6 ms·

At larger scales, these are called pumped-storage hydroelectric plants. There are currently more than 100 GW of pumped-storage capacity in the world, with effic

by kijin 13y ago

At larger scales, these are called pumped-storage hydroelectric plants. There are currently more than 100 GW of pumped-storage capacity in the world, with efficiency ranging from 70% to 87% [1]. They are, in fact, some of the largest batteries we've ever built. They store electricity by pumping thousands of tons of water uphill when demand is low, and letting it fall back down past a bunch of turbines when demand is high. Water is much easier to handle than a solid block of steel, and it's much more scalable as well. You just need a hill and some water, possibly an already existing reservoir. Pumps can be turned on and off almost instantly to meet fluctuating demand. There's one about 10 minutes' drive from where I live. It's marvelous, and the two artificial lakes (one at the top, one at the bottom) also make nice parks for the public to enjoy. Since pumped-storage plants seem to work so well, I wonder if there will be any need to install smaller versions in each home. It's probably going to be difficult to match the efficiency of much larger units. Maybe these will be more useful as backup batteries. [1] https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity https://en.wikipedia.org/wiki/Pumped-storage_hydroelectricit...

hrjet 13y ago
The only drawback I see with pumped-storage hydroelectric plants is that there could loss of stored energy due to evaporation. I don't know how much loss does it amount to on a sunny day.
- logicallee 13y ago
  it could also rain in your pond and give you free energy.
  - Tloewald 13y ago
    This is in fact the entire principle of hydro-electric power (incidentally, a form of solar power since the water-cycle is driven by heat from the sun).
- JshWright 13y ago
  Another drawback is that building a reservoir on top of a mountain can be a little trickier than originally thought... http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_Station#Upper_reservoir_breached http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_S...
  - kijin 13y ago
    Many pumped-storage plants just dam an existing valley to create the upper reservoir. Easier than trying to build a gigantic swimming pool on top of a mountain, and probably safer as well. Of course, in order to do this, you need some very rough terrain, so it's not suitable for flat countries.
ErikRogneby 13y ago
There is a proof of concept using gravel instead of water as well. http://www.energycache.com/ http://www.energycache.com/ http://www.youtube.com/watch?v=G3nz_kU604s&feature=youtu.be http://www.youtube.com/watch?v=G3nz_kU604s&feature=youtu.be
- Tloewald 13y ago
  No-one is denying the concept would work -- it's just an enormously expensive way to save remarkably little energy. A Macbook Pro battery -- 63.5 Wh -- can store as much energy as a 46kg mass suspended in a 500m shaft operating with 100% efficiency. Now, which do you think costs more to build and maintain?
Tloewald 13y ago
I suspect that the big problem with this concept (vs. the hydroelectric example) is going to be the amounts of energy involved. Let's suppose the shaft is 500m deep and a 100kg battery -- potential energy is simply F * z, so F = 980N and z is 500, which gives you 490kJ. A wH is 3.6 kJ (you'll need ~10-20 of these to run an iPad for an hour). You're going to need a really big weight and a really big shaft. This shouldn't be surprising -- with a fairly small motor and good gearing you could raise a remarkably large weight a remarkably long distance with relatively little energy. Also note that with a hydroelectric dam, the storage mechanism also happens to be the power generation mechanism (dam + turbine) so you aren't incurring huge additional construction and maintenance costs relative to just building the power source, so even if you replaced the weights with a giant tank of water, the entire storage mechanism is extra capital investment and maintenance on top of the solar panels. If the fundamental problem you're trying to solve is baseline power, it's probably more efficient to bring power in from somewhere the sun is shining (8000 miles away, say): "As of 1980, the longest cost-effective distance for Direct Current transmission was determined to be 7,000 km (4,300 mi). For Alternating Current it was 4,000 km (2,500 mi), though all transmission lines in use today are substantially shorter than this." (Wikipedia)
- maxcan 13y ago
  You only need a large shaft if you construct the weight out of some material other than the matter from a neutron star.
- Pxtl 13y ago
  Yeah, the problem is simply practical - digging a shaft like that and keeping it from filling with water is expensive.
  - sp332 13y ago
    Having a shaft full of water would reduce the efficiency, but as long as the weight still sinks, it will still work.
    - maxmcd 13y ago
andrelaszlo 13y ago
Apparently, there's a "Renaissance for Pumped Storage in Europe"[1] [1] http://www.hydroworld.com/articles/print/volume-19/issue-3/articles/new-development/renaissance-for-pumped-storage-in-europe.html http://www.hydroworld.com/articles/print/volume-19/issue-3/a...

