### Author Topic: Energy storage by moving concrete blocks  (Read 7674 times)

0 Members and 1 Guest are viewing this topic.

#### GeorgeOfTheJungle

• Super Contributor
• !
• Posts: 2704
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #75 on: August 06, 2019, 09:28:12 pm »
One kWh is 3600*1000 joules. You'd need lots of m or lots of h to get one of those from mgh...

In the video they say it can store 30MWh. That's 30e6*3600 joules = mgh => mh = 30e6*3600/9,8 = 11020408163 ergo if it were , say, a 100m tall tower (that's a 33 stories high skyscraper), the mass would have to be (at least) 110204081,63, which is a block of 110204 tons of concrete at a 100 meters high in the sky, with all the 110204 tons at the very top of the tower.
« Last Edit: August 06, 2019, 11:46:50 pm by GeorgeOfTheJungle »
The further a society drifts from truth, the more it will hate those who speak it.

#### Marco

• Super Contributor
• Posts: 4931
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #76 on: August 06, 2019, 11:49:43 pm »
I don't think any potential energy storage system will be able to compete with pumped hydro, either traditional or ocean floor (ie. you pump the water out of a concrete sphere). Solid matter is inconvenient to work with.

#### Domagoj T

• Frequent Contributor
• Posts: 463
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #77 on: August 07, 2019, 07:28:57 am »
Full disclosure: I did not run any numbers on this, I'm away from the computer, but this just entered my mind and can't shake it. Consired this a runaway train of thought.

What if the system is inverted and under sea? Anchor it to the seabed and have big steel baloons tied by cables to the winch at the bottom (or have a pulley and the winch with the generator on shore).
Sea is fairly calm once you go deeper than 20 m, but there are currents to consider. Oil rigs have that solved. I suppose some type of control surfaces could be employed to help with position control by taking advantage of up/down movement.
Big military submarines reach couple of hundred meters regularly.
What do you think?

#### ebastler

• Super Contributor
• Posts: 3689
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #78 on: August 07, 2019, 08:25:25 am »
A big concrete block should be much cheaper to make than a big hollow sphere that has to withstand significant pressure, especially if you want to pull it deep down to store lots of energy. If you need one winch per sphere, or some tricky mechanism to switch spheres over between the winch/generator and some ground anchors, that adds to the complexity. Stacking blocks and relying on gravity to ensure they stay where they are seems simpler.

#### Kleinstein

• Super Contributor
• Posts: 8057
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #79 on: August 07, 2019, 09:25:56 am »
There was an odd proposal out there to build concrete spheres to sink to the ocean and pump water in an out. However this is not much different than building small dams the size of spheres, just under water and the other way around.  Small installatons suffer from too many pipes / pumps. Things like motors/generators tend to be higher efficiency if larger.  Actually moving things under water adds trouble with cables.

Stacking blocks sound simple, but pumping water is even simpler (if one has a suitable mountain). A ton of concrete in a damm can easily hold back more than 1 ton of water.

#### Marco

• Super Contributor
• Posts: 4931
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #80 on: August 07, 2019, 12:51:49 pm »
On the other hand the underwater solution doesn't need a high flow pipeline. You pump water a couple of meters, yet with the same pressure difference as a mountain based system with a long pipeline between the reservoirs.

Fraunhofer institute estimated they could do it cheaper than pumped hydro up a mountain.
« Last Edit: August 07, 2019, 12:55:04 pm by Marco »

#### SiliconWizard

• Super Contributor
• Posts: 5649
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #81 on: August 07, 2019, 01:00:54 pm »
Underwater systems have the added benefit that they are a lot less dangerous. A huge concrete sphere accidentally "falling" underwater if anything breaks will make a lot less harm than its open-air counterpart.

#### Domagoj T

• Frequent Contributor
• Posts: 463
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #82 on: August 07, 2019, 02:57:17 pm »
A big concrete block should be much cheaper to make than a big hollow sphere that has to withstand significant pressure, especially if you want to pull it deep down to store lots of energy. If you need one winch per sphere, or some tricky mechanism to switch spheres over between the winch/generator and some ground anchors, that adds to the complexity.

Yeah, it would be more expensive to make the steel sphere, especially since you also need the anchor.
Regarding the pressure, wouldn't pressurizing the sphere at to half the design depth pressure help?
There is still metal fatigue to consider. How many times can the device be subjected to pressure changes before welds fail? I tried looking up that number for real world submarines, but was not able to find an instance where it is mentioned how many dives a sub had before decommissioning, or if it's even a consideration. I suppose that would be classified.

