THERE’S SO MUCH WIND IT NEEDS STORING

Wind’s unprecedented worldwide growth is getting lots of press this week as a result of the release of the Global Wind Energy Council's Global Wind Energy Report 2007.

UK wind energy growth has been stymied somewhat by objections to its intermittency. While Denmark, its neighbor across the North Sea, gets almost a quarter of its electricity from wind, the UK gets only 1%, despite having an estimated 40% of Europe’s wind potential.

A UK academician believes he has the solution: Compressed Air Energy Storage (CAES). Flexible conical containers 600 meters down on the ocean floor, 50 meters wide at their tops and 80 meters at their bottoms. Made from plastics, these giant "baggies" would hold air compressed into them by the wind turbines.

The key is the depth, where the natural depth pressure will create enough storage compression at no expense of energy to make the economics work out. The concept will also work for storing tidal energy.

Professor Seamus Garvey, Nottingham University: "Drawing a mass down within the blade of the piston itself compresses the air…With tidal power you can use a hydraulic ram. This can take a large flow of water at a low pressure. Out of that it can then give you a small flow of water at a high pressure."

Onshore turbines would have to use too much energy to generate enough compression force but offshore turbines in 40 meter depths will work. Pipes would carry the air to the deep water bags. Steep shelves off France and Portugal and around the Mediterranean periphery would be ideal. Professor Garvey: "You could put wind turbines on these shelves and within a few hundred meters, or kilometers, you could be in 600-meter-deep water…"

There is also ongoing research into floating turbines, with which such a system might be feasible.

There are a variety of CAES proposals for geologic storage of wind. (see WIND ENERGY: THE NEXT GENERATION). There are 2 operating CAES sites, in Huntorf, Germany, and in McIntosh, Alabama. Xcel Energy is also experimenting with batteries in Minnesota (see BATTERY TO STORE WIND).

None of the experiments look economically promising but eventually somebody is likely to figure out the right equations.

This German schematic needs no translation. In Professor Garvey's concept, the containers would be giant conical baggies deep under the water. (click to enlarge)

Where to store wind-powered energy? Under water!
Matthew Knight, April 1, 2008 (CNN)

WHO
Professor Seamus Garvey, Nottingham University; Global Wind Energy Council

This and the next diagram - from Ridge Energy - demonstrate CAES with geologic storage. Here the air is pumped in under pressure... (click to enlarge)

WHAT
Compressed Air Energy Storage (CAES) might be the solution the UK is looking for to quell its uneasiness with wind energy's intermittency. Based on new projections of huge growth in Europe's wind energy industry in the GWEC's Global Wind Energy Report 2007, the UK would profit from overcoming its misgivings and developing its enormous wind assets.

WHEN
- 2003 world wind capacity: 39.4 gigawatts
- 2006 world wind capacity: 74.2 gigawatts
- 2012 predicted world wind capacity: 240.3 gigawatts

...and here the air is "dispatched." The Garvey concept is similar except a giant baggie on the seabed substitutes for the cavern and no drilling is necessary, just scuba. (click to enlarge)

WHERE
- Over 60% of world wind capacity has been built in Europe.
- Denmark will be getting 25% of its electricity from wind by the end of 2008.
- 1% of world electricity comes from wind.

WHY
- The storage “bags” will be held in place by ballast and cables.
- According to Garvey, the economics figure out if the containers are under enough pressure from the ocean to hold 25 megajoules of energy for every cubic meter of storage.
- Garvey’s work will proceed thanks to a 3-year grant from German energy power E.ON.

Research is investigating floating offshore wind turbines. Operational word: "Research." (click to enlarge)

QUOTES
- Professor Garvey: "I was thinking about how textile composites and textile structures might be relevant in the context of renewable energy…A polyester reinforcement at the core with probably a polythene layer around that…"
- Professor Garvey, commenting on wind energy’s slow UK growth due to concerns about intermittency: "We're probably the richest country per head in the world in terms of renewable energy…But we're way behind Denmark, Germany and the United States."