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Storing Green Power

by Christine A. Ethier

As anyone looking at power generation through increasingly greener means will attest, the storage of wind, water and solar created power is a central issue.

Sodium Sulphur Battery

One such storage unit is being developed by NGK Insulators of Japan and involves sodium sulphur batteries which can contribute a few megawatts of power to offset times of peak output requirement. Xcel Energy has been operating a one-megawatt wind-to-battery energy storage system since October 2008 at an 11 MW wind farm South Dakota.

image courtesy of XcelEnergy


There are basically two types of energy storage needed in the market. Firstly, there are bulk storage devices designed to make mainly wind and solar power available when needed. On the other hand there are “grid stabilization" systems such as the flywheel manufactured by Beacon Power that delivers 1 megawatt of electricity for about 15 minutes in order to maintain a steady frequency and to smooth out differences in both grid demand and supply. Some of these stabilization systems will be up and running by the end of 2010.

image courtesy of Beacon POWER

Lithium-Ion Battery

Another possible grid storage system is currently being developed by A123 Systems. This system involves using lithium-ion batteries assembled into megawatt-size batteries. A123 Systems, Inc. develops and manufactures advanced lithium ion batteries and battery systems for the transportation, electric grid services and commercial markets.

image courtesy of A123 SYSTEMS

Flow Battery

A completely different type of battery, the flow battery, uses large containers filled with liquid electrolytes that flow over a bank of fuel cells to generate an electrochemical reaction. One such system, the brainchild of VRB Power Systems, uses vanadium and can store several hours of electricity. It is currently in use in King Island, Australia to back up peak demand in wind turbine powered areas. According to Prudent Energy, the system lasts longer than traditional battery systems.

image courtesy of Prudent Energy

Compressed Air

Another exciting option for several hours or even days of energy storage is compressed air energy storage (CAES) that requires a limestone cavern or a similar geological feature. Today there are two such facilities operating, one in Germany and one in Alabama, USA. When energy demands peak, the air is released to run a gas turbine which is said to reduce fuel consumption by 25 percent. The following link outlines the successful operation of the German plant over the last 20 years.


image courtesy of Saarland University

A CAES project is currently being developed in the Iowa Stored Energy Park. It will operate much the same as the other two already in operation. In the night when energy requirements are low and energy costs are cheaper, the turbines will compress air and pump it underground into either salt domes or other underground spaces. It will be released when needed in peak demand times. The facility is set to be online in 2011.

A Boston based company called General Compression is involved in the invention of a wind turbine that would have an air compressor in the housing behind the turbine's blades. After its compression and storage, the air would be released to turn an expander that makes electricity. The company feels that there are enough geological formations in the US to provide years of compression and to offset the cost of huge power plants that are becoming increasingly necessary in the western part of the country.

image courtesy of IOWA Stored Energy Park

Molten Salt

In the area of solar power, improved solar thermal plant designs use hot water or molten salt to supply energy even when the sun isn’t out. SkyFuel uses reflective troughs or Fresnel lenses to focus light onto a pipe that circulates molten salt transferred to storage containers. The salt can then produce energy during times when energy is at its highest cost.

image courtesy of SkyFuel

Many companies are developing alternatives to the batteries in use today – they are searching for better chemistries that are not only cheaper but are less dangerous to our environment. All of these technologies will eventually work in concert to solve our problems with the costs and the other disadvantages of getting power from the grid.


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