Denmark’s largest battery – one step closer to storing green power in stones

The concept of storing renewable energy in stones has come one step closer to realisation with the construction of the GridScale demonstration plant. The plant will be the largest electricity storage facility in Denmark, with a capacity of 10 MWh.


Grant Announcement


Pea sized stones heated to 600?C in large, insulated steel tanks are at the heart of a new innovation project aiming to make a breakthrough in the storage of intermittent wind and solar electricity.

The technology, which stores electrical energy as heat in stones, is called GridScale, and could become a cheap and efficient alternative to storing power from solar and wind in lithium-based batteries. While lithium batteries are only cost-effective for the supply of energy for short periods of up to four hours, a GridScale electricity storage system will cost effectively support electricity supply for longer periods – up to about a week.

“The only real challenge with establishing 100 per cent renewable electricity supply is that we can’t save the electricity generated during windy and sunny weather for use at a later time. Demand and production do not follow the same pattern. There are not yet commercial solutions to this problem, but we hope to be able to deliver this with our GridScale energy storage system,” says Henrik Stiesdal, founder of the climate technology company Stiesdal Storage Technologies, which is behind the technology.

In brief, the GridScale technology is about heating and cooling basalt crushed to tiny, pea-sized stones in one or more sets of insulated steel tanks. The storage facility is charged through a system of compressors and turbines, which pumps heat energy from one or more storage tanks filled with cool stones to a similar number of storage tanks filled with hot stones, when there is surplus power from wind or the sun.

This means the stones in the cold tanks become very cold, while they become very hot in the hot tanks; in fact up to 600oC. The heat can be stored in the stones for many days, and the number of sets of stone-filled tanks can be varied, depending on the length of storage time required.

When there is demand for electricity again, the process reverses, so the stones in the hot tanks become colder while they become warmer in the cold tanks. The system is based on an inexpensive storage material and mature, well-known technology for charging and discharging.

“Basalt is a cheap and sustainable material that can store large amounts of energy in small spaces, and that can withstand countless charges and discharges of the storage facility. We are now developing a prototype for the storage technology to demonstrate the way forward in solving the problem of storing renewable energy – one of the biggest challenges to the development of sustainable energy worldwide,” says Ole Alm, head of development at the energy group Andel, which is also part of the project.

The GridScale prototype will be the largest storage facility in the Danish electricity system, and a major challenge will be to make the storage flexibility available on the electricity markets in a way that provides the best possible value. Consequently, this will also be part of the project.

The precise location of the prototype storage facility has yet to be decided. However, it will definitely be in the eastern part of Denmark in south or west Zealand or on Lolland-Falster, where production from new large PV units in particular is growing faster than consumption can keep up.

The full name of the innovation project is ‘GridScale – cost-effective large-scale electricity storage’, and it will run for three years with a total budget of DKK 35 million (EUR 4.7 million). The project is being funded with DKK 21 million (EUR 2.8 million) from the Energy Technology Development and Demonstration Program (EUDP).

In addition to the companies Stiesdal and Andel, the partner group comprises Aarhus University (AU), the Technical University of Denmark (DTU), Welcon, BWSC (Burmeister Wain Scandinavian Contractor), Energi Danmark and Energy Cluster Denmark.

The partners will provide an energy system analysis and design optimisation for a stone storage facility as well as optimize the technical concepts and mature the GridScale technology to a ready-to-market scalable solution.

For example, the European energy system model developed by AU will be combined with the model for optimising turbines developed by DTU to gain insight into the potential role of the stone storage facility in a European context and to optimise the design:

“The transition to renewable energy changes the way the energy system works – simply because wind and solar energy are not necessarily produced when we need it. Therefore, we need to find out how the technical design can best be adapted to the energy system and in which countries and when in the green transition the technology has the greatest value. We will look to identify the combination of energy technologies that will provide the greatest value for the storage solution. I think that stone storage technology has a huge potential in many places around the world and could be of great advantage in the green transition,” says Associate Professor Gorm Bruun Andresen from the Department of Mechanical and Production Engineering at Aarhus University.


From EurekAlert!

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April 29, 2021 2:03 pm


Zig Zag Wanderer
Reply to  Pauleta
April 29, 2021 4:37 pm

Why? In a lot of places these days, there is way too much solar power being generated when it’s not needed. The spot price goes negative.

Reply to  Zig Zag Wanderer
April 29, 2021 4:57 pm

The spot price goes negative.
Perfect. Dump the power into the ground. The more you dump the more $$ you earn. No need to try and save any power at all.

Zig Zag Wanderer
Reply to  Ferdberple
April 29, 2021 5:05 pm

Dumping it does happen as I understand it, but storing it to make more money later is a better economic decision.

Reply to  Zig Zag Wanderer
April 30, 2021 12:20 pm

Storing it makes the energy very expensive and that “free” nonsense goes right out the window. The carbon footprint skyrockets and the environmental damage does the same. But when we are talking fantasy, it really does not matter, does it?

It doesn't add up...
Reply to  Zig Zag Wanderer
April 30, 2021 6:17 pm

Storing it requires a subsidy – the negative price plus the normal market price – in order to make it viable. Mostly, it is cheaper to curtail than to store except for short periods. Frequency of charge/discharge cycles, round trip efficiency, round trip margin and cost are the key parameters.

Reply to  Zig Zag Wanderer
April 29, 2021 5:41 pm

There is not solar power or wind power generated when it is not needed. Solar is converted back to heat and wasted, incidentally heating the atmosphere. Wind turbines are shut down to delay wear. Both are demolished or abandoned in place, usually before their service life expires, when the subsidies run out or when maintenance becomes too expensive.

Last edited 3 months ago by dk_
Reply to  dk_
April 29, 2021 11:18 pm

girff will be along any time now to tell us all about UK wind power

comment image

Reply to  fred250
April 30, 2021 8:34 am

If you like: it’s absolutely brilliant. end of commercial.

(don’t think I don’t appreciate how much effort you have to put into cherry picking those graphs)

Reply to  griff
April 30, 2021 11:34 am

Poor little twerp.. Note the date…

They cherry-pick themselves, I just post them as they happen.


Reply to  griff
April 30, 2021 12:23 pm

I just cherry-pick your evening meal girff-twerp. !


comment image

Last edited 3 months ago by fred250
Reply to  dk_
April 30, 2021 7:43 am

when you say “demolished” as a lot of contracts say to remove. Non of them remove the massive cube of concrete that remains disrupting future food growth and ground water flows

Reply to  dk_
April 30, 2021 12:25 pm

Since it’s NOT ABOUT ENERGY BUT ABOUT GREED, none of that matters. When it’s stealing as much taxpayer money as possible and destroying the planet so the rich can get richer producing nothing but harm, when waste and destruction are the goal, not something to avoid, none of what is mentioned by dk matters. IT ONLY MATTERS IF THE RICH GET RICHER. That’s all “renewable energy” is–A GOLD RUSH FOR THOSE WHO CAN AFFORD TO PLAY THE GAME, with nothing but destruction for those who cannot.

Jean Parisot
Reply to  Zig Zag Wanderer
April 29, 2021 5:44 pm

In Denmark?

Reply to  Jean Parisot
April 29, 2021 6:02 pm

I saw a surprising number of u/s windmills on visits to Denmark 5+ years ago – I assume they’re all working now …?

sky king
Reply to  Jean Parisot
April 29, 2021 6:15 pm

Coldest winter I ever felt was one spent in Aarhus working on a Tele Danmark project. Locals had no problem though – riding their bikes over snow getting to work.

Joseph Zorzin
Reply to  sky king
April 30, 2021 3:44 am

Oh, isn’t it great to go back to the 19th century.

Reply to  Joseph Zorzin
April 30, 2021 7:26 am

An easy way to reduce our carbon emissions.

Craig from Oz
Reply to  Jean Parisot
April 29, 2021 10:23 pm

Rotten things are traditionally found in Denmark… 😀

Reply to  Craig from Oz
April 30, 2021 7:27 am

They don’t jump the rotten shark, they EAT the rotten shark.

Reply to  IainC
April 30, 2021 8:34 am

I think that’s Icelanders?

Mike Lowe
Reply to  Zig Zag Wanderer
April 29, 2021 7:58 pm

I am always doubtful about any scheme which requires transfer from say the generator to some cables to some storage device and back again. The accumulating losses must often approach the amount generated. I suppose those piles of stones will be very well insulated, but the greater the temperature difference to the outer covering, the more doubtful will be the result of the whole exercise. And all for an end result for which there is no convincing argument. I’m looking forward to the time when the politicians are finally compelled to realise that their dream of eliminating fossil-fueld cars can come to nought!

Reply to  Mike Lowe
April 30, 2021 12:33 am

I think the scheme would make sense if it all started with using the excess power generated by wind and solar to mine the basalt rock, crush it, screen it, grind it, etc, and on to filing up those silos with the graded, pure basal rock or optimum granulation. I would like to see all of this done without a molecule of fossil fuel being used.

Rod Evans
Reply to  Lrp
April 30, 2021 1:33 am

Making the steel for the crushers and making the steel for the storage tanks will prove an interesting challenge without the coal needed to make steel.

Rainer Bensch
Reply to  Lrp
April 30, 2021 2:53 am

…and insulated with what?

Reply to  Lrp
April 30, 2021 6:25 am

Lrp, while your observation makes complete sense, it’s unneeded, provided we just let the pricing mechanism work. Which means, of course, that no grants, subsidies, and tax rebates are used to subvert the price mechanism. If there’s a sufficient profit at the end of the process to drive additional resources toward the method, that would imply that the power is economically generated.

More likely, though, it will turn out to be another waste of tax dollars.

Reply to  Mike Lowe
April 30, 2021 12:28 pm

It fascinates me that people who live “off-grid” use 110V electricity most of the time. A tremendous amount of energy is lost in the converting of DC to AC (which is also done with commerical energy–massive waste). If anyone really cared, DC would be used off-grid and would indicate people understood what they are doing.

Reply to  Sheri
April 30, 2021 3:03 pm

Sheri, most of us who live “off-grid” have weighed the pros and cons of the DC/AC trade offs. It isn’t for you to try and insult us for the choices we make.

Reply to  chemman
May 1, 2021 10:08 am

So list how you decided. If it’s such a solid decision, why are you whining that I disagree with your choice? Show me where I’m wrong.

Tombstone Gabby
Reply to  Sheri
April 30, 2021 6:11 pm

G’Day Sheri,

It all has to do with what electrical appliances you want to have. The last TV receiver I saw that was run on 12VDC was a portable unit, 9″ B&W CRT, with analog tuning.

For Recreational Vehicles, in the calculations for battery capacity/PV panel wattage, the allowance for loss, DC to AC is 10%.

