Accommodating high levels of variable generation
After brief but intense interest in energy storage during the 70’s and 80’s, the return of inexpensive fossil fuel dampened the sense of urgency created by insecurity about our energy future. Most notably, thermal energy storage for air-conditioning applications has matured into a robust commercial product, with broad manufacturing and marketing support.
Flow batteries that employ liquid electrolytes, such as the vanadium redox or zinc-bromine, provide excellent scalability because the liquid electrolytes can be stored independently of the power producing cell.
Presidio, Texas has installed a 4 MW sodium-sulphur battery for emergency backup, claimed to be the largest battery of this type in the US.
They have a high energy density and charge/discharge efficiencies in the range of 90%.
Much of this development is at the ‘demonstration’ phase with several projects funded through the American Recovery and Reinvestment Act (ARRA).
Familiar consumer (albeit advanced) battery technology such as lead-acid, nickel-metal hydride, nickel-cadmium and lithium-ion are being supplemented by an array of additional battery designs.