Batteries To Store Wind Energy 275
Roland Piquepaille writes "Scientific American reports that Xcel Energy, a Minneapolis-based utility company, has started to test a new technology to store wind energy in batteries. The company is currently trying it in a 1,100 megawatt facility of wind turbines in Southern Minnesota. The company started this effort because 'the wind doesn't always blow and, even worse, it often blows strongest when people aren't using much electricity, like late at night.' It has received a $1 million grant from Minnesota's Renewable Development Fund and the energy plant should be operational (PDF) in the first quarter of 2009. If this project is successful, the utility expects to deploy many more energy plants before 2020 to avoid more polluting energy sources."
Re:Seems silly to use this. (Score:2, Informative)
I believe that more isn't being done with flywheels because storing energy in flywheels costs much more than the NaS batteries.
Re:a dam sounds like a pretty good battery to me (Score:1, Informative)
It has always been my understanding that this type of energy storage has always been the most efficient for large scale stationary energy storage. There are several implementations of similar technology that don't pollute like batteries and don't cost nearly as much for the same storage capacity.
Vanadium redox (Score:3, Informative)
sounds like a cool potential battery technology too. The battery element determines the power, and the amount of energy storage is only limited by the size of the tanks.
http://discovermagazine.com/2008/oct/29-the-element-that-could-change-the-world/ [discovermagazine.com]
Re:I'd want to store it in a hydro tank... (Score:5, Informative)
Re:Store the energy in a massive weight (Score:4, Informative)
Assuming concrete is reasonably environmentally friendly this would be a pretty clean solution.
Concrete has a massive carbon footprint. The calcination of lime releases a lot of CO2, on top of the fossil fuels used in manufacture and transport.
Re:I'd want to store it in a hydro tank... (Score:3, Informative)
they do that here in Ireland [wikipedia.org]
ive been at the facility few years back, quite impressive engineering stuff (for a small country)
Re:a dam sounds like a pretty good battery to me (Score:4, Informative)
Oklahoma already has two hydo plants and one pumped storage plant. You don't need huge elevation changes, a few hundred feet will do.
Re:batteries? (Score:3, Informative)
Capacitors, at least the few I have seen, generally want to release their stored energy all at once. How is this addressed when supercapacitors are used? For example, let's say you have a supercapacitor that can power a light bulb for eight hours. How do you make it actually provide a lower current over those eight hours instead of providing all of that energy in a single instant and frying the bulb?
By understanding I=V/R [wikipedia.org].
A capacitor has a certain voltage (whatever you charged it to) and an internal resistance. The load (light bulb) you attach also has a certain resistance. The discharge rate is determined by those two resistances (added together) and the voltage. The "all at once" just means that the internal resistance is almost zero, so if you connect a load that also has zero resistance the capacitor will discharge very quickly. If your load doesn't have near-zero resistance, there won't be any real difference from using a battery.
Re:Seems silly to use this. (Score:3, Informative)
Re:Seems silly to use this. (Score:4, Informative)
3. Given the high velocities - what will happen when they fly apart? Also, the gyroscopic effects they generate while spinning.
For a stationary plant, have it spin horizontally, and build it underground.
If it does suffer a catastrophic failure, loss of life and damage to surrounding infrastructure should be minimal
Re:Store the energy in a massive weight (Score:4, Informative)
I did some calculations (yay!), and came up with the following: Raising the Empire State Building (365,000 tons of material) to the height of one meter would store a little shy of a megawatt hour of energy.
I'm imagining this weird future city where the buildings slowly rose and fell as energy was stored and withdrawn. It's a cool thought, but it seems that the engineering difficulties would be considerable, and the payoff not so much.
A system where water was stored at the top of a skyscraper might be more feasible (putting the weight a hundred times higher means you only need 1% of the material. You might be able to do something with water, or a block on a chain. But the storage payoff seems relatively small.
It might make more sense to deal with material that's already being lifted up and dropped down. Like integrating some sort of storage and release system for the water already being pumped to the top of skyscrapers. Given separate reservoirs for potable water and sewage, and some leeway about when to pump water in and release waste out, something might be arranged.