Stacking blocks and relying on gravity to ensure they stay where they are seems simpler.

I'm not sure. There are some problems with that method too (I suppose most of them are mentioned by Thunderfoot).

#### GeorgeOfTheJungle

• Super Contributor
• !
• Posts: 2704
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #83 on: August 07, 2019, 09:29:57 pm »
Ok, say it can store 30MWh, but what is the max feasible power output?
The further a society drifts from truth, the more it will hate those who speak it.

#### SparkyFX

• Frequent Contributor
• Posts: 659
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #84 on: August 08, 2019, 02:28:19 am »
Fatigue and fatigue related impact on overall efficiency might be the biggest concern about this - next to the amount of CO2 produced just for the concrete and the unused energy in start and stop of the motion... No doubt that there could be a working prototype, but this is really about longevity and which efficiency is acceptable for a storage concept; i would not operate this in an area with earthquakes or high wind.

It would not even need to be a freestanding tower, something similar could be installed in closed mines under ground, which do have longer slopes or elevator shafts. It might not be as many and rather small, but longer distances and higher weight would be possible, as there is a support structure enabling some safety features in case of a failure. The longer distance would offset the problem with losing to much potential energy through stacking next to a very limited height of a freestanding tower.

There are other similar concepts, like lifting weights with water pressure to store energy using conventional pumps and turbines. The weight could be locked in place and it would mean less moving (wear)parts, plus the benefits of a mass with higher density than water in the system and a lower loss by hydraulic control. This could shrink the required volume for a pumped storage hydroelectric plant by the difference in density of all media used and enable to use it in places otherwise not suitable.

However, since a few years Power2Gas is the concept that gains a lot of traction here, it uses the natural gas network as storage, small and big installations are in the making and working. Given that gas turbine generators allow a fast start of electricity production and are all over the place to cover shortages, this makes more sense. Not saying it is that easy, because hydrogen penetrates some materials and combustion processes are never fully ideal.

#### NANDBlog

• Super Contributor
• Posts: 4928
• Country:
• Current job: ATEX certified product design
##### Re: Energy storage by moving concrete blocks
« Reply #85 on: August 08, 2019, 08:26:26 pm »
There was an odd proposal out there to build concrete spheres to sink to the ocean and pump water in an out. However this is not much different than building small dams the size of spheres, just under water and the other way around.  Small installatons suffer from too many pipes / pumps. Things like motors/generators tend to be higher efficiency if larger.  Actually moving things under water adds trouble with cables.

Stacking blocks sound simple, but pumping water is even simpler (if one has a suitable mountain). A ton of concrete in a damm can easily hold back more than 1 ton of water.
Yeah, but in fact you are not pumping water anymore. In a regular " two lake " system, you are pumping water and using a generator. In the sunken bubble, you actually need to pump compressed air, which is much less efficient. Not to mention anchoring it down, as others said.
I dont know, it seems sketchy. On the other hand Fraunhofer is highly qualified. Do you have a link?

#### coppice

• Super Contributor
• Posts: 6032
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #86 on: August 08, 2019, 08:35:28 pm »
There was an odd proposal out there to build concrete spheres to sink to the ocean and pump water in an out. However this is not much different than building small dams the size of spheres, just under water and the other way around.  Small installatons suffer from too many pipes / pumps. Things like motors/generators tend to be higher efficiency if larger.  Actually moving things under water adds trouble with cables.

Stacking blocks sound simple, but pumping water is even simpler (if one has a suitable mountain). A ton of concrete in a damm can easily hold back more than 1 ton of water.
Yeah, but in fact you are not pumping water anymore. In a regular " two lake " system, you are pumping water and using a generator. In the sunken bubble, you actually need to pump compressed air, which is much less efficient. Not to mention anchoring it down, as others said.
I dont know, it seems sketchy. On the other hand Fraunhofer is highly qualified. Do you have a link?
Any scheme involving compressed gas gets complex, because the energy that goes into storage is a mix of two forms - pressure and heat - and storing heat has inevitable insulation issues if the store is intended to persist for any length of time.

#### Marco

• Super Contributor
• Posts: 4931
• Country:
##### Re: Energy storage by moving concrete blocks
« Reply #87 on: August 08, 2019, 08:37:42 pm »
Yeah, but in fact you are not pumping water anymore. In a regular " two lake " system, you are pumping water and using a generator. In the sunken bubble, you actually need to pump compressed air, which is much less efficient.
No, they want to pump the water and pull a poor vacuum.

Smf