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Air batteries!!!!! I love them. Thoughts?  RSS feed

 
Joshua Myrvaagnes
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what they are: compressed air energy storage--one can power 500 homes for an hour. Compress the air in daytime (with solar), decompress and power a turbine at night. Sort of like being a billionaire by day and a crime-fighter by night but almost completely different.

pluses: they don't have any icky chemicals or wear out very quickly (as lithium-ion batteries do, lead-acid [lead!])
it's 1800's technology, but optimized (they use the excess heat from compression and cooling factor from expansion)
carbon instead of steal for the casing
Danielle Fong is really smart--went to engineering school at 12, dropped out of nuclear fusion because she was uninterested in a solution that wouldn't be on the market till 2050, about 35 years too late. Clearly passionate about what she does.
90% efficiency claimed.
powers electrical appliances
potentially (??) could be used directly to cool fridges at night (i.e. the cooling effect directly, rather than transferring to electricity and back)
maybe hallakhic for use on the sabbath for religious Jews (it's not a fire or electricity directly, but a power source nonetheless--you could power a vacuum cleaner or a leaf blower, say, or maybe a blender. not sure if this might make women's lives easier in the orthodox community...potential)
funders include Bill Gates--so they have some cred ibilty in the public eye

minuses:
-not on the market yet
-need some complexity of manufacture to make the cooling/heating nozzles
-if it did explode somehow it would be quite destructive--200 atmospheres.
-it is electricitally filled up now, so not usable for the Amish. this would take some re-engineering to make it
not do-it-youreslf-able quite
funders include Bill Gates--I don't really feel so comfortable with billionaires who try to fight crime by day, potential interference.

thoughts?? anyone make a scaled-down diy version of this? could it work for a fridge overnight? compress it by using more low-tech methods, like boiling steam to push something ratcheted together and...? calling all rube gold bergs
 
Mike Cantrell
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Here's what Tom Murphy says about it.


Compressed Air
We could store energy in something akin to a spring by compressing air. A high-quality tank can store air at 200 atmospheres of pressure. If we make a big bedroom-sized tank in cylindrical form similar to the flywheel dimensions, it has a volume of 10 m³. The steel walls would have to be about 6 cm thick to withstand the stress, so that the tank would have a mass of approximately 12 tons. You did reinforce the floor, right?

We want to take a volume of air, V0, 200 times larger than our tank volume at atmospheric pressure (P0 = 105 Pa) and compress it to fit in the tank (adding two tons of mass!). If done slowly enough to maintain approximately constant temperature (several hours), the energy required is P0V0ln(P/P0), where ln() is the natural logarithm function. For our volume, this turns into 1 GJ, or almost 300 kWh—enough for 10 days of typical American electricity use. So we could get away with a smaller tank or simply charge it to a less extreme pressure.

The efficiency for compressing the air and later turning a turbine for electricity generation may be less than what one might find for a flywheel. The storage itself is not the hard part. I could go out today and get some lab-sized cylinders (~50 liters), which could store 1.5 kWh each—about like a golf-cart battery, although heavier and bulkier. But I would have a very difficult time arranging an efficient pumping and extraction/turbine system. If not for that, I would find compressed air to be an attractive system compared to batteries: minimal maintenance; no apparent cycle limitations, reasonably low-tech, and perfectly tolerant of remaining at low charge indefinitely.

Laboratories that frequently use compressed gas cylinders have strict safety protocols to prevent explosions from structural rupture due to mishandling. If houses across the land had high pressure vessels in various states of neglect/corrosion, we’d get the occasional boom. I might worry about having a gun in the house. But I’m guessing that house fires would still represent a bigger net threat.


Source:
http://physics.ucsd.edu/do-the-math/2011/09/got-storage-how-hard-can-it-be/#more-336
 
Joshua Myrvaagnes
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Thanks for posting that.

What would the weight be for a carbon fiber tank (what lightsail is using)?

I think the idea of scaling it down is a good one. It's either that or use one to power a bunch of houses in a neighborhood or a block.

Also, if you had a cheap-and-dirty turbine/compressor, and the thing could double as a cooling and heating supplement, it could be useful inside a house or just outside the house. (the nice thing about electricity is its portability, it can go through your insulated wall without compromising that, and you have choice about when you draw on the resource.

Aslo if I didn't say it before I think Danielle Fong is super-inspiring--going to engineering school at age 12 or something and then dropping out of nuclear fusion research seeing it as too slow to address the real problems, and choosing a simpler, low-tech focus and entrepreneurship to make a difference. That's a big step for an engineering-minded person to make.

Other thoughts?

Could this be made for battery-sized batteries too?? wouldn't it be nice to have a cell phone battery that didn't actually stop functioning well after the first month of use?
 
