Land purchase advances plans for underground energy storage

[Fledermaus]

The directors of the Iowa Stored Energy Park voted Tuesday to pay a Dallas County homeowner $195,000 for his house and acre of land to dig the first well for what could be the world's third underground electricity storage system.

Compressed air would be stored in a network of 13 wells 3,000 feet deep and then released at strategic times to turn the turbines on two 134-megawatt electricity generators.

The stored energy project is promoted as not only a source of non-fossil-fuel energy but also a way to store some of the surplus electricity generated during nonpeak hours by Iowa's wind turbine farms.

The house and land just west of Dallas Center will be bought from Ray Keith. The Stored Energy Center also is negotiating a potential lease with another Dallas County landowner, John Mortimer, but the two sides have yet to reach an agreement.

Stored Energy Park officials hope to have the first well drilled by fall. The well will test the ability of Iowa's subsurface rock to hold air compressed up to 1,400 pounds per square inch.

http://www.desmoinesregister.com/article/20090617/BUSINESS/906170347

[vincna]

1. Are you sure it's non-fossil?

The compressed air storage systems I have seen route the compressed air into the combustion section of a combustion turbine generator where fuel is burned to increase the temperature and volume of the gas before it is expanded in the turbine section. In a normal combustion turbine, there is a compressor mounted on the same shaft as the turbine and about a third of the power produced by the turbine is used to drive the compressor. Using a compressed air storage system is more efficient because the work that the turbine would normally do compressing air is done by a renewable resource and all of the power produced by the turbine can be used to drive a generator.

By the way, I disagree with the statement in the article about the 2003 blackout. The failure was in the high voltage transmission system and additional reserve generation would not have prevented it.

[Dead_Parrot]

2. It's fossil.

http://www.businessweek.com/magazine/content/07_41/b4053092.htm

The group is building a system that will steer surplus electricity generated by a nearby wind farm to a big air compressor (diagram). Connected to a deep well, the compressor pumps air into layers of sandstone. Some 3,000 feet down and sealed from above by dense shale, the porous sandstone acts like a giant balloon. Later, when demand for power rises, this flow is reversed. As the chamber empties, a whoosh of air flows back up the pipe into a natural-gas-fired turbine, boosting its efficiency by upwards of 60%.

But, they have pictures of wind turbines on thier website, so it doesn't count. Err, or something.

[Fledermaus]

4. Something the previous poster failed to mention.

Storing unused wind power will make natural gas power plants run almost three times more efficient. Its a hybrid system much like a hybrid car. It use the appropriate power source at the correct time to maximize efficiency.

When the CAES plant regenerates the power, the compressed air is released from the cavern and heated through a recuperator before being mixed with fuel (e.g. natural gas) and expanded through a turbine to generate electricity. Because the turbine’s output no longer needs to be used to drive an air compressor, the turbine can generate almost three times as much electricity as the same size turbine in a simple cycle configuration. This uses far less fuel per MWh produced. The stored compressed air takes the place of gas that would otherwise have been burned in the generation cycle and used for compression power.
http://www.duckdigital.net/Research/CAES_Assignment.doc

[Dead_Parrot]

5. Err, I know

If you read the selection I posted, you'll see it says pretty much the same thing (albeit with a different value). However, the article states they are promoted as... a source of non-fossil-fuel energy which they are clearly not.

So, it turns wind power into a more efficient fossil fuel. Whoop de do.

We're currently at 386.61 ppm CO₂. We want to get to 350 ppm CO₂. You do not get from 386 to 350 by addition, even if you do it three times as slowly.

[vincna]

6. It's still a good system...

You are getting more net power for the same amount of fuel burned and CO2 emitted.

[Dead_Parrot]

7. Only compared to other fossil fuel systems

Compared to not building a fossil fuel system, it's a bit of a crock.

[vincna]

8. We aren't getting to totally non-fossil anytime soon

Until we get there (maybe in 30 or 40 years), I'll take substantial improvements in efficiency wherever they can be found.

