Gravity storage of wind energy

[Adriaan Kragten]

In the recent number 8.2.2023 of Renewable Energy World I found the article: "First grid-scale gravity energy storage system undergoes commencement in China" written by Sean Wolfe. This article can be found using the link: www.renewableenergyworld.com/storage/first-grid-scale  In the article, one shows a very big building which is under construction. It is not explained how the energy is stored. May be a member of this forum can find more information about the used mechanism as this subject may be of interest.

In chapter 5.1 of my public report KD 378 I give the formulas for potential energy. Formula 38 gives the potential energy if a solid mass is lifted. Formula 39 gives the potential energy if water is lifted. In chapter 5.2 of KD 378 I give an example for a 2 MW wind turbine producing 550 kW which is lifting a mass of 250000 kg over a distance of 200 m in an old mine shaft. It takes only about a quarter of an hour to lift this mass over a distance of 200 m if the power is 550 kW. So my conclusion was that storing of energy this way isn't a good option for a big wind turbine.

The building in the article hasn't a height of 200 m and this reduces the energy storage per mechanism. The building is very big and so it can contain many mechanisms but still I doubt if this is a realistic option to store the generated energy of some big wind turbines.

[kitestrings]

Thanks for sharing Adriaan.  It seems simple in concept, but your example points to the practical challenges in doing it at larger scale.

We had some folks here a year or so ago suggesting pumped water storage at some of our ski resorts, as I understand they have done with some success in Europe.  Permitting something like this here is pretty unlikely I'd say, even if it were close to cost-effective.

I always loved my Grandmother's cuckoo clock when I was a kid.  And later, on a dairy farm, I wondered why you couldn't set up an alternating "high-drive" where you brought the cows in at the upper level each day and used their mass to run the milking equipment.  The world was much easier to save before I took physics.  ~ks

[Adriaan Kragten]

Energy storage in water is more economic than energy storage in a solid mass. Some years ago I have visited a very big plan on the border of Germany and Luxembourg. There is a river flowing at the border and at the Luxembourg side of the river, there is a lake on top of the hill which is lying about 200 m higher than the river. A large number of very big water turbines is mounted inside a big hall excavated in the hill. There is a public corridor to the hall and the turbines can be seen through a big window. If there is a surplus of electrical energy in the grid available, water is pumped into the lake. If there is a shortage of electrical energy in the grid, water flows back through the same turbines and electrical energy is generated. Germany has several of these energy storage units. The project exists already for many years and during my visit one was making a new hall with many extra turbines to increase the capacity. If you use water, it is relatively easy to pump very large masses.

[MattM]

Using a natural location like a lake depends on natural ebb and flow of water.  I am sure playing God with a lake and river can have brutal consequences.

[Mary B]

Energy storage in water is more economic than energy storage in a solid mass. Some years ago I have visited a very big plan on the border of Germany and Luxembourg. There is a river flowing at the border and at the Luxembourg side of the river, there is a lake on top of the hill which is lying about 200 m higher than the river. A large number of very big water turbines is mounted inside a big hall excavated in the hill. There is a public corridor to the hall and the turbines can be seen through a big window. If there is a surplus of electrical energy in the grid available, water is pumped into the lake. If there is a shortage of electrical energy in the grid, water flows back through the same turbines and electrical energy is generated. Germany has several of these energy storage units. The project exists already for many years and during my visit one was making a new hall with many extra turbines to increase the capacity. If you use water, it is relatively easy to pump very large masses.

Also VERY inefficient! A LOT of losses!

[Adriaan Kragten]

Energy storage in water is more economic than energy storage in a solid mass. Some years ago I have visited a very big plan on the border of Germany and Luxembourg. There is a river flowing at the border and at the Luxembourg side of the river, there is a lake on top of the hill which is lying about 200 m higher than the river. A large number of very big water turbines is mounted inside a big hall excavated in the hill. There is a public corridor to the hall and the turbines can be seen through a big window. If there is a surplus of electrical energy in the grid available, water is pumped into the lake. If there is a shortage of electrical energy in the grid, water flows back through the same turbines and electrical energy is generated. Germany has several of these energy storage units. The project exists already for many years and during my visit one was making a new hall with many extra turbines to increase the capacity. If you use water, it is relatively easy to pump very large masses.

Also VERY inefficient! A LOT of losses!

In the corridor to the turbine hall there is an exposition about the turbines. The efficiency is mentioned and it was rather high. As I remember well, the efficiency of pumping upwards was about 0.7 and the efficiency of the backwards flow was the same. So the total efficiency is about 0.7 * 0.7 = 0.49. This is by far not as high as possible for modern batteries but for the same capacity you need an enormous battery bank which will certainly not live as long as these turbines. If you compare the efficiency with storage in hydrogen, it is still a lot better. I think that one has made the correct calculations about the pay back time of the investment and that it is worth while other wise the plant would not have been extended. The extra power which can be generated during peak hours has a very high value.

