Energy storage enables renewables to be utilized when they’re most needed by the electricity system and can help mitigate demand spikes that increase electricity rates for all, including marginalized communities.
Energy storage technologies range from lithium batteries (the same rechargeable technology found in cell phones and electric vehicles) to pumped hydro and thermal energy systems.
Long-Duration Storage
Energy storage systems collect electricity, store it as another form of energy such as chemical or thermal storage, and deliver it at another time. Common examples include lithium-ion batteries which use electricity to recharge themselves; hydroelectric dams which store potential energy stored as gravitational potential power; fossil fuels like coal and gasoline which have stored ancient solar energy over thousands of years and become fossilized over time;
Many energy storage technologies provide grid services over durations ranging from milliseconds to days or weeks, but those designed specifically for shorter ancillary services, which correct imbalances between generation and load generation, tend to operate most easily within two hour increments or less.
Long-duration storage provides resource adequacy over longer durations, and has become the focus of California procurement efforts and efforts aimed at finding technologies capable of meeting these longer duration requirements. Competitors for this space include pumped hydro, gravity-based, compressed air, flow battery systems as well as lithium-ion as a current market leader.
Short-Duration Storage
Short-duration storage is essential to integrating more renewable energy into the power grid, since intermittent renewables typically need to be scaled up or down quickly. Energy storage systems allow us to bank surplus power for use when necessary – helping reduce emissions while creating a more resilient grid.
Batteries and flywheels offer energy storage solutions suitable for millisecond to four-hour duration ranges. These devices store kinetic energy that they then return back into the system in short bursts.
Medium duration storage will be necessary to balance daily cycles of demand and solar PV forecast errors as illustrated in Exhibit 3. Batteries and established technologies like pumped hydro may compete for this use case alongside various emerging storage technologies like smart charging EV’s as demand side flexibility options. Longer duration storage solutions must address multi-day wind events, transmission constraints on low demand weekends, seasonal wind production variations, as well as transmission constraints on weekends with no demand, balanced with seasonal wind production variance. Competition could come from batteries, compressed air energy storage (CAES), iron-air and liquid air energy storage (LAES).
Thermal Storage
Energy storage market is rapidly developing, offering services across multiple segments of the electricity grid: transmission (to alleviate congestion and optimize grid efficiency), distribution network (for demand flexibility for homes and businesses) and even retail networks.
Energy storage also supports renewable expansion by alleviating the need to curtail generation when there is excess supply relative to demand, enabling new sources of clean energy to shift into gear more rapidly, helping accelerate transition towards net zero emissions goals within an economy.
Long-duration energy storage technologies like thermal energy storage offer grid services currently provided by fossil fuel peaker plants during times of high electricity demand. Unfortunately, these plants emit air pollution and often reside within urban centers causing adverse climate impacts on low-income communities and communities of color.
Hydrogen Storage
Hydrogen storage utilizes electrolysers to convert electricity to hydrogen, then store the gas until low demand periods when refuelling or power generation may be needed. When necessary, stored hydrogen can be converted back to electricity through fuel cells compatible with mobile applications or gas-fired power plants.
Hydrogen has a lower volumetric energy density than compressed natural gas and should be stored in insulated tanks to preserve its quality and low boiling point near absolute zero, necessitating cryogenic storage facilities that require close proximity to population centres for safekeeping.
Hydrogen can provide grid services beyond battery storage such as static reserve, regulation of voltage and frequency regulation and load shifting. Hydrogen can be deployed at transmission, distribution and generator level as well as behind-the-meter applications at commercial buildings and homes – it may even co-locate with renewables!