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Energy storage: Taking Solar from Intermittent to Dispatchable

Generally seen as the holy grail of solar and other renewable energy sources, electric energy storage is no longer something in the uncertain future. Rather it is a present reality that a small but growing number of utilities and solar firms are developing and deploying today.

A new report from the Solar Electric Power Association, “Electric Utilities, Energy Storage, Solar: Trends in Technologies, Applications and Costs,” looks at this fast-emerging sector and its potential benefits for utilities, consumers and the general public. Drawing on information from the Department of Energy’s Global Energy Storage Database, the report analyzes 215 distributed generation energy storage projects developed by or in partnership with utilities.

“Electric energy storage (EES) has the potential to provide services to the grid, utilities, and downstream customers by improving power quality, reliability and adding needed capacity. EES should enable more solar to be installed on the grid while reducing the operational impacts of this variable resource,” the report says.

Or, as Terry Allison, a senior engineer at American Electric Power, said to SEPA researchers, “Storage is absolutely necessary and it’s getting cheaper.”

The report highlights a number of key trends and challenges that could shape ongoing growth and use of EES.

Utilities’ EES investments are emerging as key driver of the evolving energy marketplace while also allowing for more diverse and distributed energy resources such as solar. The number of utility-owned storage projects jumped 33 percent from 2012 to 2013, while third-party owned projects increased by 44 percent.

Storage provides a range of benefits for utilities. Beyond its quick response and load smoothing capabilities, storage may provide voltage support and frequency regulation and allow utilities to generate and store electricity when it is less expensive and then put it on the grid at times of peak demand. Deploying ESS could also push back the need for expensive upgrades to utilities’ transmission and distribution infrastructure.

While lithium ion batteries have become increasingly popular, utilities are also testing other battery technologies, such as sodium sulfur, advanced lead acid, flow batteries and flywheels. Storage batteries are also being connected to the grid at different points – on transmission lines, as well as primary and secondary distribution lines.

The tipping point for storage may come more from policy and legislative decisions than from technology breakthroughs, such as the California Public Utilities Commission’s mandate that the state’s investor-owned utilities have 1.3 gigawatts of storage on the grid by 2020. Such state and matching federal initiatives could provide the necessary momentum to lower costs and drive market maturation. Looking at compared per-kilowatt, or levelized, energy costs, ESS can range from $216 to $329 per megawatt hour – more than twice the cost of utility solar but competitive with diesel generator costs of $297 to $322 per megawatt hour.

New and innovative business models will be needed to ensure utilities, third parties and customers have opportunities to invest in and benefit from growing deployment of energy storage in support of solar. In particular, the ability of ESS to provide multiple benefits simultaneously must be recognized and appropriately valued.


Matched with forecasting and power control systems, the growth of storage technology can transform solar and other renewable generation from an intermittent to a fully dispatchable form of electricity.

The full report is available at