Joshua Myrvaagnes
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Also, the compression temperature and cooling issue, lightsail says they've solved that by injecting water in during compression so it can go faster and also reclaims that energy for useful purposes, in case that wasn't clear from my original post.

Personally, I see homesteaders written all over this thing, long before the utility companies would adopt it.

As for explosion, does carbon fiber corrode? what damages it?
 
Troy Rhodes
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Love the idea, still can't buy it. This has been tantalizing/close for decades. I'm beginning to think it's like fusion driven electricity "too cheap to meter". Always just a few years away...

 
Mike Cantrell
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Joshua Myrvaagnes wrote:Thanks for posting that.

What would the weight be for a carbon fiber tank (what lightsail is using)?


Carbon fiber composites are super light for their strength.

According to this vendor of carbon fiber tubes, their stuff weighs .065 lbs/cu in.

Steel weighs .2904 lbs/cu in..

Murphy's example bedroom-sized tank below, instead of weighing 24,000 lbs would weigh 5,371 lbs.

The material (before forming it into that enormous cylinder and having it delivered and installed), instead of costing $24,000, would cost... you better sit down while I do the math. I've dealt with carbon fiber a tad in the past, and it's exorbitant.

Ok, how about $4.66/ cu in. That gives you.... $385,059 for your bedroom-sized tank.



Joshua Myrvaagnes wrote:
As for explosion, does carbon fiber corrode? what damages it?


The key to understanding carbon fiber is to remember that it's effectively a superman version of fiberglass. We all understand glass pretty intuitively, and we can grasp the idea behind fiberglass- spin the glass into little fibers, then form them into sheets held together with epoxy or similar. Carbon fiber is just the same. It's little fibers, formed into sheets, held together with epoxy or similar.

Many binders are subject to degrading under UV exposure. You've seen old fiberglass boats. Depending on the application, carbon fiber composites can be built with different kinds of binder to be resistant to whatever they need to resist. And the carbon itself, very durable. Resists all kinds of things.
 
Steve Farmer
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You could take a bog standard 2KW workshop compressor and 2KW of bog standard solar panels. You would need no charge controllers just run the compressor when the sun shines and then link the compressors own tank up to empty gas bottles etc and then you have stored power available off the shelf now for a couple of grand.

In terms of applications, workshops run a multitude of tools from compressed air, almost all of which are concerned with converting potential energy in rotational movement. Once you have a rrotating spindle then you have the basis of industrial power sources.

This is somewhat a guess, but I think more energy goes into constructing a carbon or glass fibre tank than an equivalent steel one. The steel one will be heavier, but it will also not be flammable, unlike a glassfibre tank or even moreso a carbon fibre tank.
 
Rhys Firth
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I'm a SCUBA diver... I've handled SCUBA bottles, each 11 litre capacity bottle at 3000psi/200 Bar, has the explosive force of two hand grenades strapped to your back. You are simply exchanging Chemical (explosive) for Mechanical (compression).

NOT something I would be very comfortable with having in the back shed, 11 litre SCUBA bottles are fine 8000 litre (2M x 2M x 2M, bedroom sized) tanks? No thanks! ! SCUBA bottles need regular checks to ensure they maintain their integrity. Steel corrodes, Aluminum embrittles and cracks, Carbon is fearfully sensitive to structural integrity breaches, DON"T let your cat sharpen it's claws on your big azz tank!


If you have a property with a high point and water at a low point, FAR better would be a big tank or swimming pool on the high point and a 1/2" pipe up there from a solar driven pump and a 3" pipe down to a water turbine.
 
Joshua Myrvaagnes
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Ok, good thinking here.

I'm not clear what the "bog compressor" is, I'll have to google and see if I find out info.

The company, lightsail, is developing this for utility companies, and on that scale and with professional maintenance it seems to stand as good a chance as the grid in general--certainly outcompetes a nuclear power plant for safety in terms of the amount of damage that could happen in an earthquake or unexpected weather event. They'd be far enough way from where people live and where kitties scratch.

The smaller, more do-it-yourself version of this doesn't seem as viable.

If you can't run water up a hill and back down, you might still be able to build a tower straight up...

It sounds like steel would be fine for this, esp if you can build them on the ground or bury them under.

Seems like much better than the bad but still a ways from permanence.

I also thought, what if instead of a compression structure (in a sense) you could do this tensegritively...dont' know what that would even mean quite, but it was an idea that came from nature's designs.
 
Joshua Myrvaagnes
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Cool, I think I get this, but can you give a link or brand name? I looked up compressors and got a lot of technical jargon, maybe an off-the-shelf brand of these? and does it also act as a turbine itself to reverse the process for energy consumption? or are you only talking about mechanical energy output? that's useful, and also cooling for fridges, but it would also be great to have plain old electricity.