Reply to  Tombstone Gabby
May 1, 2021 10:09 am

Yes, the TV could be a problem. I don’t go off grid with a TV, so that was not really something I considered.

Can you show me the calculations for the allowance loss?

Tombstone Gabby
Reply to  Sheri
May 1, 2021 10:22 am

Can you show me the calculations

I have a spreadsheet that I’ve been using for years – wouldn’t help too much. Give me a day or so, I’ll scout around for you.

Reply to  Tombstone Gabby
May 1, 2021 12:30 pm

That would be much appreciated. Will check back in a day or two.

Tombstone Gabby
Reply to  Tombstone Gabby
May 1, 2021 4:47 pm

For a recreational vehicle:

INVERTERS   phred Tinseth © 1998-2002 Reproduction Permitted

(I had to go to the Wayback Machine for this.)

Efficiency– Is a critical figure. It should exceed 90% overall in [most] inverters. It should not vary much from partial to full loads. Beware of inverters that advertise 90+% overall efficiency but may drop to less than 50% at some load levels.

Further down the same page:

• Efficiency. A measurement of how small an amount of electricity an inverter uses just to run its own “innards.” If you’re just going to run a drill a few minutes, you don’t care. If your TV, VCR, computer is going to run for hours, this is a prime consideration. Some of the quality inverters mentioned idle at less than one-tenth of an amp and are well over 90% efficient. You can leave them running 24 hours a day.

Hers is a calculator page covering AC and DC loads – they assume inverter efficiency 0.9 —

(That 90% figure applies to a quasi-sine wave inverter. Pure sine wave inverters are about 5% less, and cost a lot more.)

However it doesn’t mention the second problem – with lead acid batteries in an RV. Figure for every 100 Amp Hours that get stored approximately 80 AH can be withdrawn later. Nothing to do with the inverter, but must be considered for RV installations. So approx 10% loss for the inverter, and another 20% loss via the lead acid battery.

Reply to  Pauleta
April 29, 2021 6:53 pm

Intermittent/renewables when in range. An environmental blight A niche solution with benefits.

Reply to  Pauleta
April 30, 2021 5:51 pm

The word should have been surges and even that doesn’t make sense when surges are infrequent. Engineers can produce almost anything, but making it an economical proposition probably relies on unicorns and fairy dust. IMO.

Bryan A
April 29, 2021 2:07 pm

Is this April 1st or April 29th?
Calling a storage Scheme “Grid Scale”??
I have an energy storage scheme to test also using rocks.
I require rocks of superheated and supercompressed Carbon Crystals.
I’ll require the equivalent of around 1,000,000 carats worth with a 2 carat size minimum to test viability

Last edited 3 months ago by Bryan A
Reply to  Bryan A
April 29, 2021 2:17 pm

That’s a bunch of carbon. I bet you can tax that too.

Bryan A
Reply to  Pauleta
April 29, 2021 3:31 pm

OMG I forgot about the Carbon Taxes. Wonder if I can get Guberment Funding to pay them too

Abolition Man
Reply to  Bryan A
April 29, 2021 3:50 pm

This sounds like something from the mind of a Bond villain!
Chances are then good that the GreenGang will want to look at it for both carbon capture AND photovoltaic possibilities!

April 29, 2021 2:09 pm

Efficiency is probably about 50%

April 29, 2021 2:45 pm
Reply to  IanH
April 29, 2021 5:13 pm

As stated in your link, “Based on ambitious yet realistic component performances” in other words more Unicorn farts. As a long in the tooth Professional Engineer (chemical) I’m calling this whole scheme a busted flush, a pipedream, an academic wishful thinking exercise, show the calculations if you want any credibility.

Reply to  mike
April 30, 2021 7:57 am

Hey… maybe my tooth is long too! Thermodynamic efficiency is a hungry whore; lest anyone forget, in a fairly recent vintage gas-turbine power plant, efficiencies of almost 60% have been realized.

See comment image

Before the cheering section gets winded (ahem), let us remember that the record-attaining efficiencies were had under exacting test conditions, not while trying to supply a significant but still variable power output to a quixotic seasonal / daily / hourly demand load.

One cannot really ever beat the thermodynamic equation, in the end.

Zig Zag Wanderer
April 29, 2021 4:38 pm

Doesn’t matter if the energy being generated can’t be used for anything productive, as PV is often.

William Astley
April 29, 2021 5:15 pm

You are too kind. The heat at 600C …. before the vessel cools….

Must be converted back to electricity. The efficiency of this scheme to produce electricity is 0% because no one would pay for necessary equipment to make electricity from hot rocks.

The green scams need to produce 24/7 electricity, not hot rocks. And the rocks only stay hot for about a week.

The green scams need a magic battery. The magic battery an entire country’s wind and sun electric power production… … transferring energy from windy summer months… at which time Germany for example cannot use that energy. To cold winter months when there are cold windless days and high electrical demand because everything is electric heated and their is little solar.

To convert the heat at 600 C back to electricity… the idiots/dreamers must find a way transfer heat from the hot rocks…

To water to make steam…. And then dreamers would need to have steam turbines and generators to produce electricity.

A reservoir system with pumps, works with about 50% efficiency.

Aaron Schnelle
Reply to  William Astley
April 29, 2021 6:32 pm

Electrical > Mechanical > Thermal > Mechanical > Electrical.
Each of these conversions has a maximum efficiency associated with it. Stacked on top of the Solar/Wind capacity factors and is economic viability really possible? Or do we even care any longer?

Pamela Matlack-Klein
Reply to  Aaron Schnelle
April 30, 2021 1:22 am

They will play around with this for a while until the futility of the scheme dawns on the ones paying the bills. Then it will be quietly abandoned and nothing more said.

Reply to  Pamela Matlack-Klein
April 30, 2021 10:19 am

I don’t think it’s REALLY about efficient grid-scale storage. It’s simply a scheme to enrich the promoters at taxpayer expense. I think you’re probably right about the outcome.

oeman 50
Reply to  Aaron Schnelle
April 30, 2021 8:49 am

Good point Aaron. But I would phrase it another way: Each of the conversions has losses that stack up. I think this is a thermodynamic Rube Goldberg scheme.

Reply to  Aaron Schnelle
April 30, 2021 9:29 am

Anything is economically viable with other people’s money. As the article stated, storage is the only obstacle to a 100% “green” energy system. Never mind economics, when people can’t afford the bills demand goes down.

Mike Lowe
April 29, 2021 8:00 pm

Is that going into the store PLUS coming back to the grid? It’s 2 way traffic!

Nick Graves
April 30, 2021 12:29 am

Yes, my inbuilt 2nd law of thermodynamics-ometer went off the scale once I started reading.

Reply to  Nick Graves
April 30, 2021 10:20 am

Pesky laws, who needs ’em?

Reply to  TonyG
April 30, 2021 4:40 pm

Obama people thought they could change them too

April 30, 2021 4:22 am

Indeed. The fact that this article did not address efficiency is a big tell.

April 30, 2021 5:48 am


Richard Page
April 29, 2021 2:13 pm

We’ve gone backwards. I thought windmill technology from the middle ages was bad enough but this is Paleolithic technology – heat some rocks as a ‘source’ of energy?

Zig Zag Wanderer
Reply to  Richard Page
April 29, 2021 4:39 pm

It’s not a source, it’s storage of energy which is useless at the time of production.

Richard Page
Reply to  Zig Zag Wanderer
April 30, 2021 4:24 am

Zig Zag – if the energy is stored in the rocks, however it got there or whatever unused surplus it happened to be, then it will be a ‘source’ at some later point when it is needed.

Reply to  Richard Page
April 29, 2021 4:46 pm

comment image

Reply to  DonM
April 30, 2021 12:35 am

Patent pending?

Pamela Matlack-Klein
Reply to  DonM
April 30, 2021 1:24 am

I use one of those bed warmers to roast green coffee beans and make popcorn. Some antiques are still useful today.

Tombstone Gabby
Reply to  Pamela Matlack-Klein
April 30, 2021 6:23 pm

G’Day Pamela

“Some antiques are still useful today.”

Yup, and some of us even leave comments.

Patrick MJD
Reply to  Richard Page
April 29, 2021 11:25 pm

“Richard Page

I thought windmill technology from the middle ages…”

It’s older than that. Try 4th – 6th century.

Reply to  Patrick MJD
April 30, 2021 2:21 am

BC actually!

Dave Allentown
Reply to  Patrick MJD
April 30, 2021 9:22 am

The vertical post windmill was a Middle Ages invention originating in or near Holland, around 900 or 1000 A.D. It was revolutionary for its ability to improve the lives of the masses. The earlier windmills to which you refer spun on a different axis. They were clever but not revolutionary.

Patrick MJD
Reply to  Dave Allentown
May 1, 2021 12:08 am

They are still windmills, using wind to do work which is OK in some applications but not for reliable, grid scale, power generation. It is still non-modern technology used in a highly modern world.

Last edited 3 months ago by Patrick MJD
April 29, 2021 2:14 pm

GridScale? or StoneAge? We’ll be pushing cars with our feet like Fred Flintstone.

Reply to  Alan
April 29, 2021 2:59 pm

Originally, they had planned to use balls instead of stones, but being in Denmark, they couldn’t find any.

David Blenkinsop
Reply to  Alan
April 29, 2021 8:14 pm

Who needs steam turbines, when you can just have the 600 degrees C continuously scorching a giant dodo bird’s tail feathers, in order to keep it running d.c. generators off a treadmill?

Reply to  Alan
April 29, 2021 9:33 pm

Yabba dabba do!

Reply to  Alan
April 30, 2021 5:20 am

Gritstone or grit is a hard, coarse-grained, siliceous sandstone.

Ed Zuiderwijk
April 29, 2021 2:21 pm

If you ever had the bad fortune of renting a place ‘heated’ with storage heaters, full of bricks warmed up on off-peak electricity, then you know it won’t work, especially when it’s freezing outside.

Reply to  Ed Zuiderwijk
April 29, 2021 3:07 pm

I remember a hot sommer day in Swizzerland at about 1660m hight near the source of the Inn , dark blue sky, sun heating stongly, near the wild young river a lot of stones in all sizes, most basalt.
A steak put on a table size stone was ready to eat after 5 minutes, a nice place for a BBQ without grill but very fine regional wine.

Reply to  Ed Zuiderwijk
April 29, 2021 3:18 pm

If y’all know me, you know I like back-of-the-envelope calculations. I chose the tanks filled with basalt to be the size of a football field, ten feet deep. Here are the calculations on how many units that size it would take to power Texas for one week, as we saw last winter. The [1] below indicates a computer output line. Whatever follows a # is a comment.

