5 ms·

What's the advantage to having these under water? Aesthetics? It's gotta be way more expensive to have them under water.

deleted 10y ago
[deleted]
carpo 10y ago
You don't need a mountain
kwk1 10y ago
In traditional pumped storage, you use the pressure of water pumped up some elevation to generate electricity by spinning a turbine as it falls back down. In this instance, you use the pressure of the bottom of the ocean and pump the water out, so that when it is allowed to flow back in, it spins a turbine and you generate electricity. It's necessary to the design for them to be underwater.
- ddeck 10y ago
  Sorry to nitpick, but the concept works just as well above water. It also has the benefit of not requiring the pressure vessel. Building a swimming pool of the same volume 700m up the side of a mountain, pumping water up and using it to drive a turbine on the way down is the same concept (and would give the same energy storage capacity [Pi * 4/3 * (30/2)^3 * 700 * 1000 * 9.81 / 3600 / 1e6] = ~27 MWh (assuming 100% efficiency). I would imagine the benefit of doing this in the ocean is that the plumbing is simpler (don't need to lay the pipes) and you don't need to find a 700m mountain and available land for the pool, pipes and base station. In the undersea version, what you're really doing when you pump the water out of the vessel is lifting the entire ocean level by a minuscule amount and then generating power when you allow it to fall back down.
  - kwk1 10y ago
    Right, you're just describing traditional pumped storage. I suppose I should clarify because I didn't actually say what the advantage was, just the ways that the two designs are similar, but different. In short, the advantage is that it exploits the same concept but in a very different way that avoids the pitfalls of traditional pumped storage. The (dis)advantages: - Safety. Dam failure is pretty catastrophic (see Vajont Dam disaster.) Although it's yet to be seen what failure of this device would look like, it's likely to be much less threat to human life. It would probably kill or deafen nearby marine life. - Ecological concerns: a dam flooding a mountain valley destroys possibly unique ecosystems, and causes uncontrolled greenhouse gas emission as all the vegetation now underwater rots - Land availability: land is at a premium, but seabed is abundant Also, mountains for pumped storage are not always near population centers, and are often not near sources of renewable production that need the pumped storage. In that case, you have to transmit power from its point of generation to its point of storage to its point of use. In this scenario, with these spheres potentially being used as anchor points, the transmission distance between generation and storage is ~700m, and then you just need to transmit to your nearest coastal city of choice.
    - sitkack 10y ago
      This undersea design also doesn't have to deal with losses in the piping system.
guelo 10y ago
The energy is stored when all the water is pumped out of the sphere. To use the stored energy you let the water into the sphere, the surrounding water pressure pushes the water in and spins a turbine which generates the energy.
mkj 10y ago
If it wasn't underwater you'd need a very strong pressure vessel. Instead you rely on water pressure.
deleted 10y ago
[deleted]
namlem 10y ago
You're relying on water pressure instead of gravity to run the turbines. It's for coastal areas that don't have mountains.
jcoffland 10y ago
One of the biggest advantages, vs. pumping water up hill in to an open basin like a reservoir, is that you don't loose energy due to evaporation.
- snovv_crash 10y ago
  Well you do, it's just the opposite. Instead you get the air dissolving into the seawater, and having to be continually topped up. And if you're building an enclosed system, why not put it above ground instead. No evaporation problems then.
oconnore 10y ago
The advantage is having it built out of concrete. But because concrete has compression strength, not so much tensile strength, you need to store negative pressure not positive pressure.
- theoh 10y ago
  The available pressure at 700m underwater is considerable. There's no equivalent reservoir of high-pressure fluid on the surface (the atmosphere is at a much lower pressure, obviously). (The pressure difference in submarines is notably much bigger and more troublesome than the pressure difference spacecraft in a vacuum need to resist.) So surely it's the high pressure at depth that's the attractive resource here? Pumping a gas into a cavern could offer a positive pressure solution, and I'm pretty sure that's been proposed already.
  - snovv_crash 10y ago
    You get exactly the same pressure from traditional pumped storage of the same height. (Well, ignoring the tiny density difference between salt and fresh water)
- ddeck 10y ago
  That's not an advantage to having it underwater. In an above water version using a 700m mountain, the vessel to hold the water would use far less concrete. It's basically a swimming pool.
  - danmaz74 10y ago
    Not a swimming pool, but a reservoir, and there are already many used for pumped storage. The problem is that you can only do that where the local conditions allow it: you need space for the higher and lower reservoirs, space for laying down the pipes, and enough cheap water to refill the reservoirs (because of evaporation). The possible big advantage of this solution is that it could be built wherever the sea is deep enough and partially use the existing infrastructure of offshore wind farms.