[kristopher]

9. CAES is an enabling technology

It is part of the overall system of GHG reduction that is achieved by using more intermittent technologies and storage. Sorry of that is so hard for you to grasp, but the overall reductions that are enabled by systems like CAES are exactly what we are striving for.

As far as I can tell your criticism is based totally on ignorance of both what the goal is and how the elements work together to achieve that goal. For example: Who said that the source of gas used in the turbines of a CAES system has to be fossil fuels. You can achieve the same output with biologically sourced methane, ethanol or biodiesel. This particular project is a demonstration project where the primary aim is to evaluate the actual performance of multiple, geographically dispersed wind farms working with a central energy storage facility - in this case it it CAES. It will also give us data about pumped hydro and any other form of storage that we can scale up (such as the heat pump/gravel system that has lately caught my eye).

The fact is you are just bitchy because those nuke cooling towers are not growing in number. Gomen, ne.

[vincna]

11. Who's criticizing?

I like the system a lot and it should be built. I wasn't factoring in the use of the fuels you mentioned which would further improve the idea by reducing the need to burn fossil fuels. One question though: Wouldn't the fuels you mentioned have the same carbon footprint as natural gas?

I interpreted Dead_Parrot's post to mean we shouldn't build the project and I disagreed.

[kristopher]

15. It wasn't a response to your post.

Note in the upper right corner it shows the post being replied to. It is easy to lose track of the discussion, isn't it? I do it frequently.

[Dead_Parrot]

12. No, I'm bitching that it's labled as "energy storage"

Hell, a Porsche 911 turbo uses air carrying otherwise wasted energy to burn more fuel more efficiently, but that doesn't mean it's a "source of non-fossil-fuel energy".

If they were building an actual energy storage facility - such as pumped hydro (and Jpak dug out a subterranean version a while back), or the gravel pump idea, or a GWh-scale vanadium redox plant, or an Utsira-esque hydrogen plant, I'd have a bit more time for it: Even a shit load of V2G plug-ins would be a start.

All they are actually proving is that you can back up wind farms with gas. Denmark figured that out years ago, but maybe the news hasn't reached deepest Iowa yet.

[vincna]

13. It most certainly is an energy storage system

The stored compressed air eliminates the compressor section of a combustion turbine. In a conventional turbine, about 1/3 of the energy provided by the fuel is used to drive the compressor and the rest is used to drive the generator which produces electricity. In this system, the air is already compressed (using energy produced by the wind farm), so all of the energy provided by the fuel is used to drive the generator. As a result, you get about 50% more net electrical energy with the same amount of fuel. That 50% difference is the stored energy.

Your analogy to a Porsche 911 is a poor one. You can't store the energy from the turbo, shut down the engine and recover that energy later. With a CAES System, you can.

[kristopher]

3. The GHGe modeling for the CAES system

When evaluating the CAES system described in the article, it is properly viewed as a part of the larger system it is built to complement. Wind with no backup has a CO2e footprint of 5-25g CO2e/kWh. Baseload wind power that utilizes a CAES storage system jumps to between 67-104g CO2e/kWh.
For comparison, a typical coal plant in the US emits between 900-1000g/kWh and a combined cycle natural gas plant comes in around 400-500g/kWh.

Data from
Emissions and Energy Efficiency Assessment of Baseload Wind Energy Systems
Denholm, Kulsinski and Holloway
Environ. Sci. Technol. 2005, 39, 1903-1911

[Nihil]

10. OK ... after reading this thread and the OP article a few times ...

... I now understand the "fossil/no it isn't" debate that was going on.

> Compressed air would be stored in a network of 13 wells 3,000 feet deep
> and then released at strategic times to turn the turbines on two
> 134-megawatt electricity generators.

When I first scanned this post, I made a silly assumption ... I thought
that the compressed air storage operated in the same way as pumped hydro,
i.e., that the air was pumped into storage when surplus power was available
so that it could be released via (air-driven) turbines to generate power
(the "stored power") when required.

