economy would follow suit and start working with either hydrogen fuels cells, supercapacitors, kinetic storage, or chemical batteries based on the R&D they did.

Instead it's been consumer electronics that led the way and heavy industry is stuck with chemical batteries because that's what worked best on an MP3 player.

Don't rule out hydrogen just yet - at least not for cars (and then using your car as a generator to power your home):


I'd be very surprised if hydrogen vehicles work out. Hydrogen is not a source but rather a store of energy like a battery is. There's a few practical and technical issues:

1 it would require building out entirely new infrastructure, running up against severe NIMBYism at this point. It's incredibly hard to even build new power lines right now. Try a highly combustible, very leaky gas.

2 it's far cheaper to just strip H2 from natural gas, which releases carbon (unless you capture it, increasing cost), so not carbon free unless you force using electrolysis from renewable power sources

3 Electrolysis efficiency is ~70%, fuel cell efficiency is ~60%, so round trip efficiency is <50%. Much more waste than a battery (~80%). You're both using essentially the same electricity to create the power, but hydrogen is wasting more of it, so will necessarily be more expensive

4 in vehicles, fuel cells end up charging the battery toi power the motor anyway, so the energy loss from the battery is a wash

The one thing they have is range and speed to refuel, but as batteries get cheaper and better that will be minimized before H2 gets big enough to take over.

There's lots of big companies with smart people who are still pushing for this so hopefully they know what they are doing (mostly in Japan it seems)

Possibly a bit off topic,but why do we charge the batteries at stations rather than switching them with full ones?

probably because we park our cars, instead of giving them away when we reach our destination, and getting one when we need to go again.

Have we figured out a good way to store Hydrogen that avoids leakage? I've heard that even thick-walled stainless steel vessels can leak ~1% a day.

Yeah, you coat the cell interior with platinum. Adds significantly to the cost and complexity of production though.

and use platinum in the fuel cells. the real-world problems are pretty obvious though - Pt is worth stealing and it's expensive 'cause there aint that much of it so you can't expect to use 100x as much as now and not expect the price to change. FC's are niche. Batteries won.

I guess storage tech is optional for auto and heavy industry - you can use diesel engines or whatever. For smartphones and the like though there is not much option apart from developing batteries.

It would really be something if that miniature nuclear reactor NASA tested ended up being viable for cars, realizing one of the dreams from the early nuclear age.

Given that even a small reactor still requires considerable shielding, generates waste that could be used for nuclear proliferation (if ammassed), and emits harmful radiation, I would say chances of a nuclear car for the every man are slim to none.

There's that, but on the other hand, small gasoline vapor explosions are quite harmful and require considerable shielding, and generate waste that is destroying our ecosystem.

The nuclear waste problem seems to be not so severe in the age where everything is tracked every second; and it doesn't need to be solved completely - just raise the cost of (illegal) waste extraction to be considerably higher than getting it from alternative sources, and you're set.

Yeah, but we are talking about thousands of small reactors driving along highways... that will never scale.

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 because it scaled up so well and was old tech. Fuel cells, too, seems to fall more into the backup/spot generation/remote generation+NG access niches.

Looking on the bright side, anything that drives Li efficiency/density research is probably a very good thing.

> it's a fairly energetic explosion

So is a lithium battery explosion. So is a gasoline explosion. So is a flour mill explosion. So is a wind turbine explosion.

Energy is energy, and losing control of energy is never great, no matter where it comes from. So while I catch your meaning, it might be better to phrase it with respect to how controllable that energy is.

From what I know of flywheel storage, the problem mostly comes down to keeping the wheel from coming apart, and containing it when it does. The nice thing about using flywheels for grid storage is that you can bury them and make them large. The earth contains your explosion risk and the lack of jostling means that your bearings don't need to take as much stress and limits that failure risk.

I would disagree with you slightly. Energy is not totally fungible. I can punch you in the face or shoot you with a gamma ray (edit: though of course, I would never do either), and it would have very different effects, potentially. Same for a fastball vs a small caliber weapon. Heat, light, and kinetic energy are important distinctions - particularly when you have a bunch of 30k flywheels in close proximity and one of them catastrophically fails. Now, I know that's the first thing someone would think about deploying a bunch of them and they would take precautions. Li batteries are less kinetic and more thermal and that's a bit easier to manage/less likely to cascade.

I thought the trend in flywheels was magnetic suspension and removing mechanical linkages? Admittedly I haven't kept up.

> that's a bit easier to manage/less likely to cascade.

What gives you that impression? Seems to me that it explodes if you contain it, and if you don't contain it, it can spout jets of thermal energy at virtually any angle. With flywheels you need to arrest it in bulk heavy objects that don't tend to sustain fire. That seems a lot simpler to me.

The bigger problems with flywheels are cost of manufacture and (depending on the technology used) efficiency for overnight storage.

> I thought the trend in flywheels was magnetic suspension and removing mechanical linkages? Admittedly I haven't kept up.

IIRC flywheels with limited motion gimbals (to reduce the tolerances on the wheel) are becoming more popular, still magnetic bearings.

What gives you that impression?

Insulation is cheap, effective, and very compact. And it's easy to transfer heat quickly, also (either via injecting lots of cold extinguisher or flush lots of hot oxidizing gas)?

Cool, thanks for the update on flywheels. I ... am not trying to create a false dilemna, here. Fuel cells for stranded methane deposits are great. Flywheels have outstanding responsiveness and energy density. Li / compressed air / pumped water et al scale well. They all fit into a more resilient grid storage strategy that permits a transition to periodic sources of input from non-renewable base load.

Except we've had a carbon free baseload tech for decades now.

