> From Heinz.Wenzl@...
> Some more comments on efficiency and use of batteries for spinning
> 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.
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
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.
Dr Andrew Tuckey
Energy R&D Engineer
Powercorp Pty. Ltd.
Trade Development Zone
Darwin, NT 0828
Phone: +61 8 8947 0933
Fax: +61 8 8947 0925
My deepest sympathy to the family and friends of the victims of the terrorist
attacks, and to the whole of the USA.
May the Lord comfort them.