4 ms·

> What is wrong with present methodologies of energy storage? For example using surplus power to pump water up hill, to later recuperate during peak hours? Say

> What is wrong with present methodologies of energy storage? For example using surplus power to pump water up hill, to later recuperate during peak hours? Say you want to store 1 kilowatt-hour of electricity (most places in the United States, about $0.12 worth). That's 3.6 million joules of energy. The potential energy gained by moving an object away from the Earth is approximately m * g * h, were m is mass, g gravity, and h height. g is approximately 10, and in a home system let's say h is also approximately 10. Probably less. Then the amount of water you need to move is approximately 36,000 kilograms. At 1 kilogram per liter, that's 36,000 liters or approximately 9,000 gallons. For comparison, that's roughly the size of a moderate swimming pool. And of course, there are many other problems: converting electricity to pump action to water movement to potential energy back to electricity is not 100% efficient. That much water is extremely heavy; there's a reason swimming pools are often built in the ground. Etc. And all that for just 1 kilowatt hour! My urban apartment uses O(10) kilowatt hours per day, so even if only a small fraction of that must be stored, my roommate and I would require a swimming pool or three. Hard to find space in a city...this could all be done remotely, but then transmission loss cuts the efficiency further.

Nanzikambe 12y ago
And now I know :) Thanks for taking the time to make this detailed & informative reply! So basically the point is that Vanadium presents the most efficient method of power storage we know of to date?
- sanxiyn 12y ago
  I don't think so. In energy storage, pumped-storage hydroelectricity(PSH) is still the undisputed king. It currently represents >99% of installed capacity, and has a quite good efficiency. As I understand, Vanadium redox battery is not more efficient than PSH. And no energy storage system is proven to scale to PSH scale. About the only problem with PSH is need for a reservoir and hence site selection. In Europe, it is said that Norway, which has lots of good sites for PSH, alone, can support entire energy storage demand of Europe. As I understand it is more problematic in US.
  - throwawayaway 12y ago
    To what extent could you pressurize the water to restrict the volume? I can imagine an egg timer style device with heavy pressurised immiscible liquids and some turbine in the middle that you turn over physically instead of pumping. someone has already had the idea: http://www.myfreeinventions.com/electricity-generation/portable-hydroelectricity-generator-for-remote-areas-made-from-recycled-parts/ http://www.myfreeinventions.com/electricity-generation/porta... oh here's another one - might be interesting to strap two of these together: http://fivegallonideas.com/hydroelectric-generator/ http://fivegallonideas.com/hydroelectric-generator/
    - sanxiyn 12y ago
      Well, air compresses better. People are trying to store energy in compressed air. I found LightSail Energy to be interesting. http://www.lightsail.com/ http://www.lightsail.com/
    - gus_massa 12y ago
      From http://en.wikipedia.org/wiki/Properties_of_water#Compressibility http://en.wikipedia.org/wiki/Properties_of_water#Compressibi... > The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume. With some simplifications, the stored energy is approximately P*deltaV/2 (when P>>1atm), where P is the pressure and deltaV is the volume change. So in 1 litter (1/4 galon) at -4Km, the energy is only 400J (.1Wh), and you need submarine grade technology to store it. The potential energy of 1 litter (1/4 galon) of water at 40m (130 ft, a 15 story building) is also 400J (.1Wh) and is much easier to build.
    - pantalaimon 12y ago
      the volume of a liquid hardly changes under pressure.
  - lucaspiller 12y ago
    The biggest site in the UK (built in the 70s for the same problem from nuclear power) was built into an abandoned quarry, surely there must be plenty of those around? http://en.wikipedia.org/wiki/Dinorwig_Power_Station http://en.wikipedia.org/wiki/Dinorwig_Power_Station
colanderman 12y ago
Not really relevant to the discussion, but O(10) doesn't mean "approximately 10". O(f(x)) denotes a function that is bounded by a constant multiple of f(x), and really only makes sense in the context of a dependent variable x. (e.g. O(2^x) denotes an exponential-bounded relationship with x). So O(10) in the above context effectively means your apartment uses some unknown number of kWh.
- dhimes 12y ago
  When dealing with numbers, the notation means "order of magnitude," which is the nearest power of 10. Strictly, this places is between 5 and 50 (4 rounds down to 1, 51 rounds up to 100). Most people use it a little more loosely in conversation. More than 1, not 100, etc.
  - stcredzero 12y ago
    I didn't know this. I'm used to just talking about "order of magnitude."
  - dllthomas 12y ago
    While I've occasionally seen O(...) used to mean "approximate upper bound" or even "approximate bound" in a more general way than the math for Big-O notation would permit, I've assumed it was either error or analogy, not a specific other function. Can you give a citation for this being an established usage? (Note that I'm certainly familiar with orders of magnitude, just not this notation for them.)
    - dhimes 12y ago
      It may be informal. I seem to recall people also using ~ for this, as in "The detector is measuring eV, but this effect is ~ meV |O(meV) so we won't see it."
- stcredzero 12y ago
  To expand on this: O(10) is the same as O(9) or O(1) and O(k). (k is a constant) Key to understanding this: Note that if you graphed out all the above as functions, they would all be horizontal lines. O is about the kind of function something is, specifically relating to how fast it expands.
SixSigma 12y ago
We have a 1728MW pumped storage facility here in Wales. http://en.wikipedia.org/wiki/Dinorwig_Power_Station http://en.wikipedia.org/wiki/Dinorwig_Power_Station http://www.electricmountain.co.uk/ http://www.electricmountain.co.uk/