It's kind of bizarre how nuclear had achieved a sort of counterculture renaissance. It has many, many drawbacks too numerous to go into here that are technical and sociological in nature.

And anyway, you tried to be too clever. I said "non-renewable" and not "carbon free" just to avoid this conversation. Unless you can start synthesizing utility grade quantities of well-behaved fissile material at a net energy surplus then it's not renewable even if we have decades/centuries of supply.

> Unless you can start synthesizing utility grade quantities of well-behaved fissile material at a net energy surplus then it's not renewable even if we have decades/centuries of supply.

Someday, even the Sun will run out of fuel. In the long run, we are all dead - unless someone figures out how to reverse entropy.


We still have 5 billion years to figure that out. Until then we should probably stick to worrying about energy problems of today.

edit: Love reading that short story, it somehow never gets old.

We don't need billions of years though, "hundreds of years" of fuel is hopefully long enough for us to figure out the tech that will get us through the next couple hundred years after that. And nuclear is fine for that. We're not talking kicking the can down the road by 20 years, we're talking hundreds or perhaps thousands of years of fuel.

Humans are plenty smart and the people of tomorrow will be better equipped to solve tomorrow's problems.

It's not even a matter of "ripping off a band aid" and paneling up the planet - solar panels aren't going to last hundreds of years either, we will be lucky to get 30 years out of them. Can we make more, sure, but we could also do nuclear and then make solar panels in 500 years when we're running out of fuel.

The biggest problems are that we need to come up with the political will to reprocess waste (extracting additional usable fuel and compacting the amount of true waste that needs to be disposed of) and then dispose of it in a proper repository rather than just letting it sit around on-site indefinitely Fukushima-style.

If you listen very hard, you can hear my eyes rolling through your computer. But I enjoyed reading the story and begrudgingly admire your pedantry on the matter!

Some animes have theorized a different method for reversing entropy. Like nuclear fission, we may be able to release a tremendous amount of energy by smashing the dreams of young girls and harnessing the power of their tears.


It's not renewable, but it is closer to carbon-neutral than fossil fuels. Advocates generally push it as a stopgap measure for climate change, after we transition away from baseload coal and before we transition to baseload renewables.

Batteries don't like insulation, in fact preferring active cooling.

Which is itself a good thermal-runaway damper, to speak to the second sentence of your second paragraph.

>So is a flour mill explosion

Having witnesses a corn silo explosion, I was unprepared for the ferocity of that ignition.

>So is a wind turbine explosion

Off to YouTube...

The Hornslet collapse[1] is the one I was thinking about in particular. It is especially daunting now that I've toured a site for myself. Those things are huge!

[1] https://en.wikipedia.org/wiki/Hornslet_wind-turbine_collapse

Ever seen a tire come off of a semi?

Assuming the flywheel keeps its integrity it's much harder to predict the "blast radius" of where that thing is going to go.

Are buried flywheels used in practice? Is the flywheel axis aligned with the Earth rotation axis? Do they pull a vacuum around it?

Yes, in cases, to the first two. Containment is frequently buried concrete vaults.

Not AFAIK for the last, though precessional torque bearing load is a nontrivial consideration.

Thanks for this response. My untrained guess is that precessional torque would cause more loss than air friction, assuming the wheel is cleanly symmetric (ex. no bolt heads sticking out). It's fascinating how many paths there are to push something up various kinds of potential energy gradient in a way that it mostly stays there by itself but is still available to us to access in a controllable way.

Wikipedia claims flywheel loss rate circa 2013 of 5% per day. https://en.wikipedia.org/wiki/Flywheel_storage_power_system

That compares to recent estimates of Tesla li-ion loss rates at under 5% per month -- 0.16% per day.

Amber Kinetics is one company building fixed flywheel storage products. http://amberkinetics.com/

They have one 32 kWh, 5-ton, 98% steel flywheel installation on Oahu; pictures here: http://amberkinetics.com/hawaiian-electric-and-amber-kinetic...

Frictionaal losses are part of the consideration, but just plain bearing wear is a bigger one AFAIU.

Angular momentum in 100 kWh - multi MWh rotational systems is large.

Also flywheels don't give off noxious fumes during failure.

For now. If you want to use one for long term energy storage, though, you're going to need to invent some kind of room temperature superconductor and frictionless surfaces. Who knows whether those would be noxious or not.

Why? Magnetic bearings and copper work just fine...

Are you sure? Metal fumes and vaporized epoxies are usually pretty toxic.

...or during production (relatively speaking).

> So is a lithium battery explosion. So is a gasoline explosion. So is a flour mill explosion. So is a wind turbine explosion.

No, they're not all the same.

Compressed air, flywheel, flour mill - very dramatic events.

Lithium battery - much more mild, typically.

Gasoline - it depends.

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.

There’s a kind of Moore’s law in batteries, but the multiplier looks more like inflation than 2x.

Any tech that falls outside of the growth curve seems to run into issues with production or cost that delay it until it fits under the curve. Something cheaper and easier gets picked first.

The first modern EVs had lead acid batteries. More sophisticated than your starter battery, sure, but lead acid all the same. Which is why Tesla was a big deal. We talked about LiPo for something like fifteen years before it showed up in consumer electronics, and then they started catching on fire.

All of this stuff is painfully slow. The big story in EVs is how crazy efficient the motors can get. A company I used to follow (whose name is escaping me now) had a motor that was 95% efficient in its sweet spot. They had scaled up the design to 100 HP.

Yeah electric motor efficiency is awesome. Back in 2005 I had a film-canister sized motor capable of 300W at 90% efficiency, and magnets and motor design have just improved since then.

