The Future of Wind Power May Be Underground 223
Hugh Pickens writes "When the wind is blowing, it is usually the cheapest peaking power available. However utilities need consistent always-on power from large, cheap coal and nuclear power plants that are the backbone of the electric grid. Wired reports that operators are looking at Compressed Air Energy Storage (CAES) using abandoned mines and sandstones of the Midwest to store compressed-air. This converts the intermittent motions of the air into a steady power source by using it to run air compressors to pump air into an underground cave where it's stored under pressure. The first CAES plant in the United States actually went online in McIntosh, Alabama in 1991 where engineers created a geological pocket 900 feet long and up to 238 feet wide in a dome by pumping water into it to dissolve the rock salt. When the (briny) water was pumped back out, the salt resealed itself and they had an air-tight container."
Generate a Vacuum (Score:5, Interesting)
Instead, build long tunnels between major cities, evacuate them down to between 0 and 3 psi, and run high speed trains through them. The trains would need very little energy to run thru the extremely thin atmosphere, and the pressure diffential can be used to generate electricity when needed. 2 birds, 1 stone.
Re:Efficiency (Score:3, Interesting)
No. It's far *less* efficient. Li-ion batteries have round-trip efficiencies in the 90s (some chemistries in the upper 90s). Compressed air storage has a round trip efficiency generally under 50%. Sometimes significantly.
There was an interesting article the other day about storing electricity in molten aluminum/alumina -- basically, turning today's electrolysis method of making aluminum into a reversible process. They claim to already have better than lead-acid prices, but far longer cycle life, as well as li-ion energy density. Could be interesting, although I haven't seen an efficiency stat. Also, since it runs hotter than a Zebra cell, I doubt it'd scale down well. But who knows.
Re:Load leveling Vs. Supply leveling (Score:2, Interesting)
Hydro isn't always an option, and even though nuclear would go a long way to solving these problems, it also has limitations. For one, nuclear plants need coolant, which is generally a lake or river (again, geographically specific). For another, the FUD about nuclear energy isn't going away, so a lot of suitable areas won't be considered. Now, I'm not saying wind isn't similarly limited; but I am saying that wind power may work in places where neither hydro or nuclear will (dry, arid climates leap to mind). For the places where all three are an option (or similar energy storage techniques, such as alternately pumping/draining water between two adjacent bodies of water), all the better.
Honestly, why is it that people think JUST solar or JUST hydro or JUST $hyped_fuel_source is the answer? Unless we develop cold fusion at some point soon, our power will probably be taken from whichever the easiest source is at any given location, and we'll have a cornucopia of power stations - and maybe even distributed power generation (solar panels on peoples' roofs)!
Re:Efficiency (Score:2, Interesting)
No. It's far *less* efficient.
There was an interesting article the other day about storing electricity in molten aluminium/alumina
We already have fuel cells that consume aluminium. They're only about %40 efficient, but they are 100-1000 times cheaper than hydrogen fuel cells. So, without any technology development, the "aluminium economy" is %25 efficient (%70 percent efficient electrolysis, %40 percent efficient fuel cell). I think if you re-designed an aluminium fuel cell, you could get 90 percent efficiency, so you would have overall %60 efficiency. Not great, but it works. My idea is to use the ZEBRA electrolyte, (or maybe another electrolyte like it) to avoid corrosion and inefficiency in the al-air fuel cell.
Re:Efficiency (Score:4, Interesting)
Your right that compressed air is a less energy efficient storage medium than Li-ion batteries, but only for the first couple of years. Li-ion battery storage capacity decreases at about 20% a year because of natural degradation. Consider the cost to frequently manufacture, replace and dispose of batteries compared to the wear cycles of a compressed air container which is probably measured in decades.
My point here is that the maintenance cost for compressed air energy storage is quite low compared to other options. You also have to consider the cost of making the storage devices. Steel tanks are mostly hollow and we are already really good at making them. We are good at recycling steel too. Air storage, unlike fuel cells or batteries options which consume lots of metals and require complex electronics to regulate, compressed air is extremely cheap and simple.
