Together Better than Alone: Network of Wind Farms Can Generate Smoother Power Supply
Wind is a clean and never ending source of energy, but also an unreliable one, because it blows intermittently. This intermittency and unpredictability of wind patterns has always prevented wind power from being used as a regular electricity supply, but now two researchers at Stanford have shown that linking distant wind farms together would result in a smoother power source and could also reduce the final cost of wind-generated energy.
The explanation to this improved reliability is that connecting wind farms located in distant geographical locations with different wind patterns increases the chances that, at any given moment, the wind will be blowing in at least some of the sites. Thus the joint power supply will be steadier than that from each wind farm.
Archer and Jacobson calculated that 33% to 47% of the wind power generated during a year in a wind-farm array could be used as a “firm” power source, as dependable as the power produced by a coal-fired power plant.
Jacobson, an associate professor of civil and environmental engineering at Stanford, said that, although other researchers had studied the interconnection of wind farms, no one had ever quantified how reliable the combined energy output would be.
“This is the first time the reliability of wind has been gauged against coal-fired power plants,” Jacobson said.
In their study, Archer and Jacobson used real wind data from 19 sites in the Midwest of the United States of America. At all the sites, the average annual speed of the wind was at least 6.9 meters per second at the height of the hub, which is 80 meters above the ground for modern turbines.
The hourly and daily-averaged wind speed measurements the researchers used had been collected during the year 2000 by the National Weather Service. Archer, a consulting assistant professor of civil and environmental engineering at Stanford and a research associate in the Department of Global Ecology of the Carnegie Institution, said the information was originally collected at 10 meters above the ground, so she and Jacobson had to design a technique to extrapolate the data to the hub height.
Archer said she tried an enormous amount of combinations among the 19 sites to compare the resulting benefits. She concluded that, to obtain a significant amount of base load power, the array had to include 10 or more wind farms.
As an additional and hidden gain, Archer found that the interconnection reduced the transmission needs by one fifth, which would make the final cost of wind power cheaper.
In the Stanford researchers’ model, all the wind farms in the array would connect to a common point in the grid that would then distribute the electricity in a single, powerful channel. But the number of transmission cables needed to transmit the electric power from the collecting point to the consumers would be less than the number of wind farms in the array.
“If you had ten wind farms connected to that common point, the chance that the wind would be maximum at all ten farms at the same time is basically zero,” Archer said. Because all the connected wind farms would never be operating simultaneously at full capacity, the number of cables needed to transmit the wind-generated electricity could be reduced.
Archer and Jacobson calculated that this reduction in transmission cables would be 20 percent.
“That is: you can connect ten wind farms for the cost of eight,” Archer said. The associated loss of energy would be of only 1.6 percent.
“Right now, transmission is the biggest barrier for the large-scale implementation of wind farms,” said Jacobson, who also pointed out that the cost of transmission increases when the wind-generated electricity has to travel longer distances.
The researchers said the wind farms in the array could be up to 850 km away and still be economically viable. Further than that, “it would be an economical decision: am I willing to pay more in transmission costs to connect them from farther away because I get more smoothing?” said Archer.
Archer, Cristina and Jacobson, Mark. "Supplying baseload power and reducing
transmissions requirements by interconnecting wind farms." Published in the November 2007 issue of the American Meteorological Society's Journal of Applied Meteorology and Climatology
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Shaky Foundations for Offshore Wind Farms
Texas has both West Texas and off shore wind resources. In 2005 the Electric Reliability Council of Texas (ERCOT) looked at the Reliability of Wind power in Texas. . Texas is considered second only to South Dekota in wind energy potential, and a great deal of money is being invested in Texas wind farms. Here is what the ERCOT found: 1. Wind generated electricity was not significantly less expensive than other sources, based on the Texas experience. 2. In order to take advantage of preposed wind generation projects, three billion dollars would have to be invested in the statewide electrical grid. 3. Wind Generated electricity was not reliable.
ERCOT currently assigns 10% of the installed capacity of wind turbines to its calculation of the ERCOT peak capacity reserve margin. Based on a review of historical data of actual wind turbine generation during ERCOT system peaks (from 4 p.m. to 6 p.m. in July and August), the average output for wind turbines was 16.8% of capacity. However, the data also showed that for any hour during these months, the output of the wind turbines could range from 0% of installed capacity to 49% of installed capacity. Because of wind's intermittency, the ERCOT Technical Advisory Committee, considered recommending a wind capacity value of 2%.
Stephen R. Connors of MIT analized data from the National Oceanic and Atmospheric Administration (NOAA), U.S. Environmental Protection Agency, and other data sources tracking off shore wind speeds, electricity demand, and power systems operations over time for the North East. Conner found that offshore wind farms in the Northeast would generate far more electricity in winter than in summer, when electricity demand is highest. Connor noted about New England off shore wind power that "it?s not there when you need it most?midday during the summer when demand and prices are high,?
