Storing Wind Energy Underground

Wind is the fastest growing energy source in the United States. Over the last five years, wind energy output has increased tenfold. Unlike most other forms of energy used to produce electricity, wind is a variable energy source. Some wind energy may be wasted when too much energy is produced and more energy might be needed when there is not ample wind available.

A very promising technology is being developed called compressed air energy storage (CAES) that can store large quantities of wind energy. Surplus wind energy is used to pump air into layers of porous sandstone in the earth below. This underground cavern is sealed with dense shale and acts like a huge balloon. When demand for energy increases, air flows up into a natural gas-fired turbine, boosting its efficiency by 60% or more.

This technology is being implemented at the Iowa Stored Energy Park in Dallas Center, Iowa. The energy park is scheduled to be complete in 2011 after 8 years of construction. This 268-megawatt system will cost $200 million to construct, with funding from the Energy Department and municipal utilities across Iowa, North Dakota, South Dakota and Minnesota.

Batteries are also being developed that can store wind energy. American Electric Power and Siemens Wind Power are experimenting with large-scale batteries that could store a megawatt of energy. Such technologies are very pricey and could have a high environmental price tag and have a much smaller storage capacity than CAES.

The future looks bright for compressed air energy storage and wind energy. Being able to store off-peak wind energy until demand and electric rates are higher allows wind energy to be a more lucrative and consistent energy source.

goals of Night Wind project.

The random production of wind energy cannot easily be accommodated on the grid by switching on and off conventional energy suppliers, like coal fired power plants, which would lead to an increase of CO2 emissions, rather than the reduction of CO2 emissions which is desired.

In order to accommodate the random production of wind energy in the grid, it would be most convenient when alternative (renewable and conventional) electricity producers could balance out the difference between production of wind energy and electricity demand. The Night Wind project aims to store wind energy produced at night in refrigerated warehouses, and to release this energy during daytime peak hours.

Nature adds some more details about the first tests of the Night Wind idea.

Later this year, van der Sluis's team will start a demonstration project by setting up a wind turbine next to the Netherlands' largest coldstore, in Bergen op Zoom, a small town in the SouthWest of the country. It shouldn't be technically difficult, he says — it's really just a question of developing software to match the temperature of the warehouses with electricity demand, turning the fridge on and off as the supply from the wind plant and the demand from consumers change during the day.

This project will officially end in June 2008 and I hope it will be a success. In the mean time, you can read this short presentation of the project, from which the diagram above has been extracted (PDF format, 3 pages, 100 KB).

Sources: Declan Butler, Nature, February 7, 2007; and various other websites

You'll find related stories by following the links below.

Storing wind power in cold stores

According to Nature, a European-funded project has be launched to store gigawatts of electricity created from wind into the refrigerated warehouses normally used to store food. As the production of wind energy is variable every day, it cannot be easily accommodated on the electricity grid. So the "Night Wind" project wants to store wind energy produced at night in refrigerated warehouses and to release this energy during daytime peak hours. The first tests will be done in the Netherlands this year. And as the cold stores exist already, practically no extra cost should be needed to store as much as 50,000 megawatt-hours of energy.

Here is how Nature describes the — simple, but brilliant — idea behind this project.

The idea seems simple. Say you lowered the temperature of all large coldstores in Europe by just 1°C during the night when electricity demand is low, then let it rise 1°C by switching them off during the day when demand is at peak. The net effect would be that the warehouses would act as batteries — potentially storing 50,000 megawatt-hours of energy — and the food wouldn't melt.

Before going further, below is a diagram illustrating the idea: wind energy is optimally stored or released by following the electricity consumption patterns (Credit: Night Wind project)

Optimum storage or release of wind energy

In European jargon, the official denomination of the Night Wind project is "Grid Architecture for Wind Power Production with Energy Storage through load shifting in Refrigerated Warehouses." And it is led by Sietze van der Sluis, head of refrigeration and heating technology at The Netherlands Organization for Applied Scientific Research (TNO) in Delft.

Click Here to see the goals of this Night Wind Project