The other thought I had about this was that it could be acceptable for use on the sabbath for observant Jews--maybe make some Jewish women's lives easier? you wouldn't be making fire on the sabbath, if you're using mechanical energy only.

Steve Farmer wrote:You could take a bog standard 2KW workshop compressor and 2KW of bog standard solar panels. You would need no charge controllers just run the compressor when the sun shines and then link the compressors own tank up to empty gas bottles etc and then you have stored power available off the shelf now for a couple of grand.

In terms of applications, workshops run a multitude of tools from compressed air, almost all of which are concerned with converting potential energy in rotational movement. Once you have a rrotating spindle then you have the basis of industrial power sources.

This is somewhat a guess, but I think more energy goes into constructing a carbon or glass fibre tank than an equivalent steel one. The steel one will be heavier, but it will also not be flammable, unlike a glassfibre tank or even moreso a carbon fibre tank.
 
Joshua Myrvaagnes
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how much energy would be stored in a SCUBA tank? 300 bar is what I read, and that seems to be about 300 atmospheres...but the size of the tank is much smaller than the bedroom.


googling is easier than math:

So for a 230 bar 12L tank we have 230*12*450 Joules. 1242000 joules!
You're not impressed? You don't have a feel for a joule perhaps?
A joule is one watt for one second. so 1242000 joules is 3 kilowatts for just under 7 minutes.
That would boil 3.5 litres of water and so make coffee for everybody on the boat?
Still doesn't seem much does it? The trick is to release it in an instant.
In a previous life (see CV) I used a unit of energy that was 4.184x1012 joules representing the energy released by 1000 tons of TNT.
That works out at about 1866000 joules per pound.
In metric units the tank contains the energy in 300 grams of TNT. A normal hand grenade has about 150 grams.

Hum. That works out at 650 grams for my 10L twins at 300 bar.
Just behind my head? Now I see why people worry about it.


(http://www.nigelhewitt.co.uk/diving/maths/tank.html)

3 Kw for 7 minutes...about .3 KwH. Not a lot, but that could power your laptop for nighttime usage plus a night light or flashlight. (When your laptop battery starts being really lame after about six months).

"Your average laptop, with its far bigger screen, uses about 72 kWh[/year], costing some $8 a year." (forbes) so, about .12kWh/day.
 
Joshua Myrvaagnes
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two hand grenades' worth of pressure buried deep underground doesn't sound too scary to me. Not totally safe, but minimal potential damage to humans and felines and squirrels.
 
Dillon Nichols
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Joshua Myrvaagnes wrote:two hand grenades' worth of pressure buried deep underground doesn't sound too scary to me. Not totally safe, but minimal potential damage to humans and felines and squirrels.


Well, that was for a scuba tank, no? So if 11 litres @ 200bar is 2 hand grenades, 8000 litres @ the same 200bar is about 1450 hand grenades. Not a very precise measurement, but suffice to say, a big fuckin' bang!


Steve Farmer wrote:
You could take a bog standard 2KW workshop compressor and 2KW of bog standard solar panels. You would need no charge controllers just run the compressor when the sun shines and then link the compressors own tank up to empty gas bottles etc and then you have stored power available off the shelf now for a couple of grand.


Yes, you could; I'm planning to do this on a small scale with a couple small 12V compressors and some old propane tanks. Barring DC compressors you presumably need an inverter, and that might be happier with a battery, and thus a solar charge controller... At least, the ones I've used have been that way.

Just to be clear for others, though, this isn't very close to the described system, since the readily available compressors and storage tanks are NOT capable of 200bar aka 3000psi. More like 150-250PSI without getting into rather less than bog standard...

So, same concept, but something like an order of magnitude less energy density in the storage portion.

For example, in metric because it seems to be less confusing in this case, my '30lb' RV size propane tanks are about 0.0284 cubic metres capacity. At 200PSI (max rated pressure of my compressors, and below what the tanks can handle when used for propane), this is about 39k newton-metres. Release that over 1 hour (3600 seconds) and you get less than 10.88 newton metres per second for one hour, which is AKA 11watt-hours.

Yeah, 11wh. Not so exciting. And then consider the various inefficiencies and losses involved in getting that power back out of the tank, and it sounds pretty lame to me. I'm only doing it because I have the compressors and tanks anyway, and might as well charge em up while the sun shines.


Joshua Myrvaagnes wrote:I'm not clear what the "bog compressor" is, I'll have to google and see if I find out info.


This is a figure of speech, he means just a regular, commonly available compressor as used for powering air tools in many workshops.




I could be wrong, but I have the impression that a water pump will generally outlast an air compressor, which would be a point in favour of pumping uphill vs compressing air...


This page discussing various energy storage methods might be of interest. http://mb-soft.com/public2/storing.html
 
Rhys Firth
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Joshua Myrvaagnes wrote:how much energy would be stored in a SCUBA tank? 300 bar is what I read, and that seems to be about 300 atmospheres...but the size of the tank is much smaller than the bedroom.