Nanzikambe 12y ago

And now I know :) Thanks for taking the time to make this detailed & informative reply! So basically the point is that Vanadium presents the most efficient method of power storage we know of to date?

sanxiyn 12y ago
I don't think so. In energy storage, pumped-storage hydroelectricity(PSH) is still the undisputed king. It currently represents >99% of installed capacity, and has a quite good efficiency. As I understand, Vanadium redox battery is not more efficient than PSH. And no energy storage system is proven to scale to PSH scale. About the only problem with PSH is need for a reservoir and hence site selection. In Europe, it is said that Norway, which has lots of good sites for PSH, alone, can support entire energy storage demand of Europe. As I understand it is more problematic in US.
- throwawayaway 12y ago
  To what extent could you pressurize the water to restrict the volume? I can imagine an egg timer style device with heavy pressurised immiscible liquids and some turbine in the middle that you turn over physically instead of pumping. someone has already had the idea: http://www.myfreeinventions.com/electricity-generation/portable-hydroelectricity-generator-for-remote-areas-made-from-recycled-parts/ http://www.myfreeinventions.com/electricity-generation/porta... oh here's another one - might be interesting to strap two of these together: http://fivegallonideas.com/hydroelectric-generator/ http://fivegallonideas.com/hydroelectric-generator/
  - sanxiyn 12y ago
    Well, air compresses better. People are trying to store energy in compressed air. I found LightSail Energy to be interesting. http://www.lightsail.com/ http://www.lightsail.com/
  - gus_massa 12y ago
    From http://en.wikipedia.org/wiki/Properties_of_water#Compressibility http://en.wikipedia.org/wiki/Properties_of_water#Compressibi... > The low compressibility of water means that even in the deep oceans at 4 km depth, where pressures are 40 MPa, there is only a 1.8% decrease in volume. With some simplifications, the stored energy is approximately P*deltaV/2 (when P>>1atm), where P is the pressure and deltaV is the volume change. So in 1 litter (1/4 galon) at -4Km, the energy is only 400J (.1Wh), and you need submarine grade technology to store it. The potential energy of 1 litter (1/4 galon) of water at 40m (130 ft, a 15 story building) is also 400J (.1Wh) and is much easier to build.
  - pantalaimon 12y ago
    the volume of a liquid hardly changes under pressure.
- lucaspiller 12y ago
  The biggest site in the UK (built in the 70s for the same problem from nuclear power) was built into an abandoned quarry, surely there must be plenty of those around? http://en.wikipedia.org/wiki/Dinorwig_Power_Station http://en.wikipedia.org/wiki/Dinorwig_Power_Station

colanderman 12y ago

Not really relevant to the discussion, but O(10) doesn't mean "approximately 10". O(f(x)) denotes a function that is bounded by a constant multiple of f(x), and really only makes sense in the context of a dependent variable x. (e.g. O(2^x) denotes an exponential-bounded relationship with x). So O(10) in the above context effectively means your apartment uses some unknown number of kWh.

dhimes 12y ago
When dealing with numbers, the notation means "order of magnitude," which is the nearest power of 10. Strictly, this places is between 5 and 50 (4 rounds down to 1, 51 rounds up to 100). Most people use it a little more loosely in conversation. More than 1, not 100, etc.
- stcredzero 12y ago
  I didn't know this. I'm used to just talking about "order of magnitude."
- dllthomas 12y ago
  While I've occasionally seen O(...) used to mean "approximate upper bound" or even "approximate bound" in a more general way than the math for Big-O notation would permit, I've assumed it was either error or analogy, not a specific other function. Can you give a citation for this being an established usage? (Note that I'm certainly familiar with orders of magnitude, just not this notation for them.)
  - dhimes 12y ago
    It may be informal. I seem to recall people also using ~ for this, as in "The detector is measuring eV, but this effect is ~ meV |O(meV) so we won't see it."
stcredzero 12y ago
To expand on this: O(10) is the same as O(9) or O(1) and O(k). (k is a constant) Key to understanding this: Note that if you graphed out all the above as functions, they would all be horizontal lines. O is about the kind of function something is, specifically relating to how fast it expands.

SixSigma 12y ago

We have a 1728MW pumped storage facility here in Wales. http://en.wikipedia.org/wiki/Dinorwig_Power_Station http://en.wikipedia.org/wiki/Dinorwig_Power_Station http://www.electricmountain.co.uk/ http://www.electricmountain.co.uk/