Wind power has become booming business in the USA. Two sites totalling nearly 300 MWe have been installed in the Mid West USA, one at Lake Benton II in Minnesota, the other at Storm Lake in Iowa.

One of the fastest growing energy sources in the world is wind power, particularly in Europe, Asia and North America. Projected growth figures indicate that there could be over 30 GWe of installed wind power around the world by 2003, from the current level of about 12 GWe. The World Energy Council estimates that new wind generating capacity worldwide will total between 180 and 474 GWe by 2020. During the 1990s, wind power has been the fastest growing energy technology in the world, with an annual growth rate of a massive 22.6 per cent.

In the 12 months between July 1998 and June 1999, the USA saw a dramatic surge of activity in which wind companies added some 895 MWe of new generating capacity. In addition to this, more than 180 MWe of equipment was installed in repowering projects. Together, these projects represent an investment of over $1 billion. This growth has also been matched elsewhere in the world; in 1991, the European Wind Energy Association (EWEA) set a goal for European installations of 4000 MWe by 2000, but that target was reached in 1997.

In the USA, growth has been driven by the increased environmental awareness, by the improved cost-competiveness of wind power, and by the large potential resource capacity. A federal government study estimates that the resources in a 12-state region from North Dakota to Texas and from Wyoming to Minnesota are sufficient to generate 10 thousand TWh annually, or more than three times total US electricity use. To generate that much electricity from oil, 16 billion barrels a year would be required, or 60 per cent of the world total. The US government hopes to adopt a policy that will require electrical utilities to obtain 7.5 per cent of their energy portfolios from renewable sources.

Wind turbines are becoming increasingly cost-competitive. The cost of wind energy per kWh is down by 30 per cent from 1987, and kWh prices are expected to fall by a further 20-30 per cent over the next five years. According to Enron Wind, compared to wind turbines built in 1981, modern turbines generate 56 times the power at only 9 times the cost. According to the American Wind Energy Association, the cost of producing electricity from wind energy, when levelised over the life of the plant, has fallen from 38 cents/kWh in the early 1980s to 4-6 cents/kWh today.

At the Federal level, the expiration of the wind Production Tax Credit (PTC) on 30 June, 1999 has been a significant factor in this wind boom. The PTC provides a 1.5 cent/kWh, adjusted for inflation, incentive designed to level the playing field with conventional generating technologies.

More than half of this year’s new wind capacity in the USA was installed in two states: Minnesota and Iowa. Two new wind projects in the region by Enron Wind exemplify the trend. These projects are Lake Benton II, in Minnesota, and Storm Lake, Iowa.

Minnesota has abundant wind energy resources and has enacted legislation to encourage the use of wind energy.

Lake Benton II

Lake Benton II is a 104 MWe wind power facility which will produce 355 GWh. It is the third largest wind farm in the world.

In April 1998, Lake Benton Power Partners, a subsidiary of Enron Wind Corporation, signed a contract with Northern States Power (NSP) to supply NSP with 104 MWe under a 25-year power purchase agreement (PPA). Renewable energy forms 20 per cent of NSP’s output.

There are 138 wind turbines on the farm, the turbines being 750 kWe Z750 machines from Zond Energy Systems, the largest wind turbines manufactured in the USA. Ninety people were employed during construction, and NSP now employs 5 people on-site to operate and maintain the facility.

Zond’s Z750 series wind turbines use a variable speed, constant frequency configuration which allows a selectable power factor to be used, improves power quality and increases the aerodynamic efficiency of the turbines while at the same time reducing mechanical loads (see the panel on p55 for more details on this technology).

There are four phases of wind projects that are either built or planned at Lake Benton. When complete, the Lake Benton site will have a total capacity of 425 MWe, when the wind is blowing over 30 mph. The first phase at Lake Benton, Lake Benton I, was a 107 MWe farm with 143 turbines, and when built, it was the world’s first 100 MWe wind farm.

NSP plans to build 825 MWe of new wind capacity by 2012.

During the 2 years it took to develop Lake Benton I and II, NSP was involved in developing about 40 per cent of all new wind generation completed in the USA during that time.

The turbines are able to withstand hurricane loads of up to 131 mph as a once in 50 year occurrence, and up to 99.8 mph as a yearly occurrence.

NSP selected the Lake Benton site because it had one of the state’s highest and windiest locations – Buffalo Ridge, a glacial plateau in the south west corner of Minnesota. This location has an average wind speed of 16.1 mph, 2 mph higher than any of the other sites assessed by NSP.

The farmers involved in the project receive an annual payment for the use of their land. While the wind farm extends over a large area, but the actual footprint is very small. This makes wind power ideal to help farmers earn additional income.

Storm Lake

Storm Lake, located in Buena Vista and Cherokee Counties in north west Iowa, is a 193 MWe wind power facility that will produce 650 GWh per year, making it the single largest wind power project in the world today.

In March 1997, Enron Wind Corporation signed a 20-year PPA with MidAmerican (which has a total capacity of 8300 MWe) to provide it with 113 MWe of wind capacity. In July 1997, Enron Wind also entered into a 20-year PPA with IES Utilities, a subsidiary of Alliant Energy (with a total capacity of 5231 MWe), to provide IES with 80 MWe of wind capacity.

There were 150 people employed during construction, and 20-30 people are employed in ongoing O&M jobs.

The project uses 257 Zond Z-750 series wind turbines, identical to those at Lake Benton II. The turbines are certified for a 30-year fatigue life.

Construction began in October 1998, with completion in June 1999.