1. Germany
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    27 Jul '14 11:56
    Originally posted by humy
    arr but that brings me back to one of my original ideas which is to build two reservoirs at different levels especially built for this job underground very close by to the turbines wherever they are. That way you could have turbines at the top of the hill and store the energy hydroelectrically underground without the mechanical energy having to be transferred t ...[text shortened]... setup should still eventually pay for itself and be cost effective in the very long run.
    The idea is not feasible simply because the energy density of water stored at realistic altitudes is too low. The technique is already applied near existing hydroelectric plants/natural reservoirs, but would be too expensive to construct on flat land from scratch.

    Read more:
    http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
  2. Standard memberDeepThought
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    27 Jul '14 14:42
    Originally posted by twhitehead
    I think flywheel technology might be a better idea.
    But I am not convinced that the advantages of keeping it local are significant.
    Or just have a weight that is lifted. How much energy are you planning to store? I've got to agree with Kazet, there's a potential problem with feasibility with all these ideas.
  3. Joined
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    27 Jul '14 14:474 edits
    Originally posted by KazetNagorra
    The idea is not feasible simply because the energy density of water stored at realistic altitudes is too low. The technique is already applied near existing hydroelectric plants/natural reservoirs, but would be too expensive to construct on flat land from scratch.

    Read more:
    http://en.wikipedia.org/wiki/Pumped-storage_hydroelectricity
    I did say that my idea would probably not be cost effective. It was just an idea.
    As twhitehead suggested, flywheel energy storage may be more cost effective. But, if room-temperature superconductivity is ever discovered, I bet the most cost effective idea by far would be to store the energy as magnetic energy in superconducting energy storage rings which in theory can have an energy density about half of that of petrol which is extremely high and high enough by any stretch of the imagination. But such superconducting rings would have to be kept deep underground for safety reasons because of the danger of explosive magnetic quenching.
  4. Cape Town
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    27 Jul '14 15:44
    Originally posted by DeepThought
    Or just have a weight that is lifted. How much energy are you planning to store?
    I considered the weight idea but decided it would be too big.
    We want to store roughly 2 hours worth of output from a wind turbine - or possibly more.
  5. Cape Town
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    27 Jul '14 15:45
    Originally posted by humy
    As twhitehead suggested, flywheel energy storage may be more cost effective.
    I suspect that flywheel technology would not be mechanically driven so it would not actually serve the purpose - which was to avoid conversion to electricity prior to storage.
  6. Standard memberDeepThought
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    27 Jul '14 18:581 edit
    Originally posted by twhitehead
    I considered the weight idea but decided it would be too big.
    We want to store roughly 2 hours worth of output from a wind turbine - or possibly more.
    Just a bit, a 1.5 MW wind turbine would generate 10.8 Gigajoules of energy in 2 hours. So a mass of 1000 tonnes would need lifting to a height of 1 km. Or to raise it only 10 m say, a cube of lead of side length 20 metres weighing 100,000 tonnes. This isn't feasible.

    With a flywheel the kind of thing you are thinking of only exists in quite specialized settings, this is cut and pasted from the Wikipedia page on Flywheel energy:
    Other similar high power applications are in tokamak fusion (like the Joint European Torus) and laser experiments, where very high currents are also used for very brief intervals. JET has two 775 ton flywheels that spin up to 225 rpm. Each flywheel stores 3 GJ.
    Three or four like that per windturbine would do it.
  7. Cape Town
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    27 Jul '14 19:48
    http://en.wikipedia.org/wiki/Flywheel_energy_storage#Wind_turbines
    Flywheels may be used to store energy generated by wind turbines during off-peak periods or during high wind speeds.
    Beacon Power began testing of their Smart Energy 25 (Gen 4) flywheel energy storage system at a wind farm in Tehachapi, California. The system is part of a wind power/flywheel demonstration project being carried out for the California Energy Commission (Beacon Power Press Release March 2010).


    http://en.wikipedia.org/wiki/Grid_energy_storage#Flywheel
    Powercorp in Australia have been developing applications using wind turbines, flywheels and low load diesel (LLD) technology to maximise the wind input to small grids. A system installed in Coral Bay, Western Australia, uses wind turbines coupled with a flywheel based control system and LLDs to achieve better than 60% wind contribution to the town grid.
  8. Cape Town
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    27 Jul '14 19:52
    http://en.wikipedia.org/wiki/Beacon_Power
    In 2009 Beacon received a loan guarantee from the United States Department of Energy (DOE) for $43 million to build a 20-megawatt flywheel power plant in Stephentown, New York.[9][10]
  9. Standard memberDeepThought
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    28 Jul '14 20:221 edit
    Originally posted by twhitehead
    http://en.wikipedia.org/wiki/Flywheel_energy_storage#Wind_turbines
    Flywheels may be used to store energy generated by wind turbines during off-peak periods or during high wind speeds.
    Beacon Power began testing of their Smart Energy 25 (Gen 4) flywheel energy storage system at a wind farm in Tehachapi, California. The system is part of a wind pow ...[text shortened]... d control system and LLDs to achieve better than 60% wind contribution to the town grid.
    Problem is Beacon power filed for bankruptcy on 30th October 2011, they've been bought out by a finance company, who want them to develop 20 MW systems. Each of their flywheels weighs 1.3 tonnes.
    From the page on flywheels:
    This potential solution [to the problem of providing uninterruptible power supplies] has been implemented by EDA in the Azores on the islands of Graciosa and Flores. This system uses an 18 megawatt-second flywheel to improve power quality and thus allow increased renewable energy usage. As the description suggests, these systems are again designed to smooth out transient fluctuations in supply, and could never be used to cope with an outage of couple of days or more. The most powerful flywheel energy storage systems currently for sale on the market can hold up to 133 kW·h of energy.
    133kWh is about 0.5 GigaJoules. What I'm getting quite strongly from this is that what flywheels do is buy you a bit of time to switch power source. Don't misunderstand me I'm not knocking the idea, but you just can't generate all your electricity all the time with wind power.

    For comparison Dinorwig Power Station, a pumped hydroelectric facility can provide 1.65 GW of power for 6 hours. It's primary use is to cope with popular television programs ending and a few million people putting the kettle on.

    http://en.wikipedia.org/wiki/Dinorwig_Power_Station
  10. Cape Town
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    28 Jul '14 20:53
    Originally posted by DeepThought
    Don't misunderstand me I'm not knocking the idea, but you just can't generate all your electricity all the time with wind power.
    I believe solar and wind complement each other quite well although you do still need something like biogas, or even conventional fossil fuel gas to fill in the occasional gaps.
    However, I believe both solar and wind can fluctuate significantly over short time scales and flywheel technology might be intended to smooth it out so as to allow for a lower installed capacity requirement.
    Clearly several companies think it is useful for something and have put quite a lot of money into it.

    I personally think that we need to increase installed wind and solar capacity until they can at least provide 100% power when they are at their best. When we get there we can discuss how to proceed. Until we get there, the argument that wind and solar are not reliable enough on their own just doesn't cut it as the vast majority of countries are a very long long way from totally relying on either of them.
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