Cure for the Common Coal: Can Wind Power Replace Traditional Fossil Power?

It appears that the American people believe that they can have it all: protecting the environment, conserving their way to energy independence, growing / maintaining their personal standard of living, all while continuing to successfully compete in the global market. History proves otherwise: humankind’s existence from an energy perspective is characterized by two irrefutable facts: (1) our need for energy grows year after year and (2) our sources of energy continually move from low-density sources (i.e., our physical labor or those of animals) to high-density sources (i.e., super-critical fossil plants and nuclear power) to meet this growth. Both of these phenomenon feed one another: man’s inexorable, relentless need to improve his standard of living (i.e., replace his physical labor with that of machines) and a need to do this at the lowest possible cost, both in terms of physical resources and economic value.

Is it possible to achieve both objectives through “green energy” sources? While this is a question whose answer could fill many pages, it can be easily put into perspective by examining the energy density and efficiency of a traditional plant versus that of a wind turbine – a green source of energy about which we read daily in the paper. In other words: how many megawatts (Mws) per acre can be produced by a traditional fossil plant versus that of a wind turbine?

For a traditional fossil plant, I have assumed the design capacity of Tennessee Valley Authority’s Paradise Fossil Plant. This plant is unique in that it is a fifty-year-old facility, with full environmental controls, sited on 800 acres. It is capable of producing 2259 Mw. The acreage on which it sits includes coal fields, mines, rail access, and barge access. Even though all acreage is not used for generation, it conservatively provides a good proxy for the total acreage used by such a facility to fully meet its generation capability. It is a matter of simple arithmetic to calculate the energy density utilization: 2259 Mw / 800 acres equals 2.82 Mw per acre.

For wind power, the calculation is not as straightforward. Few wind power farms exist. However, the following information is provided by Wind Watch (http://www.wind-watch.org/). “For best results, [wind turbines] require 10 rotor diameters of clearance in the direction of the wind and 3 rotor diameters in every other direction. In a line of several turbines perpendicular to the wind (as on a mountain ridge), the GE 1.5 Mw model would need at least 32 acres and the Vestas V90 78 acres for each tower. In an array that can take advantage of the wind from any direction, the GE needs 82 acres and the Vestas V90 needs 111 acres. In practice, the area used varies, averaging about 50 acres per Mw of capacity.” Assuming this is true, the energy density for wind is 1 Mw / 50 acres which equals 0.02 Mw per acre.

Historical US energy consumption, population, and gross domestic product data is published by the Energy Information Administration. The attached graphic shows this information through 2005, the last year for which complete annual data has been published. Based on this data, one can calculate the average annual energy consumption per person over the complete historical period to be 0.465 billion BTUs. Using a conversion factor of 3415 BTU per kilowatt-hour, this is equivalent to 136,164 kw-hr per person. This is equivalent to 0.0155 Mw-year per person. In other words, a generator of 0.0155 Mw capacity operating continuously for one year would produce the quantity of energy consumed by one person to meet his or her personal energy requirement and produce his or her contribution to the country’s GDP.

Using this information we can answer the energy density question. For a traditional power plant, 0.016 Mw/2.82 Mw per acre or .0057 acres (247 square feet) per person is required to meet a person’s energy consumption requirement. For a wind turbine, 0.016 Mw/0.020 Mw per acre or 0.8 acres (34,848 square feet) per person is required to meet a person’s energy consumption requirement. Alternatively, 1 acre of pristine forest used for coal generation, at 100% capacity, will support 176 people; whereas, the same forest used for wind generation would support 1.25 people at 100% capacity.

The above analysis assumes that both wind and fossil generators operate continuously. In fact, a typical wind turbine operates approximately 20% to 30% of the time at its rated capacity. An excellent capacity factor is 40%. This compares to a typical capacity factor of 70% to 80% for a fossil plant. Considering these factors, 1 acre of land used for a fossil plant (70% capacity factor) would support 123 persons. The same acre used for wind generation (40% capacity factor) would support 0.5 people.

So the next time you think about supplying the energy needs to 100,000 people, you should consider the environmental consequences of building an 800 acre fossil plant or denuding 200,000 acres of pristine forest (assuming the wind is blowing).