> (specbas=840) #specific heat basalt, J/kg/°
[1] 840
> (densbas = 1520) # density basalt, kg/m3
[1] 1520
> (enclvol=30*15*3) #enclosed volume, one football field 10′ deep, m3
[1] 1350
> (kgstone=densbas*encllen) # basalt weight, kg
[1] 2052000
> (jperdeg=specbas*kgstone) #joules to raise basalt by 1°C, j/deg
[1] 1723680000
> (degswing=400) #usable temperature swing, deg
[1] 400
> (jtot=jperdeg*degswing) #total joules available per cycle, j
[1] 6.89472e+11
> (genereff= .3) # efficiency heat to electrical
[1] 0.3
> (transeff=.95) # efficiency transmission lines
[1] 0.95
> (reheateff=.95) # estimated efficiency, reheat basalt
[1] 0.95
> (totwh=jtot/3600*genereff*transeff*reheateff) #total energy available per cycle, watthours
[1] 51854040
> (texascon=335e12) # Texas annual electricity consumption, watthours/yr
[1] 3.35e+14
> (numneeded1week=round(texascon/365/totwh*7,-3)) # number needed to power 1 Texas for 1 week
[1] 124000

So we’d need 124,000 of these football-field-sized insulated tanks, plus the associated generation and heating infrastructure, to power Texas for a week.

Not holding my breath here …


Last edited 3 months ago by Willis Eschenbach
Abolition Man
Reply to  Willis Eschenbach
April 29, 2021 4:02 pm

Now, Willis!
How many times do we have to tell you not to torment the Green kiddies with facts and figures!
I can now see that the true goal of GangGreen is to devolve humanity back to pre-Paleolithic times; before the use of fire became common! First windmills, then biomass (wood fires) and now heated rocks!
The next step back in time will be to live in trees and forage for fruits and vegetables, as our distant hominid ancestors did! Sadly, that type of diet won’t adequately support full brain development and function, but most leftists won’t know the difference!

Charles Higley
Reply to  Abolition Man
April 29, 2021 7:13 pm

Yesterday I read something about how we should be encouraging forest living.

Rick C
Reply to  Willis Eschenbach
April 29, 2021 4:17 pm

Thanks Willis. I was just about to open Excel and do a similar reality check. Maybe then illustration in the article was meant to be at scale – i.e. One wind turbine, 4 houses, one small commercial building and 1 4.7 million Euro “grid scale” storage system.

Reply to  Willis Eschenbach
April 29, 2021 4:22 pm

I spotted a minor typo.

So we’d need 124,000 of these football-sized insulated tanks,…

They are football field-sized tanks. Now if they could get that much energy stored in a football, well, that would be a breakthrough. 😉

Reply to  PaulH
April 29, 2021 4:35 pm

Thanks, Paul, fixed. I hate typos and brain dropouts …


Tombstone Gabby
Reply to  Willis Eschenbach
April 30, 2021 6:29 pm

G’Day Willis,

You might check my reply to Pamela above.

Jean Parisot
Reply to  PaulH
April 29, 2021 5:47 pm

I think we can do that, but you have to withdraw it once.

Reply to  PaulH
April 29, 2021 6:21 pm

I would think a football sized quantity of Plutonium could produce that much heat.

Reply to  Drake
April 30, 2021 2:27 am

“a football sized quantity of Plutonium”
Probably in half a second or so!

Bruce Cobb
Reply to  PaulH
April 30, 2021 8:04 am

The quadium bomb (“Q-bomb”) had enough energy in it to destroy the world, and was about the size of a football.

Reply to  Bruce Cobb
May 1, 2021 9:26 am

I read The Mouse That Roared when I was a kid, and I enjoyed it immensely. 🙂 I should read it again, someday.

Reply to  Willis Eschenbach
April 29, 2021 5:04 pm

There you go again Willis! Confusing science and technology with an emotional narrative. It isn’t meant to work, just to keep the Green Dream alive…while more money is ploughed into subsidising dysfunctional windmills.

Reply to  Willis Eschenbach
April 29, 2021 5:09 pm

In IanH’s link

they proposed a 1GWH facility on a 5 Hectare site (>12 acres or about 800 x 800 ft square) but they did not say how tall the tanks would have to be

if my math is correct, to cover Texas sized consumption for one week offline would require 6425 of them

a football field is 450 m^2 a hectare is 10,000 m^2 so each site is 22.2 football fields

total area about 143,000 football fields so a similar area that you came up with, Willis
of course it would be an array of tanks so 15% overage for space between tanks for pipes would account for that much difference

Just for the cost of vessels at one site estimated 340m pounds or $470m.
SWAG total site cost $800m including labor, piping, turbine/generators, substation, etc? Build 6425 of them costs $5T? Spread cost over 20 years, $250b per year.

Getting sick of the math… would like to get down to how much extra cost per kwH consumed.

However, here is their own assessment:

This indicates that if the PTES systems can sell their dispatchable electricity at the current cost of renewable energy which we have assumed to be £50/MWh based on a scan of current published prices2, then it would take more than 50 years to recover the additional capital expenditure of the coupled system.

Their “current cost of renewable energy” is $0.70 per kWh… jeez I think current midwest rates are around $0.12/kwh.

So the cost of “zero emissions” alone is going to be 0.70 per kWh (today’s cost of renewable energy) and you will have to add whatever extra cost of all this thermal storage infrastructure is going to add to it. Lets just conservatively assume $1 per kwH So if you are paying $150 a month electric bills just think of paying $1200 a month (an extra $13k a year) to “save the earth”.

Reply to  Willis Eschenbach
April 29, 2021 7:19 pm

It appears there may be an error in the volume of the football field
@100m x 50m x3m = 15,000 cubic metres

April 29, 2021 9:15 pm

Cold, you’re mixing metres and feet. The football field is 30 m x 15 m, 3 m deep.


Reply to  Willis Eschenbach
April 29, 2021 9:34 pm

Geez Willis, I wish our rugby team only had to make 30m to score a try from a long kick-off.
It always seemed like 200m, even though it was really just 100m.

Reply to  Willis Eschenbach
April 29, 2021 9:42 pm

I thought football fields were 100 yards long, 120 if you count the endzones.
They are also 53 1/3 yards wide.

AC Osborn
Reply to  MarkW
April 30, 2021 1:42 am

Their “football” is not our “football”, their “soccer” is our “football”, very confusing

Reply to  Willis Eschenbach
April 30, 2021 12:16 am

…and Willis is mixing feet and yards! Why don’t you Yanks just metricate, then we can all miscalculate together.

Abolition Man
Reply to  paranoid goy
April 30, 2021 3:07 am

That’s part of the plan to keep Americans miseducated! Judging by the last election, it’s succeeding swimmingly!

Reply to  paranoid goy
April 30, 2021 5:28 am

We tried metricating once.. just didn’t work out.

Reply to  Willis Eschenbach
April 30, 2021 3:24 am

“The football field is 30 m x 15 m”

Maybe a field for 5 year olds is that size ?

Reply to  Willis Eschenbach
April 30, 2021 3:30 am

Willis, Maybe you are thinking of a basketball court?

In the National Basketball Association (NBA), the court is 94 by 50 feet (28.7 by 15.2 m).

Michael S. Kelly
Reply to  Willis Eschenbach
April 29, 2021 7:27 pm

Excellent rundown, Mr. Eschenbach. I did much the same thing myself prior to reading your comment, only with phase change materials. They should be much more compact, but aren’t. This is one of those ideas that has a surface appearance of plausibility, but when looked at through just first-order eyes, is an obvious loser.

Liquid air energy storage is at least a little better, but not by much.

Reply to  Willis Eschenbach
April 29, 2021 8:44 pm

Yes, but you would use only half the football fields in Texas. 😉

Last edited 3 months ago by Phil
Reply to  Willis Eschenbach
April 29, 2021 10:09 pm

The density of basalt is about 3000kg/metre cubed.

Reply to  Ariadaeus
April 30, 2021 12:21 am

What would be the flow rate of heat through a football-field size block of pebbles at each level of ‘discharge’?
( Apple pies take a long time to cool down owing to the slow rate of heat loss, so would the heat transfer be fast enough? )
UK is now at 3 weeks of negligible wind, so we would need a lot of these batteries, and there will be a lot of holes in the ground where the stones are mined.
Mines are never popular with NIMBYs, who are probably in the forefront of promoting wind energy.

Richard Page
Reply to  StephenP
April 30, 2021 4:30 am

Presumably, if this system is useful because basalt cools slowly, then it would face similar problems as it would presumably heat slowly as well. Or is basalt a miracle substance that heats rapidly but cools very slowly?

paul courtney
Reply to  Richard Page
April 30, 2021 12:26 pm

Mr. Page: I expect some guy named ziz zag will wander in to explain the miracle, how the heat is created for free from “surplus” wind, so the “heating slowly” doesn’t impede the miracle. I’m happy to have Denmark make mistakes from which we can learn. This scheme looks wasteful enough to find favor with greens.

Reply to  StephenP
April 30, 2021 8:48 am

StephenP, no problem there. The developed world would just outsource the mining in the same way that we do it now, slave labor coupled with little concern for the environment in Africa and China.

Michael S. Kelly
Reply to  StephenP
April 30, 2021 12:00 pm

In my fantasy world, it would become federal law to require any proponent of wind energy to allow a Vestas 4 MW wind turbine be installed on his/her property.

Reply to  Willis Eschenbach
April 30, 2021 3:21 am


> (enclvol=30*15*3) #enclosed volume, one football field 10′ deep, m3

How big is a football field (in metres)?

I thought they were around 100m long by 60-70m wide.

I hate using wiki, but…

Last edited 3 months ago by fred250
Reply to  Willis Eschenbach
April 30, 2021 7:30 am

@Willis, second mug of coffee and second reading of the article…

Many have already noted the error in line 3 – a football field is not 30 meters, it is more like 110 meters (with end zones).

So, 124,000 / ~3.7 = 33,513.

However, there are three more considerations here.

1) You are basing the calculation on a solid mass of basalt. They are using “pea-sized gravel.” So, I’m taking 20% of the volume as air gap.

33,513 x 1.25 = 41,891.

2) Also, basalt is a terrible thermal conductor, and worse with the air gaps – this will need many lines for whatever working fluid they are using to extract the heat. SWAG of 20% of the storage volume lost here, too.

41,891 x 1.25 = 52,364.

3) The calculation misses that the scam scheme requires two equivalently sized tanks, one “hot” and one “cold.”

52,364 x 2 = 104,728.

So, still pretty gol durn’ed close.

(I also think that your conversion/transmission efficiencies are rather optimistic, too, but I have no handy backup for that.)

Patrick B
Reply to  Willis Eschenbach
April 30, 2021 9:20 am

Now figure out how many wind turbines we need to generate the necessary electricity for the first two weeks of August in a typical year in Texas. To supply air conditioning for both the immediate need and to “charge” up the storage for all the slow wind that occurs daily at that time of year.