This system isn't like that at all ... it just seems to be using off-peak
power to put a mild supercharger on a gas turbine which, although
increasing the latter's efficiency (=good) is not in the same league as
the true energy storage solutions (pumped hydro, gravel bed, flywheel, ...).

:think:

[kristopher]

14. Apparently you still don't understand this very simple concept.

When you compress the air (using surplus energy - otherwise known as spilled energy - from the seven associated wind farms) it is like pumping water up the hill. When you release the compressed air, it is like letting the water run back down the hill.

Is the Jack and Jill story simple enough? CAES is one of the best energy storage solutions out there. It has geographic limitations but they aren't nearly as severe as pumped hydro.

NREL/JA-620-38270.
Posted with permission.
Renewable Energy 31 (2006) 1355–1370
www.elsevier.com/locate/renene
Improving the technical, environmental and social performance of wind energy systems using biomass-based energy storage
Paul Denholm*
National Renewable Energy Laboratory, 1617 Cole Boulevard, Golden, CO 80401-3393, USA
Received 27 November 2004; accepted 1 July 2005
Available online 24 August 2005
Abstract
A completely renewable baseload electricity generation system is proposed by combining wind
energy, compressed air energy storage, and biomass gasification. This system can eliminate
problems associated with wind intermittency and provide a source of electrical energy functionally
equivalent to a large fossil or nuclear power plant. Compressed air energy storage (CAES) can be
economically deployed in the Midwestern US, an area with significant low-cost wind resources.
CAES systems require a combustible fuel, typically natural gas, which results in fuel price risk and
greenhouse gas emissions. Replacing natural gas with synfuel derived from biomass gasification
eliminates the use of fossil fuels, virtually eliminating net CO2 emissions from the system. In
addition, by deriving energy completely from farm sources, this type of system may reduce some
opposition to long distance transmission lines in rural areas, which may be an obstacle to large-scale
wind deployment.

2005 Elsevier Ltd. All rights reserved

http://74.125.95.132/search?q=cache:UcmElZ84dGcJ:www.nrel.gov/docs/fy06osti/38270.pdf+greenblatt+CAES&cd=21&hl=en&ct=clnk&gl=us

[Nihil]

16. On the contrary, I understand *exactly* what is happening (now).

> When you compress the air (using surplus energy - otherwise known as
> spilled energy - from the seven associated wind farms) it is like pumping
> water up the hill. When you release the compressed air, it is like letting
> the water run back down the hill.

Correct. That is exactly how pumped water storage works but not exactly
how CAES works in this example as you don't just "release the compressed
air", you have to have an external fuel-powered turbine to make use of
the stored energy.

> Is the Jack and Jill story simple enough?

It's simple enough to make the same mistake as I initial did as (deliberately
or otherwise) it skipped the "add external fuel here" step. As such, it sucks
as an educational tool and is pretty crap as entertainment for the kids.
:P


We can disagree on pumped hydro but CAES is still good because of the
key section of your post:
> Replacing natural gas with synfuel derived from biomass gasification
> eliminates the use of fossil fuels, virtually eliminating net CO2
> emissions from the system.

That's what makes CAES an appealing solution: the blending of several
different renewable aspects to allow storage with near zero CO2 emissions.


Like I said in my previous post, I had misunderstood the nature of the
compressed air storage system - thinking it was a simple store & release
mechanism not a store & release-to-fan-combustion one - so, as long as the
fuel being burned is renewable, I apologise and now agree it is a good idea.

:hi:

[kristopher]

17. Even burning natural gas it is a good storage medium

That's because, as described above, it is a technology that enables the use of wind and solar on a large scale.

It is a slight improvement in the carbon footprint when the stored energy comes from off-peak coal and we burn natgas.

It is a significant improvement in the carbon footprint when the stored energy comes from renewables and we burn natgas. This is because the total amount of power made usable far exceeds the amount of power that actually flows through the CAES system. This system produces less than 10% of the carbon emissions from a typical coal plant.

It is obvious that the full benefit is obtained by using renewables and biofuels, however, a 90% reduction in the carbon from baseload electricity is hardly something to sneer at.