MAR 09

We seem to feature new ideas for methods of generating power every week on EcoGeek. Varieties of methods for harnessing energy from wind, waves, and the sun are being investigated and developed by scientists and inventors all over the globe. But many of these power sources are intermittent, compared to the steady output that is available from combustion of (most often) non-renewable fossil fuels.

One of the regular complaints from opponents of wind or solar power is that it is sporadic or unreliable. "The sun doesn't shine at night;" "The wind doesn't always blow when you need it;" and other complaints are leveled against renewable power systems. That doesn't mean they aren't useful, though. Instead, the grid needs to be better equipped to store that power when it is generated and then draw from it again when demand rises. It's part of the 21st century grid our power system will need.

Ars Technica has a story on power storage that is well worth reading. It looks at some of the theoretical options for power storage, as well as current technologies that are already in use.

Hydroelectric storage is one of the most common methods for storing energy, and has been around for nearly a century. Water can be pumped uphill when surplus power is available, and then allowed to flow back through generating turbines when demand for electricity rises.

From the article:

[I]t's no surprise that grid-level storage actually dates back to 1929 in the US, when the first pumped-water plant opened. These facilities combine a standard hydroelectric facility with a pump that runs when electric supply exceeds demand. The excess power pumps water uphill into a reservoir, where it can be harnessed when power supplies drop. All told, pumped hydro now has the capacity to supply about three percent of a typical day on the US grid. So, grid-level storage isn't a possibility; it's a reality.

One such facility in Ludington, Michigan on the shore of Lake Michigan has the capacity to generate up to 1,872 megawatts of electricity.

Battery storage systems are another option. Batteries intended for grid storage are different from more familiar battery types such as lithium-ion or lead-acid. Large scale systems using technologies such as flow batteries or sodium sulfur batteries may find a growing place in grid energy storage solutions. Already, in Japan, a wind farm has been equipped with 34 megawatts of sodium sulfur battery storage capacity to store wind power generated at night for use during the day, and, in Minnesota, Xcel Energy is testing a similar system with about 1/10th the capacity. A lot of these batteries are ill-suited for small scale, portable applications (where lithium ion systems are the batteries of choice), but are well suited for large scale, fixed location installations. And grid-tied storage is just that kind of industrial scale application. While not every location has the water resources to be able to do pumped storage, large chemical battery systems offer very high energy storage density and can be installed almost anywhere.

For locations without the water resources or elevation changes necessary for water storage, compressed air energy storage is another possibility. Abandoned mines can be used as pressure vessels into which air is compressed when surplus power is available, and then that pressure is used to generate electricity when demand for power rises.

Flywheel systems are also receiving some attention. Flywheels are wheels which spin at high speeds; when energy from an outside source is applied to a flywheel, it is stored as rotational energy. Flywheels are currently used to provide backup power in certain scenarios, but because they can store intermittent power, they lend themselves to renewable power storage as well.

All of these technologies should find their way into greater use as part of the updating and modernization of the current grid infrastructure. As more renewable sources are added to generating capacity, it only makes sense to have the ability to effectively use that energy. And even the most benighted renewable energy deniers must admit that having capacity in the grid for dealing with peak demands is a benefit to the electrical infrastructure.

Comments (20)

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rocks in the head
written by This e-mail address is being protected from spambots. You need JavaScript enabled to view it , March 09, 2009

raise large rocks/weights and store the energy as gravitational potential. both cheap and efficent.

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Flywheels.
written by Twist9, March 09, 2009

Those flywheels bust be immensely heavy, on a scale rarely conceived of. They must be the size of a building to hold any full percentage of the grid supply.

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do we really need storage?
written by kballs, March 10, 2009

These studies/articles always assume we can produce more renewable/solar/wind power than total instantaneous demand on the adjacent grid... which has probably never happened and won't for a long time. Why not use current generation (coal, nuclear, hydroelectric, natural gas) to take up the slack and not worry too much about this until we CAN actually generate more renewable power than total demand.

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written by kballs, March 10, 2009

More on my reasoning: Renewable power storage DOES need to be worked on, but it's not in any way a roadblock to current adoption that so many make it out to be.

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written by Justin, March 10, 2009

Every time I read about this I wonder what all the fuss is about because the solution seems so simple: pump water uphill and let it flow downhill when you need it. Never realized it was so widely deployed. But the basic principals seems simple, albeit the scale a little daunting. But, it seems to me, prefabricated structures, or... elevated water towers containing over 1million gallons are fairly common. Just pump the water up and down. I'm not sure how much stored energy 1million gallons of elevated water contains, but the designs themselves seem to be fairly simple, and since water is available nearly everywhere at some point or another, and since you're not losing any water, just pumping it from a lower reservoir to an upper reservoir and then back again... a good amount of rain seems like it could fill it up.

Or, even better, just.. a hill with a flow line and pumping seems like it could also store this fairly easily. We're talking windmills, albeit the actually towers don't take up much of a footprint, it seems that they land they're built on should be readily available for this type of storage.

Like this article said, its been around for nearly a century, so there has to be a very developed science and engineering around this to calculate the costs.


