Eye on electricity: Battery performance in New Zealand

New Zealand is building more renewable electricity generation. However, renewable generation (like wind and solar) vary with the weather, so renewable electricity supply may not match up with demand. Grid scale batteries soak up excess renewable electricity and then release it back to the grid when needed. Some batteries also provide extra services like instantaneous reserves - spare capacity which can quickly respond in an unexpected event that causes a large drop in frequency.

Grid-scale batteries maximise the benefits of renewable energy and provide extra resilience during times of tight electricity supply. Additionally, these batteries, alongside more renewable generation, will help off-set the impacts of retirement of thermal generation and support New Zealand’s transition to a low-emissions economy.

At the moment there are three grid scale batteries the New Zealand electricity system: Rotohiko (35MW/35MWh), Ruakākā (100MW/200MWh) and Glenbrook-Ohurua (100MW/200MWh). Typically, a grid scale battery charges when prices are low and discharges energy back into the grid when prices are higher. This is called energy arbitrage.

Supplying both energy and instantaneous reserves

Grid-scale batteries can offer both energy and instantaneous reserve into the electricity market. Figure 1 shows the breakdown of batteries being dispatched for reserve vs energy. Note, instantaneous reserves are not necessarily supplying anything, that generation is just ‘earmarked’ for reserves if they are needed. Rotohiko and Ruakākā have dispatched more often for instantaneous reserves than energy since commissioning. Glenbrook-Ohurua battery has only recently commissioned and is not offering reserves but may do so in the future.