Saturday, October 11, 2008

Wind energy myths on the grid

Michael Goggin has written a paper for the trade group American Wind Industry Association titled "20% Wind Energy by 2030: Wind, Backup Power, and Emissions". It is an attempt to claim -- in the face of conflicting evidence and reason -- that wind energy, even at substantial "penetration", does not require extra "backup" capacity and substantially reduces carbon emissions from other fuels.
The "no reduction in emissions" myth

Wind opponents sometimes argue that wind energy doesn't actually reduce the fuel use or harmful emissions of other power plants. On its face, this claim does not make sense: utility system operators must precisely balance the total supply of electricity with the total demand for electricity at all times, so the electricity produced by a wind plant must be matched by an equivalent decrease in electricity production at another plant.
The unstated part of that equation is that a decrease in electricity production does not necessarily mean an equivalent decrease in fuel use or emissions. In other words, a thermal plant simply diverts its steam past the turbines, but it doesn't stop creating steam. That is because it may take several hours to reheat. Plants that can switch on faster must use more fuel to do so (like stop-and-go city driving versus steady highway driving). Plants that can modulate their electricity production do so by operating at a lower efficiency, i.e., with more emissions.
• In 2007, wind energy in the U.S. reduced CO2 emissions by over 28 million tons, equivalent to taking almost 5 million cars off the road. On average, each Megawatt- hour (MWh) of wind energy -- the amount produced by two typical modern wind turbines in an average hour -- reduces CO2 emissions by 1,200 pounds.
There is no citation for this claim, because it based only on the above assumption that reduction of electricity production is the same as reduction of fuel use is the same as reduction of emissions. It is not based on actual data.
• The U.S. Department of Energy's (DOE) 20% Wind Energy by 2030 Technical Report calculated that obtaining 20% of our electricity from wind energy by 2030 would [emphasis added] cut cumulative CO2 emissions by over 7.6 billion tons.

• The DOE report found CO2 emissions would [emphasis added] be reduced by over 825 million tons in the year 2030 alone, an amount equal to 25% of all electric sector carbon dioxide emissions in that year -- the equivalent of taking 140 million cars off the road.

• The DOE study also found that wind energy would [emphasis added] cut the amount of natural gas used for electricity generation by 50% in 2030.

• A study by the grid operator in Texas found similar results, concluding that adding 3,000 megawatts (MW) of wind energy to the state's grid would [emphasis added] reduce CO2 emissions by about 5.5 million tons per year, sulfur dioxide emissions by about 4,000 tons per year, and nitrogen oxide emissions by about 2,000 tons per year.

• In regions where a large share of electricity comes from coal power, the emissions savings of wind energy can be [emphasis added] even larger. A DOE analysis found that Indiana could [emphasis added] reduce CO2 emissions by 3.1 million tons per year by adding 1,000 MW of wind power.

• The 30 MW Kaheawa wind plant in Hawaii directly offsets power from oil-burning power plants, reducing oil imports by almost 10 million gallons per year.
The company web site cited for this statement actually says: "Kaheawa Wind will [emphasis added] eliminate the use of over 236,000 barrels of oil or 69,000 tons of coal annually." (236,000 barrels = 9,912,000 gallons.) So again, offsetting the electricity production (which is rarely all oil or all coal based) is not the same as reducing fuel use or emissions, and thus it is not actual data cited but conjecture based on incorrect assumptions. In short, these are made-up numbers that have a shaky relationship with reality.
The "backup power" myth

Sometimes wind opponents claim that because wind energy output varies with the wind speed, wind plants require an equivalent amount of "backup power" provided by fossil fuel plants, negating the environmental and fuel savings benefits of wind energy. Understanding why this myth is false requires some explanation of how the electric utility system operates.