Reply to  Willis Eschenbach
April 30, 2021 3:23 pm

(enclvol=30*15*3) #enclosed volume, one football field 10′ deep, m3
Not sure about this calculation. A standard American football field is 109.75 meters in length and 48.8 meters in width. So the enclvo should be 109.75 x 48.8 x 3

Reply to  Willis Eschenbach
April 30, 2021 5:10 pm

The engineer in me tells me that the tanks probably cannot be that large.
Because the radial thermal expansion of a 300 foot diameter steel tank when heated would be much greater than the rocks causing the rocks to settle into the space which would then resist the contraction during cool down. Unless I’m missing something the tank would fail after a number of cycles.
What am I missing as a former designer of large diameter flat bottom crude tanks?
There are other issues if flat bottom like friction restricting thermal expansion at 600 C.

B Clarke
Reply to  Ed Zuiderwijk
April 29, 2021 3:36 pm

Ed we do have twenty year old storage heaters that provide adequate heat, but expensive to run even on economy 7 night charging rate, we looked at next generation storage heaters as replacements, the good news is they are cheaper to run. The bad news is there called smart SHs they turn off in a draught ,which defeats the object, and only heat up to what you used the previous day, so if the next day is considerable colder your colder, thats smart! Smart as a con they save the power supplier from supplying, its a EU Directive ,like reducing the wattage on vacuum cleaners to save power, when in reality you have to vacuum twice to get the same results as a older 2000 watt machine.

Reply to  B Clarke
April 29, 2021 5:13 pm

I save water by flushing the lo-flo toilet 10 times to duplicate 1 flush in the old toilet. Progressive policies in action.

And don’t ask your plumber what happens to turds in the plumbing when there isnt sufficient flow.

sky king
Reply to  Ferdberple
April 29, 2021 6:30 pm

I’m renting an apt in the Philippines built in the 1980s by the US Navy – 2 inch lines to commercial style American Standard john. Unstoppable!

Just moved from a very high-end villa with 4 low-flow johns throughout but with plumbers friend in each. One of them took 1 month to unclog.

Reply to  Ferdberple
April 29, 2021 6:37 pm

They move down the line a little at a time, a couple of feet each time the 1.6 gallons of water flows by.

Old houses from the 50s to the 70s were mostly designed with the waste piping running from the location of the washing machine through the house past all the other fixtures to the street, so that every time you wash clothes, you would “wash” out your waste piping. At that time most houses had bathrooms back to back to save materials and labor for installation.

Modern houses are, in general, no longer designed that way. The architect does not care about saving materials since it is all plastic now and inexpensive compared to copper and cast iron of years ago. The labor is cheaper too, takes less time to install with plastic.

Another problem caused by evil oil, right BigOilBob?

April 29, 2021 2:38 pm

I have set up a Google Alert for this one. I suspect it will go the way of “Molten Salt” heat storage created by reflecting sunlight to a tower of salt……ffs.

B Clarke
April 29, 2021 2:38 pm

How do they turn hot stones back into a electric current ? If this is possible wont there be a large loss of energy in transmission?.

Patrick H.
Reply to  B Clarke
April 29, 2021 2:59 pm

Really! I don’t get it. Do they have some magic whirlygig in there?

Reply to  B Clarke
April 29, 2021 3:08 pm

A Strerling motor turns a generator 😀

Loren C. Wilson
Reply to  B Clarke
April 29, 2021 6:39 pm

It’s the large loss in converting the heat back into electricity (work). The universe does not let you get back what you put in. The maximum efficiency is near 70%, but that is just at first. as the hot rocks cool and the cold rocks warm, the efficiency goes down. I have a more complete post in this thread explaining the natural theoretical efficiency of the process.

Nick Schroeder
April 29, 2021 2:40 pm

How long has the home grown solar industry used stones for heat storage?
60 70 years or so?

Reply to  Nick Schroeder
April 29, 2021 6:44 pm

Mom’s house has stones held together by cement in the form of concrete, poured on top of Styrofoam for the floor, with south facing sliding glass doors to expose the floor to the sun for PASSIVE solar heating. The house was built in the early 80s. The site was well suited for the use.

Not used much though, Mom is 90 and can’t get to the basement to open and close the curtains, and her geothermal heat pump works well.

Charles Higley
Reply to  Drake
April 29, 2021 7:19 pm

The wonder of passive systems is that the more passive the house systems, the more active the homeowner. Constantly adjusting things is not my idea of retirement.

April 29, 2021 2:42 pm

The same technology was being developed in Newcastle a decade ago:

Curious George
Reply to  IanH
April 29, 2021 6:30 pm

January 9, 2019, to be precise.

Reply to  Curious George
April 30, 2021 7:36 am

I give people a break on this kind of thing, CG – I know that 2020 FELT like a decade to me!

April 29, 2021 2:47 pm

“Basalt is a cheap and sustainable material that can store large amounts of energy in small spaces, and that can withstand countless charges and discharges of the storage facility.”

I think they mean it can withstand getting hot and cold quite a few times?

April 29, 2021 2:51 pm

At least the drawing is appropriately scaled.

Gordon A. Dressler
Reply to  Mike
April 29, 2021 3:19 pm

Maybe, maybe not. A wind turbines in common use a decade or so ago was rated at about 1.5 MW at peak output . . . today, the common super-large onshore wind turbine is rated at 2.5-3 MW peak output.

The above article says the GridScale thermal battery storage demo system will have a capacity of 10 MWh equivalent electrical storage. I seriously doubt they will ever get that capacity from a system that is, on a volumetric basis, only about 3 times the physical size of a single modern large wind turbine.

michael hart
April 29, 2021 2:57 pm

Oh yeah. They’ve discovered some form of thermal energy storage which eluded generations of engineers before them and isn’t much troubled by the Laws of Thermodynamics? Puleezze.

Maybe not so much a product of Aarhus University, but maybe a product of Arse University.

michael hart
Reply to  michael hart
April 29, 2021 3:02 pm

…and Carnot is probably cycling in his grave.
I’m embarrassed to have not thought of that joke earlier.

Neil Jordan
Reply to  michael hart
April 29, 2021 4:14 pm

You’re correct about the discovery. Look at the lateral pipe thing that splits the green arrow into a red arrow and blue arrow. The pipe has pleasant accommodations for Maxwell’s Demon. The Demon inspects the green arrows from the windmill. The hotter arrows go out the red pipe. The cooler arrows go out the blue pipe. When the houses want to be warmer or cooler, they call the Demon who roots through the arrows in his tanks to send out the correct ones. If you expected a \sarc, I’m fresh out now. My next post will have two to make up.

Gordon A. Dressler
April 29, 2021 3:01 pm

From the above article: “The storage facility is charged through a system of compressors and turbines, which pumps heat energy from one or more storage tanks filled with cool stones to a similar number of storage tanks filled with hot stones, when there is surplus power from wind or the sun.”

Well, the basic Carnot efficiency of pumping thermal energy from a cold reservoir to a hot reservoir is miserable. Thermodynamics 101.

Now, let’s also throw in the step-by-step inefficiencies associated with the full cycle of:
1) converting the wind-generator AC power output voltage and frequency to that needed for driving the air compressors,
2) moving air along piping and through the pebble beds (aka pump/compressor work inefficiencies and pipe/bed friction losses),
3) thermal energy losses associated with not-perfectly-insulated storage “reservoirs”,
4) expanding the “hot” air across turbines to generate electricity, especially considering that turbines really don’t work efficiently with widely varying density of the working fluid at the inlet (i.e, non-constant inlet temperature and/or pressure), which is pretty much inevitable as thermal energy is extracted from the “storage reservoir”, and
5) adjusting the turbine-generated electricity to the required frequency and phase stability required to “lock into” the grid (same issue that exists with electricity coming directly off the wind turbines).

On top of the physics, one would need to perform a LCOE (levelized-cost of electricity) analysis for this “thermal battery system”, just as one needs to do for an “electro-chemical battery system”, to see if it makes economic sense at its design reserve capacity (i.e., MWh of reserve to the grid).

Reply to  Gordon A. Dressler
April 29, 2021 3:45 pm

Gordon D. — Looks like we were posting at about the same time on similar tacks. You are absolutly correct. Given Denmark’s location and topology, they’d get at leat 10 times farther with small, localized traditional power production on natural gas. I guess engineers aren’t sciency enough to be listened to.

John Bell
Reply to  Gordon A. Dressler
April 29, 2021 4:26 pm

Dreadful efficiency, I bet, single digit.

April 29, 2021 3:05 pm

So “excess” electricity runs compressors to move ‘heat’ from one tank to another and when needed the ‘heat’ is released to spin a generator making electricity? I’m sure the real explanation is more complicated than that but I don’t get it.

April 29, 2021 3:08 pm

Sounds like pouring more good money after bad.
The best ways of producing electricity from a large heat differential that I am aware of: Stirling generator, Dielectric Peltier/Seebeck solid-state, and steam power engine-generator. Steam requires a great deal of heat transfer for significant electrical production, but doesn’t need the cold sink to operate. The other two need very large generation facilities to produce significant electrical energy. All three require substantial maintenance, and eventually replacement within about twenty five years. The Peltier/Seebeck effect devices use variously rare-earth doped silicon carbide for manufacture at quite a large scale volume; probably not in Denmark. Peltier devices produce DC energy, requiring synchronized inversion to be used on the power grid.
Wind and solar generation also require high maintenance and replacement within about 25 years.
Means of heat transfer for Peltier or Sterling requires a lot of plumbing, either stainless steel or else higher maintenance materials.
All of the materials require huge amounts of fossil fuels as raw input as well as for manufacture. As with wind and solar generation, few of the manufactured components can be recycled using current technology.
When manufacture, maintenance, and retirement are counted in, carbon savings are virtually nil. It only works if con artists continue to cook the books about carbon footprint.
Recycled lead acid, Iron Nickel, or Nickel Metal Hydroxide, battery storage could be implemented for much less, require about as much maintenance and upkeep, but could be distributed throughout the service area requiring much less additional distribution infrastructure than central thermal storage. Just don’t plan on getting an EU subsidy for it.

Tony Taylor
April 29, 2021 3:35 pm

Portable geothermal. Did they check whether it would be more efficient to dig up and relocate a volcano?

John Bell
April 29, 2021 4:02 pm

Fossil fuel would be so much simpler and more efficient and works any time. jeesh!

April 29, 2021 4:03 pm

B.S. detector went off instantly when I read this article, and completely melted when I read the claimed efficiency is 60-65%!!! We can only get that from a gas turbine mated to a steam generator and these scammers claim they can run turbines and compressors backwards and forwards and get the same efficiency??? Rube Goldberg and Carnot are doing a tango together in their graves.

