There is a common misconception that Australia will need to match each kW of wind and solar capacity with an equivalent amount of storage. In fact, only a fraction of storage for each kW of variable renewables – between one fifth and one third – will be necessary to meet demand.
This year’s annual GenCost report from the CSIRO explains the reason for this is that even though the generation mix is being changed, and significantly more wind and solar – in terms of rated capacity – is being built to replace coal, maximum demand is not being changed. This means that the amount of storage or dispatchable generation needed to meet maximum demand is not changing either.
How much storage is needed?
The amount of storage required does depend somewhat on the level of wind and solar input. For a grid with a low level – up to 50 per cent – of variable wind and solar, hardly any additional storage is needed because the “back-up” is already in place, largely to support coal generators that either fail or cannot ramp up quickly enough to meet demand spikes.
For a grid with a high level – 90 per cent or more – of variable wind and solar, the report suggests that between one fifth to one third of storage will be needed per kw, to ensure there is enough supply to meet demand.
This is because, in a high variable renewable system, maximum demand will be significantly lower than the capacity of variable renewables installed. The report points out that, as the variable renewable generation share increases, summer or winter peaking events may not represent the most critical day for back-up generation. For example, during summer, solar PV generation is high and consequently storages are relatively full and available to deliver into the evening peak period. A more challenging period for variable renewable system might be on a lower demand day when cloud cover is high and wind speed is low.
These days with low renewable generation and low charge to storages could see the greatest demands on storage, peaking and other flexible capacity. As such it may be that the low demand level on these low renewable generation days is a more important benchmark in setting the amount of additional back-up capacity required.
The data
The CSIRO used a modelling approach which accounted for these factors across nine historical weather years. The result they found is that, in 2030, the NEM needs to have 0.20kW to 0.34kW storage capacity for each kW of variable renewable generation installed. The data showed that, demand at the point of lowest renewable generation is substantially lower than maximum demand. That existing and new flexible capacity is slightly lower than maximum demand indicating some variable renewable generation is available at peak demand (across the nine weather years examined). Finally, that flexible capacity exceeds demand at minimum renewable generation and the required existing and new flexible capacity to support variable renewables is a fraction of total variable renewable capacity.