Officials beef up forecasting for popular but fickle power source
An electrical emergency in Texas last week has grid officials and power companies re-examining how they manage wind energy, an increasingly popular but potentially fickle power source.
Wind turbines don’t emit greenhouse gases, unlike conventional power plants. But wind power requires astute handling or it can affect reliability and power prices. Grid officials have fretted for some time that construction of enormous wind farms could jeopardize grid stability.
In response to its shortfall, Texas officials now are speeding up plans to improve wind forecasting. U.S. officials also are looking at other nations that manage far larger wind resources deftly.
California’s grid operator is seeking bids from wind consultants. It also is considering ways to tailor power consumption by big users so they could more closely match wind production, as well as ways to store wind energy for use later.
“Wind needs a dance partner,” says David Hawkins, principal engineer for renewable energy at the grid-running California Independent System Operator in Folsom, Calif.
A cold front blew through West Texas on Feb. 26, temporarily lifting wind production. When it subsided, wind speeds dropped, turbines slowed and productivity dropped by 80% to 300 megawatts from about 1,700.
The situation was exacerbated by greater-than-expected energy demand and by lower availability of some fossil-fuel units. To get the system back in balance, the grid operator declared an emergency and tapped big customers who had agreed to be cut in exchange for cash payments.
The problem “showed us we need much better wind forecasting tools,” said Kent Saathoff, vice president of system operations at the Electric Reliability Council of Texas, a quasipublic, nonprofit corporation that operates most of the state’s high-voltage transmission system.
Currently, ERCOT accepts estimates of energy production from turbine owners or their agents. Texas now is working on building up its own computer capacity and monitoring to improve forecasting. It isn’t clear how much the effort will cost.
Shortages degrade reliability and push up prices. Wholesale power prices surged to $1,055 a megawatt hour in West Texas on Feb. 26 versus $299 elsewhere in the state. In a long-planned move, Texas on Saturday raised its price ceiling to $2,250 a megawatt hour from $1,500. Two days later, it hit the ceiling for the first time as wind production again trailed off. “Demand was going up as wind production was going down, so it amplified the effect,” said Dan Jones, the state’s independent electricity-market monitor.
Last year, the wind-power sector grew by about 45% in the U.S. as generators added 5,244 megawatts of wind capacity, led by power company FPL Group Inc. Globally, 20,000 megawatts of capacity was added last year, costing about $36 billion, according to the Global Wind Energy Council, a trade group based in Brussels.
Nationally, grid operators have been notified that up to 147,000 megawatts of wind turbines may seek to connect to the grid in coming years, though a significant proportion won’t get built. Currently, the U.S. has about 16,818 megawatts of wind capacity, enough to power 4.5 million homes, according to the American Wind Energy Association, a trade group. That amounts to less than 1% of U.S. power.
In California, there are plans to more than double wind capacity in the next few years once $1.8 billion in transmission upgrades are completed in the Tehachapi Mountains, which separate the northern and southern parts of the state.
The state’s grid operator is looking at techniques turbine owners could use to smooth out electricity flows, including developing technology to store energy at night, when wind turbines are more active, for use the next day. Large-scale deployment still is years off.
California is looking at ways to ratchet back electricity demand to meet small dips in wind output so it wouldn’t have to rely as much on power plants that burn fossil fuels. To do that, it is developing a program that would allow it to control the energy used by big water-conveyance pumps and other pieces of equipment, under a voluntary arrangement.
Wind tunnel modeling of the Tehachapi Mountains shows air currents often swirl and don’t follow a linear path, something that makes it trickier to predict the output of the 4,200 megawatts of turbines expected to be built there in the next five years. Another complication is that wind speeds typically sag in the morning as demand rises.
FPL Energy, a unit of FPL Group, does its own wind modeling to predict the output of its 7,500 turbines for the following week, day and two-hour period. It acquired WindLogics Inc., a wind research firm, in 2006.
The chief executive of a big international turbine manufacturer believes that the U.S. has taken a short-sighted approach with federal tax credits that come and go, and with no federal policy to provide consistent support and guidance.
“The U.S. has a fantastic wind resource,” says Ditlev Engel, chief executive of Vestas Wind Systems AS, a Danish firm with 35,000 turbines in operation globally. “If it were an oil resource, you’d drill, drill.”
By Rebecca Smith
6 March 2008
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