Zig Zag Wanderer
Reply to  PCman999
April 29, 2021 5:13 pm

Well, that’s what physicists have calculated. See a link above in the comments. I’m dubious that 60% is practical, but it’s probably nearly 50%.

Edit: link

Last edited 3 months ago by Zig Zag Wanderer
Old Cocky
Reply to  PCman999
April 29, 2021 5:30 pm

They’re different efficiency measures. Carnot efficiency doesn’t care about the heat source, just the temperature differential.

Of course, that 60 – 65% figure is probably just the efficiency when generating electricity, not the full heating/cooling cycle, or heat losses during storage.

Reply to  PCman999
May 2, 2021 9:55 am

The heat sink in the Carnot cycle proposed is cryogenic, so efficiencies would be higher than working against a 100C (or whatever) combined cycle heat sink. But yes, it seems a Heath Robinson proposal. I am not an advocate of this storage system, of lithium batteries or of the giant underground pumped hydraulic piston schemes. The only storage scheme in use at present is Lithium batteries, which are not economically recyclable AFAIK – unlike lead acid, perhaps basalt peas could be recycled into a component of highway surfaces, and the giant caverns for the pumped storage reused for landfill. (When some sort of load following fast reactor technology gets going).

April 29, 2021 4:05 pm

Every one of these “green-energy storage processes” is predicated upon the assumption that the energy source is both abundant and virtually free. If you could achieve those things, then the serious inefficiencies of storage and regeneration might be worth ignoring. Of course, if the original energy source was both abundant and free, why on earth would you need to store it for regeneration?

Reply to  DaveK
April 29, 2021 4:25 pm

It has been proposed that Molten Salts Reactors could melt a reservoir of salt overnight to be used the next day for peak hours generation. One of the most promising MSRs uses some lithium….if there is any lithium left after Elon Musk produces batteries at 1/2 the current cost….yes, that might be the biggest whopper Elon has told to date.

Zig Zag Wanderer
Reply to  DaveK
April 29, 2021 4:50 pm

It’s abundant and free when we don’t want it. The idiocy of PV is that it’s available when not wanted, and the price goes negative. The goal is to make some use of that.

I’m not saying it’s a good or workable idea, but that is the goal.

Reply to  Zig Zag Wanderer
April 29, 2021 5:27 pm

No need to return negative $$ to grid. Just dump it. The more you can dump the more you earn.

It doesn't add up...
Reply to  Zig Zag Wanderer
April 30, 2021 7:26 pm

The problem is that if (for ease of exposition) 50% of the power is surplus then the PV must earn 100% of its income from the 50% that is salable, which immediately doubles its effective cost. If the price for the surplus portion is negative, then the price on the portion used must rise to compensate. Otherwise you don’t have a viable investment. Levelized cost calculations need to take proper account of this.

Of course, the more you invest in renewables the more you will get unusable surpluses. Once the nameplate capacity exceeds demand at times of peak production you have a surplus. In fact, it kicks in sooner than that because grids will need to run with other generation on line for stability, backup, and balancing, since solar generation fluctuates with clouds as well as the angle of the sun.

Solar can sort of work with storage in low enough latitudes, where more or less a daily surplus in the middle of the day can be stored for use for the evening rush hour except during bad weather. At higher latitudes surpluses are confined to summer months, denting the economics. Seasonal storage is a prohibitive cost.

Wind tends to have higher capacity factors, but is much more subject to extended lulls and well below average levels of generation. Because maximum generation can occur at both high and low demand, surpluses are much less certain and also highly variable. That tends to stretch storage projects beyond viability when attempting anything more than short term output smoothing and grid stabilisation..

It doesn't add up...
Reply to  It doesn't add up...
April 30, 2021 8:42 pm

Footnote: Making solar work with storage can be quite hard, even in tropical locations:

With wind thrown in:

Reply to  DaveK
April 30, 2021 2:22 am

But what “if the energy was both abundant and free” ….. but intermittent?

April 29, 2021 4:14 pm

The point is the inconveniently timed energy production by renewable sources can be shunted to cheap stones rather than dumped. Sure, there are losses to and fro, but something is better than absolutely nothing.

Zig Zag Wanderer
Reply to  MISteve
April 29, 2021 4:46 pm


paul courtney
Reply to  Zig Zag Wanderer
April 30, 2021 12:54 pm

Mr. Wanderer: I understand you’re not promoting this, but you seem to be all too willing to find a way to recover renewable energy that would otherwise be lost. You are so concerned with “the point” that you seem to overlook this- spending $20b to recover $20 worth of electricity makes it very easy for me to miss “the point”.

Reply to  MISteve
April 29, 2021 5:32 pm

something is better than absolutely nothing.
Why? If the price is negative a low cost means to dump the surplus will earn more $$ without the high cost overhead of returning it to the grid.

Reply to  Ferdberple
April 30, 2021 12:31 am

dump the surplus will earn more $$

So you have repeatedly said. Now remove the subsidies, and try your other thinking cap…

It doesn't add up...
Reply to  Ferdberple
April 30, 2021 7:39 pm

Prices go negative because dumping has a cost. In the present regime that cost is firstly the subsidies paid out that are foregone through curtailment. There are other costs in curtailment, depending on the technology being curtailed. Fixed costs can only be recovered from earnings either from compensation for not operating, or higher prices while operating. That applies to any kind of generation. There may be operational costs on top of that.

Reply to  MISteve
April 29, 2021 5:36 pm

The point is that the description of renewable is false, as is carbon-free. And that less efficient. more expensive than existing, proven means of energy storage doesn’t make the false economy of fake renewables more efficient, just more attractive to subsidy by virtue-signaling fools.

The Dark Lord
Reply to  MISteve
April 29, 2021 5:40 pm

actually, the opportunity costs of “something” may actually be worth less than nothing … they are simply throwing good money after bad …

Last edited 3 months ago by The Dark Lord
Reply to  MISteve
April 30, 2021 8:09 am

Costs do matter, you know. Say you shunt to the cheap stones $100 worth of electricity (at average market rates) but the process of converting it to heat and then back to electricity costs $60 and the losses are 50%. So you then have $50 worth of electricity to sell (given the 50% loss in conversions) at the average market rate. You’ve generated a loss of $10 every time you do this.

The point is, shunting to “cheap” stones has a cost, both in conversion losses and in construction and operating costs. It’s quite possible, more likely probable, to lose money in such a venture.

But if you get grants, interest-free guaranteed loans, subsidies, and tax credits, Voila! Money for the propagators at zero risk to boot. A net loss to society, but who considers that anymore, when there are pockets to be greased all around?

It doesn't add up...
Reply to  MISteve
April 30, 2021 7:34 pm

It ain’t necessarily so. The storage has a cost, which must be covered by the margin earned by storing and redelivering. In fact, the reason we don’t have more storage is because that margin is inadequate, especially since earnings also depend on he number of times the storage is turned over per year, which limits the viablility very sharply. If you are smoothing out wind gusts, that is a high frequency operation. If you are storing a surplus for redelivery during peak hours daily you have 365 margin earning opportunities a year. If you are trying to cover for periods of low wind or dull weather, that frequency drops sharply. Try to vcover for seasonal variation, and you are down to once a year. And don’t forget that a bad year may be 1 in 20 or 1 in 50.

Rich Lambert
April 29, 2021 4:27 pm

When I was a child I used to sleep in an unheated uninsulated bedroom. In the cold winter my folks would heat a brick on the stove, wrap it in a newspaper and put it at the foot of the bed. It would work for a couple of hours. It would help you get to sleep but that’s about it.

Zig Zag Wanderer
Reply to  Rich Lambert
April 29, 2021 4:46 pm

These tanks are insulated

The Dark Lord
Reply to  Zig Zag Wanderer
April 29, 2021 5:37 pm

the brick was insulated as well … so what …

Reply to  Zig Zag Wanderer
April 29, 2021 9:48 pm

So is a bed

Reply to  Rich Lambert
April 29, 2021 5:35 pm

A hot water bottle will heat the bed longer than a brick of the same weight because of the high specific heat of water, and the limits to how high you might heat the brick.

Reply to  Rich Lambert
April 29, 2021 7:44 pm


April 29, 2021 4:31 pm

Just to add (non-fossil) fuel to the fire: when surplus power can be obtained from wind turbines is completely unpredictable. Situations that require significant drawdowns of your stored power are completely unpredictable. To have any confidence level that the stored power will be recharged sufficiently to satisfy the next drawdown will require massive over engineering of everything.

The basic concept of backing up unreliable power generation with energy storage is going to be uneconomical, unreliable, or both.

Zig Zag Wanderer
Reply to  jtom
April 29, 2021 4:47 pm

I think PV is a better candidate

Reply to  Zig Zag Wanderer
April 29, 2021 9:49 pm

In some places, it can be cloudy for weeks at a time.

Zig Zag Wanderer
Reply to  MarkW
April 29, 2021 10:37 pm

This is the point. They claim to be able to store the energy for weeks. I’m dubious, but if true, it may be effective.

Climate believer
Reply to  Zig Zag Wanderer
April 29, 2021 11:04 pm

 – up to about a week.

Reply to  Zig Zag Wanderer
April 30, 2021 12:30 pm

I’d want to see ALL the math on that one.

It doesn't add up...
Reply to  Zig Zag Wanderer
April 30, 2021 7:43 pm

The problem with that is that you don’t get to turn over the storage often enough. If you store for 10 weeks, then you are getting just 5 stock turns a year, or 1/73rd of the earning potential of a daily requirement..

Clay Sanborn
April 29, 2021 4:48 pm

Store the excess energy by making synthetic fossil fuels that will be burned in all the requisite “green energy” backup fossil fuel generators. Of course when the synthetics run out, burn fossil fuels. Really want to be efficient – get rid of all “green energy” and burn fossil fuels; spend new money on new forms of nuclear – e.g. LFTR

Robert of Texas
April 29, 2021 4:52 pm

Are they using solar or wind power to dig up, crush, and transport the rocks? Or make the steel tanks? Or produce the wind turbines or solar panels?

It doesn’t even matter if this idea sort of worked…they still have not replaced fossil fuels.

Zig Zag Wanderer
April 29, 2021 4:57 pm

I must admit to being confused as to why they want to store insulated cold rocks too. In what way do they contribute to the (re)production of electricity?

Edit: ok, I guess if they use the cold rocks to chill a gas down to a liquid. I wasn’t thinking properly.

Last edited 3 months ago by Zig Zag Wanderer
Reply to  Zig Zag Wanderer
April 29, 2021 5:16 pm

The system is a heat pump. roughly three times the energy that is used to pump the heat arrives at the hot spot. The other rocks are cooled and the energy taken out adds to the electrical energy. Basic aircon or refrigerator principle in reverse. The extra energy is in fact solar energy that heats the ‘cold’ rocks in summer, So saying its 50-65% efficient is a con – its just turning low grade solar energy in warm ground into high grade energy in hot rocks, and then of course getting it back out is woefully inefficient.

