October 30, 2000
Researchers at Spain’s national energy center, CIEMAT, reported on a survey of small wind turbine technology at the European Wind Energy Association special topic conference in Kassel, Germany.
CIEMAT’s Ignacio Cruz summarized the status of small turbine technology based in part on measurements at the Spanish test field at Soria in the highlands northeast of Madrid, and in part on a survey of trade literature. Cruz, the manager of the Soria test field for stand-alone wind systems (Projecto de Sistemas Aislados con Energia Eolica), reached conclusions mirroring those posted by several small wind aficionados on the discussion group awea-wind-home during the past several years.
Importantly, Cruz found that small wind turbines today were developed principally by “handicraft,” and that the “maturity” of the technology is far below that of medium-size, grid-connected turbines. Neither conclusion will surprise denizens of awea-wind-home.
Small Turbines Cost More
The average cost of small wind turbines for stand-alone applications is also greater than that for grid-connected turbines, says Cruz. Currently costs range from 3,500 to 10,000 Euros/kW for stand-alone installations in contrast to the 1,000-1,350 Euros/kW for medium-size, grid-connected turbines. (1 Euro = US$1, though the value of the Euro relative to the US$ has declined significantly this year.) The average cost for the wind turbine alone (from 1,500 to 5,000 Euros/kW) is more than twice that for commercial wind turbines at 700 Euros/kW. The specific cost for small wind turbines range from 300 to 1,000 Euros/m2. The specific cost for commercial turbines is about 300 Euros/m2.
Small Turbines are Less Efficient
Cruz found that small wind turbines convert less of the energy in the wind to electricity than today’s medium-size commercial turbines. The maximum conversion efficiency of small turbines from 100 W to 5 kW varied from 0.22 to 0.31. In contrast, medium-size, grid connected turbines reach conversion efficiencies of 0.45.
The difference between the two technologies may be even greater. Cruz based his calculations on a survey of power curves found in trade literature. While the power curves for many commercial grid-connected turbines have been verified by international testing laboratories, very few–if any–power curves for small wind turbines have been independently verified. Power curves for many small turbines are inflated.
Measurements at the Wulf Test Field in California’s Tehachapi Pass found some power curves off by 15-20% at 28 mph and one wind turbine off by more than 30% at 15 mph. (See WindStats, Summer 2000, Vol. 13, No.3, pages 7-13.) The peak efficiencies for the five turbines tested varied from 0.20 to 0.26.
Room for Improvement
CIEMAT’s Cruz concluded that the market for small turbines looks promising, but the technology needs improvement. Cruz suggested improvements in reliability, and in passive regulation systems. He also found that “there is a lack of norms, standards, and guidelines” for stand-alone wind turbines that may retard development. Specifically, Cruz called for optimization of small wind turbine rotors and control systems with an emphasis on passive yaw and passive rotor regulation.
Few Test Fields Hinder Progress
Cruz decried the absence of test fields where the “performance and feasibility” of small wind turbines can be measured in accordance with internationally accepted procedures. Such test fields are essential, Cruz says, for optimizing and improving performance. Test fields are also critical for providing consumer confidence through standardized testing like that for medium-size, grid-connected turbines.
With such a frank initial assessment, CIEMAT’s small turbine testing program is off to a promising start. Time will tell whether subsequent technical papers will be as forthcoming with data on measurements of actual wind turbines tested in the winds over Soria.