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Air compressor as energy storage?

Discussion in 'Home Power and Microgeneration' started by Taunto, Feb 19, 2007.

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  1. They turn of the waterflow and turbines, and pump water into the basin
    using electrisity they buy on the electric spot-market. (even though
    you get one price on your bill for a given period of time, the price
    of electricity fluctates a lot during a 24 hour period, and from day
    to day.)
  2. Not realy. It has a lower cost per kW the more/faster it produces.
    I expect that there is some kind of "sweet spot" where the price per
    kW is lowest.

    If it is shut down for a few hours due to low electricity prices, you
    still got salaries. capital costs etc.
  3. You do not have a storage lake, you got one lake where water is
    drained. (possibly with connecting lakes, but if so, only to maximise
    the area where you can collect rain.
    Other utilities. Nuclear, coal and hydro-dams that has to produce
    because their storage capacity is full or near full. Or even hydro
    plants that rely on rivers without dams.
    The storage lake and main source is the same thing. You pump the water
    from other sources. Possibly collection sites at lower altitudes or
    from a lake/river.
    The lower the usage of the baseload(minimum supply of electricity) the
    lower the price of the electricity gets. If it is not sold(used), it
    needs to be "burned of".
    Its not free, but the cost of running them is lower than the price you
    get when you are using the pumped water to generate electricity at a
    later point.
  4. I am a bit uncertain about the usage of the term pumps/turbine here.

    Even though you may use a pump as a turbine by reversing the flow, I
    belive that the utilities uses blade/spoon turbines than are more
    effective, but cannot be used to pump water.

    Offcource, it may be cost effective to use pumps as turbines in this
    setting (lower capital costs). But without beeing completely sure, I
    would put my bet on seperate pumps and turbines.
  5. AJH

    AJH Guest

    The pumped storage system in Dinorwig, Wales uses the same reaction
    turbines both for the generation and pumping, they're vertical axis
    with inlet guide vanes, I was astonished they had the ability to pump
    600metres head in a single stage.

    I cannot see it being viable for domestic use but I can envisage a
    high head water reservoir being pumped by a direct driven wind turbine
    as being feasible on the 30kWhr/day scale.

  6. Again there's no disagreement, the sum is quite simple, the cost of
    grid power is made up of capital charges, fuel cost and
    operation+maintenance cost. So large simple plants with low fuel costs are
    favoured other than for your peak shaving. The pumped storage schemes
    profit on the difference between the two costs.

    There is scope for the domestic owner to save though because, in UK at
    least, the bulk of the delivered cost of grid electricity is the
    distribution cost, not the generation cost. In fact the difference seems
    to be about a factor of 4.

    So if you had a cheap means of generating electricity or direct pumping
    and the right site, then storing the water at high head and generating
    through a pelton wheel may bear looking at the figures. I've not satisfied
    myself of any circumstance where it would be competitive with grid power,

  7. Guest

    Not quite the same, but along similar lines-

    Early settlers often relied on "thundermills" for sawing wood or doing
    useful work. These mills were on small streams that only had
    sufficient power when the stream was full from winter runoff or heavy
    storms, hence (I guess) the name derived from mills that operated when
    or after there was thunder in the area.

    Later mills often employed multiple dams to store as much of the flash
    runoff as possible and to accumulate stream flow into a useful burst
    of power. One grist mill in the town where I grew up had three dams
    on the same stream, yet only the lowest dam had a penstock and pelton
    wheel. The upper dams added capacity, but not additional power. The
    storage wasn't pumped, but served a similar purpose to pumped power.

    Using otherwise wasted storm runoff to power a pump leading to a
    storage pond could be an example of where pumped storage makes sense.
    As an example, my stream has a relatively low head, but there is a
    nearby area about 60 feet above the stream that could be easily and
    fairly inexpensively turned into a pond. Would it be cost effective?
    Probably not for just power, but if irrigation, fire protection, stock
    and wildlife watering, augmenting a later low stream flow to help keep
    (stocked) fish in a hole in the stream alive, and other possible uses
    are figured in, it might make marginal sense.

    I can think of other situations, like a microhydro setup below a power
    dam with a regular peak use discharge schedule, where utilizing the
    heavy flow might be the only practical method of getting sufficient
    power. Would batteries be better for storing it? Possibly, but a
    small side canyon or gully that could be dammed would be very tempting
    for pumped storage. Such a setup would involve a lot of governmental
    meddling though, so it might not be worth it from that aspect alone.

    Perhaps the key is similar to co-generation, where instead of heat and
    power, the symbiots are water and power. Like this: :)

  8. AJH

    AJH Guest

    OK I've not come across the same here, though we do have a number of
    old tidal impoundment mills, they lead to highly unsocial working
    Well I suspect wildlife and turbines don't go well together but your
    points are much the same as mine. I suspect the reaction turbines are
    too capital expensive and I haven't any idea how efficient the old
    wind powered well pumps are/were but they and pelton wheels are fairly
    simple technology. The advantage of a pelton turbine looks like its
    ability to follow a synchronous load by simply varying the jet.
    On the other hand a modest pond above and below a decent drop may not
    suffer too much regulatory interference??
    Saves walking into a cold shower :)

  9. HVAC Guy

    HVAC Guy Guest

    The pumped water example given goes like this: At night, buy
    electricity at 1.5 c/kwh to pump some water to a high elevation, then
    during the day use that water to generate electricity to sell at 4

    (the example given says that the pumping process is 75% efficient,
    which I'd like to know how they got that efficiency so high, but
    that's another matter).

    So even with pumping loss, you're still making maybe 2+ c/kwh.

    But the flaw is this. What is the other guy doing burning (or
    consuming) his fuel and only getting 1.5 cents at night in the first
    place? Why doesn't he conserve it too so that he can make more $$$
    during the day by selling it at 4 cents like you're doing?
  10. HVAC Guy

    HVAC Guy Guest

    Which means that other types of plants that can't scale their output
    within a few hours would presumably be looking for technology to be
    able to do so, because it's in their interest to be able to scale-back
    production so as not to over-supply the market which leads to a low
    price for their output.

    The supply of cheap electricity at night is a by-product of
    operational limitations of current plant design and I'm sure it's not
    intentional and perhaps future plants will not have this limitation.

    The other strategy to always run the big plants at full output and
    convert excess demand into other forms of energy storage (like
    batteries, generate hydrogen, etc) is so stupid because of the energy
    conversion losses and the infrastructure needed for society to use the
    alternate forms. This strategy again is based on the assumtion that
    the big plants can't, or won't, or don't want to scale back output to
    meet demand. The best solution IS to scale back output so that you're
    not burning your main fuel stock when you don't have to.
  11. HVAC Guy

    HVAC Guy Guest

    So? What does that have to do with anything?

    If he's making money at 1.5 cents, then he's making even more at 4
    That's not his problem.
    Yes, he's a real bonehead. Since he's selling his juice cheap to the
    guy running the pumped storage plant, the pump can come on line during
    the day and the market price is 4 cents. But if the pump wasn't
    there, then the spot price would be 6 cents, and the guy running the
    other plant would be making MORE money.
  12. Eeyore

    Eeyore Guest

    You don't have a good grasp of business and economics do you ?

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