Clean power from a never-ending source

Mining Chronicle
June, 2007 Page: 118
By Dr Rovel Shackleford Optec Pty Ltd

In the 1990s, the California wind farm market began to be affected by the expiration or forced re-negotiation of attractive power purchase contracts with the major California utilities: Southern California Edison and Pacific Gas and Electric. And much of the existing inventory of 1980s wind turbines were really an albatross around the wind industry's neck. Renewal was needed, and - buoyed by "green power" initiatives in Colorado, Texas and elsewhere - US wind energy development resumed in 1999, with a much broader geographical base.

A variety of new wind projects were installed in the US in the late 1990s, including a cluster of Zond Z-40 turbines operated for a utility in southwest Texas, a wind plant of 46 Vestas machines planned for Big Spring, Texas, a 10-megawatt wind plant in northern Colorado, a number of plants in the upper Midwest, and the "re-powering" of some projects in California. Some of these involve foreign machines manufactured in the US. There's a sense that the industry is finally on the move again, with over 8,000 megawatts of new capacity planned for 2007/8 in the US alone.

The cost of energy from larger electrical output wind turbines used in utility-interconnected or wind farm applications has dropped from more than $1 per kilowatt-hour (kWh) in 1978 to under $0.05 per kWh in 1998, and is projected to plummet to $0.025 per kWh when new large wind plants come on line. The hardware costs of these wind turbines have dropped below $800 per installed kilowatt in the past five years, underpricing the capital costs of almost every other type of power plant.

It's difficult to accurately compare the costs of wind plants and fossil fuel plants because the cost drivers are so different. Low installed-cost-per kilowatt figures for wind turbines are somewhat misleading because of the low-capacity factor of wind turbines relative to coal and other fossil-fuelled power plants. ("Capacity factor" is simply the ratio of actual energy produced by a power plant to the energy that would be produced if it operated at rated capacity for an entire year.) Capacity factors of successful wind farm operations range from 0.20 to 0.35. These can be compared with factors of more than 0.50 for fossil-fuel power plants and over 0.60 for some of the new gas turbines.

However, the use of "capacity factor" is also misleading because wind has a "rubber" capacity factor that varies with the density of the wind resource. But that wind resource is constant for the life of the machine and is not subject to manipulation or cost increases. One reason why fossil fuels are so popular with investors is that many of the risks are passed on to consumers.

Fossil fuel shortages result in an increase in revenues for investors, who are actually rewarded for speeding the depletion of a non-renewable resource or not investing enough of their profits in support infrastructure, which drives up prices. If a big oil coal or gas company could start charging for the wind, they would make sure that wind energy development happened. In late 1996, with the purchase of Zond Systems by Enron (a now-defunct gas mining and distribution company), the possibility of this happening became very real. (Even though Enron proved to be a poor steward for the Zond technology, the subsequent purchase of what was one of the only viable Enron divisions by GE Energy in 2003 maintained US visibility in the large wind turbine market.)

Since the late 1970s the US cost goals for wind energy have continued to be about $0.04 per kilowatt hour, despite inflation. Wind turbines have consistently been able to arrive at that level, but by the time they get there, another reduction in the cost of nonrenewable fossil fuels has taken place and the bar is lowered further.

Cost per kilowatt hour figures of $0.04 or less (in 1998 dollars) are now commonly projected for advanced US wind turbines in 17 mph or better wind regimes, where capacity factors of over 0.40 can be achieved. That means that the wind energy cost goals of 1980 - which seemed daunting or impossible at the time - have been met many times over. (This fact should be remembered by those doubting the achievability of recently refigured cost goals, which are now closer to $0.025/kWh.)

The lower cost of energy from these advanced turbines is partly a result of higher efficiencies and rotor loading made possible by improved rotor design, shedding of fatigue loads provided by teetered hubs and flexible structures, and other innovations such as variable speed operation. But reduced weight and material usage and high reliability are perhaps more important factors in the cost equation. Costs of smaller systems vary widely, with installed costs from $2,000 to $3,000 per installed kilowatt. Energy costs for small turbines of $0.12 to $0.20 are still the norm in the US market.

Worldwide, there are 10 to 12 manufacturers of large, utility-scale systems, marketing 200kW to 3MW systems of various configurations, including three-bladed machines with full-span pitch control and two-bladed, stall control machines with teetering hubs. European manufacturers like Tacke, Micon, Vestas and Enercon have commercialised turbines with more conventional rotors, but featuring such important innovations as low speed generators and complete variable speed systems incorporating advanced power electronics. Recently, GE Energy (which purchased the wind division of defunct Enron) has adopted the European design philosophy in the US, with its merger of the technical expertise of Zond and Tacke.

One of the latest innovations being investigated in the US and Europe is the addition of a hinge at the nacelle tower attachment, allowing the turbine to "nod" up and down in response to turbulence and wind shear (the difference in wind speed at the top and bottom of the rotor disk). This configuration has been tested at Riso and promises substantial reductions in rotor and drive-train loads and in control system costs. A model intended for commercial development operated in California for several years and has been investigated by the National Wind Technology Centre. However, such innovations may not be necessary for wind to meet its cost goals for several years.

European wind turbine power ratings pushing two megawatts, Denmark's Riso Laboratories touting its new wind turbine airfoil designs (modelled closely after pioneering activities in the US.), and the U. S. company Enron marketing machines from both the U.S. and Europe, there is really very little difference between European and U.S. technology. The last remaining major area of controversy is the issue of two versus three blades for large wind turbines. Theoretically, a two-bladed machine should be less expensive and more efficient than a three-bladed one.

But considerable refinements are still needed to offset the greater stability and lower per-blade loads of three bladed designs. And the optical illusion of speed fluctuations and out-of-plane rotation associated with two-bladed machines makes them less attractive to some onlookers. Time will tell if one design will win out or if both will be able to exist in specific applications.

In the near future, wind energy will be the most cost effective source of electrical power. In fact, a good case can be made for saying that it already has achieved this status. The actual lifecycle cost of fossil fuels (from mining and extraction to transport to use technology to environmental impact to political costs and impacts, etc) is not really known, but it is certainly far more than the current wholesale rates. The eventual depletion of these energy sources will entail rapid escalations in price which - averaged over the brief period of their use - will result in postponed actual costs that would be unacceptable by present standards. And this doesn't even consider the environmental and political costs of fossil fuels use that are silently and not-so-silently mounting every day.

The major technology developments enabling wind energy commercialisation have already been made. There will be infinite refinements and improvements, of course. One can guess (based on experience with other technologies) that the eventual push to full commercialisation and deployment of the technology will happen in a manner that no one can imagine today.

There will be a "weather change" in the marketplace, or a "killer application" somewhere that will put several key companies or financial organisations in a position to profit. They will take advantage of public interest, the political and economic climate, and emotional or marketing factors to position wind energy technology (developed in a long lineage from the Chinese and the Persians to the present wind energy researchers and developers) for its next round of development.