Would work a little bit on a small scale – and in grid terms 10MWh is very small indeed. UK’s Dinorwig pumped storage station is just under 10 GIGA watt hours…And that is only useful to smooth out daily peak demand.

Zig Zag Wanderer
Reply to  Leo Smith
April 29, 2021 10:38 pm

I understand it is a proof if concept, that is why it is small.

April 29, 2021 4:58 pm

10MWh? Shakes head in despair and disbelief…

April 29, 2021 5:01 pm

Why not use the surplus power to lift the rocks? When you need power let them drive a turbine as they fall back down. No need for insulation to keep the rocks hot.

Last edited 3 months ago by ferdberple
Zig Zag Wanderer
Reply to  Ferdberple
April 29, 2021 5:07 pm

It’s been proposed. I don’t think it’s economic.

You probably need to consider how high you need to raise a stone to store the same PE as raising it to 600C would store KE.

Last edited 3 months ago by Zig Zag Wanderer
Reply to  Zig Zag Wanderer
April 30, 2021 12:52 am

A hundred kilo stone lifted 5 meters stores me, what, 5kJ, at 80-90 percent efficiency for lifting, at least 90 for the release cycle. 6kJ in, 4.5kJ out, with zero losses during the storage cycle, using materials and techniques known to the Romans (except the motor), and maintenance consists of greasing pulleys and cables.
Not ideal, but cheap and nasty, using energy that would otherwise be “dumped into the ground for subsidies”. Even at 40% efficiency, it still kicks any thermal storage system’s butt. And I don’t milk you for subsidies!
Now show us the ‘back of your envelope’, with special attention to construction costs and maintenance schedules.

Reply to  Ferdberple
April 30, 2021 1:07 am

Why not use the surplus power to lift the rocks

Tried to get funding for that once. Management had a good laugh at my science fiction, then I found someone that actually built such a system. Management decided my idea is old hat, and if it worked, they would have known about it by now.
The need I sought to fulfill was the regular power outages and cable theft ubiquitous in these parts. Batteries, generators and even fuel is like a fresh turd for thieveing flies, but who wants to steal concrete slabs? Management opted for higher insurance premiums instead. Week later, someone managed to ‘liberate’ a four ton generator from a cell tower site without so much as bothering to open the gate. I decided not to participate in the resulting “WTF happened” meeting. Apparently the insurance company got so upset, they raised the premium… the meeting was hot on that topic, I was told.

Reply to  Ferdberple
April 30, 2021 12:32 pm

I read about that in Africa. It was a bag of rocks that slid down and lit ONE lightbulb. I think the “why” is pretty obvious.

It doesn't add up...
Reply to  Ferdberple
April 30, 2021 7:56 pm

Graviticity reckon that their system of weights and pulleys in a mineshaft could compete with grid batteries for providing short term grid stabilisation. But it is only ever going to be a few MWh per installation. Currently undergoing test rig trials.

More ambitious schemes involving a very large cylinder of rock (say 500-1000m diameter) have been proposed, but are hopelessly impractical.

Abolition Man
April 29, 2021 5:15 pm

If they add a few more pumps, some loops of piping and throw in some other intermediate steps to the process, I think this could qualify as a genuine Rube Goldberg!
Other than that it has the look of the usual Green Blob contraption; highly over estimated rating and/or efficiency, with little chance of being proven practical without lots of OPM add into the process!

navy bob
April 29, 2021 5:24 pm

Wouldn’t the air around cool stones be, you know, cool? How much heat would you be able to pump, and why would you pump it to hot stones that already have plenty of heat? And how did the hot stones get hot in the first place? Clearly, I’m missing something.

Joel O'Bryan
April 29, 2021 5:28 pm

“which pumps heat energy from one or more storage tanks filled with cool stones to a similar number of storage tanks filled with hot stones, when there is surplus power from wind or the sun.”

What is the working fluid? They never note what it is on the website:

They write on their website:

“The charge-discharge system comprises one compressor-turbine system for charging and another similar but differently dimensioned system for discharging.

The charging system is operated in a heat pump cycle. The COP (Coefficient of Performance) is on the order of 250%, depending on the temperature ranges.

The discharging system is operated in a so-called Brayton cycle, similar to the cycle of a gas turbine. The efficiency is on the order of 20-25%, again depending on the temperature ranges.

The total round-trip efficiency is the product of the charging COP and the discharging efficiency. For serial production systems the round-trip efficiency is expected to be 55-60%.

The charging cycle is 250% efficient??? Not clear what that even means.

They also write:

“The total specific cost of the thermal storage materials, including storage tanks, insulation, etc. is expected to be less than 10 EUR per kWh for serial production systems. In comparison, conventional battery storage systems typically have storage capacity costs in the range of 200 EUR per kWh.”

What one gets directly out of a charged battery is direct current electricity. It’s electricity ready to go into an inverter to push AC electricity onto the grid. Other than an inverter, there are no other “parts” besides hooking into a substation of transformers and capacitors.

But what comes out of the storage tanks is simply heat. Heat that must them be put through a heat exchanger to make dry steam to turn a turbine to turn a generator if one wants electricity, and not simply hot water to cycle through homes and offices for heating. That process is probably 50% efficient at best. That €10/kWh quoted cost does not include an electrical generation system.

The other huge problem with heat storage is that the first 50% of whatever megajoules of heat out is at a much higher temp than the last 50% of heat energy. That steady decline in temperature differential between hot and cold reservoirs reduces the rate of discharge possible on that diminishing return. That is the max power output steadily and rapidly decreases as the system discharges.

If the discharge heat is used to make electricity 24/7 until the wind starts blowing again (3-7 days later), there will be no heat for homes near the final days.

Supposedly this is all proprietary, but I’d like to see what is really happening behind the physics of the charge and discharge phase. There is no free lunch in thermodynamics.

But in reality like all renewable projects, where they write, “… it will run for three years with a total budget of DKK 35 million (EUR 4.7 million). The project is being funded with DKK 21 million (EUR 2.8 million) from the Energy Technology Development and Demonstration Program (EUDP).”
Really this is just harvesting OPM.

Last edited 3 months ago by joelobryan
Joel O'Bryan
Reply to  Joel O'Bryan
April 29, 2021 7:32 pm

I did do some reading on heat pumps. Been almost 4 decades since I had that thermo class.
COP explained:

Reply to  Joel O'Bryan
April 30, 2021 11:50 am

If the expander (turbine) is only 25% efficient, this means that this is the MAXIMUM theoretical efficiency. Almost seems like they are adding instead of multiplying. and 25% eff. for an expander is ridiculously low. Looks like a poorly edited article.

April 29, 2021 5:38 pm

Why would anyone living next to the Baltic need a stored source of “cold” material?

Joel O'Bryan
Reply to  dk_
April 29, 2021 5:51 pm

The greentards hate it when power plants discharge warm water into a cold ocean. aka, thermal pollution.

Jean Parisot
Reply to  Joel O'Bryan
April 29, 2021 6:53 pm

My fishing rod is under the impression that fish love it.

Jean Parisot
April 29, 2021 5:43 pm

Why not use pea sized enriched uranium and call it a battery?

April 29, 2021 5:45 pm

You are probably better off to crack water into hydrogen using the windmill power and storing it the windmill towers. Burn the hydrogen to create power as required.

This would allow long term power forecasts based on the volume of hydrogen stored in the towers.

With proper design the hydrogen can be pressurized without pumps while the oxygen is separated for resale and to avoid explosions.

The oxygen and hydrogen would probably be worth more than the electricity produced by the windmills.

Reply to  Ferdberple
April 29, 2021 8:46 pm

This is what Norway intends to do. For some reasons why it will not work, see “Considering Ammonia” by Kevin Kilty, today at this same web site.

Additionally, there basically is not any excess power generated by wind and solar. When there is not enough demand, operators feather windmill blades to delay maintenance and subsystem failure. When solar is on, conventional plants must partially or fully shut down. When solar shuts down due to weather or subsystem failure, conventional plants waste energy and heat spinning up to meet the demand, else the reduction causes brownouts or complete power outages. Even hydro dams must reduce the flow when there is not enough demand. Surplus power is created only by conventional power production means, and then only as long as it takes for the automatic or human operators to throttle it back. Power that is excess to demand is always shed as heat, directly, and at the power production facility.

If Wind, Solar, or other fake renewables were committed solely to charging storage systems OR exclusively to producing hydrogen, ammonia or (not AND) syngas, they would still need to be subsidized — which is how Norway may end up implementing their program. They can’t multitask.

Nowhere in the article are any claims made for how long this granite pebble system will take to spin up. For a grid storage system, consider any spin-up or spin-down time that is less than instantaneous production on demand as representing wasted energy, or/AND a service interruption.

Reply to  dk_
April 30, 2021 9:54 am

Additionally, there basically is not any excess power generated by wind and solar.
That is not correct. Renewables typically do not operate at spot price because you need to guarantee supply to qualify for spot pricing.

Renewables typically get a FIT price which encourages production regardless of supply. This is why renewables destabilize the grid.

Reply to  dk_
April 30, 2021 10:14 am

it will not work,
As KK noted, cracking water works. It is simply easier energy wise to crack hydrocarbons or ammonia.

But ammonia and hydrocarbons come with their own problems, as of course does hydrogen.

The problem is that there is no such thing as a solution that is free of problems. This includes green solutions.

April 29, 2021 5:59 pm

The only real challenge with establishing 100 per cent renewable electricity supply is that we can’t save the electricity generated during windy and sunny weather for use at a later time.

What an absurd assertion! And stated as if this is fact.

Reply to  Independent
April 29, 2021 8:49 pm

The real challenge is that there is no renewable electricity supply, and certainly no means of production that is carbon free.

Reply to  Independent
April 30, 2021 12:59 am

Explain yourself, without reverting to costly and short-lived chemical batteries, hydroelectric reservoirs on flat land, or airy-fairy nonsense like the proposed pebble tanks above. We just have no cost effective, reliable and efficient storage available, period.

Reply to  paranoid goy
April 30, 2021 8:38 pm

Yes, that is one major problem. But there are many others, beginning with the amounts of land and materials necessary to generate that volume of “renewable” energy (not really renewable when you consider what it takes to build and that windmills and panels wear out after 15-30 years). That’s not even going into what it would take to construct the transmission lines, etc. The point is there are a lot of challenges with “establishing 100 percent renewable electricity supply” and it’s idiotic to say battery capacity is the only relevant issue.

