Flow batteries for net zero in New Zealand

Abstract

Flow batteries (FBs) are characterized by relatively high round trip efficiencies and benefit from high scalability. The storable energy and the power of charging and discharging the battery can be increased by increasing the size of the electrolyte storage tanks and the electrodes. Charge and discharge cycles covering many hours may be designed with flow batteries. This makes flow batteries a better choice than lithium‐ion batteries for large‐scale energy storage systems, particularly for non‐dispatchable renewable energy systems such as wind and solar, where the energy generated is highly variable and requires effective energy storage solutions. However, flow batteries also have some disadvantages, including a higher cost per unit of energy stored compared with other batteries, as well as the use of materials that in some cases are toxic, expensive, or scarce. Additionally, flow batteries cannot solve the energy storage issues over long times of a grid only supplied by non‐dispatchable electricity such as wind or solar, namely intermittency and summer to winter variability of solar, or low wind days of wind. Despite these limitations, the potential benefits of flow batteries in terms of their scalability and long cycle life, and cost‐effectiveness in case their design could be improved, making them one of the key contributors progressing towards net zero. Specifically in New Zealand, in the progress toward net‐zero the total energy supply (TES) cannot be covered by only expanding wind energy production and pumped hydro energy storage (PHES). Solar photovoltaic and likely nuclear energy supply will have to be introduced. Not all of the TES will be electrified, part of the TES will need coverage by green hydrogen fuel. Hydrogen energy storage (HES) will have to grow much more than PHES, energy storage by FBs as well as lithium‐ion batteries (LIBs) will also have to be included, given their complementarity to the other energy storage systems.