Rock Batteries

[kristopher]

Green pioneer: Isentropic: Rock battery could store electricity
Cambridge firm finds way to save excess power in gravel
Danny Fortson

POWER from the wind and the sun is the future, we are told. There’s just one snag – these power sources aren’t dependable. Unless there is a way to store electricity in times of plenty we will need a lot of back-up power, probably fossil-fuelled, to tide us over when the clouds move in or the wind stops blowing. And that’s not very green.

Isentropic, a five-man outfit in Cambridge, thinks it has the answer: a gravel battery. It may sound distinctly low-tech, but the company has come up with some clever engineering to make tanks of rocks into electricity stores. It comes from an idea pioneered in the 1830s by John Ericsson, the prolific Swedish inventor who designed a hot-air engine and the USS Monitor, the ironclad warship of the American civil war. Mark Wagner, a former hedge-fund manager who is now the company’s chairman, said Isentropic came about because of another boat. A sailing enthusiast, he was on the lookout for new hydrofoil designs in his attempt to set a world speed record. When he came across a novel model on the internet, he called its designer, John Howes, an engineer at the Civil Aviation Authority. “We worked on the boat for a while, but then he told me about this heat pump he was working on.” That was eight years ago.

Isentropic’s “battery” works like this. An electrical current feeds a heat pump, a bigger version of the device that keeps your fridge cold. The fridge in your kitchen uses electricity to drive a tiny heat pump to create a temperature split, chilling the inside of the fridge and warming the back.

Isentropic’s system uses Howes’s pump to heat argon gas to 500C on one side while cooling it to -150C on the other. The hot and cold gas is then passed through two giant gravel tanks, heating one and cooling the other. The power is stored in the gravel as a temperature difference. When power is needed, the process can be instantly reversed and the heat pump now works like an engine — the extreme temperatures are brought together and turn the engine, which powers a generator to create electricity.

Today most of the...

http://www.timesonline.co.uk/tol/news/environment/article6493372.ece

[Nihil]

1. K & R & info

I was going to ask a couple of questions (scale & efficiency)
but decided not to be so lazy and went looking for it myself ...
:hi:

The company's web site is at http://www.isentropic.co.uk/

It appears that each cylinder (one for hot side, one for cold side)
is 8 metres in diameter and 7 metres tall for a 30MWh installation.

The round trip efficiency is claimed to be over 70%.

They also reckon ("because gravel is such a cheap and readily available
material") that the cost per kWh can be kept very low - $80/kWh.

The image below looked familiar so I suspect that you have posted it
in a previous thread on the subject ... but it deserves a repost!

[madokie]

2. We have one of those

A pumped storage lake. Pump it full late night and early mornings then use the power in the mid day.

http://pepei.pennnet.com/articles/article_display.cfm?article_id=255995

I might add: Some of the best bass fishing I've done is in this lake.

[kristopher]

5. Yes, posted an article before

This one seemed a little more informative.

[phantom power]

3. I wonder why they use argon.

Nitrogen is fairly inert, if that's what they're after, although maybe not at 500C.

[Dead_Parrot]

4. My guess would be thermal conductivity

Argon is a pretty good insulator, hence it's use in insulated windows: A barrel of gravel topped off with Ar will stay hot (or cold) a lot longer than a barrel of gravel topped off with N.

[hunter]

6. Why the heat pump?

Why not straight resistance heating?

But at those temps you've really got to start talking about chemical storage methods.

[kristopher]

7. There are systems that store energy as heat for use as heat

This one stores energy in the form of a temperature differential so that it can be reconstituted into the most versatile form of power - electricity.

The power loss incurred in storage is similar to that of a pumped hydro system, but it doesn't suffer from the space or geographic constraints that limit pumped hydro. It is also extremely inexpensive to build this system.

[madokie]

8. I'll be surprised if we don't see these starting to be built

I know GRDA, local power company, like their pumped hydro storage system they have now.

