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Compressed air wind energy storage

Certainly, two of the hurdles to relying on wind power for producing energy are the intermittent nature of the wind itself, and the fluctuating prices producers get for feeding the resulting power into the grid.

One minute the wind is blowing (at a high enough rate to make power) and the next it isn’t. Worse, sometimes when the wind is blowing, power is selling for the lowest possible price, and when the turbines are still, power is worth the most. It’s enough to make a wind farmer or utility pull its hair out.

While wind power generation may be the fastest growing segment of the renewable energy business, and the raw materials used to make energy are ostensibly free, the whole business is a virtual Garden of Eden: paradise, but with some flaws.

Building wind farms is expensive, and relying on them to generate either a sufficiently steady source of power for the world - or revenue for the operator - is a sketchy affair.

But work is being done to counteract these two negative pressures on the industry.

Systems for storing wind energy created when the going is good and releasing it for use when the turbines aren’t humming are being worked on now. But to date, industry sources say that there is not one operating wind farm in the world with this ability, although energy storage systems have been in use in other branches of the energy generation business since 1978.

Catching up with an old idea

In a 2003 paper entitled “Large Scale Energy Storage Systems”, six students of engineering at Imperial College London noted that compressed air energy storage (CAES) systems typically relied on plants burning fossil fuels to compress the air stored in large underground caverns, which then used this air to produce energy at peak hours.

Also, besides burning fuel to complete the compression work in the first place, this air was mixed with natural gas and itself burned in a turbine to create the electricity.

The researchers also noted that another approach, called compressed air storage (CAS) would hold the compressed air in man-made vessels, but that “current technology is not advanced enough to manufacture these high-pressure tanks at a feasible cost. The scales proposed are also relatively small compared to CAES systems.”

A few years later, this is exactly the road now being taken by the industry, and by at least one technology developer.

Earlier in 2005, a Vancouver, B.C. company, Encore Clean Energy Inc., released news about a system it is working on that will allow wind energy producers to store energy in the form of compressed air in underground steel tanks or pipes, and release it through a special generator to create electricity when it is needed.

The company’s CEO, Dan Hunter, says his firm aims to be the first to build this kind of system for a wind producer and will use its unique technology to do it.

Encore will make use of its core technology, the Magnetic Piston Generator (MPG), as the turbine for its wind energy storage systems.

The MPG is a unique pressure-driven linear engine designed to generate electricity with higher fuel efficiency and lower emissions than conventional internal combustion engine-powered electric generators or even hydrogen fuel cells, according to the company.

The MPG can use many different sources of energy - one of them the compressed air from these proposed wind energy storage facilities - to generate the pressures required to propel the MPG's "Magnetic Piston" at high velocities, back-and-forth, through a linear alternator to generate power according to Faraday's Law of Induction.

“This is a new device. The MPG was basically invented in March (2005),” he said.

Hunter agrees that compressed air storage for use in making energy has been around for a long time, but the idea of using it in conjunction with wind energy is fairly new and doubly intriguing, because the wind energy is “free” and has lower environmental costs than buying and burning fossil fuels.

Those differences alone should make the task of researching and promoting wind energy storage a simpler affair. He notes, however, it’s still going to be a long process of research and development before the first compressed air wind storage system is online.

There are difficult engineering tasks associated with using straight compressed air to drive the secondary turbines (or in Encore’s case, it’s MPG product) that would produce “wind” power when the wind is not blowing, or when a wind energy producer wants to take advantage of higher prices by creating more power at peak times.

These problems include the high pressure needed for commercially meaningful output and the resulting low temperatures of the air if not reheated.

Compressing the air in the first place, at least, is not one of the problems Encore envisions. Hunter’s company predicts that if a wind facility made a certain amount of power at non-peak times, only about 25% of it would be used in compressing the air in the first place, leaving 75% of the initial production available for resale later at higher prices.

Larry Shultz, an Encore director, wrote that “1000-kW of non-peak intermittent wind power generated at 2 a.m., that would otherwise be sold directly to a utility for the worst non-peak price, of 3-cents/kWh, for example (generating $30 in revenues), could instead be used to electrically or mechanically compress air at high pressure into storage pipes or tanks located next to, or built inside the wind turbine tower itself. The “heat of compression” will also be utilized to increase the efficiency of the process by minimizing the energy consumed in the compression process.

“If, for example, 25% of the wind energy produced is, in turn, consumed by the air compression and storage process, then the remaining 750-kW of compressed energy could be sold during peak-demand times at prime peak prices of >10-cents per kWh, generating $75 in revenues - a 250% improvement in gross revenues for a wind farm owner.”

“This retrofit wind energy storage solution should enable wind farm owners to earn the highest prices for the power they generate and give local utilities the kind of peak, on-demand, power availability that Utilities pay the most for, but which up until now, current wind farm owners could not reliably guarantee.”

While his company is working on wind energy storage solutions involving its MPG generator, Hunter says other companies may be working in other directions.

“Compressed air is very under-utilized for this area,” he said. “There are certainly problems with compressing and releasing air” but these won’t be ongoing obstacles, he noted.

Business should be brisk

Although the first working wind energy storage installation at a wind farm might still be long off, these development efforts seem to be coming at the right time. Demand for them should be brisk in the near future.

The British Wind Energy Association (BWEA) recently reported that 2005 was a record year for the British wind industry. The BWEA said, “Some 19 new wind farms totaling 500 megawatts (MW) will be commissioned this year, including the largest offshore wind farm so far built in UK waters. This new wind power capacity will provide carbon free power for the equivalent of 300,000 homes.”

The BWEA also noted a “further 970 MW of new projects are already under construction, for expected commissioning in 2006.”

The Canadian Wind Energy Association (CWEA) says its “goal is to encourage investment in wind energy for 10,000 MW by 2010, providing 5% of Canada’s electricity”.

And Canadian hydro generating utility, Hydro Quebec, announced on October 31, 2005, that it would call for tenders for the purchase of 2000 MW of wind-generated electricity from within the province of Quebec, starting in 2009 and continuing until 2013, “to meet the long-term electricity needs of Québec customers”.

Farms like these, going online when storage technologies may be better refined and with a built-in market, may be some of the first in the world to adapt compressed air wind energy storage solutions.

However, the market itself also has issues. The development of these products is not finished and their final costs are unknown. In addition, the customers may not yet realize they need them.

“Most facilities have a problem with intermittent power generation, but most don’t worry about it yet,” Hunter said. He thinks as time goes on they won’t be able to do anything but think about it.

Even the potential client list for a wind energy storage developer is a moving target. In Britain, wind power now provides a modest 0.6% of electricity supply, according to the BWEA, “a poor showing compared with Denmark's 18%.” One could see the newest technology, such as wind energy storage systems, take hold in the countries with the lowest output, and thereby the most to gain, or the total opposite could occur, wherein the technology is adopted by the countries farthest along on the wind energy generation timeline.

But all industry suppliers face this same question. There is no more threatening impediment to this business than to any other part of the industry supply chain. The problem may just be that many wind farm operators and utilities haven’t really decided that intermittence or price/power arbitrage questions are yet problems.

And for that, innovators like Encore may just have to wait for the winds to change.

Contact information for Encore Clean Energy Inc., or its CEO, Mr. Dan Hunter:

Dan Hunter
Encore Clean Energy Inc.
Vancouver, British Columbia, Canada

Bryce Finley is a Canadian public relations worker and former photographer and journalist who represents several technology companies from Canada, and takes a keen interest in clean, green energy sources.

Finley, author of four books, is 41, lives in British Columbia and is building a self-powered, off-the-grid float home that floats in the ocean.

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