Small-scale energy storage for integration of renewable supplies with smart grids

Rapid expansion of renewable energy is occurring throughout the world due to national government financial incentives, state government mandates, and public perceptions regarding green energy. In the United States, wind power is the predominant source of renewable energy with cumulative installed capacity of over 60,000 MW as of 2012. However, integration of renewable into existing grids or proposed micro-and smart-grids is expensive with the US National Renewable Energy Laboratory estimating costs to range from US $3.5 to $5.0/MWh particularly since the unreliable nature of wind does not increase reliable generation capacity. Conventional generation facilities are therefore still needed to ensure demands can be met at all times. Storage represents one of the grand challenges facing areas with large seasonal variations in energy supply and demand. Although a number of studies suggest that grid systems in large balancing areas could handle up to 20% renewable penetration without additional storage, recent evidence suggests the lack of storage requires negative pricing at the wholesale level during periods of high power, low demand. Furthermore, smaller micro-and smart-grids will benefit from improved flexibility brought on by increased storage. While numerous studies and installations of large pump storage projects exist globally, the availability of large off-channel reservoir sites in the US is relatively limited. Investigation of smaller facilities (<=150,000 m³) would greatly improve utility in micro-and smart-grid systems. This study examined the initial feasibility of a scenario involving small storage, high head. A model has been developed to examine the trade-offs between cost, size, power generation, water supply, and other environmental services.