[DamonHD]

My understanding is that *round-trip* losses in GB grid pumped hydro schemes are nearer 25%.

eg https://en.wikipedia.org/wiki/Dinorwig_Power_Station  "The plant runs on average at 74–76% efficiency."

that is, similar territory to lead-acid systems, and indeed my home LiFePO4 AC-coupled batteries all told.

Rgds

Damon

[SparWeb]

There's a lot of experience doing this in Canada:

https://en.wikipedia.org/wiki/Sir_Adam_Beck_Hydroelectric_Generating_Stations

Today, pumped storage is being promoted as a way to even out fluctuations in wind and solar.  But pumped storage is not new.  It has been used for generations for the opposite reason:  Keep the coal and nuclear power stations running at their optimum efficiency, pumping water at night, discharging it through turbines in the day.  This makes the region's system more efficient overall.  If you focus your attention on one particular site and ignore the rest of the community or other power stations, then you can make up your mind that pumped storage is inefficient. 

[JW]

 

Also VERY inefficient! A LOT of losses!

 If its a water tank storage device' height from the ground of the thing. even if you got the effect working harder to get the water storage pumped up to the tank.

[Adriaan Kragten]

My understanding is that *round-trip* losses in GB grid pumped hydro schemes are nearer 25%.

eg https://en.wikipedia.org/wiki/Dinorwig_Power_Station  "The plant runs on average at 74–76% efficiency."

that is, similar territory to lead-acid systems, and indeed my home LiFePO4 AC-coupled batteries all told.

Rgds

Damon

The problem with efficiency is that often it isn't well defined. What I mean is the total efficiency electrical power out / electrical power in. You have the efficiency loss in the motor/generator and the efficiency loss in the turbine. This very big motor/generator can have an efficiency of 0.95. So if the pumping efficiency is 0.7 it means that the efficiency of the turbine is 0.7 / 0.95 = 0.737. This is already rather high for a turbine based on a centrifugal pump. But 0.7 is only the efficiency for pumping water upwards. If the water is flowing backwards, you have about the same efficiency resulting in a total efficency of 0.7 * 0.7 = 0.49. So I think that an average total efficiency of 74 % - 76 % is impossible but 25 % is also not realistic for a modern power plant.

[DamonHD]

That is what I mean also.

Look at "Commercial Efficiency" (p26) in refererence 16 ob that Wikipedia page, from the people who run the station.

https://web.archive.org/web/20140307091954/http://www.iprplc-gdfsuez.com/~/media/Files/I/IPR-Plc/Attachments/presentations-pdfs/2005/hydrosite05.pdf

"Import 1 MWh ... Export ~.75 MWh"

Rgds

Damon

[electrondady1]

There is some kind of failed oil man from Alberta trying to take advantage of a two price scheme a liberal government set up here in Ontario. There is one price for electricity in the day time and another cheaper price for electricity during the night. This "entrepreneur" wants to pump pristine water from Georgian bay up a hill to an artificial lake during the night and then release the water and generate electricity to the grid during the day . he will profit from the difference in price. local people including myself are against the project.

[dnix71]

I worked for the TVA one year over 40 years ago. They gave me a tour of one of the hydro units. Back then 1/6 of total output was hydro. The Tennessee River is in a gorge and they used unneeded nuke energy at night to fill a man-made swimming pool at the top of Raccoon Mountain. That, coupled with having Tennessee remain in 2 time zones, made management of peak loading much easier.
The lake leaked a couple of years ago and required repair, but 45 years of daily operation has been a pretty good run.

https://en.wikipedia.org/wiki/Raccoon_Mountain_Pumped-Storage_Plant

The sum of all wind contracts the TVA has doesn't even equal what Raccoon Mountain can put out for 22 hours, though. https://www.tva.com/Energy/Valley-Renewable-Energy/Wind-Energy-Contracts

To get an idea of round trip efficiency at RM, it takes 28 hours to fill and 22 hours to drain.

[joestue]

he will profit from the difference in price. local people including myself are against the project.

Nimby lol

[bigrockcandymountain]

I've always thought the abandoned parts of the potash mines here in sask would make good places to do pumped hydro.  They are thousands of feet deep in a place where large elevation changes are hard to come by. 

I even did the math on how much water it would take for a days worth of power storage.  It was a very small amount with that large an elevation change.

[Adriaan Kragten]

There is some kind of failed oil man from Alberta trying to take advantage of a two price scheme a liberal government set up here in Ontario. There is one price for electricity in the day time and another cheaper price for electricity during the night. This "entrepreneur" wants to pump pristine water from Georgian bay up a hill to an artificial lake during the night and then release the water and generate electricity to the grid during the day . he will profit from the difference in price. local people including myself are against the project.