Mike Cowan of Western Area Power Administration?s Upper Great Plains Region reports that Western?s Upper Great Plains Region has about 150 megawatts of wind power that has been installed, but that generation from wind was insignificant during the hottest days of summer. The Upper Great Plains are considered to have the greatest potential for wind generation in the country.
The Tennessee Valley Authority installed a wind generating Farm on Buffalo Mountain in East Tennessee. Buffalo Mountain is considered one of the windiest spots in Tennessee. During Augusts, Buffalo Mountain receieves enough wind to generate electricity 7% of the time. The wind resources of the entire American South East are considered poor.
David Dixon studied the performance of California's wind generators during California's "heat storms" during the summer of 2006. Dixon stated, "By most people?s analysis, wind?s performance was disappointing. Specifically during this period of peak demand, statewide wind often operated at only 5% of capacity, or less."
California has 2,500 MW of rated wind generating capacity. On July 24, 2006 California Electrical demands peaked at over 50.000 MWs. Wind generation plumited to around 5% of rated capacity that day. There were record heat waves in California, the East Coast and the Southern States, during July 2006.
Clearly then the notion that linking wind generators is going to smoth power production does not survive empirical tests.
Joseph Somsel has observed, "the advocacy of wind power comes from three sources - rent-seeking entrepreneurs angling for corporate welfare, daydreamers, and politicians seeking to avoid difficult decisions. "
The big problem with wind is reliability.
The problem is worst during the summer when electrical demands are at their peak.
When advocates of wind energy talk about its costs, they seldom include the costs of duplication. In wind rated capacity means nothing. In order to get for wind to generate 20% of the electricity a country wants, you have to build give times the rated capasity. Even then, as the experiences of California, Texas, and Germany shows you may get almost no power from your system on some days.
Other costs include the costs of building and maintaining access roads, the cost of building and maintaining an electrical grid connecting the wind farm to the grid, the cost of running inspection and
maintance equipment, the costs of maintance, and of course the cost of building, maintaining, and operating a back up system. The Danish experience has shown that the cost of operating and maintaining off shore wind farms is higher than land based wind farms.
What if you don't want to back up with fossil fuels generated electricity? I priced batteries for back up systems. (This information was not easy to find.)
Wow, them suckers are expensive.
I also looked at pump storage as a back up plan. Pump storage is not cheeper than nuclear power, is less safe, and less reliable.
Renewable energy requires back up power plans. Back up power either emits CO2, or is at least as expensive per KW as nuclear power.
Your capital cost expectation for renewable post carbon electricity appear to be un realistic.
You argue that wind power has no fuel costs associated with it. But reliable wind generation requires that backup fossil fuel power plants constantly keep their generators spinning. The cost of fuel to keep back up generators is part of the cost of wind energy. The cost of producing electricity from back up generators is also part of the cost of a wind generated story.
I have found that the advocates of wind power seldom tell the whole wind power story. The seldom spend time talking about the disadvantages. Wind generated electricity is useful now in cutting CO2 emissions. For this reason I do not object to it. but if we want to generate 100% of our electricity carbon free, then wind is simply not the way to go. - Charles
--- Scitizen wrote:
Subject : Reply to your comment to What'sReally Wrong
With Nuclear Power?
Comment & Response :
It is most unfortunatethat you close the debate at
this point. I findit amazing that you describe the
Chinese cost of$1200 Per KW expensive. A recently
proposed coalfired electric plant in West Virginia had
anestimates cost of $2.33 billion for 629 MWs
ofgenerating capacity. That is $3,656 per KW.
An wind offshore wind project of Long IslandPower
Authority would have installed 40-turbineoff Long
Island. The Installed generatingcapacity was to be
140 MWs. Since wind generatorrare ly produce even
half of their rated power,and rarely produce any power
at all more than onethird of the time. The average
output of the windfarm would have been less than 12
MW. The costwas estimated to be $1 billion. Now
consider thatwind generators are considered to be
doing verywell, if they produce power one third of the
The same account discusses a second off shorewind farm
near Cape Code. The 468-megawattproject will cost up
to $1.7 billion to build. The project owner
estimated average of output ofthis facility 182 MW.
A two billion dollar nuclear power plant isquite a
bargan compared to recently quoted pricesfor coal and
wind powered plants.
[Response]Charles, I don't think either of us have
ashortage of arguments, and we can continue thisdebate
over the course of the next few months, asI will be
writing more on precisely these issues.
The coal fired plant you mention in WV soundsabsurd,
and you are correct that offshore windturbines have
capital costs per installed kW inthe same ballpark as
Looking at onshore wind turbines, however, and
thenumbers drastically improve. 2006 model
turbinesfrom Gamesa, Vestas, and GE were in the $1,000
perinstalled kW range, and those numbers are set
toimprove, along with capacity factors, which tendto
be in the high 30s for newer wind farms thatare
Given that wind has better capital costs thannuclear,
and that it has no fuel costs (where asfuel costs
account for 15 percent of a nuclearplant over its
lifetime), it seems like a deal tome.