Overview of Power Grid Operations

System operators always maintain significant "operating reserves," typically equal to 5-7% or more of total generation. These reserves are used to deal with the rapid and unpredictable changes in electricity demand that occur as people turn appliances on and off, as well as the very large changes in electricity supply that can occur in a fraction of a second if a large power plant suffers an unexpected outage. Instead of backing up each power plant with a second power plant in case the first plant suddenly fails, grid operators pool reserves for the whole system to allow them to respond to a variety of potential unexpected events.
That is exactly why wind energy facilities can not claim to be replacing other sources. Because wind energy production is intermittent and highly variable -- and typically a small percentage of total generation -- the facilities are like "negative demand" to the grid, balanced by the operating reserves.
System operators use two main types of generation reserves: "spinning reserves," (regulation reserves plus contingency spinning reserves) which can be activated quickly to respond to abrupt changes in electricity supply and demand, and "non-spinning reserves," (including supplemental reserves) which are used to respond to slower changes. Spinning reserves are typically operating power plants that are held below their maximum output level so that they can rapidly increase or decrease their output as needed. Hydroelectric plants are typically the first choice of system operators for spinning reserves, because their output can be changed rapidly without any fuel use. When hydroelectric plants are not available, natural gas plants can also be used to provide spinning reserves because they can quickly increase and decrease their generation with only a slight loss of efficiency. Studies show that using natural gas plants or even coal plants as spinning reserves increases emissions and fuel use by only 0.5% to 1.5% above what it would be if the plants were generating power normally.

Non-spinning reserves are inactive power plants that can start up within a short period of time (typically 10-30 minutes) if needed. Hydroelectric plants are frequently the top choice for this type of reserve as well because of their speedy response capabilities, followed by natural gas plants. The vast majority of the time non-spinning reserves that are made available are not actually used, as they only operate if there is a large and unexpected change in electricity supply or demand. As a result, the emissions and fuel use of non-spinning reserves are very low, given that they only rarely run, the fact that hydroelectric plants (which have zero emissions and fuel use) often serve as non-spinning reserves, and the very modest efficiency penalty that applies when reserve natural gas plants actually operate.
There are two important things to note here. First, no-carbon hydro and low-carbon gas are the sources most likely to be used to balance the fluctuating feed from wind turbines. Yet, the industry always compares the equivalent carbon from coal, oil, or automobiles, when any carbon savings would actually be minimal. Second, since wind must be balanced as "negative demand", those other plants would have to be used more. In the case of gas, that means more carbon emissions, not less.
Accommodating Wind Energy

Fortunately, the same tools that utility system operators use every day to deal with variations in electricity supply and demand can readily be used to accommodate the variability of wind energy. In contrast to the rapid power fluctuations that occur when a large power plant suddenly experiences an outage or when millions of people turn on their air conditioners on a hot day, changes in the total energy output from wind turbines spread over a reasonably large area tend to occur very slowly.

While occasionally the wind may suddenly slow down at one location and cause the output from a single turbine to decrease, regions with high penetrations of wind energy tend to have hundreds or even thousands of turbines spread over hundreds of miles. As a result, it typically takes many minutes or even hours for the total wind energy output of a region to change significantly. This makes it relatively easy for utility system operators to accommodate these changes without relying on reserves. This task can be made even easier with the use of wind energy forecasting, which allows system operators to predict changes in wind output hours or even days in advance with a high degree of accuracy.

Moreover, changes in aggregate wind generation often cancel out opposite changes in electricity demand, so the increase in total variability caused by adding wind to the system is often very low. As a result, it is usually possible to add a significant amount of wind energy without causing a significant increase in the use of reserves, and even when large amounts of wind are added, the increase in the use of reserves is typically very small.

The conclusion that large amounts of wind energy can be added to the grid with only minimal increases in the use of reserves is supported by the experience of grid operators in European countries with large amounts of wind energy, as well as the results of a number of wind integration studies in the U.S.
Actually, the experience in Europe is the opposite of this claim. As wind "penetration" increases, the ability of existing reserves to balance it quickly diminishes and more excess capacity has to be added. See for a summary. The fact is that the wind doesn't always blow, even over a whole continent at the same time. Therefore, the grid has to be built as if the wind isn't there, because so often it won't be. And with the wind turbines added in, the grid needs even more capacity -- and more high-voltage interconnection lines -- to balance that energy.

The bottom line is that very little can be achieved with large-scale wind power on the grid. It simply adds expense and impacts without replacing other expenses or impacts to any degree that can justify it.

tags: wind power, wind energy, wind turbines, wind farms, environment, environmentalism