[hunter]

9. The ideal Carnot efficiency of the beast is 84% at maximum charge.

This effiecency quickly degrades as the machine discharges.

The real world efficiency is much less than 84%, PLUS it leaks energy at a very considerable rate.

Pumped hydro is almost always going to be less expensive and much more efficient.

Check the math:

1-(-150+273.15)/(500+273.15) = 84%

[kristopher]

10. Reeeeeeeally?

"Pumped hydro is almost always going to be less expensive and much more efficient."

Do you mean that? Since the main market for this storage is to levelize power from wind turbines, and since the vast majority of our high quality wind resource is located in land that is best described as "flat as a pancake", I honestly doubt that it is going to be more cost effective to use pumped hydro than this system. There is a similar consideration associated with the offshore wind resource off the east coast, where both population density and inhospitable terrain make pumped hydro projects very hard to accomplish.

Not sure where your numbers are coming from, nor what their significance is supposed to be. The company claims about 70% round trip efficiency in the storage process. The heat pump itself they are touting as delivering 99% isentropic efficiency. If you have some reason to question those claims, you'll need to make the argument more clear for me.

[hunter]

11. "99% isentropic efficiency" means .99 X .84

Not that I believe that. And I become less convinced the more I read.

http://www.isentropic.co.uk

Sorry. Sounds like magic to me.

Jon Howes seems like a nice guy. I think he should run like hell away from Mark Wagner.

[kristopher]

13. Judging from the lack of substance in your reply

...you have no basis for your remarks.

.99 x .84 isn't a statement of anything. Unless you can be more specific, it is pretty difficult to conclude anything except you are once again talking trash and acting like you have a clue.

Do you have a basis for rejecting the claim of a round trip efficiency of 70% or not?

If so lay it out.

Do you have a basis for rejecting the claim of the heat pump itself achieving the claimed efficiency? If so lay it out.

My research tells me that it is unremarkable for heat pumps to break 90% isentropic efficiency, so the claims seem extremely plausible to me.

[hunter]

14. Do you know what the hell you are talking about?

Or do you just sell trash "green energy" securities?

It's simply bizarre to be talking about the isentropic energy as it relates to the overall gravel storage scheme.

"oooooo, look at the shiny....um, whatever the hell it is... 99% efficient!!!"

What a load of crap. You've got the proposed working temps right there in front of your face. That gives you an efficiency of 84% if the whole damned thing was a perfect machine. That's just ludicrous. Where is the unicorn?

Okay, Jon Howes may have created a nifty little ericsson engine (I might guess a thermoacoustic sort of machine from the hints he's dropping) but it can only approach the efficiency of the theoretically perfect but practically useless carnot machine. And for the most part the efficiencies of actual heat engines do not approach the theoretical efficiency.

Couple an awkward and leaky heat storage system to this machine and it's very difficult to imagine how the claimed 70% efficiency might be achieved.

The overly complex microwave lighting system described on Mr. Wagner's other site seems to be a very similar sort of property.

It begins to look more to me as if someone is packaging "green" patent portfolios, just as very questionable mortgages were packaged and sold before the crash, or how very questionable carbon trading deals are being packaged.

This appears to be junk, and I'm not buying.

[kristopher]

15. "it's very difficult to imagine"

Quoting the only part of your post with substance: "it's very difficult to imagine"

In other words you have no *evidence*, you are simply skeptical.

That's fair enough, however having seen how very poor your knowledge base is regarding our electrical system and the energy issue in general, I'll treat your skepticism with some skepticism of my own.

[hunter]

16. Keep digging, my knowledge base regarding our electrical power system is very deep...

I'm sure Mr. Howes has built a nifty little heat engine, but he needs to sell the machine as an efficient air compressor or specialty heat pump. Otherwise he destroys his credibility.

"70% efficiency" for this gravel scheme is not credible but a simple compressor that doesn't throw away large amounts of energy as waste heat is credible.

