Storage systems attached to renewable energy generation facilities including mega (large-scale) solar power plants and wind power plants are actively being introduced abroad. According to "World Renewable Energy Storage Business Overview," a survey report issued recently by Nikkei BP CleanTech Institute, storage batteries are introduced for three purposes: (1) measures against short-cycle fluctuations in renewable energies, (2) measures for improvement of the supply-demand balance (measures against long-cycle fluctuations) and measures against issues regarding heat capacity of local grids and (3) supply of power to off-grid regions and operation of microgrids during emergencies.

64MWh storage battery used at 98MW wind power plant

Storage projects for measures against short-cycle fluctuations (1) are intended for prevention of short-period instability of voltage and frequencies of the grid power due to the large-scale introduction of renewable energies. For this purpose, the real-time control of charging and discharging are done in seconds or minutes. The storage batteries are installed responding to the requests of grid operators responsible for maintenance of grid power quality or regulating authorities, or as measures to prevent penalty charges in many cases.

A typical project is the "Laurel Mountain" storage battery station, a 64MW facility that was constructed in 2011 and is attached to a wind power plant with an output of 98MW in West Virginia, the US (Fig. 1), which is owned by major independent power producer AES Corporation of the US.

Fig. 1: The "Laurel Mountain" storage battery station (source: AES Energy Storage)

The storage battery station was constructed and is operated by AES Energy Storage, which is a subsidiary of AES Corporation and is the largest storage battery integrator. The state has a system to impose a large penalty charge if fluctuations in the power generation amount exceed the allowable range due to sudden changes in the weather, and the risk is reduced by the storage batteries.

AES Energy Storage also makes a profit by participating in the ancillary markets of the US grid operators PJM (Pennsylvania-New Jersey-Maryland) and ISO-NE (ISO New England) using the storage battery plant, and profitability is ensured for the lithium ion storage batteries.