Not only does materials overall matter little, but Lithium is also super cheap compared to the other materials in the batteries. There's a lot more of Nickel in a Li-Ion battery and it's much more expensive per volume and weight as well.

The batteries would be called Nickel-Carbon or something like that rather than Lithium-anything, if they were named by the amounts or costs of materials in them.

Why can’t we bury flywheels to protect from any explosions?

I've seen utility installations done like this. More expensive but safer.

Well yeah you can bury anything to keep it safe, but at what cost?

The utility flywheel installations I'm aware of are underground. More cost, but safer.

I suspect large-scale fixed installations are more likely to end up using some kind of flow battery:


The big advantage there is independent scaling: peak discharge is tied to the total membrane area / pumping capability while capacity is tied to the amount of reactants that can be stored.

I'm pretty excited about the potential benefits of flow batteries. Hopefully they can get the tech to work economically for grid storage.

In a sense then you could say it's the Javascript of energy storage.

Not the best on technical merits alone, but good enough along with a massive force of investment and wide adoption.

I think the surname of John B. Goodenough, one of the early Li-ion pioneers, is apt for the status of the technology.

I'll be damned, this wasn't a troll. Today I learned...


Just yesterday I was talking to my friend regarding this. The key idea is, humans are really good at driving the price down to bare material cost via agressive production line automation. For e.g. without all the automation including subpart a single phone with all the technology would easily cost upwards of billion. So comparing ANY technology regarding their future prospects, we can easily deduct that which ever can be made fully automatically in production line will thrive in the end. ( Compare solar cell with all other renewable technology. Sooner or later energy produced by solar cell will bypass all other combined by tenfold or more.)

> are really good at driving the price down to bare material cost via aggressive production line automation

I've noticed this with steel products and plastics.

Brings up one advantage batteries have, they are small. That you need to make a trillion of them works directly towards the cost being a small percentage over material and energy inputs.

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.

I toured a datacenter 5 years ago or so - and yes, they had a big flywheel for temporary power loses (until they could get the generators running)

That's only if they don't /cant run the entire DC of battery -whilst the gensets come online this is how telco exchanges / central offices work and important ones may have power supplied via different routes.

Some DCs do, but the need to keep them spinning 24/7/365 is a big maintenance issue, so given the advances in battery tech, I'd assume batteries would supplant flywheels for cost and safety reasons.

> but the need to keep them spinning 24/7/365 is a big maintenance issue

So is keeping batteries up to date. Many a failure has been attributed to stuff like:

- batteries gone bad without anyone noticing over the years (lack of acid, crystallization, loose contacts, dust in cooling components, ...)

- switch-over between grid and battery inverters fails somewhere

- some part of the inverters fail when they're idling for years and then have to go into full load suddenly

A huge flywheel only needs bearing lubrication, that's it.

For the most part, but every few years the bearings will need replacement. This means shutting the entire thing off and dismantling it for several hours. For redundancy, you therefore need multiple flywheels to cover for the maintenance periods.

Batteries can and indeed do go bad without warning, but current sophisticated UPS monitoring systems are able to detect failures, track battery ages and raise alerts (whether anyone actually acts on those alerts or not is another matter...). I've also found that lead-acid batteries last longest as long as there is some amount of power continuously trickling through them - I have an APC UPS at home with its original batteries from 2010, and they still provide ~1h of runtime at 20% load. And with most DC-grade UPSen, batteries can be replaced in situ without powering the device or any connected equipment off.

As of about 10 years ago our data centers always had 1 out of 4 generators configured with a big M/G flywheel on the output shaft. The flywheel momentum guaranteed generator start, I don't know the latency but it was on the order of a handful of cycles.

Some of them do, but the overhead is ridiculous. I don't have the data in mind, but I think that the NoBreak brand consumes 20kW+ just idling. It's ridiculous

Only some of them have flywheels. The large telco datacenter I visited had huge pallets of batteries to cover the time needed for the diesel generator to start.

Might be more a telco thing as they tend to regard serious outrages as a one every one or two generations as just about acceptable.

There is still one more possible alternative, if only we can get the physics to work: room temperature super conduction. That - if it ever comes to fruit - is going to cause a whole pile of revolutions and unlike most other ideas that rest upon unobtanium actually has a chance of success.

How would room temperature super conduction be used for energy storage?

Or would it just make all of the other technologies much more efficient?

Energy storage in superconducting loops. This is done on a small scale already for ride-through and power stabilization purposes but it is expensive due to the non-room temperature super conducting technology used which requires cooling down the superconductor.

Flow batteries are looking pretty good. Costs are coming down, and the very high (some say unlimited) cycle life could give an advantage over Li-ion for stationary applications.

On the other hand, used Li-ion from electric vehicles could be so widely available that they also win for stationary storage.

Interesting times.

My concern with batteries is we're so gung ho on producing these, we haven't stopped to consider the environmental impact from the manufacturing process or the incredible task of recycling these once they've outlived their usefulness.

It reminds me a lot of when people pushed plastic for everything in order to save the trees and reduce paper consumption. Some 40 years later, we're now trying to get off plastic and dealing with massive environmental issues surrounding nearly every kind of plastic.

>we haven't stopped to consider the environmental impact

We have. We've painstakingly analysed the energy and material inputs and the pollution outputs of the entire lifecycle of a lithium battery pack. After considering all these factors, lithium batteries remain an attractive energy storage option.


>the incredible task of recycling these once they've outlived their usefulness

Recycling lithium battery packs is complex and hazardous, but no more so than a multitude of other industrial processes. There is already substantial recycling capacity, thanks in part to the EU's WEEE directive. Using existing technologies, only 1% of the pack mass goes to landfill. We can't yet recover all of the lithium in a useful form, but we can recover most of the cobalt.


