91–100 of 135 posts
Earlier quoted context omitted.
> some of your more off the beaten path ideas Any references? I'd love to read more.
Here's one: http://daniellefong.com/2010/02/11/how-law-shapes-the-busine...
I'm confused why this technique is better than just compressing air?
Air heats as it compresses. If you cool it, you lose pressure and thus energy. So you would have to keep it hot. It's problematic because it's less dense then and because you'd have to insulate it. Water stores much much more heat per volume and you don't have to handle the pressure if you keep the heat modest. This way your air pressure vessel can be smaller and probably uninsulated.
But I'm going to be that guy who says it will not work, and cannot work, based on fundamental thermodynamic theory. Here goes:
1. The best efficiency of a thermodynamic cycle is 1-TL/TH, where TL is the temperature of heat rejection from the cycle, and TH is the temperature of heat addition to the cycle. TL and TH are ABSOLUTE scale temperatures.
2. In the proposed system, TH is necessarily low, no higher than the temperature generated during compression. Efficient compressors work at low temperatures, usually no higher than 450 K (certain INEFFICIENT compressors, eg gas turbine compressors go as high as 700 K, the mechanical inefficiency gets converted into heat).
3. If Dani Fong, please comment on the above. I would be most happy if there was something wrong in my analysis, and the new technology was a success.
Congrats, DaniFong! You're one of those people where 10 years from now it is going to blow my mind that I got to share an Internet message board with you.
Back at you tptacek!
How much air would you need to supply all the power required by all the homes in California? Here's my attempt to answer that question: The first stop is to get a sense of what the realistic energy density of these approaches might be. A quick search lands you here: http://en.wikipedia.org/wiki/Compressed_air_energy_storage#E... My take-away: 1 m3 of air = about 300,000 J How much energy does a typical house in the U…
Your calculations appear be within an order of magnitude of correct :-) One other way to think of the number of shipping containers needed: actually the average american home uses 30 kwh/day. At our target energy density and efficiency we've been attempting to reach 30 kwh per m^3. 1 m^3 is approximately the internal volume of a refrigerator. So each home gets 1 fridge worth of storage. Not so bad ;-)
Being within an order of magnitude is absolutely fantastic for a quick set of calcs with unverified data pulled out of various 'net sites!
So, about 6,000psi for 1m^3 ?
I was just looking at this:
http://www.nuvair.com/storage-storagetank.shtml
Their NUVT6000 tanks will do it. Specs:
Outside diameter: 9.4in
Height: 52in
Weight (empty): 195lbs.
Air capacity at pressure: 510.5 ft^3
Internal volume: 2640 in^3
To double check, the internal volume of these tanks is given at 2640 in^3. 25 tanks come in at 66,000 in^3, which is just over 1 m^3.
What this highlights for me is just how large a vessel might be required to store such a volume of air at 6,000psi due to how strong it has to be. The external volume of these 25 tanks is approximately 1.5 m^3. Not too bad. We are taking about a 5 x 5 tank layout; about 4 ft x 4 ft and, say, 6 ft high with hoses, fittings and other hardware. They would weigh-in at about 5,000lbs, which might require some accommodations for a typical home garage.
Do these numbers describe what you are trying to accomplish to a reasonable approximation?
How noisy is the process of getting the energy back out of this storage system?
I had to look at a comparison with the energy density of current Lithium-Ion batteries:
http://en.wikipedia.org/wiki/Lithium-ion_battery
Volumetric energy density: 900 to 1,900 J/cm^3
If I assume 1,000 J/cm^3, that would require about 108,000 cm^3 in Lithium-Ion batteries or 0.108 m^3. Yikes! On first inspection, a 1 m^3 bank of Lithium-Ion batteries would allow you to run a house for ten days!
Not sure what that conclusion means, but Lithium-Ion, cost and other issues aside, looks very interesting.
How about gasoline? I know, horrible, but I have to ask.
http://en.wikipedia.org/wiki/Energy_density
Volumetric energy density: 34,000,000,000 J/m^3
I won't do the numbers, but Liquid Propane looks very interesting.
Clearly your long term competition might very well be electrochemical battery or graphene supercapacitor technology.
I realize you are working on a method to be used in storing excess energy for later delivery (or smoothing out the spikes in infrastructure demands). If I was looking for emergency power backup today I think I might have a very serious look at Liquid Propane. I has none of the storage problems of gasoline (namely that it degrades if not attended to) and it is very easy to use for cooking as well as lighting, if required.
Would I want every house in my neighborhood to have LP tanks, gasoline tanks, compressed air tanks or huge banks of Lithium-Ion batteries? Probably not.
All of these options are scary in one way or another. Imagine Hurricane Sandy, Katrina or a good size earthquake here in CA in a scenario where every home has one of these technologies. Could get scary very fast.
Same issues as with electric cars. Very interesting until you have an incident involving several cars. Formula 1 teams had to make special accommodations to use their electrical KERS systems, some of which run at 375V.
Because of this I would think that your technology (or any other high-duration, high energy-density storage solution) might be best deployed at the substation or generation point rather than installed in every home. Most people are not really equipped to intelligently deal with electricity. Sometimes it is a good idea for power to go out.
Earlier quoted context omitted.