If our choice is cheap simple but supposedly inefficient storage of 50% via compressed air or storing 0% via other supposedly more efficient but unaffordable and unsustainable methods the choice is pretty simple.
Re:Unwater Bags (Score:4, Interesting)
I think the losses in the CAES system are due to the fact that it is a non-adiabatic process (a diabatic process?, i.e. one where heat can be lost from the system). When you compress the air, the temperature rises, and some heat is lost to the surrounding ground. But if the cycles are fast enough, those losses may be reduced -- i.e., you allow the air to re-expand, which cools it, and it sucks heat back from the ground. Since heat moves slowly through the ground, you may be able to get a lot of it back before it goes anywhere. The innovation in the Alabama system was to use waste heat in the turbine's exhaust gases to replace this lost heat as well.
I think the solution you propose is isobaric (constant pressure) and isothermal (constant temperature), but still not adiabatic. Some of the energy used to compress the air is converted to heat, and that heat would be lost to the ocean instead of raising the temperature of the air.
A better solution might be to use pre-inflated air bags (or air boxes?) attached to pulleys on the bottom of the ocean. Use a motor to pull the other end of the rope, and you would draw the air bag downward, storing energy. Play out the rope and the rising air bag would turn the motor (now acting as a generator), generating electricity. You could also do this with stones or bags of silt/gravel, just raising and lowering them from the surface.
The problem is, you would need a lot of air bags or stones to store any significant amount of energy. If the stones or gravel have a density of 2000 kg/m^3 (similar to "Gravel, wet" according to http://www.simetric.co.uk/si_materials.htm [simetric.co.uk], higher than "Clay, wet excavated" (1600) but lower than concrete (2400)), then they will have a net weight in water of about 1000 kg/m^3 (i.e., a downward force of about 10000 Newtons per m^3). Air bags would exert a similar force upward. If you can find a near-shore location with a depth of 1 km, you could store 10000 N * 1000 m = 10 MJ of energy per cubic meter of material, which is about 3 kWh/m^3. A 100 MW wind farm (presumably closer to shore) would generate 100,000 kWh of electricity per hour when the wind is blowing, so if you wanted to store 6 hours of energy from this wind farm, you would need to raise and lower about 6 * 100,000 / 3 = 200,000 cubic meters of stone or air (e.g., 200 large chunks, each 10 meters across). I suppose it could be done...
Conversion losses (Score:3, Interesting)
Re:Unwater Bags (Score:3, Interesting)
the losses in the CAES system are due to the fact that it is a non-adiabatic process
the solution you propose is isobaric (constant pressure) and isothermal (constant temperature)
Either an adiabatic or an isothermal process will allow high efficiency. In the adiabatic process the heat from compression is stored in the air and in principle no energy is lost through the compression and decompression. In an isothermal process all of the extra heat from the compression is transferred to some external reservoir (ocean, atmosphere, etc). If this heat is transferred back to the air when decompression occurs the air leaves the system at its original temperature (as for an adiabatic process) and no energy is lost. An isothermal system can actually store more energy since the stored air is at low temperature and hence a greater quantity may be stored within a given volume and pressure limit.
In real systems what happens is heat is lost during compression and in storage and that heat is not fully returned to the system during decompression. The air leaves at a lower temperature and energy is lost. Some compressed air energy storage schemes have resorted to using natural gas to reheat the air since heat exchangers for a true isothermal process are impractically large.
Re:Efficiency (Score:3, Interesting)
No. You could use anything from an efficient spinning wheel with a lot of potential energy and very little friction (think super heavy pottery wheel with an engagable generator/motor) to a super-conductive coil (or looped superconductive powerline) to just stash the energy for a bit. And these will almost certainly be more efficient.
