Shell Wind Energy and TXU subsidiary Luminant Energy planning a 3,000 MW wind megaproject in Texas panhandle and are considering compressed air energy storage to firm and shape project's output
[From the Star-Telegram (Fort Worth, TX):]
TXU Corp.'s generating subsidiary and Shell WindEnergy plan a huge Panhandle wind farm that could include the use of compressed air to generate electricity when there's not enough wind to spin the big turbines.
The 3,000-megawatt facility is slated for windy Briscoe County, southeast of Amarillo, Luminant Energy and Shell said Friday. That would rank as the world's largest single installation and roughly matches the wind farm recently announced by Texas investor Boone Pickens, whose Mesa Power is seeking to install 2,000 to 4,000 megawatts of wind power in four Panhandle counties.
The companies did not say when they expect to begin the project or what it might cost. They said they also plan to work together on other renewable-energy projects in the state.
"We are very excited about this project, using compressed air to provide power when we need it, without pollution," said Tom "Smitty" Smith, director of Public Citizen's Austin office, which has criticized TXU's plans to build more coal-fired power plants. He said that if all health and environmental costs are included, "this is the lowest-cost way to generate electricity," a view shared by Shell in recent testimony before the Public Utility Commission.
"Our approach is a cost-effective solution for consumers," John Hofmeister, president of Shell Oil Co. in Houston, said in a prepared release Friday.
Putting wind to work
The new project further solidifies Texas' standing as the nation's No. 1 wind-power generator. According to the American Wind Energy Association, the state had 2,768 megawatts of wind capacity at the end of 2006, including 240 megawatts at two Shell facilities.
It also would mark TXU's first direct ownership of a wind farm, although the Dallas-based utility is the state's largest purchaser of wind power and the No. 5 purchaser nationwide, it said.
Greg Wortham, director of the West Texas Wind Energy Coalition in Sweetwater, said the use of compressed air to balance the unpredictability of wind power represents what he called the industry's "holy grail" -- the ability to store wind energy so that it is available on demand, just like electricity from traditional power plants that rely on natural gas, coal and nuclear energy.
On average, wind farms operate at peak capacity only about 30 percent of the time. That drops even lower during the hottest summer days in Texas, when wind drops at the same time electricity demand surges.
Two compressed-air energy facilities are in use worldwide, one in Germany and one in Alabama. Neither uses wind, but both use electricity generated in periods of low demand to pump air into underground storage. Then, during times of peak demand, that pressurized air is mixed with natural gas to drive generators.
Using compressed air
Alabama Electric Cooperative has operated a 110-megawatt compressed-air generator since 1991, spokesman Mark Ingram said. He said the utility uses electricity generated at night from one of its coal-fired units to pump air into a 19 million-cubic-foot, underground salt cavern.
The air, stored at more than 1,000 pounds per square inch, is retrieved the next day and mixed with natural gas to drive a turbine that can produce electricity on 14 minutes' notice, Ingram said. Because of the air's added energy, it requires only a fraction of the amount of natural gas that otherwise would be burned to generate the same power.
The Iowa Stored Energy Park is the only announced project that combines wind and compressed air to generate electricity. That facility, which will use an underground water aquifer to store compressed air, plans a 2011 completion date.
Although wind power has become a fashionable source of nonpolluting electricity, its variability poses challenges in the demanding, day-to-day management of electricity supply and demand. Wind turbines perform best at wind speeds of roughly 10 mph to 35 mph, according to the American Wind Energy Association.
"It's stronger in the spring and fall, weaker in the summer. Further, it blows more consistently in the early morning and evening," said Bill Bojorquez, vice president of system planning at the Electric Reliability Council of Texas, operator of the electricity-transmission grid that serves most of the state.
"The compressed-air technology promises to solve the second problem," he said.
Bojorquez said that ERCOT managers consider only 8.7 percent of reported wind capacity to be reliable when they are scheduling supply.
As a result, a wind-power provider must arrange a backup supply from another generator or rely on ERCOT to buy power to make up for a shortfall, which can get expensive during peak demand.
As for the seasonal variation, he said, that would depend on how long the air can remain in storage under pressure.
That doesn't seem to be a problem, at least not in the natural gas storage business.
Rand LaVonn, a spokesman at Atmos Energy, North Texas' natural gas utility, said Atmos buys and stores natural gas in the spring and fall so it is available in the summer and winter.
It stores gas underground at pressures up to 3,000 pounds per square inch, he said, where it remains in storage throughout the year.
Wind farms that supply a more constant stream of electricity also would help make the construction of high-voltage transmission lines more cost-effective, because the wires must be designed to carry a peak load whether it's delivered or not.
The Public Utility Commission last week recommended eight [Competitive Renewable Energy Zones] as the best routes for new transmission lines to serve Texas wind farms.
One of those zones includes Briscoe County, the site of the Luminant-Shell wind farm and, in Wortham's words, "the platinum region" of Texas wind resource.
I don't normally blog on specific project announcements for wind projects. However, this project is notable for two reasons:
a) it's size: at 3,000 MW this is a true megaproject, and if completed would probably be the largest wind project in the world. For comparison, there is roughly 11,000 MW of installed wind power capacity in the United States. The entire Northwest (OR, WA, ID and MT) currently has 1500 MW installed, while California and Texas lead the pack with around 3,000 MW each.
b) the (possible) use of compressed air energy storage: the possible use of CAES to shape and firm some of the output of this large plant is very notable.
While integrating intermittent wind resources onto regional grids hasn't posed too much of a problem so far (adding wind requires some new operating procedures, but hasn't been too challenging or costly so far), as wind power scales rapidly to becoming a major source of energy in various utilities' mixes, it will become more of a challenge.
One particular problem is the rate at which wind farms ramp up - wind farms can ramp up faster than other plants can be taken offline, potentially creating grid instability problems. The ramp rate of a plant can be controlled by curtailing production at the wind farm (simply turning off a couple turbines during quick ramps for example), but wind plant operators are reluctant to do so since it entails lost production and revenue.
CAES or other energy storage options present an alternative to curtailing output: simply send a portion of the output to the energy storage device to save for later.
The use of CAES to shape and firm wind power seems to be catching on. In addition to this announcement, a group of Iowa municipal utilities said they are planning on constructing a wind farm that will be paired with a CAES system back in January 2006 and BP is also reportedly looking into the concept.
Meanwhile, a new wind turbine technology firm, General Compression, is taking the idea and running with it. They plan to build and install turbines that compress air directly, avoiding the wasteful conversion of wind energy from mechanical energy in the turbine to electricity and then back to mechanical energy in the compressor. Instead of generators, their turbines feature compressors that would directly compress air for storage in either an underground pipeline system and/or natural geologic storage formations like salt caverns, if available.
While their first prototype won't be built until 2009, it remains to be seen if General Compression can succesfully commercialize this concept, but who can deny the appeal of clean, fully dispatchable, on-demand wind energy?!
[A hat tip to Wind Energy Weekly]