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.
AARHUS UNIVERSITY
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.
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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.
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.
I understand it is a proof if concept, that is why it is small.
10MWh? Shakes head in despair and disbelief…
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.
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.
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.
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.
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.
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.
https://euanmearns.com/short-term-energy-storage-with-gravitricity-iron-versus-ion/
More ambitious schemes involving a very large cylinder of rock (say 500-1000m diameter) have been proposed, but are hopelessly impractical.
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!
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.
“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:
https://www.stiesdal.com/storage/the-gridscale-technology-explained/
They write on their website:
The charging cycle is 250% efficient??? Not clear what that even means.
They also write:
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.
I did do some reading on heat pumps. Been almost 4 decades since I had that thermo class.
COP explained:
https://industrialheatpumps.nl/en/how_it_works/cop_heat_pump/
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.
Why would anyone living next to the Baltic need a stored source of “cold” material?
The greentards hate it when power plants discharge warm water into a cold ocean. aka, thermal pollution.
My fishing rod is under the impression that fish love it.
Why not use pea sized enriched uranium and call it a battery?
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.
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.
Additionally, there basically is not any excess power generated by wind and solar.
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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.
it will not work,
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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.
What an absurd assertion! And stated as if this is fact.
The real challenge is that there is no renewable electricity supply, and certainly no means of production that is carbon free.
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.
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.
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…
Leave it to the Scandinavians to adapt sauna to grid scale!
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.
Thanks Loren.
People a lot smarter than me may understand this, and think no it’s not completely nuts.
Adding stones to intermittent/renewables in an expanded occupation of green spaces.
Who needs green spaces when you can make tons of money off destroying the landscape and the government will pay you to do it?
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.
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?
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
https://datawrapper.dwcdn.net/VyrHt/2/
They are now importing German power prices.
What’s the efficiency of this contraption? From the description given in the article I’d be surprised if it’s above 50%.
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.
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.
.
…… so is unicorn farming !!
You’re kidding, right?
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.
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.
“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.
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.
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.
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.
They fall for this because they have zero math or science skills and run on emotion, not thought.
Does the basalt mine and crush itself or are they creating green jobs by employing people to pick up the stones one by one?
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.
From the chap who did the original design work but is no longer involved:
From: https://www.theengineer.co.uk/grid-scale-pumped-heat-energy-storage/
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.”
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.
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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.
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.
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.
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?