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Re: Spinning Reserve Comments on efficiency and use

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  • tuckey@ieee.org
    ... Heinz, I take your point. Batteries charged/discharged at 10% of their Ah rating have proven themselves (by 10% I mean that the maximum rate of
    Message 1 of 1 , Sep 19, 2001
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      > From Heinz.Wenzl@...
      >
      > Some more comments on efficiency and use of batteries for spinning
      > reserve
      >
      > Andrew Tuckey wrote that batteries get destroyed very quickly if they
      > are used for spinning reserve applications where current fluctuates too much
      > and too quickly. Well it depends.
      >
      > The 17 MW/17MWh battery storage by BEWAG used for spinning reserve
      > applications in the Berlin grid achieved 7000 times the nominal capacity in
      > energy throughput. The daily capacity throughput was approx. 2.5 times the
      > nominal capacity.
      >
      > The battery was cooled, the electrolyte was stirred, single cells were
      > supervised and the battery was subjected to regular equalisation charges,
      > and the energy throughput happened in a partial state of charge. It was
      > extremely well designed. I do not see a reason why a smaller battery should
      > not achieve the same lifetime under similar conditions.

      Heinz,

      I take your point.

      Batteries charged/discharged at 10% of their Ah rating have proven themselves
      (by 10% I mean that the maximum rate of charge/discharge for a 100Ah battery
      is 10A so fully discharged in 10 hours).

      I gather from the above figures for the BEWAG battery storage, the batteries
      had the ability to be charged/discharged at 100% or their Ah rating. I.e. a
      17MW charge/discharge rate for a 17MW battery therefore fully discharged in 1
      hour.

      Well designed batteries can do this.

      However, for grid stability we are talking of discharging our "battery" from
      100% capacity to 25% capacity in 60 seconds or less. So we can exceed our
      nominal capacity in throughput in a number of minutes.

      With this time frame batteries do destroy themselves. Alternatively one could
      install a large enough battery so that the discharge rate is never more than
      some specific value (100% Ah rating) but the capital costs are prohibitive.

      We are using our system for grid stability; i.e. frequency control. This need
      only be done on a second by second basis, and we need only 60 seconds of
      energy reserve since we can bring other (Diesel) generators online in less
      than one minute.

      > Efficiency in/out is only one of the requirements of an energy storage
      > in renewable energy, the other is energy loss during standby-operation
      > when the energy is not required. It really depends on the installation
      > and the systems operation what is more important. Flywheels, for
      > instance, have a very high in/out efficiency but the losses (as a
      > percentage of energy stored) are extremely high - 100% per day or more.
      > With the high cost per kWh in renewable energy, these stand-by losses
      > can be crippling.

      I agree with all of that. I guess you could say we are using our system to
      store short-term power, not energy.

      Regards
      Andrew


      --
      Dr Andrew Tuckey
      Energy R&D Engineer
      Powercorp Pty. Ltd.
      Export Drive,
      Trade Development Zone
      Darwin, NT 0828
      Australia

      Phone: +61 8 8947 0933
      Fax: +61 8 8947 0925
      Web: www.pcorp.com.au
      Email: tuckey@...


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      May the Lord comfort them.
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