The Great Lakes Zephyr - Wind Energy & Hydrogen Journal

Quoting This month's AWEA Windletter on how the cost of electricity is derived from operational figures for a utility scale wind plant:

"The main drivers that impact the cost of electricity from a wind plant are the following: the yearly amortized cost of building and maintaining the plant, divided by the amount of electricity produced.

This can be expressed through the following formula:
cents/kWh = (capital recovery cost + operations and maintenance cost)/ (kWh/year)).

Additional revenue streams, such as the production tax credit and a 'green' credit where available, further reduce the cost to the consumer that the wind farm owner must charge to gain a good return on investment.

Money In

In order to determine how much electricity a wind farm could produce, the first place to start is to get a good idea of the wind resource available. Since the energy in the wind is related to the cube of the wind speed [Power in the Wind (W/m2)= (wind speed)3 x ½(air density) x swept rotor area], small variations in the wind speed can lead to large changes in power output. For example, according to industry estimates from a couple of years ago, a wind farm at a site with wind speeds of 7.15 m/s (16 mph) would cost 4.8 cents per kWh, where one at a site with wind at 8.08 m/s (18.07) would cost 3.6 cents per kWh, a 25% reduction in cost.

In general, utility-scale wind farm developers look for wind speeds of greater than 7 meters per second (m/s, 15.66 miles per hour) at the height the generator will be placed. Wind speed measurement technology is improving, which helps developers more clearly define what the potential energy resource at specific sites and different hub heights will be.

Electricity production is also related to the swept rotor area, which is a factor of the square of the length of one blade. Since energy production is exponentially related to size, but the cost of the turbine is related linearly to size, the drive toward larger turbines has been one of the main factors behind wind power's dramatic reduction in costs.

Another main element in determining how much electricity a wind farm can produce is the reliability of the technology how much of the time the wind farm is available to operate. Where some of the early wind turbines that were installed in California were available to produce electricity less than a third of the time, today's technology is available to take advantage of good winds more than 98% of the time.

Money Out

After determining how much electricity a wind farm could produce, the next question is how much it will cost to build and maintain.

The benchmark figure that the wind industry uses to calculate costs for installing a wind plant is $1 million per megawatt of installed capacity. According to Gates, about 70% of a project's cost is the turbine itself. Other industry analysts confirm that about 10% goes toward legal and financing fees, and about 20% goes toward construction. In addition to the economies of scale related to turbine size discussed earlier, larger wind farms also bring economies of scale in construction and transaction costs. Assuming the same wind speed of 8.08 m/s, the same wind energy analysis as above estimates that a 3-MW wind farm would produce electricity that cost 5.9 cents per kWh, whereas a 51-MW wind farm would produce power for 3.6 cents per kWh, a nearly 40% drop.

A rule of thumb for operations and maintenance costs is about one-half to two-thirds of one cent per kWh generated.

The other main cost factor that must be put into the final cost of energy calculation is the capital recovery cost, or how much money needs to be returned to the debt and equity providers. For debt, the longer the term of the loan and the more secure the power purchase agreement, the lower the interest rates will be. For equity, returns vary with risk. According to Gates, because the technology is a relative newcomer, the perceived risk of a wind farm may be higher than the actual risks, which leads to higher requirements for returns on investment.

After calculating how much electricity the wind farm is likely to produce and how much it will cost to finance, build, and maintain it, one can get a good idea of what the electricity will cost to produce. Other revenue streams such as the value of the production tax credit and "green credits" help to provide an adequate after-tax income to the owner, while keeping the price of electricity low enough to compete with other resources.

In the best wind resource areas with the value of the production tax credit taken into account, wind has been reportedly selling on the wholesale market for prices less than three to four cents per kWh, a level that compares well with the cost of power from new coal or gas-fired facilities. "

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Clearly proper siting is imperative in being cost-competitive with fossil fuel and nuclear, but also clearly, there are plenty of sites within the U.S. that meet the siting requirements for energy density of wind power - including the Great Lakes.