World’s biggest battery is a huge success story

2 April 2018

Tesla’s South Australia battery, the largest grid connected battery storage site in the world, is exceeding all expectations. This article, with extensive extracts from an article in The Conversation by Dylan McConnell, a researcher at the Australian German Climate and Energy College, Melbourne, describes how the Tesla battery at the Hornsdale wind farm has performed to date. Staff report

In the short time since the Hornsdale power reserve was officially opened in South Australia its immediate achievements in successfully smoothing power outages and absorbing excess grid energy has excited much interest locally and internationally.

The aspect that has generated the most interest is the battery’s rapid response time in smoothing out several significant energy outages that have occurred since it was installed.

Following this early success, the state of Victoria has also secured an agreement to get its own Tesla battery built near the town of Stawell.

Generation and consumption

Over the full month of December, the Hornsdale wind farm power reserve, which consists of a 100 MW/129 MWh lithium ion Tesla manufactured battery, generated 2.42 GWh of energy, and consumed 3.06 GWh.

Since there are losses associated with energy storage, it is a net consumer of energy. This can be 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%.

Figure 1 shows the input and output from the battery over the month. It shows that on several occasions the battery generated as much as 100 MW of power, and consumed 70 MW. The regular operation of the battery moves between generating 30 MW and consuming 30 MW.

The generation and consumption pattern is rather noisy, and does not appear to show a pattern. This is true even on a daily basis, as can be seen in Figure 2. This is related to services provided by the battery.

Frequency control ancillary services

There are eight different FCAS markets in the National Electricity Market (NEM). These can be classified in two broad categories: contingency services and regulation services.

Contingency services are there to stabilise the system when something unexpected occurs. These are ‘credible contingencies’. The tripping of a large generator is an example.

The resulting imbalance of supply and demand moves the frequency of the power system 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 therefore a total of six contingency markets. Frequency governing is effected 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 their capacity is set aside, and is available to respond to frequency changes. Providers are 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. Figure 3 shows how the power reserve responded to one incident on power outage, when one of the units at Loy Yang A tripped on December 14 last year.

Regulation services

The regulation services are similar to contingency services, in that they help maintain frequency in the normal operating range. Regulation may have to raise or lower the frequency, and therefore there are two regulation markets.

However, unlike contingency services, which essentially wait for an unexpected change in frequency, the response is governed by a control signal, sent from the Australian Energy Market Operator (AEMO). In essence, the AEMO monitors the system frequency and sends out a control signal at 4-second intervals. This signal alters the output of the generator to maintain the supply and demand balance. This is also one of the main services that the battery has been providing. Figure 4 shows the output of the battery closely following the amount of capacity it has enabled in the regulation market. 

Victoria state project

The Victorian government has also recently secured an agreement for its own Tesla battery. This agreement, to be realised in conjunction with a wind farm near the town of Stawell, should see a battery providing a similar services in Victoria.

This battery may also provide additional benefits to the grid. The project is located in a part of the transmission network that AEMO has indicated may need augmentation in the future. This project may be able therefore to illustrate the benefits that battery storage can provide in strengthening the transmission network. 

Tesla Tesla’s giant battery storage site, Hornsdale wind farm
Tesla Figure 1. Generation and consumption of the Hornsdale Power Reserve over the month of December 2017. Source – AEMO
Tesla Figure 3. The Hornsdale Power Reserve responding to a drop in system frequency. Source – AEMO
Tesla Figure 4. Output of Horndale Power Reserve compared with enablement in the regulation raise FCAS market. AEMO
Tesla Figure 2. Generation and consumption of the Hornsdale Power Reserve on the 6 January 2018. Source – AEMO

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