Back in the late 1800s, city planners met to try to come up with some plan for dealing with "the manure problem". Large cities couldn't handle the amount of manure produced by the horses in the city. They ended the meeting early, because they couldn't come up with any sort of plan.

Then cars came along and they were all like "Yay! The pollution problem is solved!"

I too wonder what the impact of so many lithium batteries is going to be. I mean, I know they are saying that they are extremely recyclable, and I hope that's true. But I wonder what the unintended consequences of this switch is going to be.

We can look at the current (used) battery market, the disposable Duracell thingies and such. I think there's a good recycling program for them, but even so, part of used batteries end up getting lost and in landfills and such.

(That's the silicon valley clip explaining the London manure problem being solved by the replacement of horses with cars.)

Maybe it's just me, but not a fan of bare links unless the URL is descriptive.

Not economical to recycle Lithium right now.

Recycled lithium is as much as five times the cost of lithium produced from the least costly brine based process. It is not competitive for recycling companies to extract lithium from slag, or competitive for the OEMs to buy at higher price points from recycling companies. Though lithium is 100% recyclable, currently, recycled lithium reports to the slag and is currently used for non-automotive purposes, such as construction, or sold in the open-markets. However, with the increasing number of EVs entering the market in the future and with a significant supply crunch, recycling is expected to be an important factor for consideration in effective material supply for battery production.

Closed loop recycling, where the recycled materials are sold back to OEMs, is likely to help against potential price fluctuation of metals or compounds. EV battery recycling is expected to play a significant part of the value chain by 2016 when large quantities of EV batteries will come through the waste stream for recycling.


This guy actually goes to a lithium "mine" in the middle of the desert...


Do you think it’s better or worse than the initial mining?

> 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 something that ran my house all night, I'd need a storage tank larger than said house.

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.

On the other hand, flywheels can be easily buried underground, and easily contained. The max power of a flywheel is known, so it's just a matter of putting enough concrete between humans and flywheel, a straightforward and inexpensive engineering problem. And unlike compressed air, the containment isn't under constant, wearing pressure.

You can bury the air tanks too and avoid most of the danger, but that's expensive and makes them harder to maintain. The big advantage of flywheels is that when they fail you know the energy will be discharged in a particular plane. You can orient them such that nothing vital is in that plane (like your house!). With compressed air all bets are off.

SCUBA tanks have a "burst-disk" or a weaker part of the tank that is designed to fail first, rather than the whole thing exploding and launching shrapnel. It's still violent and can throw some shrapnel, but it's much less. Also when SCUBA shops fill tanks they usually put them into a container that would somewhat contain that.

I imagine something similar could be done. It's not like there are zero safety mechanisms with compressed air.

A berm would split the difference for cost and maintenance.

Not necessarily, 1.3MJ (360 Wh; but screw that unit) of diesel isn't much of an explosive under normal circumstances. It really depends on the maximum power output under normal operation, and whether it can occur uncontrollably.

Energy density and release rate tend to have inverse relations, for a given energy mechanism.

TNT has about 1/10 the energy density of petrol or diesel. Capacitors have lower capacities than batteries.

People say that but searching youtube for exploding lithium ion batteries they seem to make fairly lame bombs. More some flames come out maybe a foot and then they burn eg https://youtu.be/SMy2_qNO2Y0?t=1m57s

I'm not sure they ever explode in a bomb like way?

Batteries don't explode in anywhere near the same fashion as an air tank, but they do include the added complication of adding a huge conflagration to the mix. So your house is burnt down instead of shattered and scattered all over the neighborhood.

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.

... and they too can be buried. Seems a bit more attractive than compressed air.

Not really. A good bomb has high velocity. Lots of high energy storage methods are slow reacting.

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

No different than people who have LP tanks outside their homes. Or fuel oil tanks buried in their yards. Or coal bins in their basements. Or natural gas lines coming their house. Or pretty much any other storage method except a dam for your water wheel, but even that can burst and flood your home.

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.

Water is pressurized. The pressure is a function of gravity and depth, but that is still a lot of pressure.

my english is flawed, I was trying to say that. Water is not pressurized but feel scarier than air for most people, so they go care free around compressed gases.

Water is pressurized. However, it is not compressed. That's an important distinction.

I'm fuzzy and since water is incompressible, "pressure" may not have the same meaning on water than on other substance

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.

Failed water lines can ruin your house. Failure of a compressed air vessel of sufficient size could turn your house into shrapnel flying fast enough to endanger your neighbors.

I thought this too, but read the rest of the article.

Spoiler alert: State of the art is 30x better

I picture Rick Moranis operating a large space-based vacuum cleaner.

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.

There are clubs and people all over the United States (often in rural areas) dedicated to building home-made steam powered machines and vehicles.

Unfortunately, these real-life steampunks (not cosplay kids) usually also would rather spend time working on their projects and not documenting them, so there's not very much on the internet compared with the number of people active in the hobby.

Keep an eye out at county fairs and small town carnivals and rodeos. They usually show up.

> This would light a home for an hour, with LED bulbs and careful usage.

Do you have the equivalent of 50 LED bulbs (60W equivalent [1]) burning at a time? Do you consider that careful usage?

[1] https://www.amazon.com/Philips-Classic-Glass-Non-Dimmable-Li...

Depends on the tradeoff. The tl;dr of the article is that there's a tradeoff between pressure and efficiency. You can store at higher pressures in smaller vessels, but it's much less efficient. Low pressure (larger vessels) can be extremely efficient. In between, there are hacks to increase efficiency using heat exchangers and the like.