The point is that generated energy has a different value depending on the demand. So in the middle of a sunny day the value of solar energy is very low because all solar panels are producing maximally and the demand is low. But if a wind turbine is producing high power when it is dark, this power has a high value because the demand is high. This different value of the power results in different prices, not only for what you supply but also for what you consume. So someone who creates a storage to reduce this problem does something good. It doesn't matter if he stores energy in water or in batteries. Why would it be a problem if he is rewarded for his activities and if he makes a profit out of his investment?

In The Netherlands we have the so called "Salderingsregeling". This means that owners of solar panels get the same price per kWh for supplied energy as for consumed energy as long as the total yearly demand is larger than the feed back energy. But this means that they get much more than the real value. The difference isn't paid by the gouvernment but by people who have no solar panels as the electricity company compensates the losses by a higher selling price. This is really unfair. One should not get more back than the real value at the moment of supply.

[Bruce S]

Here in Missouri , we've had pumped hydro for 40+ years before having any problems.
Back in 2005 it failed, with no lives lost. It was completely rebuilt holding upwards of 1.5B US Gal of water.

There's a few people on U-tube doing solid mass and water flow posts. Since water's density is well known, math is an easy exercise.
There was a very nice were, a member posted all about his wall crawler Gen he built using Lego blocks. Was cool to read, and it worked.
Highly efficient? Not likely, but he knew that , more of why not when you have the items already available. Also a good exercise in math.

Cheers
Bruce S   

[bigrockcandymountain]

I don't think 75% efficiency is a deal breaker for round trip efficiency on any storage system.  Power generated by solar and wind is pretty darned cheap per kwh.  Still cheap even if you have 25% lost to storage, except the cost of the storage needs to be added in.

The big question is how much does that storage cost.  S550 surrette 1500 cycles at 50% dod.

8 pcs 6v $4000
10 kwh at 50% dod x 1500 cycles 15000 kwh
$4000÷15000= 27c per kwh stored. 

That's not very good.  That's why we try to use power as it is generated and not run much through the batteries. 

I know every project would be different, but i wonder what the cost per kwh of pumped hydro works out to. I think in an ideal location and at a large scale, it would be pretty cheap.

[SparWeb]

In some regions where the electricity spot price is allowed to float minute by minute, there are sometimes shut-downs that drive the price of electricity way up.  The average user wouldn't have any idea because the rate is averaged monthly.  However, these guys building storage will watch the spot price keenly, and any time they see it ramp up they get ready to put some stored energy on the grid.  The price in Alberta can spike up 10X for an hour, several times per year due to unplanned outages.  Anybody ready with a reserve to dump on the lines will make a killing.

Large scale pumped hydro is very cheap.  Cheap enough to pay for the Welland Canal.

[Bruce S]

The Taum Sauk dam, I think cost about $700M back in the 60s holding 1.5B USgals operated up til 2005 when it over-topped <-? So 40+ years of daily use.
It's rebuilding didn't get finished until 2010 due to higher and much needed safety features and is still going strong.
BTW: The lower part used to be fun to swim in during summer months! Water was always crystal clear and nicely chilled. We used to be able to drive up to the top, but I think they stopped that. Haven't been out there in a very long time.

[JW]

 
 https://en.wikipedia.org/wiki/Gravity_battery

[Crockel]

Maybe they could use the excess solar and wind power to drive the compression cycle of a geothermal heat engine. Use the electricity to pump air down a deep intake shaft where it would heat up and expand and then vent it through a turbine on a connected exhaust shaft. It would store energy like a battery but be over 100% efficient.

[DamonHD]

It won't be even 100%.  Laws of physics and all that.

But compressed air energy storage or CAES (including possible storage of heat at compression to be used at expansion) seems to be a serious contender at scale.

Rgds

Damon

[JW]

 

It won't be even 100%.  Laws of physics and all that.

Its the Second Law of Thermodynamics'

[Adriaan Kragten]

 

It won't be even 100%.  Laws of physics and all that.

Its the Second Law of Thermodynamics'

It depends on what Crockel is meaning, if more than 100% is possible. If electrical power is available from solar or wind and if this power is used for the compressor of a heat pump, the produced heat power can easily be a factor four higher than the electrical power. But then this isn't called the efficiency but the COP-value. The heat can then be stored in the ground and although there will be substantial losses because of the storage, the nett outcoming heat power can be much higher than 100 % of the electrical input power.

[Crockel]

I'm thinking it would behave according to the Rankine cycle like a steam engine. Excess solar or wind power from the grid could be used to drive a compressor to pressurize a well shaft and underground chamber where it would be heated geothermally. Then the heated pressurized air would be extracted through an adjacent well shaft to drive a turbine.

https://en.m.wikipedia.org/wiki/Rankine_cycle

There'd be losses due to pressure leaks through fissures and heat loss through the exhaust shaft, but it should produce more power than it uses.

Water would work even better than air as long as there is sufficient heat to keep the water above the boiling point until after the turbine.