by kijin 13y ago

hrjet 13y ago

The only drawback I see with pumped-storage hydroelectric plants is that there could loss of stored energy due to evaporation. I don't know how much loss does it amount to on a sunny day.

logicallee 13y ago
it could also rain in your pond and give you free energy.
- Tloewald 13y ago
  This is in fact the entire principle of hydro-electric power (incidentally, a form of solar power since the water-cycle is driven by heat from the sun).
JshWright 13y ago
Another drawback is that building a reservoir on top of a mountain can be a little trickier than originally thought... http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_Station#Upper_reservoir_breached http://en.wikipedia.org/wiki/Taum_Sauk_Hydroelectric_Power_S...
- kijin 13y ago
  Many pumped-storage plants just dam an existing valley to create the upper reservoir. Easier than trying to build a gigantic swimming pool on top of a mountain, and probably safer as well. Of course, in order to do this, you need some very rough terrain, so it's not suitable for flat countries.

ErikRogneby 13y ago

There is a proof of concept using gravel instead of water as well. http://www.energycache.com/ http://www.energycache.com/ http://www.youtube.com/watch?v=G3nz_kU604s&feature=youtu.be http://www.youtube.com/watch?v=G3nz_kU604s&feature=youtu.be

Tloewald 13y ago
No-one is denying the concept would work -- it's just an enormously expensive way to save remarkably little energy. A Macbook Pro battery -- 63.5 Wh -- can store as much energy as a 46kg mass suspended in a 500m shaft operating with 100% efficiency. Now, which do you think costs more to build and maintain?

Tloewald 13y ago

I suspect that the big problem with this concept (vs. the hydroelectric example) is going to be the amounts of energy involved. Let's suppose the shaft is 500m deep and a 100kg battery -- potential energy is simply F * z, so F = 980N and z is 500, which gives you 490kJ. A wH is 3.6 kJ (you'll need ~10-20 of these to run an iPad for an hour). You're going to need a really big weight and a really big shaft. This shouldn't be surprising -- with a fairly small motor and good gearing you could raise a remarkably large weight a remarkably long distance with relatively little energy. Also note that with a hydroelectric dam, the storage mechanism also happens to be the power generation mechanism (dam + turbine) so you aren't incurring huge additional construction and maintenance costs relative to just building the power source, so even if you replaced the weights with a giant tank of water, the entire storage mechanism is extra capital investment and maintenance on top of the solar panels. If the fundamental problem you're trying to solve is baseline power, it's probably more efficient to bring power in from somewhere the sun is shining (8000 miles away, say): "As of 1980, the longest cost-effective distance for Direct Current transmission was determined to be 7,000 km (4,300 mi). For Alternating Current it was 4,000 km (2,500 mi), though all transmission lines in use today are substantially shorter than this." (Wikipedia)

maxcan 13y ago
You only need a large shaft if you construct the weight out of some material other than the matter from a neutron star.
Pxtl 13y ago
Yeah, the problem is simply practical - digging a shaft like that and keeping it from filling with water is expensive.
- sp332 13y ago
  Having a shaft full of water would reduce the efficiency, but as long as the weight still sinks, it will still work.
  - maxmcd 13y ago

andrelaszlo 13y ago

Apparently, there's a "Renaissance for Pumped Storage in Europe"[1] [1] http://www.hydroworld.com/articles/print/volume-19/issue-3/articles/new-development/renaissance-for-pumped-storage-in-europe.html http://www.hydroworld.com/articles/print/volume-19/issue-3/a...