How reliable is wind power?
Texas wind farm (AP)
How many homes can be powered by a wind turbine?
It sounds like a fairly straightforward question -- but it's actually a very complex and contentious issue. And it's one of the issues at the heart of public hearings this week on whether Maryland should allow wind turbines in state forests. The other big question, of course, is whether the 40-story wind turbines on mountaintops would hurt the rural beauty and tourism industry in Western Maryland.
The hearings are scheduled for 6:30 p.m. Wednesday in Western Maryland, at the Garrett College Auditorium, at 687 Moser Road in McHenry; and at 6:30 p.m. Thursday in Annapolis, in room 161 of the Arundel Center at 44 Calvert St.
David McAnally, president of the Pennsylvania-based U.S. Wind Force company that is proposing to lease about 400 acres of state land in the Savage River and Potomac State forests in Western Maryland, has said his 100 turbines could power about 55,000 homes. That's more than the combined populations of Garrett County (where the turbines would be located) and adjacent Allegany County.
But Baltimore conservationist Ajax Eastman and other critics of the project claim this number is inflated. "Wind turbines are only an intermittent energy source and incapable of producing much electricity during the summer months when demand for electricity is highest," Eastman wrote in a letter to The Sun. "The wind blows least during the summer. Rather than powering 55,000 Maryland homes, the 100 turbines would generate only enough electricity to equal the amount consumed by 17,000 average residential customers during the summer months."
I looked into this question. And I concluded that the U.S. Wind Force numbers (which the company said were only an estimate) are not that far off from estimates by other groups of how many homes could be powered, on an annual average, by 100 turbines, each producing 2 megawatts of power.
For example, the Electric Reliability Council of Texas, which runs the electrical distribution system in the state with America's largest amount of wind power, says that during the hot months when the winds are slower in Texas, 1 megawatt of wind power can light up about 200 homes. Using this figure, the U.S. Wind Force turbines in western Maryland would power about 40,000 homes in the summer. During the cooler and windier months of the year (using the Texas figures of 1 mw of wind powering about 500 homes for the non-summertime period), the Western Maryland turbines could power about 100,000 homes.
Average those two (somewhere between 40,000 and 100,000), and the numbers aren't all that different from the U.S. Wind Force estimate. Nor are the numbers all that far off from the estimates given out by the Maryland Department of Natural Resources (1 mw of wind powers about 350 homes on an annual basis) or the American Wind Energy Association, a wind power trade group (1 mw wind powers 250-300 homes).
But those rough annual approximations mask a more significant underlying issue. Wind power is not "controllable or predicable," and it is "highly dependent on weather conditions" as the Electric Reliability Council of Texas puts it.
"When the electricity is needed the most in the summer, the wind does't blow," said Terry Hadley, spokesman for the Texas Public Utility Commission. "So we need a variety of fuel sources."
That means wind turbines must be backed up by natural gas generators, which can be quickly fired up if the wind suddenly dies. Coal generators typically take too long to get started to serve in this backup role, and nuclear generators can't do it, because they are normally running full blast all year long.
Christine Real de Azua, spokeswoman for the American Wind Energy Association, said that wind can't be relied upon as an area's sole source of power during the summer, when the demand for electricity is highest and the wind often slows down. So at these peak times, power companies typically kick on natural gas generators to pick up the slack, she said. When there's less wind, the companies burn more natural gas. When the wind is blowing good and strong, the companies burn less gas.
"You don't count on wind to deliver 100 percent" of a community's summertime needs for electricity, de Azua said. "It can only deliver a small portion of that. But it does deliver savings in fuel, meaning you will burn less natural gas... and wind has zero emissions, so wind does help clean the electric system and it helps conserve fuel."
On average across the U.S., wind turbines generate some electricity about 80 percent of the time, she said. They don't generate any electricity at all about 20 percent of the time. They generate at their maximum capacity about 10 percent of the time. Aeraged out over a year, they generate at about 30 to 35 percent of their maximum capacity.
When the wind is down, natural gas is needed to fill the gap.
"Wind is reliable because it's part of the overall grid," said de Azua. "In Denmark, they are now getting 20 percent of their electricity from wind and the lights still go on." When wind falters in Denmark, natural gas kicks on to supplement the baseload power supplied by coal and hydroelectric power.
Jon Boone, a retired history professor and dean at the University of Maryland College Park who is a critic of the wind industry, said that one problem with building up more wind generation is that it makes the system more dependent on natural gas.
Natural gas creates less air pollution than coal, Boone said. But that means that wind turbines wouldn't be replacing a really dirty source of power -- coal. Instead, they would be replacing only a moderately dirty source, natural gas. And becoming more dependent on natural gas is risky, Boone said, because it's very expensive and supplies of it are running out in the United States. So building more wind turbines would require the U.S. to import more liquid natural gas on giant tankers from overseas.
Moreover, turning natural gas generators on and off as a backup for wind wastes some energy, he said, just as turning your car engine on and off all the time wastes gas.