On to other technologies, Wired did this piece back in May 2000. Seems like the technology should be much more developed now:

http://www.wired.com/wired/archive/8.05/flywheel.html

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written by Bob Wallace, March 10, 2009

The flywheels currently being tested for grid use are reasonably small. Hard to tell from the photos of the enclosures, but they might not much different than the size of a large truck wheel.

We don't need an lot of storage right now. That need will come as we build out the system.

We currently use some battery storage for output smoothing in wind farms. And we do use some puump-up storage. (And have for about 80 years.)

There appears to be some profit to be made by building storage, purchasing cheap off-peak power and selling it back to the market during peak demand times.

The overall problem of the wind not always blowing (everywhere), the sun not always shinning, the tides not always flowing will be solved by using a connected grid of different production methods, load/demand shifting, and storage. We'll also likely use natural gas/biogas turbines to help fill in the gaps.

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written by russ, March 10, 2009

The story and comments sound like what you hear sitting in a bar. No idea of the real problems with storage just the knowledge that someone said it would be good and the desire to appear knowledgeable.

Size is the problem with physical storage - water pumping, compressed air storage, flywheels etc.

Turndown is a problem with gas turbines - they do not operate efficiently off peak production. They are not operated like you drive a car.

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A Megawatt is STILL not a measure of sto
written by Kevin, March 10, 2009

Sorry to sound like a broken record, but a megawatt is still not a measure of stored energy, although in the case of the NaS batteries, the mistake is in the linked article and is simply reproduced here.

My first guess is that the batteries actually store 34 MWh (megawatt hours) of electricity. But it's only a guess - they might equally well mean MJ (megajoules).

The difference between a MWh and a MJ is a factor of 3600 in the amount of energy stored! That's a MASSIVE difference, and it is pretty important to know which they mean. Which is why getting the units right is not just a matter of pedantry, it's really important.

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written by Paul, March 10, 2009

What about super conductors?
The technology is not there yet but seems promising and very high efficient. I read an article about it a while back but never heard about it again. Wondering if anything happened?

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written by Jacob, March 10, 2009

the water system requires hills and water, which are somewhat rare in a desert or on the plains. The differences between peak demand and baseload are vast, and as such there only needs to be a small amount of "reliable" energy generation provided that the variables kick in during the peak times. In hot places, solar complements the peak electricity (used for cooling) very well. Perhaps geothermal or biofuel plants can provide the baseload with the intermittent power being allocated via a smart grid to when and where it is needed.

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power vs energy
written by Jeff, March 10, 2009

"Sorry to sound like a broken record, but a megawatt is still not a measure of stored energy"

Seriously, I love this site, but FFS get your basic stuff right. It's so frustrating.

W = Power
W-hr OR J = Energy = Capacity

Now maybe they meant the batteries are able to supply a max power of 34 MW, but capacity is not the word to use.

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written by SolarLad, March 10, 2009

Renewable energy and storage capacity don't have to be incompatible ideas. Concentrating Solar Power has an advantage over PV and wind in that heat is much more easily stored than electricity. CSP could be used to supplement these other renewable sources. Having multiple renewable technologies play to their strengths is probably the way to go.

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pressure vessel?
written by Adam St. John, March 11, 2009

Maybe I'm wrong, but I doubt most underground mines could safely function as pressure vessels. I don't see this as an efficient energy storage method.

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Hydrogen....?
written by Brad, March 18, 2009

I always thought that hydrogen shold be considered as a good candidate for storage of renewable energy. At least on a small scale of an off-grid property with onsite renewable generation, electrolysis of water into hydrogen storage when 'the sun is shining, the wind is blowing' and then electrical generation via a fuel cell when needed. I also think that decentralisation of energy production would be a step in the right direction.

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written by russ, March 18, 2009

Get a CE (Chemical Engineer) or someone else knowledgeable about such things to calculate the storage volume required for H2 to produce one mW of electricity.

You find you have to use cryogenic storage - suddenly it becomes super expensive and impractical - at least as we do it today.

At present there is a H2 pipeline running from Texas to Mobile, Alabama. İ believe Air Liquide still owns it. At least along that belt H2 distribution may be feasible without such a hassle as other places.

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Communications Mgr
written by Jasmine Williams, March 19, 2009

I would say Ice Storage is a form of energy storage most widely used all around the world. Ice Storage also happens to be the most cost effective of the energy storage technologies. Ice Storage uses plentiful night-time electricity, including wind which blows mainly at night to store ice, used to meet the peak demand for daytime cooling.

Storage is integral to any grid, renewable or traditional. Storage is used to balance supply and demand, from food in our cupboard to water in our reservoirs. Ice Energy Storage fixes the imbalance in our electric grid that is largely due to air-conditioning use.

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written by Carlo Schots, March 19, 2009

http://www.technologyreview.com/energy/22116/
this website describes the liquid battery developed by Donald Sadoway. It could power the whole city of New York.

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wind won't blow and the sun won't shine
written by IggyDalrymple, March 19, 2009

but the Gulfstream just keeps on keeping on.

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written by Fred, July 16, 2009

There's always going to be a new to create power.

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written by albert eddy, March 10, 2010

a round floating island any size (?400 acres) driven to
rotate (wind, powered motors etc.) would contain power
that could be used at dead times. Could also grow fish.
This unit would not need ellevation and would be ground geothermically heated.

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