GLOBAL CHALLENGES

Renewables Driving Energy Storage Innovations

Salvatore Salamone | Date: 04-29-10 | Comments

A forthcoming 20-megawatt energy storage system will use advanced battery technologies to help maintain the stability of the electric power grid.

The New York State Public Service Commission recently approved construction of a 20-megawatt (MW) energy storage system to be built in Union, N.Y. The $22.3 million project, owned by AES ES Westover, will use advanced battery technologies to help maintain the stability of the electric power grid.

This is just the latest of many new and innovative energy storage initiatives being undertaken around the world. These projects are being driven by the increased use and incorporation of renewable energy sources into power grids.

There are two main reasons of this growing interest in energy storage solutions.

First, most renewable energy (be it generated from solar, wind or tidal sources) are highly variable. Distribution and transmission systems have already been showing signs of strain in handling these highly variable sources of electricity. For example, in 2008, a New York Times article reported that the Maple Ridge Wind farm, in upstate New York, had to shut down at times because the �regional electric lines have been so congested.� Unfortunately, the situation is expected to get worse as more power comes from renewables.

Second, there is a need to address the mismatch between peak power generation and demand. For example, in many locations, wind energy can be quite significant at night when electricity demands are at their lowest. Similarly, peak solar productivity is often close to midday, while peak electricity usage is frequently later in the afternoon.

Pushing the Envelope

The New York deployment will make use of new lithium-ion battery cells and power control technologies. The system will be able to provide or absorb up to 20 MW. �[This] will help improve the ability to store energy, a critical component needed to help us further strengthen and expand our use of renewable energy,� says New York State Public Service Commission Chairman Garry Brown.

Other energy storage efforts are exploring a variety of new technologies, or at least new twists to using existing technologies. The latter is certainly the case with something called Energy Island.

Energy Island is a concept under evaluation by the energy consulting firm KEMA and the civil engineering firm Bureau Lievense. The idea is to build an artificial island in the North Sea near deep-water wind turbines. The impetus for this project is that the anticipated excess wind power from offshore North Sea turbines, especially at night, will require large-capacity energy storage solutions.

Energy Island would form a large, below-sea-level basin to hold a reservoir of water. During peak energy generation times, the excess energy would be used to pump water out of the basin into the ocean. When winds die down and the turbines are not producing much power, the flood gates to the reservoir would be opened. Gravity would cause water to flow down into the basin, driving turbines to generate electricity.

Energy Island (Source: KEMA and Lievense)

Like wind energy, solar energy is also variable and presents another obvious challenge�namely, there is no sun at night. One solar energy storage solution that is gaining favor is the use of molten salt to retain solar heat.

Molten salt has a much higher heat capacity than water, so it can store more heat in a given volume. For example, molten salt in tanks can be heated to 1,000 degrees. Such a heated salt mixture can be used to create steam to drive turbines that produce electricity. Molten salt also retains heat longer than a water-only solution. A molten salt tank can also be used as the equivalent of a heat capacitor or battery, storing heat that can be used at night or during a cloudy period to sustain the generation of electricity.

Molten salt storage has been used on a small scale for years, but last year SolarReserve announced plans for a molten salt-based plant that would store hours� worth of energy, enabling the proposed plant to provide electricity 24 hours a day.

And yet another approach under consideration in several parts of the world is to use underground storage of compressed air to help address the mismatch between wind energy production and capacity to handle the electricity by the local grid. For example, the Iowa Stored Energy Park will use wind and off-peak energy from various sources to compress air and store it underground.

Compressed air energy storage (Source: Sandia National Laboratories)

When winds die down and electricity is needed, the compressed air can be used to drive turbines to regenerate electricity for the grid. The project is being funded by the U.S. Department of Energy, managed by Sandia National Laboratories, and includes contributions from more than 100 municipal utilities in Iowa, Minnesota and the Dakotas.