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Large Wind Turbines

June 1, 1999
Paul Gipe

Latest Data from Germany's 250 MW Measurement Program 1999

An edited version of the following article appeared in the Autumn 1999 (Vol. 12, No. 4) edition of WindStats.

The latest in a series of annual reports on a German test program opens a public window on the long-term technical and financial performance of wind energy in the world's most dynamic market for wind turbines. The report on Germany's pioneering "250 MW" program has been issued by the Institut für Solare Energieversorgungstechnik (ISET) in Kassel.

Outside the German program, data on the cost, profitability, and technical maturity of wind energy technology is considered proprietary and in most countries a carefully guarded secret. ISET, and Germany's Ministry for Economics and Technology which funds the program, clearly understand the value of the data to the international wind community. While the report is in German, each section includes a summary in English for wind energy professionals outside Germany. It would be quite extraordinary if NREL in the United States or NEL in Great Britain presented reports in English with German, French, or Spanish summaries.

Like its predecessors, the 1998 annual report for the Scientific Measurement and Evaluation Program (Jahresauswertung 1998, Wissenschaftliches Meß und Evaluierungsprogramm zum Breitentest 250 MW Wind, or WMEP 1998) was prepared by ISET's wind energy bureau and is a treasure trove of data on how wind turbines actually perform in the field.

The test program was launched with subsidies for an initial 100 MW of wind turbines in June 1989. With German reunification and the unexpected popularity of the subsidy, the government expanded the program to 250 MW in 1991. Despite its name, the program includes 350 MW of nameplate capacity from about 1,500 wind turbines. These machines generated more than 700 million kWh last year. The capacity in the test program represents about 12% of that installed in Germany at the end of 1998.

Annual wind generation in Germany, a nation with 80 million people and the world's third largest economy, reached 4.5 Terawatt-hours in 1998, 1% of supply. In the land of Schleswig-Holstein wind generation produced nearly 13% and in Niedersachsen, one of the country's more densely populated states, produced almost 3%.

ISET found the probability that wind generation would rise or fall by 10% over any given period was less than 1%, alleviating utility concerns that dramatic fluctuations in the wind would cause grid instability.

Lightning still proves to be the most troublesome form of unscheduled down time though most new wind turbines are now equipped with lightning protections systems. Depending upon the level of thunderstorm activity from year to year, operators can expect 5 to 10 incidents per 100 operational years. Turbines installed in Germany's central highlands are twice as likely to be hit by lightning as those on the North German Plain or those in coastal locations.

Nearly half of all new turbines are being installed in the interior in contrast to the coastal locations that dominated the German industry just a few years ago. This trend is expected to continue and consequently outages from lightning and icing are becoming increasingly important.

Icing events are four times more likely in the low mountains of the central highlands than along the North Sea coast. These events also last four times longer in the highlands than along the coast. Combined, icing causes 20 times more downtime in central Germany than in the north near the coast.

Significantly, wind turbines in the WMEP program were available for operation 99% of the time. No doubt this finding will chagrin some manufacturers, regulatory authorities, and research organizations in North America who have publicly suggested that the availability of new and therefore "modern" wind turbines between 90% and 95% is not only acceptable but considered "good". This difference in expectations on one side of the Atlantic and actual operating experience on the other is even more striking after realizing that most of the turbines in the WMEP program are not new. Most of the turbines in the program where installed in the early and mid 1990s. The average age of turbines in the German test program is about six years.

To date there's no evidence that the increasing age of the program's fleet has led to increasing maintenance costs. The cost to operate, maintain, and insure the turbines in the program during 1998 ranged from 24 DEM (US$14.5) per kW of capacity for contemporary machines in the 770-850 kW class to 62 DEM (US$37) per kW for older, smaller machines. Turbines in the MW class, those 980-1050 cost slightly more to operate, maintain, and insure at DEM 35 (US$21) per kW than turbines in the 770-850 kW class.

