Storage by the Numbers - ORIGINAL CONTENT

A reliable electric grid supplied predominantly or exclusively by intermittent renewable generators such as wind turbines and solar arrays would require massive energy storage to provide continuous power to the grid when the output of the wind turbines and solar arrays was fluctuating, inadequate or unavailable.

Some renewable electricity providers have installed batteries capable of compensating for output fluctuations of several minutes duration. More recently, some renewable electricity providers are planning installation of battery storage systems capable of delivering power to the grid for up to 4 hours.

NREL estimates that the current cost of such 4-hour storage systems is approximately $350 per kWh and that it is expected to decrease to approximately $150 per kWh by 2050. Based on these estimates, 4-hour storage for a 2.5 MW wind turbine or solar array would cost approximately $3,500,000 and that cost would be expected to decrease to approximately $1,500,000 by 2050. This compares with the estimated installed cost of a 2.5 MW wind turbine or solar array of approximately $3,200,000.

It is important to remember that the 10 MWH available from the storage system must first be provided by the wind turbine or solar array. US EIA Electric Power Monthly reports that a 2.5 MW wind turbine would have produced an average of 21.2 MWh per day in 2020, while a 2.5 MW solar array would have produced an average of 14.5 MWh per day. Therefore, the electricity stored in the batteries would constitute half to two-thirds of the total electricity output of the generators on an average day. In this example, the storage system would be capable of providing more electricity to the grid in 4 hours than the renewable generators did in the remaining 20 hours of the average day.

While these 4-hour storage systems would provide some ability to tailor electricity supply to demand load shape, they would add little to electricity supply reliability during periods of low/no wind and solar availability. Storage systems designed to provide continuous electricity delivery to the grid during multiple hours or days of low/no wind and solar generation are referred to as long-duration energy storage. California has recently solicited bids for such systems with a capacity of 50 MWh or greater and a delivery time of 8 hours or greater. While such systems would represent a significant advancement of the state of the art, they fall far short of the requirements for a storage system which could continue to supply electricity to the grid through a “wind drought” such as the recent ten-day event experienced in the UK.

Form Energy claims to have developed an iron/air storage battery capable of continuously delivering electricity to the grid for up to 150 hours, or about 60% of the duration of the UK wind drought. Such a storage system for a 2.5 MW wind turbine would require a storage capacity of approximately 130 MWh, which would first have to be provided by the wind turbine. Initial estimates place the cost of such a system at approximately $20 per kWh, or approximately $2,600,000, not including installation and land costs.