deleted 10y ago

[deleted]

carpo 10y ago

You don't need a mountain

kwk1 10y ago

In traditional pumped storage, you use the pressure of water pumped up some elevation to generate electricity by spinning a turbine as it falls back down. In this instance, you use the pressure of the bottom of the ocean and pump the water out, so that when it is allowed to flow back in, it spins a turbine and you generate electricity. It's necessary to the design for them to be underwater.

ddeck 10y ago
Sorry to nitpick, but the concept works just as well above water. It also has the benefit of not requiring the pressure vessel. Building a swimming pool of the same volume 700m up the side of a mountain, pumping water up and using it to drive a turbine on the way down is the same concept (and would give the same energy storage capacity [Pi * 4/3 * (30/2)^3 * 700 * 1000 * 9.81 / 3600 / 1e6] = ~27 MWh (assuming 100% efficiency). I would imagine the benefit of doing this in the ocean is that the plumbing is simpler (don't need to lay the pipes) and you don't need to find a 700m mountain and available land for the pool, pipes and base station. In the undersea version, what you're really doing when you pump the water out of the vessel is lifting the entire ocean level by a minuscule amount and then generating power when you allow it to fall back down.
- kwk1 10y ago
  Right, you're just describing traditional pumped storage. I suppose I should clarify because I didn't actually say what the advantage was, just the ways that the two designs are similar, but different. In short, the advantage is that it exploits the same concept but in a very different way that avoids the pitfalls of traditional pumped storage. The (dis)advantages: - Safety. Dam failure is pretty catastrophic (see Vajont Dam disaster.) Although it's yet to be seen what failure of this device would look like, it's likely to be much less threat to human life. It would probably kill or deafen nearby marine life. - Ecological concerns: a dam flooding a mountain valley destroys possibly unique ecosystems, and causes uncontrolled greenhouse gas emission as all the vegetation now underwater rots - Land availability: land is at a premium, but seabed is abundant Also, mountains for pumped storage are not always near population centers, and are often not near sources of renewable production that need the pumped storage. In that case, you have to transmit power from its point of generation to its point of storage to its point of use. In this scenario, with these spheres potentially being used as anchor points, the transmission distance between generation and storage is ~700m, and then you just need to transmit to your nearest coastal city of choice.
  - sitkack 10y ago
    This undersea design also doesn't have to deal with losses in the piping system.

guelo 10y ago

The energy is stored when all the water is pumped out of the sphere. To use the stored energy you let the water into the sphere, the surrounding water pressure pushes the water in and spins a turbine which generates the energy.

mkj 10y ago

If it wasn't underwater you'd need a very strong pressure vessel. Instead you rely on water pressure.

deleted 10y ago

[deleted]

namlem 10y ago

You're relying on water pressure instead of gravity to run the turbines. It's for coastal areas that don't have mountains.

jcoffland 10y ago

One of the biggest advantages, vs. pumping water up hill in to an open basin like a reservoir, is that you don't loose energy due to evaporation.

snovv_crash 10y ago
Well you do, it's just the opposite. Instead you get the air dissolving into the seawater, and having to be continually topped up. And if you're building an enclosed system, why not put it above ground instead. No evaporation problems then.

oconnore 10y ago

The advantage is having it built out of concrete. But because concrete has compression strength, not so much tensile strength, you need to store negative pressure not positive pressure.

theoh 10y ago
The available pressure at 700m underwater is considerable. There's no equivalent reservoir of high-pressure fluid on the surface (the atmosphere is at a much lower pressure, obviously). (The pressure difference in submarines is notably much bigger and more troublesome than the pressure difference spacecraft in a vacuum need to resist.) So surely it's the high pressure at depth that's the attractive resource here? Pumping a gas into a cavern could offer a positive pressure solution, and I'm pretty sure that's been proposed already.
- snovv_crash 10y ago
  You get exactly the same pressure from traditional pumped storage of the same height. (Well, ignoring the tiny density difference between salt and fresh water)
ddeck 10y ago
That's not an advantage to having it underwater. In an above water version using a 700m mountain, the vessel to hold the water would use far less concrete. It's basically a swimming pool.
- danmaz74 10y ago
  Not a swimming pool, but a reservoir, and there are already many used for pumped storage. The problem is that you can only do that where the local conditions allow it: you need space for the higher and lower reservoirs, space for laying down the pipes, and enough cheap water to refill the reservoirs (because of evaporation). The possible big advantage of this solution is that it could be built wherever the sea is deep enough and partially use the existing infrastructure of offshore wind farms.