BTW, in those irrigated "pancake" flat parts of the United States you mentioned, much energy is used pumping water up and out of the ground. This is another ideal situation for energy "storage." You simply pump the water up and into a surface reservoir when the sun shines or the wind blows. On center-pivot irrigated land you could build these reservoirs in the unirrigated spaces between the circles. There are hundreds of easily implemented schemes like this that would use existing off the shelf technology -- schemes that would be more efficient and less costly than any complex unproven technology. Such projects would keep us busy for a long time. We just have to do it.

If we want to stop burning coal, we must simply stop burning coal. Legislate the coal industry out of existence. We could probably do it in fifteen years or less if we had the gumption. Waiting for the invisible hand of the market to displace coal is the worst sort of magical thinking and a lot of people on earth are going to die young because we did nothing .

[kristopher]

17. Great case in point regarding your knowledge base...

In order to harvest the stored energy of that water you've just pumped out of the 2000 ft hole in the ground all you have to do is figure out a way to install and service the pump/generator unit at the bottom of the gravity well which is at the bottom of that 2000 foot hole.

Pumped hydro is EXTREMLY limited by geography. Sure you can do it in places where the geography isn't suitable, but then it becomes a massively expensive undertaking.

You are steadily moving from the obscure to the goofy.

[hunter]

18. You are not listening.

The physics of the machine is in no way "obscure." The carnot cycle is an idealized description of heat engines, and the theory is as solid as gravity. You can't dance around the numbers any more than you could flap your arms and fly to the moon.

And then, when you talk about wind energy, you want to take the aggragate output of multiple small generators and respond to the problem of intermittant output with a centralized solution -- which is what we are doing now. Somebody puts up a wind generator or a photovoltaic system and they get the benefit of the energy, but the cost of maintaining network stability is born by everyone on the system in the form of nimble natural gas and hydroelectric plants.

I'm simply saying that small scale wind or photovoltaic systems can be matched to similar scale storage solutions. It's not "goofy" in any way. If I'm not mistaken, you seemed to be in favor of such distributed solutions, but now you turn around and try to sell an untested and very unlikely hog of a centralized system.

What's up with that?

[kristopher]

19. I'm not trying to "sell" anything

There is simply nothing you've said that in any way could be considered a legitimate critique of the gravel storage system.

You don't know the details of their product nor their engineering, yet you are making sweeping conclusions. Your support for those conclusions amounts to sample numbers given in a news article and a whole world of assumptions that are nothing more than guesses on your part.

Using the names of the people involved in the company in the familiar way you do indicates one of two possibilities - either you know these people or you want to create the impression you do in order to lend an air of inside authority to your otherwise baseless pronouncements.

Going back to your poor understanding of the electrical system: A workable renewable system is going to need a lot of storage at all levels. Buffering the grid is part of the role of that storage - again at all levels. The idea that the sample 30MWh system featured on their website means Isentropic's product is the equivalent of a "centralized system" goes almost beyond ignorance. For example the "nimble natural gas" generators you approve of are usually sized around 50-100MW, so they put out more in one hour than the entire system on Isentropic's website can store. How can you reconcile that with your characterizations regarding "centralized" systems, the claim that you understand the topic, and the implicit assumption of your reader that you are conducting this discussion in good faith?

[kristopher]

20. let's approach this from another direction

What do you think a system such as Isentropic is advertising is capable of delivering?
It seems you are adept at working out the variables involved, so perhaps you wouldn't mind walking us through the stages of the storage and retrieval process and help us evaluate the points where we should examine Isentropic's technology.

The 99% claim seems possible given what I've read, and I can't see why heat loss should be a major factor. If you have this type of data on hand it would help everyone.

Are there operating characteristics that require us to "oversize" the system in order to ensure a certain rate of delivery in the power, analogous to a deep discharge issue in chemical batteries? For example would a 30MWh system actually maintain 50MWh at full capacity and never drop below a theoretical 20MWh worth of heat?

[troubledamerican]

12. We'll have to criminalize gravel. Like they criminalized hemp.