Beyond that, this is being pushed in the article as a rural/off-grid approach. For urban residential, it makes a lot more sense to centralize storage and run houses off a regular grid, than to try to make each house an independent entity.

In the medium run, we need to shift the grid itself from the current baseline+peak model to a solar+storage model (rolling wind into this), with distributed metering on the storage grid. Capture solar/wind power when the sun shines and the wind blows, and sell it when consumption outstrips supply, with pricing set dynamically on a distributed network.

Once you have that, for on-grid purposes, we'll probably see a diverse world of storage - car batteries, compressed air, industrial battery sites, water storage, thermal storage, etc.

An LED light bulb uses 11 watts. You must be lighting your home with 33 bulbs if that only lasts you an hour. If you only use 4 bulbs, that will last over 8 hours.

My home as got many 3W led bulbs for small lamps. 7W is the norm

My four lb lawnmower batter stores 120wh. Quite the contrast.

An added benefit is you could power your air-tools with something like this without having to convert to electrical energy. As a former off-gridder, that's actually a really big plus.

Another non conventional way to store energy is using gravity power modules (example: http://www.gravitypower.net/)

Storing hydrogen from electrolysis via solar panels also sounds interesting. Basically once your batteries are charged you start making hydrogen.

Similar to those gravity power modules: a company called Ares (https://www.aresnorthamerica.com/) is trying to use much smaller concrete 'cars' on rails to store energy. Not sure of the status of it but it looked promising to me.

The direct use of compressed air is interesting. Taking it to the extreme, you could have compressed air as your primary utility piped through your home, and have appliances that run off compressed air. Refrigeration cycle is compression based anyway for example. You would still need some electricity for control circuits for example, but you might be able to keep the heavy lifting air-based.

In the midwest, running compressed air through a home is called amish electricity. They do use it for many things. Ive seen air-powered blenders. (Air power is a big thing for woodworking and so its use in the home too is no suprise.)

I had no idea these existed, I want these when I move back off-grid. https://www.cottagecraftworks.com/kitchen-food-prep/non-elec...

It is functional but has many issues. Water/condensation in the lines is a big deal in winter. Running pipes in walls makes leak detection difficult. They are all also very very loud.

I looked at the Ares 'team page' and I personally know the CEO of that company, but I didn't know he was working with that company. super random.

Your refrigeration example is interesting - now I'm curious if there's any refrigerators on the market that can power the compressor via compressed air intake (so it would still use closed-loop refrigerant, but the compressor would use air instead of electricity)

Nah, there's water-based computers, there could be compressed air computers.

Picturing the different logic gates running on compressed air is a hoot.

You should check out Ted Chiang’s story “Exhalation.”

That’s the one. I have no special insight into the legality, but it looks legitimate to me.

I assume you'd still need electricity for things like lighting, right? (I can't think of a way to directly generate light from air pressure without converting it to electricity first.)

Generate heat through friction ... okay, that's crazy. But fire would work (& could be controlled through air flow).

My knowledge of physics is very basic and practical engineering is zero, but storing hydrogen in compressed tanks always seem very impractical to me. It's the most freaking volatile element in the universe. And atomic hydrogen reacts with pretty much anything. Leakage and corrosion.

From my armchair perspective, storying it in chemical bonds (like nature does) makes a lot more sense.

The bigger deal is how easily hydrogen leaks. H2 is small enough to squeeze through tiny holes in rubber or plastic gaskets. It's fine in a car, but keeping it in big tanks for months is something else. At least when it leaks it floats away rather than collect on the floor looking for a reason to ignite.

And, Hydrogen embrittlement makes the tanks fail prematurely. (http://www.corrosionclinic.com/types_of_corrosion/hydrogen_e...)

> And atomic hydrogen reacts with pretty much anything.

But we don't store atomic hydrogen; we store molecular hydrogen (H2).

But I would imagine a small percetage at least would break into Atomic Hydrogen, H+, H-, right? And those things are nasty.

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.

I wouldn't recommend drinking gasoline or diesel either, but cars seem to work pretty well with it.

Gasoline and diesel won't leave you permanently blind on a spoonful. Methanol is significantly more poisonous. It also burns with a colorless flame, which has been a problem in auto racing, where it is sometimes used.

Some Amish communities have a cottage industry around air powered appliances because the rules state that you can't use electricity for frivolous uses, but people still want a blender or mixer or something.

In practice I think that adding the fittings and the long hose from the tank to your work area probably makes this somewhat impractical, but it's a cute idea.

The US government looks into this at a national level. Doesn’t look like it went too well though. https://arpa-e.energy.gov/?q=slick-sheet-project/fuel-free-c...

The article focuses on a small-scale approach that has its own challenges but is different from what your document discusses.

Right. I thought it would be interesting to see it there were experimental findings on a large scale. For example put a massive solar array in the US SW. Transport the power across the country and store excess in geologically stable areas. Those storage facilities then act as power plants at night or if there were delays in sunlight.

A lot of modern automation works this way. Conveyance systems with pop-up diverts make this satisfying hiss noise as they do their work- all powered by compressed air coming from a huge tank in the parking lot.

At ETH Zurich, there is a project aiming at scaling compressed air storage to MWhs. [1]

The interesting part is that they are trying to make the storage adiabatic, i.e., they store the heat that is generated while compressing the air in a phase change material (i.e., a material that will become liquid when hot, since a lot of energy can be stored in phase transitions) and get the heat back to warm up the cold expanding gas on decompression.

The issue is that even with the phase change storage, heat will dissipate into the rock within a couple of days, making the whole process inefficient for long-term storage.

[1] https://www.ethz.ch/content/specialinterest/mavt/energy-tech...

Sounds like a promosing solution for averaging out daily fluctuations though.