“The best way to understand wind is that it’s a sporadic fuel substitute,” said Boone, who estimated that the U.S. Wind Force turbines could help power about 33,692 homes, when combined with natural gas generation. Wind turbines can't power all of western Maryland -- or all of anywhere -- because it has to be supplemented with other energy forms.
For example, the proposal to build wind turbines in the Atlantic Ocean east of Delaware's beaches also includes a plan to build a natural gas plant on shore.
Teaming up wind turbines with natural gas generators isn't necessarily a bad thing, advocates of wind energy say. If natural gas is expensive and increasingly rare -- but clean -- then it might make sense to use wind to conserve some of this valuable resource.
But as an alternative energy source, wouldn't it be better to find something that could replace coal -- which many environmentalists view as Public Enemy No. 1 when it comes to global warming -- as a year-round, dependable power generator? Some suggest nuclear power could fill this need, but it also has limits -- in that uranium will eventually run out, and disposing of nuclear waste is a political headache. Wind, by contrast, will never run out, and it creates no pollution (although some consider the turbines themselves a form of pollution.)
All of these issues are likely to be batted around during the hearings this week.
Comments
Jon Boone, a skeptic of wind power, calculates that the 100 turbines proposed in the Western Maryland state forests could help power about 33,392 homes, when combined with natural gas generation.
Here is Boone's formula:
2.0 Megawatts x 25% capacity factor (the national average for big wind turbines)=0.5MW or 500kW;
500kW x 24 hrs x 365 days=4,380,000 kWh per year per turbine;
4,380,000 kWh x 100 turbines=438,000,000 kWh annually for the entire plant;
438,000,000 kWhr/13,000 kwh average household use per year in MD*=
33,692,308 homes
*During 2003, the average consumption of electricity by MD's residential customers was 12,945 kWh
Source: http://www.eia.doe.gov/cneaf/electricity/esr/table1abcd.xls#Table1!A1.
Note this is still not 55,000 homes--or anything close to it.
Posted by: Jon Boone | January 28, 2008 5:13 PM
If you don't think wind can be used in combination with other sources for baseload power, then Google "Combined Power Plant". They have a system all setup and running in Germany.
Posted by: Jerry Brown | January 29, 2008 7:09 AM
Klaus Philipsen, a green-certified architect and planner and board member of the conservation group 1,000 Friends of Maryland, had this to say:
"As an environmentally concerned citizen I am troubled that one environmental resource (wind) is pitted against another (400 acres of forest). Careful review of the environmental benefits of wind power show that they are never as big as claimed. The installed power comes to bare only when maximum wind coincides with high demand. If there is high demand and no wind the lacking windpower has to be compensated for with other readily available environmentally friendly power sources, usually hydro-electric power of which we have little in MD. I haven't seen any comprehensive discussion of this complex context without which the proposed turbines can only be described as a damaging boondoggle.
Let me add this: I would not want to argue that there isn't a potential future for windpower, provided a lot of windpower sources are networked and windpower is balanced with the appropriate substitute power sources that can make up for lack of wind. This requires many changes to the way how our power grid currently is set up. These changes should not begin with clear-cutting 400 acres of perfectly fine and highly valuable forest on State land because these turbines would do very little to offset Marylands dependencies from fossile fuel power generation such as coal and gas while they would do immediate damage to a substantial resource for a healthy climate: forest."
Posted by: Klaus Philipsen | January 29, 2008 10:55 AM
Christi from Severna Park sent me this email:
"Thanks for your piece on turbines proposed in Garrett County. I urge you to dig a little deeper into the idea that these wind farms are clean in their NET IMPACT. We have a second home in Tucker County, WV, site of wind farm. We took the time to find out more because we saw what it did to the environment. I beg you to take the time to drive up to the newest development en route to the Mount Storm generating plant on Rte. 93 (about an hour south of Cumberland) in neighboring Grant County, WV. The beautiful ridge line was clear cut then blasted and bulldozed to build the huge access roads to assemble and maintain these behemoth turbines. Tell me how clean it looks to you. What's the net impact of removing hundreds (with plans to removed thousands more) acres of oxygen-producing forest? What about the downstream impact of destroying fragile ridgelines? They're now open to erosion and downstream water quality is significantly impacted. Ok, maybe you can dismiss that as a tree huggers rant...but look deeper into the mechanics and science of it all.
Have you considered that wind power is both variable and unpredictable? Since turbines cannot produce energy on demand, there still have to be traditional power plants ready to meet 100% of our demand. Understand this: Using wind power does NOT mean we will need FEWER or SMALLER power plants. Sure, when the fickle winds do blow, the plants can burn less coal/fuel, but because they can't plan for it, they end up operating far less efficiently. They actually end up producing more emissions per kilowatt hour when the wind turbines kick in. For coal plants a 2% reduction in efficiency translates into a 16% increase in carbon emissions. http://wvhighlands.org/wv_voice/?p=509
....I am a proponent of wind power where it makes sense. There are hundreds of turbines on the Iowa prairie where farmers are still able to till crops in very close proximity. There is very little land lost from production. But to deface entire ridgelines? Does that REALLY make sense? Go look for yourself and give the public the whole picture.
