It’s just over one month since the Hornsdale power reserve was officially opened in South Australia. The excitement surrounding the project has generated acres of media interest, both locally and abroad. The aspect that has generated the most interest is the battery’s rapid response time in smoothing out several major energy outages that have occurred since it was installed.
Following the early success of the SA model, Victoria has also secured an agreement to get its own Tesla battery built near the town of Stawell. Victoria’s government will be tracking the Hornsdale battery’s early performance with interest.
Generation and Consumption
Over the full month of December, the Hornsdale power reserve generated 2.42 gigawatt-hours of energy, and consumed 3.06GWh.
Since there are losses associated with energy storage, it is a net consumer of energy. This is often described in terms of “round trip efficiency”, a measure of the energy out to the energy in. In this case, the round trip efficiency appears to be roughly 80%.
On several occasions over the month, the battery has generated as much as 100MW of power, and consumed 70MW of power. The regular operation of battery moves between generating 30MW and consuming 30MW of power. The generation and consumption pattern is rather “noisy” and doesn’t really appear to have a pattern at all. This is true even on a daily basis, as can be seen below. This is related to services provided by the battery.
Frequency Control Ancillary Services
There are eight different Frequency Control Ancillary Services (FCAS) markets in the National Electricity Market (NEM). These can be put into two broad categories: contingency services and regulation services.
Contingency services essentially stabilise the system when something unexpected occurs. This are called credible contingencies. The tripping (isolation from the grid) of large generator is one example.
When such unexpected events occur, supply and demand are no longer balanced, and the frequency of the power system moves away from the normal operating range. This happens on a very short timescale. The contingency services ensure that the system is brought back into balance and that the frequency is returned to normal within 5 minutes.
In the NEM there are three separate timescales over which these contingency services should be delivered: 6 seconds, 60 seconds, and 5 minutes. As the service may have to increase or decrease the frequency, there is thus a total of six contingency markets (three that raise frequency in the timescales above, and three that reduce it).
This is usually done by rapidly increasing or decreasing output from a generator (or battery in this case) or rapidly reducing or increasing load. This response is triggered at the power station by the change in frequency.
To do this, generators (or loads) have some of their capacity “enabled” in the FCAS market. This essentially means that a proportion of its capacity is set aside, and available to respond if the frequency changes. Providers get paid for the amount of megawatts they have enabled in the FCAS market. This is one of the services that the Hornsdale Power Reserve has been providing.