April 29, 2021 6:07 pm

Actually, you can get rather a lot of power from a pile of stones, provided those stones have the proper mix of graphite and thorium. And you can do that without all the bother of building and connecting up a bunch of wind turbines at all! Think of the savings in materials and maintenance costs…

sky king
April 29, 2021 6:09 pm

Leave it to the Scandinavians to adapt sauna to grid scale!

Loren C. Wilson
April 29, 2021 6:15 pm

We don’t convert high-quality energy in the form of electricity into heat until we have to because it is inefficient to convert the heat back into electricity. Once it is heat, the natural principles that Carnot discovered and Clausius put into a mathematical equation apply. Take this project. Turn the electricity into het via their heat pump (a classic Carnot cycle). The maximum efficiency of getting the electricity back from the heated rocks is e = (Thot – Tcold)/Thot, calculated using absolute temperature. They talk about getting some rocks very cold, but the reason no one uses a heat pump in cold climates is that they freeze up in the winter. If the cold reservoir is 0°C or 273 K and the hot reservoir is 600 C or 873 K, then the maximum efficiency of recovering the electrical energy from the heat is (873-273)/873 = 69%. Even at the best operating conditions, you have lost 31% of the energy to heat. That efficiency decreases as the hot rocks cool and the cold rocks heat up. When the hot rocks are 400°C, the cold rocks (assuming an equal mass and heat capacity) will have warmed up to 200°C. E now equals (673-473)/673 = 30%. Thus, just part way into converting your heat back into electricity, you have thrown away 70% of your original investment. And this is the maximum possible efficiency. we still haven’t factored in reality like heat transfer through their storage tanks, non-ideal compressors and turbines, frictional losses, etc. that make the process less efficient than the theoretical limit. What a truly bad idea this is, run by scam artists.

B Clarke
Reply to  Loren C. Wilson
April 30, 2021 12:52 am

Thanks Loren.

April 29, 2021 6:46 pm

People a lot smarter than me may understand this, and think no it’s not completely nuts.

April 29, 2021 6:55 pm

Adding stones to intermittent/renewables in an expanded occupation of green spaces.

Reply to  n.n
April 30, 2021 12:33 pm

Who needs green spaces when you can make tons of money off destroying the landscape and the government will pay you to do it?

Michael S. Kelly
April 29, 2021 8:03 pm

Back in the day (beginning in 1957) NASA Ames Research Center built a 3.5 foot diameter hypersonic wind tunnel originally designed to provide air flow at Mach 14. It used a 125 ton bed of alumina and zirconia pebbles, preheated by a gas burner to as much as 4,000 F, to heat the feed air from high pressure bottles to the appropriate nozzle, and then to the test section, and exhausting to giant vacuum vessels. It had nozzles for Mach 5, 7, 10 and 14, though the 4,000 F temperature required for the Mach 14 nozzle made the pebbles give off sparks of material to the extent that they sandblasted the nozzle to near destruction.

As a result, the tunnel was limited to Mach 10, requiring “only” a 3,000 F pebble bed temperature.

The phenomenal thing about this tunnel was that it could run at Mach 10, with a 3.5 foot diameter test section, for minutes. Other hypersonic tunnels before and since relied on shock waves, yielding millisecond run times – with tunnel diameters of a few inches.

In 1975, after thousands of blows, the tunnel blew up (actually the flange between the heater and nozzle gave way), and a lot of damage was done. But no injuries, and six months later it was back in operation.

There is some utility to storing energy in hot rocks…but I doubt if it is practical for grid scale backup.

Alan Watt, Climate Denialist Level 7
April 29, 2021 8:50 pm

Why bother? Europe already has grid-scale storage. I think they call it “Norway”. Everyone else seems to be using it, why shouldn’t Denmark?

It doesn't add up...
Reply to  Alan Watt, Climate Denialist Level 7
April 30, 2021 8:04 pm

Denmark has long been in on that act. The problem for them now is that Germany is muscling in with direct interconnect to Norway. I doubt the Norwegians are happy at the consequences

They are now importing German power prices.

April 29, 2021 9:30 pm

What’s the efficiency of this contraption? From the description given in the article I’d be surprised if it’s above 50%.

Zig Zag Wanderer
April 29, 2021 10:42 pm

I believe people are knocking it down for the wrong reasons. It’s probably expensive, and only useful because unreliables are unreliable. The concept itself appears valid, and they are testing it.

If I lived in Denmark I might be annoyed at the waste of my taxes, but I don’t.

April 29, 2021 11:04 pm

Sounds a very interesting technology.
They use a highly non-ideal gas for the Carnot cycle and achieve 60% efficiency.
This is tremendous for a thermodynamic system.
It may solve the energy problem.
Double the PV capacities and store the energy for the night.
It is a true solution.

Reply to  Alex
April 29, 2021 11:20 pm

It is a true solution.

…… so is unicorn farming !!

Reply to  Alex
April 30, 2021 12:44 am

You’re kidding, right?

Reply to  Lrp
April 30, 2021 4:31 am

Well, let us check the numbers.
Let us assume, they heat the stones directly by the electricity.
This can be nearly 100% efficient.
Then, they have to extract the stored thermodynamic energy using a Carnot cycle.
The limiting efficiency for a Carnot cycle is (Thot-Tcold)/Thot
For the claimed hot temperature Thot = 600 C = 874 K and the cold temperature around freezing, Tcold = 0 C = 274 K, we get the limiting efficiency of 68%.
Probably, they work at 70% of that limiting efficiency – as most of the thermodynamic engines do. Even then, the overall efficiency is about 50%, just as they claim.
This is by far not bad.

Reply to  Alex
April 30, 2021 8:27 pm

There’s no way heating the stones with is 100% efficient. Think about how the process of converting electricity into heat and passing to massive amounts of rock. My estimate is more like 80%. Then converting the stored heat into useful work is not just about Carnot cycle, but also the efficiency of the steam turbines, etc. In short, you have no idea what you are talking about.

Reply to  Lrp
May 1, 2021 3:02 am

There’s no way heating the stones with is 100% efficient. “
Where else should the energy go? Be taken away by the Lord?
Electric heating is nearly 100% efficient.

Then converting the stored heat into useful work is not just about Carnot cycle”
Yes, a typical thermodynamic machine is never 100% efficient, but the good ones are better than 70%.
The larger the machine, the better the efficiency.

I do like the idea a lot.
It is simple, it is scalable, it is reliable, it can work now, not in “30 years, when I am retired” like the 70 years old fusion scam.
It does not need huge water reservours like the pump storage and is much more efficient than that.

Reply to  Alex
May 1, 2021 10:02 am

There will be heat losses; the higher the heat, the higher the losses. And, someone already posted with numbers about how is not scalable. Anyhow, comparing it with pumped hydro is like comparing dumb with dumber.

Reply to  Alex
May 1, 2021 2:45 am

Mama used to say: “Just ’cause it’s true, doesn’t make it right.” But she was talking about my foul mouth, not engineering. In this case, while these “pebble batteries” are obviously true, they are not right. The physical infrastructure will be expensive and disruptive, the efficiency is really low, the Time Between Failures will be something horrific, and the whole thing seems to spring from the mind of wide-eyed students with great dreams and zero real-life experience behind a spanner.
To demonstrate, I dare you go ask ten electronics engineers about their second-semester dreams of replicating the “perfect sound source” with pneumatics and a balloon. This ‘technology’ is of the same class. We are not being nasty, just realistic. Scroll down to where Alex uses maffs to prove 50% efficiency, while totally disregarding the power spent by motors, pumps, radiative losses, friction, noise, wear and tear…. He runs the entire power budget of the machinery itself, not on the power generated, but on Unicorn Farts. This is a problem for everyone else here. Well, almost everybody.
…and one has to wonder who these students’ daddies are, for them to even get the publicity for a second-year student theory project.

Last edited 3 months ago by paranoid goy
Patrick MJD
April 29, 2021 11:27 pm

Total madness. People fall for this rubbish because they have been duped in to believing CO2 is pollution and is driving climate to change in a bad way when there clearly is no evidence for that.

Reply to  Patrick MJD
April 30, 2021 12:33 pm

They fall for this because they have zero math or science skills and run on emotion, not thought.

April 29, 2021 11:43 pm

 the GridScale technology is about heating and cooling basalt crushed to tiny, pea-sized stones in one or more sets of insulated steel tanks.

Does the basalt mine and crush itself or are they creating green jobs by employing people to pick up the stones one by one?

Iain Reid
April 30, 2021 12:12 am

As usual the concentration is on intermittency, as being the only limitation to 100% renewable.
They forget, or maybe are not aware that wind and solar are asynchronous generation, i.e. cannot maintain frequency. Frequency being the most important parameter on a grid system.’
A very large percentage of synchronous generation is needed to keep the grid the balance of supply and demand and that is what frequency shows. Too much asynchronous genertaion and the grid gets uncontrollable and trips will occur.

Steve Richards
April 30, 2021 1:28 am

From the chap who did the original design work but is no longer involved:


“This is a stringing together of four highly reversible processes, two, fast, adiabatic compression/expansion, two extremely slow isobaric heat transfer processes. The engine cycle has a Carnot ratio just like any other heat to work cycle, however, the heat pumping cycle used during charge is the exact same cycle with a thermal coefficient of performance equal to the inverse of the Carnot ratio of the engine cycle. In a round-trip operation these cancel leaving the system efficiency, in this respect, independent of any Carnot limits. This is the key to the whole concept.”

Reply to  Steve Richards
April 30, 2021 8:02 am

Have they patented the device that loops through the alternate universe that has reverse entropy?

The Carnot equations apply the same for moving heat around, whether it is from hot to cold or cold to hot. It never “cancels out.”

Reply to  Steve Richards
April 30, 2021 10:36 am

the Carnot ratio of the engine cycle. In a round-trip operation these cancel leaving the system efficiency, in this respect, independent of any Carnot limits.
A math error. They are multiplying by zero (round trip).

10 * 0 = 5 * 0. Therefore 10 = 5

One of the many traps numbers have created to fool the unwary.

Reply to  Steve Richards
April 30, 2021 11:46 am

Isobaric? So what drives the turbine? And how are you transforming heat into electricity? There must be a phase change somewhere.

I also don’t understand the purpose of the cold tank.

Lux Aeterna
Reply to  JamesD
April 30, 2021 2:36 pm

Me neither. If you take heat from the cold and pump it to the hot, then as the temperature difference rises, it becomes less and less efficient, not more and more efficient, as it is akin to running an air conditioner in a window that connects two rooms. As the cold room gets colder, the a/c unit will struggle more and more to remove heat energy from it. So, while the generation process will be more efficient, any gains will be more than offset by the less efficient charging process.

Mark - Helsinki
April 30, 2021 1:30 am

Windmills, an ancient tech

and now to compliment that, the old put the fire stones under your bedding at night to keep warm.. that is also an ancient tip.

