The American patent was awarded to long-bankrupt US wind company Kenetech in 1993, and in 1995 the company sued Enercon for infringing it. A year later, Enercon technology was banned from America by the US International Trade Commission. Enercon lost a major wind plant order for Texas as a result. Since then the patent has changed hands four times among American companies, most recently being bought by GE from Enron as part of its purchase of Enron Wind last year. The much sought after intellectual property has been the subject of countless appeals and counter appeals; Enercon even counter sued Kenetech in 1997 for "losses sustained" and for abuse of the legal process, but to no avail.
It is not the technology itself, but its combination in a "unique and unusual" way that is patented according to the US Patent Office, a division of the US Department of Commerce. Enercon has consistently argued that the patent granted to Kenetech was for technology already in the public domain -- citing a wind technology text book from 1989. Such "prior art" that is publicly available cannot be patented, says Enercon. Its arguments have consistently been turned down by the American patent authorities and the courts.
The European patent, which is based on US patent 5,083,039, was granted to Enron Wind in late 1998. It is applicable in 17 countries. Enercon says its turbines do not use the same power factor control and power conditioning techniques specified in the patent.
The electronics at the heart of the dispute are essential for operation of variable speed wind turbines. Despite their extra complexity compared with stall or pitch controlled models, they have been gaining in popularity. Nearly all wind turbine suppliers today offer some form of variable speed option. The economic advantages, if any, of variable speed technology are project specific, but it is generally held that for large penetrations of wind power on electricity systems they offer greater versatility for meeting utility criteria for grid stability.