Electric Energy Storage: Digging the Foundations (Part II)

Part II of a two-part series on the development of electric energy storage. Part I addressed the storage we need. Here, we look at the technologies and the political challenges they face.

There are now four classes of electric storage technology products — mechanical, magnetic, thermal and electrochemical — but only one sub-class is deployed in a more than minimal way.

Typifying mechanical storage is the pumping of water uphill and its later release to drive a turbine. Superconductors store energy in magnetic fields. Thermal storage uses heat. Electrochemical storage uses reactions in devices like batteries and fuel cells to store and release energy.

As the first article in this series argued, storage is an essential component of a low-carbon economy, but it is mostly not ready for commercialization. The following snapshots focus on the technology with the largest current application, mechanical storage, and the technology with the most near-term promise, electrochemical storage.

"The market for utility scale storage will grow from $329 million in 2008 to approximately $4.1 billion in 10 years. While pumped hydro and CAES [compressed air energy storage] should persist as options and gobble up large amounts of dollars for a small number of projects, advanced Li-ion batteries will be the volume leader and the one technology with a clear and possibly astronomical growth trajectory." —Clint Wheelock, Managing Director, Pike Research

MECHANICAL STORAGE

Water and air can be mechanically pumped into storage areas. As needed, they can be released in ways that use their kinetic force to drive electricity-making turbines. A third mechanical storage technology, fly wheels, makes a related use of mechanical inertia.

Pumped Hydro: Nearly all of the energy storage in use today consists of pumped hydro. Its capacity equals 3% of global electricity generation. Being one of the storage technologies that delivers, very quickly, small amounts of power, it is used primarily to support power performance. There are nearly 40 operational U.S. facilities. However, there are few suitable unused reservoirs remaining near (as they must be) points of energy generation or of energy usage.

Compressed Air: Worldwide, there are only two operational Compressed Air Energy Storage (CAES) facilities. They work by pumping air into salt rock caverns, using off-peak priced energy; and then as needed releasing this air at high demand periods to drive turbines. When built two decades ago, they cost too much and delivered too little to make CAES a mainstream tool. However, the value proposition is getting better as CAES technology improves and as the cost of bulk and dispatchable energy rises. Wind farms may find CAES, in fact peaker plant technology, to be an effective complement that evens out wind's intermittence.

Flywheels: A flywheel storage system is essentially a rotating, magnetically levitated cylinder connected to a motor. It is established technology that, with enough investment, can be made better and more cheaply. It already has low life cycle costs and is nontoxic, sturdy, and capable of many recharges. Flywheels can support both grid performance (small, quick burst of energy) and grid efficiency (slower, longer-lasting discharges of energy). Large storage capabilities can perhaps be achieved through flywheel farms.

ELECTROCHEMICAL STORAGE

"... present electrochemical systems are too costly to penetrate major new markets, still higher performance is required, and environmentally acceptable materials are preferred. These limitations can be overcome only by major advances in new materials whose constituent elements must be available in large quantities in nature; nanomaterials appear to have a key role to play .... Transformational changes in both battery and capacitor science and technology will be required to allow higher and faster energy storage at the lower cost and longer lifetime necessary for major market enlargement." —M. Stanley Whittingham, 2008 Materials Research Society Energy Issue

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