Carbon-Pros Analyst Blog

Today's large-scale storage solutions include pumped hydro, compressed air, flywheels, sodium-sulfur batteries, supercapacitors, and flow batteries. No matter what technology is used, the idea behind storage systems is to use low-cost off-peak power to charge the system (store the power) and discharge the system (drawing on its stored power) during peak demand when more electricity is needed. Storage systems have the effect of smoothing out utility load profiles.

While most storage systems remain very expensive, pumped hydro and compressed air are cost-effective today. Pumped hydro is well established and makes hydroelectric power one of the most dispatchable of all fuel sources. With a storage option, hydroelectric production can be turned up or down in minutes (see post). Compressed air energy storage (CAES) is in an earlier stage of development but is starting to see commercial pilots and deployments. Both have limitations in terms of location. Hydro needs a vertical drop and plenty of land for the storage reservoir. Compressed air needs favorable geological strata deep underground (see post).

The smart grid will provide the communication and software solutions to make large-scale storage systems work. Their charge and discharge cycles need to be tightly managed to match charging with periods of excess power and to match discharging with optimal periods of demand. In a dynamic pricing environment, this is no easy task.

Utility-scale storage is a natural match for utility-scale renewable generation.

Wind Power with Integrated CAES

In the case of wind power, excess power generated when the wind is blowing (often at night, off-peak) can be used to charge any of these systems (CAES is illustrated above). An effective storage system can make wind dispatchable, greatly increasing its value to utilities. The combination of dynamic pricing and intermittent generation requires sophisticated modeling tools. To meet future needs, advanced wind forecast models are under development at the National Center for Atmospheric Research (NCAR).

Utility-scale storage systems promise to increase efficiency by better matching supply with demand. They will increase reliability by smoothing out power fluctuations. And they will increase stability by providing ride-through during short power disruptions.