Smoothing the Flow of Solar Power in California

by Dr. Imre GyukU.S. Department of Energy.

This EnerVault flow battery stores power from the solar panels and releases it as needed. | Photo courtesy of EnerVault.
This EnerVault flow battery stores solar power from the solar panels and releases it as needed. | Photo courtesy: EnerVault.

Yesterday, an almond grove in California’s Central Valley hosted the opening of the world’s largest iron-chromium redox flow battery. Originally pioneered by NASA, these flow batteries are emerging as a promising way to store many hours of energy that can be discharged into the power grid when needed.

Traditionally, electric generation follows the demands of the daily load cycle. But as more sources of renewable generation such as solar and wind are integrated into the power grid, balancing demand and generation becomes more complicated. With energy storage, we can create a buffer that allows us to even out rapid fluctuations and provide electricity when needed without having to generate it at that moment.

Unlike other types of batteries, which are packaged in small modules, iron-chromium flow batteries consist of two large tanks that store liquids (called electrolytes) containing the metals. During discharge, the electrolytes are pumped through an electrochemical reaction cell and power becomes available. To store energy, the process is reversed. With Recovery Act funding from the Department’s Office of Electricity Delivery and Energy Reliability, California energy storage company EnerVault has optimized the system to create a more efficient battery.

This pilot project in Turlock, California, can provide 250kW over a four-hour period, helping to ensure the almond trees stay irrigated and the farm is able to save money on its electrical bills.

This is how the system works:

The almond trees are most thirsty between noon and 6 p.m. The farm uses nearly 225 kW of electricity to power the pumps that get the water to the trees. Onsite solar photovoltaic panels can supply 186kW at peak power, not quite enough energy for watering the trees throughout the day. The balance could be taken from the grid, but grid electricity is most expensive from noon to 6 p.m.

This is where storage enters.

At night electricity is inexpensive, so the batteries begin to charge up. In the morning the solar panels help top them up the rest of the way. Then, during expensive peak periods, the needs of the trees are satisfied by solar and flow batteries — renewable energy optimized through storage.

While the Turlock facility is a unique application, flow batteries are not just for thirsty almond trees. For example, they could be an especially good solution for small island grids such as Hawaii, where severe wind ramps or rapid changes in photovoltaic generation can destabilize the local grid, or at military bases that need to maintain mission-critical functions.

Similarly, flow batteries paired with renewables can be used in a resilient microgrid that can continue to operate when disasters strike and power outages ensue.

In the face of changing climate conditions, energy storage and grid resiliency have become more critical than ever. Flow battery technology is expected to play a vital role in supporting the grid both in California and across the U.S.

Additional Information:

Dr. Imre Gyuk
Dr. Imre Gyuk is the Energy Storage Program Manager, Office of Electricity Delivery and Energy Reliability.
Iron-chromium flow batteries store liquids, called electrolytes, that are pumped   through an electrochemical reaction cell to release power. The process is reversed in order to store energy. This means that the batteries can store energy from the grid, and release it when the load is heaviest.

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