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 you.

They didn't forget - it's addressed in detail. They are advocating "small scale"

The low efficiency is mainly since air heats up during compression. This waste heat, which holds a large share of the energy input, is dumped into the atmosphere. A related problem is that air cools down when it is decompressed, lowering electricity production and possibly freezing the water vapour in the air. To avoid this, large-scale CAES plants heat the air prior to expansion using natural gas fuel, which further deteriorates the system efficiency and makes renewable energy storage dependent on fossil fuels.

Going "small scale" does not solve the heat problem unfortunately. If it does then the authors did not mention it. All they mentioned is how large scale plants deal with the problem.

Come on dude...

Small-scale compressed air energy storage systems with high air pressures turn the inefficiency of compression and expansion into an advantage. While large-scale AA-CAES aims to recover the heat of compression with the aim of maximizing electricity production, these small-scale systems take advantage of the temperature differences to allow trigeneration of electrical, heating and cooling power.

And then also goes in to detail about small scale iso-thermal setups that have negligible thermal losses. Apparently "author did not mention" actually means "I did not read the article".

Did you read the article? All of that is in like the first paragraph.

What the parent said was still useful I think to people who might not know this particular trope throughout the industry.

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.

I worked for a company that had old underground mines and a power company used them to fill with compressed air when energy was cheap and then release and generate electricity when it is more expensive. My company got a cut.

I used to have friends in the oil industry in the 90's, and I remember them talking about the industry maybe using dried up wells the same way.

I don't know if it ever became anything, though.

As much as people consider the oil industry a bunch of evildoers, it is always at the forefront of the absolute latest in tech. Hard problems + money does that.


Reminds me of this project from a few years ago: a two-person hot-rod driven at up to 20mph by a 256-cylinder compressed-air engine, constructed out of Lego...


Volvo diesel cars avoid turbo lag by storing compressed air. Not very relevant but interesting nevertheless https://www.roadandtrack.com/new-cars/car-technology/news/a2...

And Bosch uses compressed air to keep motorcycles on track (experimental tech) https://www.youtube.com/watch?v=3ERowrZJyfw

If you could point them backwards for a little extra thrust ...

Modern supersports are pushing ~200hp, no need for the extra weight that would generate the thrust.

The Spitfire actually used the jet propulsion of the rearward facing exhaust for an extra few horsepower. Many piston engine aircraft do this.

ABS braking does the opposite: a vacuum is stored that's used to release the brakes in short bursts.

Modern (post 1990-something) ABS has its own pump.

Air brakes on trucks run in reverse. Compressed air releases spring pressure therefore releasing the brake.

> Air brakes on trucks run in reverse. Compressed air releases spring pressure therefore releasing the brake.

I think pneumatic brakes almost universally work this way, because it's fail-safe w.r.t. line leaks. E.g. in trains the main air line is for powering pneumatics as well as releasing brakes; at nominal pressure (8-10 bar iirc) the brakes are released, at lowered pressure (3-5 bar) the brakes are fully applied. If the line ruptures or the train splits all brakes across the train are fully applied.

So, I seem to recall that the Amish sometimes use something like this to power their tools. Source: my own unreliable memory of an article I read somewhere. Anybody more knowledgeable out there able to confirm or disfirm?

There's an article about it at http://www.amishnews.com/amisharticles/amish_tech.htm which references some books that might describe it in more detail.

> Almost any electrical appliance can be adapted to work off of alternate power, such as compressed air. Some Amish women have been using compressed air to power blenders in the kitchen for years. In one house, compressed air powers a water pump, sewing and washing machines, and drills and saws in the shop. Some Amish businesses have as their specialty adapting such appliances so they can be powered by compressed air.

Not a hard confirm, but I stood there marveling at the pneumatic ceiling fans in an Amish bakery once. Each one had a little oscillating engine and some plumbing for the compressed air.

While I was researching offgrid options a few years back I came across this site and their windmill for compressed air: https://www.cottagecraftworks.com/wind-compressor-wind-drive...

They also have quite a few interesting compressed air kitchen appliances...such as mixers, grain mills.

Maybe the article was 'Amish Hackers' by Kevin Kelly?

[0] http://kk.org/thetechnium/amish-hackers-a/

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.

Propane tanks seem like great bombs too, but they are really great for backyard grills. Solid engineering can make these things safe.

Physics is physics matter how you cut it.

A compressed air tank is arguably less of a bomb than the battery under your feet in a Tesla and the cleanup is much better.

Compressed air tank failures do not result in instant fire. Most failures take the form of leaks. Catastrophic failures of properly designed pressure vessels operating at their intended pressure are basically nonexistent because a damaged pressure vessel will usually fail by leaking at the point of damage.

Lithium batteries in a Tesla (and just about everything else consumer-grade) are designed to burn rather than explode - they can produce an impressive jet of flame, but this is contained and safely vented from the battery vessel. Just like gasoline-powered cars, they catch fire, but don't (usually) go boom. They are also capable of failing in a controlled manner - lithium-polymer cells are contained in sealed pouches which expand during failure as the gas pressure rises. So long as the pouch is not breached, the battery is a very low fire risk, and is akin to a leak in an air-powered system - a low-energy release that does not harm people around it.

Compressed air, however, does explode out of any weakness in its fittings, often with no warning. Catastrophic failure of a weak joint, coupled with a pressure difference of several atmospheres, can turn any ejected fittings into artillery shells. There's plenty of videos of air compressor explosions on YouTube. Yes, this is considerably rarer than a lithium battery fire, but don't forget that lithium batteries are relatively new to the scene. Compressed air has been in use for hundreds of years and the dangers, despite being understood, are still present. A lot of them stem from human overconfidence, and the attitude of 'eh, one more bar can't hurt, can it?' Even a small workshop compressor operating at less than 10 bars can cause life-changing injuries to anyone present should it fail. I'd argue cleanup from these types of failures are much, much messier than lithium fires.