It is not super clear what the innovation is here as I am sure someone must have thought of storing compressors heat with water before. I think maybe the novel thing is to pass the water as a mist through the compressor cylinders where it can transfer energy from air much faster than if, for example there was just a heat transfer closed circuit around the cylinders. Their website states: "We have achieved these high…
The main thing is that the mist process is higher efficiency. If you compress the air, let it heat up, and THEN cool it by mixing the air with water, the pressure will be high during the compression process, which will take a lot of energy to compress it, and then cool off and reduce in pressure. That's bad. What you want is to keep the temperature as low as possible during compression, and to keep it as high as poss…
And if you do recover the heat by condensing this vapour, it is low grade heat, which CANNOT be efficiently converted back to mechanical power or electricity.
Your web site claims 90% of the "grid" energy goes to heat storage. AFAICT This is NOT POSSIBLE if the heat comes from air compression. Is this an error in presentation? A fundamental error in your concept? Or am I mistaken... please explain.
Earlier quoted context omitted.
It is not super clear what the innovation is here as I am sure someone must have thought of storing compressors heat with water before. I think maybe the novel thing is to pass the water as a mist through the compressor cylinders where it can transfer energy from air much faster than if, for example there was just a heat transfer closed circuit around the cylinders. Their website states: "We have achieved these high…
The main thing is that the mist process is higher efficiency. If you compress the air, let it heat up, and THEN cool it by mixing the air with water, the pressure will be high during the compression process, which will take a lot of energy to compress it, and then cool off and reduce in pressure. That's bad. What you want is to keep the temperature as low as possible during compression, and to keep it as high as poss…
Earlier quoted context omitted.
It is not super clear what the innovation is here as I am sure someone must have thought of storing compressors heat with water before. I think maybe the novel thing is to pass the water as a mist through the compressor cylinders where it can transfer energy from air much faster than if, for example there was just a heat transfer closed circuit around the cylinders. Their website states: "We have achieved these high…
The main thing is that the mist process is higher efficiency. If you compress the air, let it heat up, and THEN cool it by mixing the air with water, the pressure will be high during the compression process, which will take a lot of energy to compress it, and then cool off and reduce in pressure. That's bad. What you want is to keep the temperature as low as possible during compression, and to keep it as high as poss…
Earlier quoted context omitted.
The main thing is that the mist process is higher efficiency. If you compress the air, let it heat up, and THEN cool it by mixing the air with water, the pressure will be high during the compression process, which will take a lot of energy to compress it, and then cool off and reduce in pressure. That's bad. What you want is to keep the temperature as low as possible during compression, and to keep it as high as poss…
When you cool the air by mixing it with water spray, a good portion of the energy is now spent producing low temperature water vapour. So... how do you recover that energy? You'd need to condense the water vapour to get at the latent heat. And if you do recover the heat by condensing this vapour, it is low grade heat, which CANNOT be efficiently converted back to mechanical power or electricity. Your web site claims…
When you cool the air by mixing it with water spray, a good portion of the energy is now spent producing low temperature water vapour. So... how do you recover that energy? You'd need to condense the water vapour to get at the latent heat.
You're right in direction but not in magnitude. There isn't much vapor produced, because the saturation vapor density is very low. Initially it evaporates, this cools the air before compression, and then it saturates. Any additional vaporization is recovered, because it condenses on expansion.
And if you do recover the heat by condensing this vapour, it is low grade heat, which CANNOT be efficiently converted back to mechanical power or electricity.
Also, interestingly, low grade heat can be converted into energy when you have a source of compressed air. This is not a full thermodynamic cycle because at the end of the expansion, you've also expanded air.
One of the best ways to see this is to imagine an energy storage system that's a giant Carnot cycle. The energy out/energy in is T_exp/T_comp. This is higher than the Carnot efficiency -- because it's not accounting for the energy in! The Carnot efficiency is E_out - E_in/Q_in which is 1 - T_c/T_h, the familiar expression.
Your web site claims 90% of the "grid" energy goes to heat storage. AFAICT This is NOT POSSIBLE if the heat comes from air compression. Is this an error in presentation? A fundamental error in your concept? Or am I mistaken... please explain.
Actually, if the compression is isothermal (and it's an ideal gas), 100% of the energy from the grid is turned into heat, and the energy state of the air is constant. U = 5/2 NRT.
Likewise, upon expansion, 100% of the energy comes from the heat.
The state of the air changes, but not in energy -- in entropy. As the air is compressed, work is added at teh same rate as heat -- and entropy, is removed.
Earlier quoted context omitted.
Your calculations appear be within an order of magnitude of correct :-) One other way to think of the number of shipping containers needed: actually the average american home uses 30 kwh/day. At our target energy density and efficiency we've been attempting to reach 30 kwh per m^3. 1 m^3 is approximately the internal volume of a refrigerator. So each home gets 1 fridge worth of storage. Not so bad ;-)
> Your calculations appear be within an order of magnitude of correct Being within an order of magnitude is absolutely fantastic for a quick set of calcs with unverified data pulled out of various 'net sites! So, about 6,000psi for 1m^3 ? I was just looking at this: http://www.nuvair.com/storage-storagetank.shtml Their NUVT6000 tanks will do it. Specs: Outside diameter: 9.4in Height: 52in Weight (empty): 195lbs. Air…
We aim for it not to be noisy -- any noise from high pressure air rushing out represents wasted energy. Sonic booms from exhaust have this problem in automobile engines, we avoid it.
Lithium ion is indeed much more dense :-)
Consider that every car has a gasoline tank, many houses have fuel oil, and we undergird our streets with natural gas pipes, which burned down San Francisco. I submit that air has its safety issues, but that most of these can be avoided, and in particular, chain reactions, which threaten flammable energy storage, can be made a non-issue.