The calculation: 365000 tons * 907 kg/ton * 10 joules/kg * 1kWH / 3,600,000 joules. The 365000 tons figure is from this kid's site [esbnyc.com].
Re:Seems silly to use this. (Score:4, Informative)
The weight of a flywheel is far less important than the weight. Energy of motion is a product of mass times velocity squared, so doubling the rate of rotation quadruples the amount of energy stored. The ideal for many applications is to find a material that is very light, but won't fly apart at high speeds. I remember reading about somebody trying something with carbon nanofibers, but that was a long while back.
The weight doesn't matter much for energy seepage either. A good flywheel will be suspended by magnets, so regardless of the weight, the friction due to weight is effectively zero. There is still air friction and electrical losses to deal with.
Getting energy into them isn't a huge obstacle either. I've scoured the web, and it looks like the people actually selling flywheels-as-UPS solutions are claiming 90% efficiency.
Something may be missing in my understanding here. The article claims that the battery backup for the wind farm costs about three million dollars per MWH, whereas the flywheel backup system I'm looking at right now [vyconenergy.com] claims that it can give you about 200kWH capacity for about $50,000. That's $250k per MWH installed, and very low maintenance costs.
Their claims could be overblown, or I could have my math wrong, or there is something I'm missing that makes the flywheels unsuitable for this application. There might also be a huge economic opportunity, but somehow I doubt it.
Re:Seems silly to use this. (Score:3, Informative)
That first sentence was supposed to be "The weight of a flywheel is far less important than the rotation speed."
Re:Seems silly to use this. (Score:4, Informative)
Flywheels are attractive for short-term peak power delivery. They have low failure rates and easy fault detection (if the wheel is intact and spinning at the required speed, you know how much energy is available).
For long term loads (hours) flywheels aren't competitive with lead-acid batteries, let alone more exotic types such as the NaS battery the article describes. For example, the Active Power CSDC-500 [activepower.com] flywheel storage system supplies 50kW for 138 seconds = 1.92kWhr. The cabinet is 78" x 54" x 34" and it weighs just over 3 tons. Four long-term loads, a system with two 12V 100Ahr VRLA batteries [cdpowercom.com] would be 14" x 14" x 10" and weigh 140 lb.
A flywheel based system has nowhere near the energy density of a battery storage system. Peak power density is the flywheel's forte.
Aargh, units confusion again. (Score:5, Informative)
I am so sick of science writers who mess up the story because they don't understand the units of energy and power.
The article says the batteries store 7 megawatt hours. Fine.
Then it goes on to say "meaning the 20 batteries are capable of delivering roughly one megawatt of electricity almost instantaneously" WTF does that mean? Power, measured in megawatts is by definition an instantaneous unit. What's with "almost instantaneous". Also, the rate of discharge of a battery MW is unrelated to its storage capacity MWh, so the entire meaning of the sentence makes no sense.
Then the article says, "Over 100 megawatts of this technology [is] deployed throughout the world," Huh? Battery capacity is measured in megawatt-hours, not megawatts.
Then the article says, "costing roughly $3 million per megawatt" same thing. Battery cost must be proportional to megawatt-hours, not megawatts.
I suspect that their idea is to make a battery with 24 megawatt-hours of capacity able to deliver 1 megawatt of power uniformly for 24 hours, then say so.
Shame on Sciam writers and double shame on Sciam editors for not mastering such basic units in an article about energy.
How about a little economics. The article mentions two understandable numbers, an 11 MW wind plant, and 7 MWh of battery capacity. The combination of the two, allowing for wind variations during the day believably deliver 1 MW continuously to the grid. That's 24 MWh per day.
Now the batteries cost $3 million, and the wind generators cost $22 million. Total $25 million to deliver 1 MW of base load. That's $25 billion per GW.
The peak generating capacity of North America is about 750 GW. Let's say 250 GW when levelized to base load. Therefore, to supply 100% of that with wind and batteries would cost roughly $6.2 trillion dollars. Now Al Gore says, "No problem. We can do that in just 10 years." WTF is he thinking?