The comparison to lithium batteries is pretty accurate because unlike gasoline, a spark is not necessary to start the fire. However, a lithium battery fire can generally be spotted by temperature rises before it becomes dangerous. Failure of a pressure vessel is much harder to predict. Just a tiny manufacturing defect in a square-centimetre of a pressure vessel can create a weak spot that'll be the first place to fail as it comes under operating pressure, or cycled repeatedly.

Don't get me wrong, I'm interested in off-the-grid living and had not considered compressed air as a power source until reading this, but I do feel the article skips over the safety aspect of compressed air. There's a reason many of the fittings are only sold to industries - used improperly by amateurs, the pressures they're discussing could be fatal if something goes wrong. My advice to anyone reading this article is to fully understand the dangers of compressed air before building something like this.

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...

You probably keep multiple gallons of gasoline nearby, tho.

Air is far more explosive than gasoline. Gasoline is practically docile compared to the equivalent energy stored as compressed air. When a vessel of compressed air ruptures, it almost instantaneously decimates everything around it with a powerful shockwave. Think of a popping balloon, but scaled up 10000x. You think a hot water heater is bad? Just imagine the entire house being demolished in a second.

Gasoline, on the other hands, just burns in a hot concentrated fire. It takes entire minutes to kill that which is nearby.

Gasoline has to be mixed in a perfect ratio with air to be dangerous and explode. A simple leak from that enormous amount of air storage could be catastrophic. A leak of your gas tank and it just piddles out on the ground.

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

Not the same? Shoot a propane tank, it leaks. No oxygen in the tank.

There is very little outside compressed gas that can explode disastrously without oxygen. A tank of compressed gas is probably high up on the 'bomb in the house' category. Just under the water heater I suppose.

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.

Lightsail Energy tried and failed to bring this to market - not sure whether this can ultimately outperform Lithium Ion Batteries, which have all the pressure of the electronics industry behind them.

I feel like they have different applications so they're not necessarily competing. Obviously compressed air systems will never have the energy density of a battery, but they could be much more reliable. It also scales up really easily, and I think that's where the sweet spot is - I've heard of people sealing off caves to make giant air storage tanks for these projects.

"sealing off caves" - would love to see, or hear the facts. Specifically, about safety of the pressure "chamber".

https://caes.pnnl.gov/ - it's an interesting project. Apparently it's more like 'underground caverns' than caves.

I think it is more typically done with old mines. Natural caves are far more complex systems and there are environmental concerns.

you're right - it looks like the caverns being used for experimentation are the result of solution mining for salt.

The charge/discharge efficiency for compressed air is terrible since most of the energy gets wasted as heat. This plus the terrible volumetric energy storage density makes it a nonstarter for most applications.

I think the survival of this will be from them explicitly not trying to compete with batteries, but rather for a different market.

Its really interesting that they can get up to the efficiency of led acid batteries in applications for rural areas. I wonder if maintaining that large air tank is more difficult / costly than maintaining the batteries.

Its also interesting that we're only talking about 116 PSI - I'm guessing CFM is more important.

> A simulation for a stand-alone CAES aimed at unpowered rural areas, and which is connected to a solar PV system and used for lighting only, operates at a relatively low air pressure of 8 bar and obtains a round-trip efficiency of 60% -- comparable to the efficiency of lead-acid batteries. [7] 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”.

> "they do not require rare or toxic materials"

This benefit alone would make me hope for compressed air energy batteries to receive tons of funding, and become cost-competitive with other forms of batteries.

Also, consider that there are three important elements in a battery "economics":

1) Weight / energy density - how much energy can you store, per weight of the battery? Important for cars.

2) Volume / energy density - how much energy can you store, per volume of the battery? Important for cars as well.

3) Cost / energy stored - how much does it cost to store a unit of energy? This can also be divided into two elements: setup (e.g. the cost of producing the battery and deploying it) vs maintenance (how much does it cost to keep the battery alive, over the years?)

There are also other minor factors, such as reaction to environmental changes (e.g. temperatures, etc).

Peugeot is working on this for years but it got frozen last year: https://www.groupe-psa.com/en/newsroom/automotive-innovation...

An early design for the automobile ran on compressed (liquid!) air.


It might work for some applications, but in 120 years we haven't been able to make it work for cars, at least.

IIRC there are compressed air cars used in India. They aren't very good, but you get free air conditioning when they're moving and they're cheap, so they fit the market well.

I suggest anyone interested in the history of compressed air storage to also check out http://www.douglas-self.com/MUSEUM/LOCOLOCO/airloco/airloco....

There's also a few articles on the website about compressed air cars and city-wide infrastructure

> ... but in 120 years we haven't been able to make it work for cars...

Ok, but has anyone worked on the problem in the past 120 years?

https://www.mdi.lu tried to make compressed air two person urban cars (Air Pod) but with the main inventor and visionary now dead I don't know if there is much momentum left...

Has worked fine for compressed-air locomotives in e.g. mines.

I have argued unsuccessfully in the past that this technique would be an excellent data center strategy. That is especially true if you had your data center near the Columbia river and its near constant winds.

Using wind power to compress into high pressure tanks, then when you need extra energy you pull it out and pipe the air expansion pipes through heat exchanges in the data center. That way heat from the data center goes to warming up the air (better efficiency when you feed it to the turbines) and it cools the data center which is part of what one might use the energy for in the first place.

