All interconnected transmission and distribution (T&D) grids have one thing in common: Their operators must continually dispatch generators to keep the network's supply and demand in balance at all times and to maintain its voltage and frequency within very tight tolerances. Threatening to change this paradigm by adding a new variable—bulk electricity storage capacity—to the balancing equation are new and rechargeable sodium-sulfur, vanadium redox, and zinc-bromide batteries. Some of these—as well as nickel-cadmium batteries, which went commercial decades ago—have already demonstrated their ability to act as generators as large as 10 MW.
These batteries may play a role in addressing a common set of problems that T&D system planners worldwide face:
- In many parts of the world, investment in the carrying capacity of T&D systems has failed to keep pace with load growth. This oversight has increased constraints on already overtaxed systems and reduced their tolerance for faults, as the August 2003 blackout of much of the eastern U.S. and southern Ontario demonstrated.
- In the wake of the terrorist attacks of September 2001, awareness of the vulnerability of the electricity supply system to intentional disruption has raised interest in the distributed grid concept. A distributed grid has many small and geographically dispersed energy resources sited close to load centers, in contrast to a centralized grid, which draws on a few large generators far from load centers.
- The growth of the Internet and the broad and growing penetration of electronic controls for commercial and industrial processes have created a need for improved power quality and reliability. Even very brief excursions from nominal power supply voltages can cause electronic controllers to shut processes down, which can result in extended downtime, damaged equipment, and scrapped product.
The ongoing dissolution of the traditional electricity sector structure also seems to call for increased reliance on big batteries wherever feasible. According to Jason Makansi, executive director of the Energy Storage Council, one consequence of deregulation is that in many states, generation and T&D are no longer planned in an integrated fashion by one entity—the local utility. "Storage in general, and batteries in particular, can help manage the gaps created by the disaggregation of the electricity production and delivery value chain," Makansi explains.
Storage also has a critical role to play in securing the nation's energy infrastructure, much as the Strategic Petroleum Reserve does for oil, and bulk gas storage does for balancing seasonal natural gas demand and supply.
If you're responsible for T&D system planning and are ready to begin considering energy storage a viable option, the table and the accompanying box are a good place to start. The table summarizes the status of and future prospects for several battery technologies that either currently offer bulk energy storage capability or promise to do so in the near future. The following discussions and case studies explain how the new bulk-storage batteries work and how pioneers are using them to solve a number of common T&D problems.
A comparison of today's bulk electricity storage technologies
Source: Platts
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