Vocal Voices

The wind often blows when the electricity is not needed so, much of it goes to waste.

The new idea is to use it to pump water into flexible pillow tanks on the sea (lake) bed then use natural water pressure to pump it back through a generator when it is needed. Simple!

The initial pressure in the tank is at 0 psi and if it is at say, 40m depth, the external water pressure is about 75 psi. Fill it up and then let the natural water pressure deflate it but use the outflow to drive a generator as and when needed.

Sounds feasible in practice, but what about the scale?

It does sound a good idea.....

I saw this elsewhere. There was a short discussion about it. It is similar to the hydrostar system built on land. Hydrostar is around 60% round trip efficient for power storage.

https://youtu.be/cOWjwwKSR78

Because this system uses bladders and ocean pressure to create the water flow, the heat created by the initial pumping would be lost. It is very cheap on initial infrastructure, but probably around 40% round trip efficiency or about the same as hydrogen.

They could increase the efficiency by building high level tanks and raising the water, removing most of the thermal energy loss. But that has significant costs.

Good for long term storage, not competitive in the fast reacting energy market.

Great lateral thinking though.

The system is water to water so unlike air to water or vice versa (Hydrostor) there is little thermal energy loss. Ocean battery, as well as other systems of similar design, are said to have about 75% efficiency.

It is modular and scalable and is extremely well suited to quick energy release over many hours and many cycles.

https://newatlas.com/energy/ocean-batte ... y-storage/

https://newatlas.com/sea-floor-energy/2 ... ticle-body

https://newatlas.com/mit-offshore-wind- ... ticle-body

Ocean battery is more suited to the depths found in the North sea (ave depth 95 m), whereas MIT's is for deeper waters. Most of our wind turbines are in the North Sea.

In general it is a modification of old and robust technology and not too dissimilar to how we filled our Fairy liquid "water pistols" when we were young. Squeeze, dunk, squeeze again, let go - bubbles come out and the water rushes in. Take out and squeeze again and your mates get soaked.

Whenever you compress something there is heat. Water forced into bladders under the sea need pressure to fill.

No the heat transfer will not be as bad as air, but it will be there.

I did say "little" thermal energy loss. It is in the 10 thousandths of a °C per m3 / bar, so not exactly massive. These systems can cope.

On exercise we had camouflaged neoprene fuel pillow tanks in the RAF. Bowsers would come in as and when they could and use their pumps to fill them then gravity working on the weights on top would empty them into our vehicles. It was a simple system that meant we did not have lines of bowsers / vehicles as a target. Nature did most of the work.

We also had compressed air cockpit and electronics coolers. Air was taken into a tank at hundreds of bar (3,500+ psi), which got so hot that it needed insulating to protect us from touching it, but when the air was released the huge drop in pressure and increase in volume created frost on the outlet coupling, such is the thermal capacity of air. These systems are not doing that.

If they can be made to work at scale, and all the links have large working prototypes, then thermal issues will be a small part of any problems.

We can only hope that enough time and effort goes into this to maximise the efficiency.

BTW the thermal conductivity of water is 20 times higher than air and the thermal storage capacity is also significantly higher.

Even with the same heat generation you would never feel it as the next charge through the pump would cool it.

Hence why we liquid cool things.