If you put the air expansion pipes in a conveniently located source of water you could chill that water to freezing.

If the entire contents of the data center were pressurized, would it increase the efficiency of air cooling? (Denser air -> more heat capacity?)

It would certainly increase the heat capacity of the air.

Compressing air into the data center however would not be a win. During compression the air gets hot. In the system that I was pushing the compressed air tanks were outside in the wind so that they were benefiting from the cooling effects of the same wind that was pumping air into them.

Good point. Could allow for low power cooling (once pressurized, venting pressure would drop temperature of the contents without added energy), but probably not worth the trouble.

Seems like a technology that has narrow usecases like where cogeneration is possible. I guess large city's and industrial applications which can use the waste products of the thermal cycle.

For alternatives, my money in the long run is on molten salt batteries [1] for large scale. Technology also has benefit of increased industry knowledge of how to utilize molten salts safely which will benefit LFTR research.

(1) http://news.mit.edu/2018/metal-mesh-membrane-rechargeable-ba...

I would just love a couple of small vertical turbines slowly pumping up my underground storage. I live in a sometimes violent wind location, often just when I could use the energy to run the furnace. I could see easily augering 10-15ft holes , dropping in vertically buried, used, composite tanks bought off Ebay, run at a fraction of their max pressure. Easily adding more to increase capacity, as needed. Yes a little pock-pock noise of the pistons and check valves, but it would only happen when wind blows. Though, a tank failure may mean retrieving it off the roof.

This makes some sense in poor tropical nations, where rigging a mechanical system like this is quite feasible locally (instead of having to import advanced lithium batteries, along with usually exorbitant import duties etc), and some of the "inefficiency" can be used to heat, and particularly, cool spaces.

It also makes sense for oceanic wind turbines, which can use periods of high wind vs low demand to pump air into large under-sea air storage bags, using the sea as free cooling/heating towards isothermal operation.

Or, don’t ditch the batteries. They work fine.

The title of the article strikes me as one of those marketing titles possibly planted by a press release. Position the competing product as if it’s somehow bad. “Protein-free!”

I’m not buying it.

Also works for vehicles. Hydraulic hybrids capture 3x more of the braking energy.


There's a retrofit for garbage trucks that pays for itself in 2 years, or you can buy them new.


Joey Hess has been using his fridge for off-grid energy storage... With lots of data around what he's seeing. It's really interesting, and he still gets to keep his food cold.

EDIT: Not really used as a battery, but probably could be.


Isn't there a loss in efficiency due to heat? Compressing air heats it up, which is lost (this is the basic principle behind refrigeration, though it doesn't use air). And then there's the loss in converting this PE back into electricity. Are these losses less than what's lost in LiON cells?

Read the article they go into this in detail.

This reminds me of perri air from spaceballs


Also interesting is hydraulic energy storage. Any entrepreneurs want to take a shot with this system?


>Hydraulic energy storage systems store energy by compressing air similar to a battery storing energy in an electric circuit.

Wait, did you read the article? :)

Hydraulic systems and compressed air systems are usually regarded as separate things. Maybe the distinction is a bit arbitrary and the former can be regarded as a subset of the latter but there you go. edit: Google says hydraulic transmits power through fluid, compressed air through air/gas.

Pneumatic vs hydraulic is about compressible vs incompressible fluids. (Naturally, hydraulic oil is also a much better lubricator and an exceedingly superior sealant than oiled air).

Off-topic: one of my favourite Ted Chiang short stories - Exhalation[1] - is about compressed-air-based lifeforms.

1. http://www.lightspeedmagazine.com/fiction/exhalation/

> The low efficiency is mainly since air heats up during compression. This waste heat, which holds a large share of the energy input, is dumped into the atmosphere.

Wait... wait... I'm... not sure I believe the extend of this statement. If this isn't wrong it's certainly awkwardly worded.

It's interesting to see research done in this space but it's not even remotely practical yet. Their 410Wh system is more complex, five times larger, and has a much higher up front cost than an equivalent amount of lithium battery storage.

Highview claims to be able to do this at prices competitive with Lithium batteries. https://www.highviewpower.com/technology/

I'm not knowledgeable about any of this, but how does this compare to a Trompe? https://en.wikipedia.org/wiki/Trompe

When compressed air energy storage comes up, it is always worth remembering PV = nRT, the ideal gas law. And then remembering that things are not ideal.

Mechanical engineer here. The ideal gas approximation is plenty reasonable for the pressures and temperatures of interest here.


Silly question - could tires be used to do this? I mean, could one improvise a storage system via a stack of car tires?

Afaik, compressed air energy startups come and go since long time, this should be ok for use in enterprise though.

I always wanted to have an air compressor running every day on my otherwise quiet property.

How about steel springs? Rubber bands? Weights hoisted on cables?

I'd love to go nuclear ... charge your phone once a year?

Hold on... So if you take a Tesla, remove the batteries, remove the electro engine, and replace that with a trivial compressed air based pneumatic motor it would be more eco friendly, more powerful and have a higher autonomy ?

From https://en.wikipedia.org/wiki/Compressed_air_car#Disadvantag...

- A 2005 study demonstrated that cars running on lithium-ion batteries out-perform both compressed air and fuel cell vehicles more than threefold at the same speeds.

- A 2009 University of Berkeley Research Letter found that "Even under highly optimistic assumptions the compressed-air car is significantly less efficient than a battery electric vehicle and produces more greenhouse gas emissions than a conventional gas-powered car with a coal intensive power mix."

Unfortunately there are downsides, but compressed air vehicles are already a thing.



Guidelines | FAQ | Lists | API | Security | Legal | Apply to YC | Contact