300 BAR would be a HP Steel tank. The "Standard" SCUBA tank is commonly an AL80, Aluminum 80 cubic foot at 3000psi, or 11 litres water capacity at 200BAR (imperial measures like 80 cubic foot is the uncompressed volume of the contained air, Metric uses the volume of the tank and the pressure it can hold), Very few HP rigs use Alu, it's too prone to fatigue embrittlement, an Alu tank has a finite life, but steel, being elastic in a way Aluminum isn't is effectively immortal so long as it is not exposed to corrosion.

There are MANY different tanks around, I have a pair of Steel LP72's, Low Pressure 72 cubic foot, I would love to have a pair of HP120 steels, 120 cubic foot capacity at 4300psi/300BAR through that would mean changing my Yoke type regs for DIN type. as a matter of fact, the googled maths a few posts upwards mentions at the end 2x 10L at 300BAR... sounds like a twin HP120 steel setup to me, a pretty common deep/tech dive rig.


 
Trevor Walker
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Maybe what yall are onto is along the lines of air turbine compressors?
Have seen on these forums, adn on windmill sites.
Basically a windmill with direct coupled air compressor and tank on the ground.
 
Rhys Firth
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Storing energy in compressed air sounds nice, but I really do not see it as being safe on a homeowners scale, not for useful capacities of stored energy anyway.

On a commercial scale, with regular required maintenance checks and controlled access in a remote location, yes.... possible.... but not near as effective in a small scale as pimping water to store as an energy source.


With compressed air, you are storing the air as a mechanical storage with the potential expressed as a function of expansion. With low water pumped to a high point, you are storing the energy with the energy expressed as gravitational potential.
 
John McDoodle
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If you can compress the air somehow efficiently, I believe you could use one of these tesla turbines to turn the compressed air into EFFICIENT mechanical energy to drive a permenant magnet generator, to produce electricity, which should be stored into regular lead batteries (and maybe capacitors) regardless.

This is only a small micro scale model, but you get the idea
https://m.youtube.com/watch?v=_mg4THnpbus
 
Trevor Walker
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I like where this discussion is going.
See a similar thread here http://www.permies.com/t/9902/wind/Windmill-air-compressor-electric-generator

One thought is to suit the power generation to use as closely as possible to limit losses in storage or conversion.
For instance, if you don't mind the noise, there are some air driven appliances even for the kitchen.
Almost anything for the shop can be air-powered safely with purpose-built air compressor tanks. Think of a few 100 gallon air tanks chained together with a windmill-compressor to charge.
Anything not off-the-shelf, which requires rotational movement could be machined easily enough.

And very modest solar would fill the lighting needs with SMALL battery bank.

There was some reference in above thread to using the air tools as mini air conditioners (they draw heat from air as the compressed air expands). I can imagine a small air outlet aimed at a heat sink. And the exiting air used to power a small fan blowing across the heat sink. As the cold air / heatsink cools the air, the little fan would circulate room air across it, and the exhaust would also be cooler than room air. Positive pressurization of the room with filtered compressed air from an outdoor source! All you'd need is a pressure regulator before the unit, and a quick connect to tap the air tank.
 
Trevor Walker
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Of course teh use of compressed air, even with purpose-built units, requires some system design and careful tool choice so as not to make it more dangerous.
Just remember that many, many people have off-the-shelf air compressors in their garages, with off-the-shelf tools.
What MOST people don't do, though, is run them full-time, or overcharge, or make home-made air tools. Caveat.

Perhaps in a mechanical-charge situation like this, you'd also want some thermal monitoring so as not to heat the tanks too much during charging. Thats usually taken care of by thermal fuses, etc in the electric compressor. And I suspect most of teh heat is actually in the compressor, not the tank.
Of course for cold-weather freeze protection. Frozen condensate lines are NOT a good thing. Anyone planning to implement this, IMHO should be as invested in maintaining the water traps, PRVs and other safety items as in developing ingenious uses.

And a fundamental to remember is that high pressure is not really what you want for most applications. Pressure, yes, but just enough to run your tools. past that, you get nothing but more danger.
What you REALLY want is high capacity and maybe high through-put.
Capacity gives you longer tool use. Lots of big tanks means you can work all day and totally lose your hearing! (... huh?)
High throughput (large diameter fittings) gives you more "torque" so-to-speak. A tiny tank won't give you the necessary Cubic Feet per Minute (CFM) to do much, because they are not designed to dump all their air load in the kind of hurry you need to, say, run a grain mill.

With the proper safetys in place, I can see green-generated air-power as an excellent way to save on manual labor.

Will be especially interesting to hear how you solve the pressure-switching on that water-wheel-driven air compressor!
 
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