Thanks!"
Posted by: Christi | January 29, 2008 11:55 AM
Here is what David Friend of U.S. Wind Force had to say:
"Let me try to take some of the mystery out of the calculation for how many households can be served by a wind energy project. Let's go through the math.
There are several things you need to know:
How much energy will the project produce per year?
How much energy does the average household consume per year?
The real debate lies in the assumptions behind these two questions and around an understanding of what is being said. Typically, there are units attached to the numbers which are often left off, misconstrued or misunderstood. The correct unit for annual household electricity consumption is in kilowatt hours per year, which is abbreviated kWh/yr.
Due to their scale, the annual energy production from a wind farm is usually expressed in megawatt hours per year, which is abbreviated MWh/yr. There are 1000 kilowatt-hours in a megawatt hour, so we have to multiply MWh by 1000 to get kWh.
Let's do the calculation for annual energy production from the proposed wind farms on Meadow Mountain and Backbone Mountain.
The assumptions:
Number of turbines: 58+40 = 98
Turbine nameplate capacity : 2.4 MW per turbine (could be 2.0 - 2.5 MW)
Project nameplate capacity : 98 turbines x 2.4 MW = 235.2 MW
Annual net capacity factor (NCF): 25% - 35%, let's use 30% or 0.3
The math:
235.2 MW x 0.30 x 8760 hrs/yr = 618,106 MWh/yr or 618,106,000 kWh/yr
Depending on your assumptions of net capacity factor, the annual energy production could range from 515,088 MWh/yr to 721,123 MWh/yr.
Next, let's look up the annual electricity consumption for a "typical" household. An impartial reference is the U.S. Government's Energy Information Administration. Its data comes in several flavors based on the geographic region.
U.S. households : 10,656 kWh/yr
Middle Atlantic households : 7,799 kWh/yr
South Atlantic households : 13,763 kWh/yr
Unfortunately, none of these regions specifically addresses the annual electricity consumption per household in the state of Maryland. The debate can simply be over which number is more representative of the Maryland household or perhaps a Western Maryland household. Although the Middle Atlantic census region definition does not include the state of Maryland, it is perhaps the most representative - especially of Western Maryland. The South Atlantic census region includes the entire southeastern United States where household air-conditioning load is much higher, on average, than in Western Maryland. There can also be debate about the size of the average home, the average age of the structures, the number of family members per household, etc. In the end, it would be practical to assume that the average annual electricity consumption per household is probably somewhere between 7,799 and 13,763 kWh. For this calculation, let's use 10,000 kWh/household/yr.
Now, let's calculate the number of households that can be served.
Therefore, using our conceptual Meadow Mountain and Backbone Mountain projects with an installed project capacity of 235.2 MW and a 30% NCF, we decided that it would be reasonable to expect annual production to be about 618,106,000 kWh/year.
Obviously, you can come up with different answers depending on the assumption to make."
Posted by: David Friend, U.S. Wind Force | January 29, 2008 6:32 PM
The article brings up a good point that many do not consider. It seems as though each side has a different agenda with good arguments based on fuzzy math.
If you use wind power to supplement natural gas, the energy created is offsetting what needs to be created from coal fired plants. Put up enough wind turbines on mountain tops and sides where there are more wind forces and the more coal produced electricity is offset.
Am I missing something, because it seems like simple logic to me.
The real trouble is how much energy we consume. US is 4% of the worlds population, yet we use 27% of the worlds energy annually.
Some environmentalists make me laugh, its like you cannot win for losing. Environmental advocates protest wind farms and as a result use more coal fired energy.
To the environmentalists, if you need a cause worth protesting againist, take your fight to GM and the other major manufaturers and have them raise their mileage standards on SUV's or have the government raise the required efficientcy.
Did you know that 70% of Oil usage in the states is for transportaion purposes?
Posted by: John | January 30, 2008 11:54 AM
Wind energy should at least be built to the extent that existing natural gas plants can be throttled back when the wind is blowing. With wind now only 1% of the market, there's a long way to go before we have to worry about intermittency preventing further growth, or too many wind farms requiring us to build more natural gas plants. In the long run, Wind energy is cheaper than natural gas, is much cleaner than coal, creates jobs and keeps our money in the country rather than relying on foreign sources. If we are so concerned about looks why don't we complain about telephone poles versus underground wires? Telephone poles are ugly, close up, and everywhere you look. Apparently, “aesthetics” is determined largely by what you are used to. How a wind turbine farm looks on a distant ridge line should be the least of our worries.
Posted by: Norm Pettus | January 30, 2008 11:03 PM