Have computers “doing all the work now” made our scientists morons?

Rod Evans
April 30, 2021 2:16 am

What’s not to like? We are rapidly heading back towards the stone age, so we might as well adopt as much stone technology as we can absorb.
Yabba dabba do…Wilma!
I wonder why they didn’t call the project Sisyphus?

April 30, 2021 6:06 am

Next, bread from stones?

April 30, 2021 6:13 am

More stupidity from people who don’t understand thermodynamics.

If you’re going to do an energy storage system that stores heat, it’s far better to store the heat from a thermal plant (coal and nuclear work best, but even gas), and then use that heat at peak times (or when unreliables are failing to produce) to generate extra electricity.

If the system is large enough, then the way to sell it is that thermal plants can be ramped down to almost zero electricity production when the wind is blowing and the sun is shining (by storing the heat instead of using electricity), and when the sun is not shining and the wind is not blowing, these plants can overproduce their nominal capacity to pick up the slack.

That’s the way to do it, but producing electricity and then storing it as heat is just a dumb, dumb idea.

I don’t think that the Danes are stupid; they’re just trapped in a cult, and physics will have to teach them a hard lesson.

zack aa
April 30, 2021 7:05 am

use this one wierd trick to make sunshine heat rocks

Bruce Cobb
April 30, 2021 8:14 am

Nothing man does can come even remotely close to nature’s own energy storeage system: fossil fuels.

Steve Taylor
April 30, 2021 9:13 am

“The heat can be stored in the stones for many days, and the number of sets of stone-filled tanks can be varied, depending on the length of storage time required.”

So one tank will stay hot for maybe 4 days, so you then switch to the 2nd tank which by now is already cool?

Richard Page
April 30, 2021 9:33 am

Well. Not sure about everyone else on here, but I just think it’s an incredibly expensive and wasteful way to cook pizza.

April 30, 2021 9:42 am

“cheap and efficient alternative”
I’m curious HOW “efficient” – you pump heat into the stones and then extract that heat later for power (yes I understand about the hot/cold stones), ok – it seems to me there’s going to be a good bit of energy loss in that process. How much of the energy input can be extracted? Let’s not even consider storage over time: what percentage of the input can be extracted as useful energy immediately?

I notice that information isn’t present. Do they know the answer?

April 30, 2021 9:45 am

Pea sized stones heated to 600?C in large, insulated steel tanks are at the heart of a new innovation project aiming to make a breakthrough in the storage of intermittent wind and solar electricity.”

Seems to me this method was all the rage back in the 1950s-1960s, along with Buckminster Fuller structures. As new as that?

I have a sun room built on top of a gravel bunker by the previous owner to allegedly perform a similar task; build heat during the summer to radiate into the sunroom during cold weather; cool down the gravel during the winter to moderate when the sun room heats up.

Along with a massive brick wall to which the sunroom is attached.

Doesn’t work worth a dang.
Within a few days of serious winter, the sunroom requires heating. Cold air sinks and I worry about plants on bottom shelves freezing.
The sun room itself is not heated or cooled directly, house heat is shared through doors and windows.

Within a few days of late Spring or early summer, all coolness stored in the rock is gone.
A fan works best during all of the seasons

In winter, it takes 3-5 days for the wood stove to heat the brick wall mass, which does moderate winter temperatures in the sun room.
As far as the brick wall absorbing sunlight and radiating heat for hours, it appears to only work in summer.

Stop using the wood stove for a few days; a necessary function to clean out the ashes properly, and the wall cools down quickly.
The wood stove is massive yet does not have a grate for ashes to drop out below. I must spend time shoveling and sweeping, an unpleasant task if the stove is hot, so I let it cool.

The stove is a wonder.
Once the stove is lit it attracts the dog, cat and wife who are reluctant to leave an eight foot radius around the stove. A good charge of clean oak or black locust keeps the stove running easily for 8-10 hours.

April 30, 2021 10:00 am

Well, this idea will be a whale of a Sweat Lodge used by our ancient tribal friends. Or Finns and Swedes and the rest of us that like a hot steam sauna. Not a total waste.

April 30, 2021 10:05 am

Grid scale. One medium sized generator running for one hour. Or 5 wind turbines running for one hour in perfect conditions.

You would need 500 of these units to get a medium sized solar facility through the night. Each unit has some unknown amount of compressors and turbines. Imagine the maintenance on this.

Eyes Wide Open
April 30, 2021 11:39 am

I love these content-free articles. At least from the perspective of what would be of most relevance to an engineer or economist. What is the end to end efficiency (energy out vs energy in) and what is the overall cost per kwh stored? Couldn’t find anything on the net that talked to this so from my perspective this whole thing is the equivalent of vapourware . . .

April 30, 2021 11:52 am

Damming up the Baltic would probably work better and be far more reliable.

Steve Z
April 30, 2021 12:34 pm

It’s not clear what the purpose of refrigerating the cold stones might be. If the hot stones can somehow be heated to 600 C by transforming the energy from a windmill, when it is not turning one can circulate high-pressure water over the hot stones to generate steam and drive a turbine to generate electricity. But what is the purpose of the cold stones?

Reply to  Steve Z
April 30, 2021 2:56 pm


With new blog comment format I cannot tell if I am replying to a sub-poster or main dude or whatever, anyway…

The passive solar systems I am familiar with in the montains of Utah and Colorado work very well heating a reservoir of rocks or a liquid salt or even saltwater. The cooling part of the process is more complex. A very simple passive system can help heat a lotta water for your shower, and maybe some heat in the living room.

The sun energy on my deck heats up the living room at about 1 deg per 15 minutes just using the main window and door entrance. I regret not including a passive heating box outside the window and would have great heat whenever the sun hits it, which is many days a year, and more during the winter.

I do not have a lotta hope in heating rocks and then using the heat to drive turbines or anything. I place a lotta faith in venting my heated air or refrigerant to my storage pit and using it later. No cooling without lottsa help, but basic heating is very easy when living off the grid.

My garden hose gets up so hot that I have had it burst. But the idea of using wind turbines to heat a fluid and so forth just is not practical from an engineering aspect. Better to adapt the old Navajo and other native Americans’ architecture of the adobe walls for heat at night and cooler in the hot day.

Gums sends…

Gary Pearse
April 30, 2021 3:20 pm

It doesn’t say how they are going to convert this relatively low grade heat into electricity. I hope not by boiling water. It takes ~1/7 th the energy to heat water from room temp to 100°C and the other 6/7ths of it to convert water at 100 to steam at 100! I guess you could just heat the water up to 100 and distribute it nationally to make tea without boiling it.

April 30, 2021 3:36 pm

“The only real challenge with establishing 100 per cent renewable electricity supply”

Right. Umm. Nope. There would be a few other challenges, like mining all the iron, aluminium and copper required to make the vast number of wind turbines required, and making the steel and concrete and then endlessly replacing them as they fail.

Paul Penrose
April 30, 2021 3:37 pm

As soon as the article started talking about “heat energy” I stopped reading. There’s no such thing.

April 30, 2021 3:49 pm

A megawatt hour (Mwh) is equal to 1,000 Kilowatt hours (Kwh). It is equal to 1,000 kilowatts of electricity used continuously for one hour. It is about equivalent to the amount of electricity used by about 330 homes during one hour.”

So that storage system will power 330 homes for 10 hours.

April 30, 2021 4:45 pm

I keep looking for the diesel backup engine to run those turbines. The concept of heat storage and recapture completely escapes me which means it’s probably a unicorn project to capture eyeballs more than anything else.

April 30, 2021 7:13 pm

Big deal. 10 Mega Watt hours is nothing close to grid size. It can only supply one average size all electric American home with electricity for a year. But yet, their cartoon shows four houses and some sort of commercial building.

April 30, 2021 7:31 pm

Brilliant ! Take extremely high value and hugely usable energy (electricity) produced in the most expensive way (Wind Turbines / PV ) and turn it into low value high loss energy (heat) and store in stone filled tanks then somehow ? turn the heat back into electricity (steam turbine , hot/cold tanks?? ) transfer losses ???
I have an idea , why not instal 2 power supplies into homes , 1 would be the main 24 hour supply (normal) and the 2nd would be from wind and solar and solely used to heat a large hot water tank , store the excess electricity and establish reserves in every home and supply hot water at the same time . May not even require installation of new wiring into homes when a lot of homes are already supplied with 2 phase or 3 phase lines already . 1 phase for mains and the other for wind/solar .

April 30, 2021 7:43 pm

Meanwhile in CHINA !

To put some context on the scale of the Chinese coal build out, that 38.4 Gigawatt addition in 2020 ALONE equates to one massive 1,000 Megawatt coal plant coming online every 9 days – week after week – for an entire year.
For Australian readers, compare those numbers to your much contested Hazelwood and Port Augusta plants so trivial in the global scale of things.
For the (faux) environmentalists check out the brand new $30 BILLION Haoji Railway… a line expressly built for the exclusive transport of 200 million tonnes per year of coal deliveries from the open pit coal mines of Inner Mongolia. (Online pics of the mines make for interesting viewing).
So when can we expect to see St. Greta standing at a podium in Bejing and giving a stern tongue lashing to Xi?

May 1, 2021 4:26 am

“a new innovation project”
What else could an ‘innovation’ project be but new? That’s what happens when you stop teaching Latin. People no longer know the meaning of words that have a Latin derivation. But then again, this project uses solar energy from the sun.

Matthew Sykes
May 1, 2021 6:04 am

And whats the efficiency? THats the important figure we need to know because it directly impacts how many more solar and wind farms are needed. Already it is about 6 times capacity, whats it going to become, ten times? Thats a lot of wind and solar.

May 1, 2021 6:29 am

Correct me if I have got this wrong, and apologies if someone has already done the calc:

They are spending 4.7m EUR
for 10 mWh capacity
with a 3yr life.

At say 1 full discharge per week, 60% efficiency:

10 * 60% = 6 mWh per discharge * 156 wks = 936 mWh.
4.7/936 = 0.005 EUR per Wh = 5 EUR per kWh.
At full daily discharge (totally unrealistic?) = 0.71 EUR ($US0.86) per kWh.

That’s expensive. And it’s the cost to the utility, not to the end customer.

May 2, 2021 6:00 am

Finally a way to build a renewable energy powered jet aircraft! Jets have all that mechanical stuff…”turbines, compressors, etc”, and they have all that “surplus” energy…think 500 mph at 30,000 ft! Just fill the baggage compartment with asphalt pebbles, and voila! a “free” renewable energy Jet aircraft. Gotta love how intractable problems can often be solved by just throwing rocks at it.

I really need to open a business selling pet rocks……

Ethan Brand

May 13, 2021 12:31 am

That’s great,this battery need a stability test.If you want to know more about the battery test,click the web