Even if we did spend $6.2 T, there will still be periods where not much wind blows for large regions for many weeks at a time. I live where it's cold, and I know that when it hits -30F, the wind is almost always still and the sky dark, and that it can stay like that for a couple of weeks. We therefore, need to double or triple the $6.2T plus more for transmission, to provide backup power sources, plus the means of delivering the energy over large distances.
Wind and solar are wonderful for up to 15-1-20% of the total grid generation and the cost of construction and operations dominate. More than that, and reliability and deliverability of the electric supply become dominant in the economic equation.
Re:Old idea waiting for a viable implementation (Score:2, Informative)
Exactly, battery tech isn't economical yet. And it isn't improving anytime soon as batteries are pretty much at the end of their innovation (barring any major breakthrough). Similar to "how do you make a better wheel?" Batteries are the only solution in small setups, but I don't think they scale very well to really large systems.
Our current solution is to send it to the grid and pump water back up in hydroelectric plants. Wouldn't dedicated HVDC lines from solar/wind plants to hydro be a more economical alternative? Or build a local setup where you pump lots of liquid/weight up a height. It basically ends up being an ultra capacitor.
Re:Aargh, units confusion again. (Score:4, Informative)
Then it goes on to say "meaning the 20 batteries are capable of delivering roughly one megawatt of electricity almost instantaneously" WTF does that mean?
It seems pretty obvious to me... it means that the output of those batteries is available at a moment's notice, i.e. as soon as the operator presses the "gimme battery power" button. Compare that with, say, a natural gas turbine that might need 20 minutes to spin up to full power.
Re:Seems silly to use this. (Score:3, Informative)
Caterpillar offers such a system: http://www.cat.com/cda/layout?m=37516&x=7 [cat.com]. Their flywheel UPS keeps the electronics up and running allowing the diesel/gas turbine generators to start. The idea is you don't need a big battery bank that holds minutes or hours of power. You just need enough power to allow the generators to kick in and transfer switch to resume power. It is much more efficient, cost effective and low maintenance than batteries.
Another idea for high density power storage is the molten salt battery [wikipedia.org]. They are being used by GE for their hybrid diesel electric locomotives to store regenerative braking energy. The other interesting part is they can be built with relatively inexpensive and non toxic materials. The electrolyte must be heated but another interesting fact is when they cool down and solidify they can hold a charge for an extremely long time (50+ years!).
Re:Aargh, units confusion again. (Score:3, Informative)
When they refer to "megawatts" in a power plant or storage, they're generally referring to the peak output capability. For example, the 20 Megawatts almost instantaneously would mean the batteries can supply a peak power of 20 Megawatts. The "almost instantaneously" means there is no significant time delay between the request for more power and actually getting the power out (which you might have with a coal fired plant for example).
The "megawatt hours" defines the total storage capability of the battery banks rather than the on-demand peak output.
Re:How about Hydrogen (Score:4, Informative)
So if a reactor is built in the US to today's abbreviated containment standards, yes, that reactor would include a failure mode similar to what occurred at Chernobyl.
The failure mode at Chernobyl was very specific to the design of the RBMK-1000 and to it being near the end of the core life. The problems at Chernobyl were that it had a positive coolant void coefficient, the reactor was burning Plutonium (delayed neutron fraction of 0.2% versus 0.65% for 235U), the graphite moderator was not thermally coupled to the fuel or coolant, and last but not least, the scram rods increased reactivity at their initial portion of travel - the Chernobyl accident was triggered by an operator scram'ing the reactor.
American light water reactors were design explicitly to have a negative coolant void and temperature coefficient.
FWIW, I do have a degree in nuclear engineering.
Re:Seems silly to use this. (Score:4, Informative)
Put the flywheel in a permanently-sealed vacuum chamber.
no such thing. Not that it's a big deal. Commercial vac dewars and such have ports for pulling out excess atmosphere that seeps in anyway. you would use the same thing here. Wrap the outside of the chamber with LN2 pipes to cool the air inside so that is is less energetic and "falls" to the bottom of the chamber, then with the help of a turbo pump suck the chamber of all air present that is reasonable to get out.
-nB