The larger problems is that we don't have enough wind to care right now, and the problem of energy storage has nothing to do with wind. It's a modular problem that simply deals with electricity on the grid, if electricity storage is needed for the inconsistent power on the grid, then it's needed. The fact that it's needed for wind power isn't something of any consideration. Such problems should have a healthy amount of encapsulation.
The total amount of battery power on the planet could power our electrical needs for ten minutes. That's not enough. It's a problem, who cares where the power comes from. This crap reminds me of that stupid idea of building another power grid for renewable power so people could know the power they get is from renewable sources. WTF.
If compressed air works well as a battery it works well as a battery, my guess is that it almost certainly doesn't work well as a battery and the failure that is the air car is quite telling of that point. Even when you can control for everything (unlike a hole in the ground (see carbon capture)) you still can't compress and get power back at anything close to efficient enough to give it a second thought.
"Wired" as an authoritative source? Sheesh. (Score:2, Interesting)
Getting the straight poop from "Wired" is like expecting it from Fox News.
Air--pumped storage is dead from the get-go. You compress air and a goodly percentage of the energy ends up as heat, which has to be removed from the compressor cylinder heads and is lost. Then the hot compressed air loses heat to the walls of the cavern. Then when you let the air expand, it cools off and you lose pressure from that effect too.
A rough guess-- you lose 50% of the wind energy coming and going.
You can do better by pumping water uphill, where you don't have the compressive losses.
Re:"Wired" as an authoritative source? Sheesh. (Score:3, Interesting)
rough guess-- you lose 50% of the wind energy coming and going.
Rough answer, you are wrong, RTFA and RTF Thread, particularly (#31435384) http://hardware.slashdot.org/comments.pl?sid=1578760&cid=31435384 [slashdot.org]
You can do better by pumping water uphill, where you don't have the compressive losses.
no, you can't, again, RTFA
here it is 2010, and I'm still using cutesy acronyms from the early 1990s, seriously though RTFA has never been a more appropriate response
Re:Load leveling Vs. Supply leveling (Score:1, Interesting)
You are misinformed. Nuclear, as it stands, is our most reliable source of energy. The average capacity factor (actual energy output divided by possible energy output) for nuclear power plants in the US is over 90%. Nuclear power is the closest thing we have to full-blast power, and most plants last 40 years as a minimum (with plenty going for a 20 year extension after replacing critical components that are worn down).
The next closest source of energy, in terms of capacity factor, is coal - which is just below 75%. Nothing else is over 50%.
Source [nuclearfissionary.com]
Some Inside Info (Score:1, Interesting)
While I was in my hometown of Waxahachie, TX over Christmas I found out that one of the companies using this technology was looking into buying the old tunnels used for the Super-Collider that was being built there. Some of them had been filled in, but there was a considerable amount of space available for it. However, Unlike the tech mentioned here, instead of using wind power to pump the air out, they would actually buy power strait from the grid during the night, when power is cheap, and then selling the stored power during peak hours. Eventually they would suppliment the grid power with solar to increase the profit margin. It has noting to do with clean energy though, and everything to do with making money. I never heard if the deal ever went through or not.
Re:Generate a Vacuum (Score:2, Interesting)
MANY years ago, Scientific American had such a proposal. The expected costs at that point were less than purchasing a surface right of way for an interstate.
They were also looking at running them a substantial distance underground, so that gravity was used as an assist to accelerate and decelerate the train. My recollection was that the vacuum was a lot harder than 1-3 psi. I think they were talking about a few mmHg. Small enough that even running trains a 300 mph air resistance was minor.
The issue of failure modes to me is the sticky one.
Get a train derailment inside a tunnel, and you have major problems. Just how do you clear the wreckage when you are 30 miles from the nearest end. Expecially if the wreckage is shorting out the power lines.
(Ok, ok. You cut the line near the wreck, pull out hte cars,
Haul the bits out. Extend the power line a car. Repeat.
Imagine being on the train, and hearing the door gasket leaking as you go through the lock into the tunnel.
Be a cool way to move freight. Could be faster than truck, cheaper than air.