Megawatt class machines doubled their share of the German market in 1998 from that in 1997. Nearly half the turbines installed last year were turbines rated at more than 1 MW. Nearly all the remainder installed were turbines rated from 500 kW to 1 MW. By the end of 1998 there were 430 turbines greater than 1 MW operating in Germany. These machines represented 560 MW or 20% of the 2,850 MW installed nationwide.

Enercon continues to dominate the German market followed by Nordex Balcke-Dürr and Vestas. Enercon alone accounted for one-third of new capacity 810 MW installed in 1998. Nordex installed 16%, Vestas 14%, AN Bonus and Tacke 9% each, NEG Micon 8%.

Unlike other wind energy markets in the world, the German market is so dynamic and diverse that it can support several second tier manufacturers such as DeWind (3% or 24 MW), and Südwind (2.4% or 19 MW). There are also a host of innovative third tier manufacturers who are trying to capture niche markets. They accounted for 6.4% of the German market or some 50 MW. In many countries, for example France, Great Britain, and the Netherlands, installing 50 MW in any one year from domestic manufacturers would be quite an accomplishment. In the German market they fall into the "andere" or "other" category.

And if there's any question about the direction of wind technology, the WMEP report puts it to rest. In 1998 two-bladed wind turbines accounted for 40% of the German market. These were principally supplied by the Dutch manufacturer Lagerwey. In 1989 nearly 20% of all wind turbines were downwind. By 1995 all new turbines installed in Germany used rotors upwind of the tower and by 1997 all new turbines used three blades. What was once called the "Danish" design of stall-regulated, upwind, three-bladed turbine accounted for 40% of the new turbines last year. The remainder used pitch-regulated, three-bladed, upwind rotors. Yet despite Enercon's dominance of the market, two-thirds of the turbines installed in 1998 used induction generators. However, the use of variable speed operation is steadily, but only modestly, increasing. Last year 46% of new turbines operated at variable speed, up slightly from 43% in 1997.

Some 50% of the wind turbines or 36% of the installed capacity is owned by private individuals, mostly farmers. Only in Denmark are there as many individuals owning and operating wind turbines as in Germany. Assuming that installed capacity is worth about US$1500 per kW, German farmers own a staggering US$1.5 billion.

Almost one-third of the turbines in the WMEP program contribute directly to their owners's electricity consumption. Of the 700 million kWh produced by turbines in the program, 2% was used on site. The wind turbines themselves consumed 1.6 million kWh or only 0.2% of the electricity they generated.

ISET reports that utility caused outages caused 6.8 hours of downtime for the typical wind turbine in the WMEP program.

Of interest to those monitoring projections of annual generation from new turbines in new wind regimes, such as the upper Midwest of the United States, is annual specific yield of turbines in the WMEP program. Annual specific yields for the best turbines at the best sites in Schleswig-Holstein, that is on the North Sea Coast, don't exceed 1,250 kWh per square meter of rotor swept area. (See WindStats Vol. 12. No. 3, Summer 1999)

ISET projects that the average purchase price per kWh for wind-generated electricity in Germany will drop from DEM 0.1679 (US$0.10) in 1998 to DEM 0.1652 (US$0.099) this year. This is a slight decline from the high of DEM 0.1728 (US$0.104) per kWh in 1995.


The WMEP offers page after page of valuable data from the world's most comprehensive wind turbine monitoring program.

ISET's report on the WMEP program offers 422 pages of valuable data from the world's most comprehensive wind turbine monitoring program. Copies of WMEP 1998 can be purchased for DEM 30 from ISET, Königstor 59, D34119 Kassel, Germany; +49 561 72940; fax: +49 561 7294 100.

Disclosure: Paul Gipe has consulted to NRG Systems, SeaWest, USDOE, NREL, NASA, AWEA, KWEA, DGW, the Izaak Walton League, the Minnesota Project, and written for numerous magazines. From 1984 to 1985 he worked for Zond Systems.

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