Northern Power Systems (NPS) of Waitsfield, Vermont, has developed an advanced 100 kW turbine specifically designed for cold climes. The Northwind 100 uses a direct drive low-speed generator, similar to the E-40 concept pioneered by German company Enercon, and advanced power electronics to compensate for the variable speed generator. The direct drive generator avoids the need for a transmission and, more critically in cold climates, for transmission fluid. According to the company's Lawrence Mott, this is a critical consideration as transmission fluids can easily thicken in sub-zero temperatures. The result is greater availability and less down time.
The nacelle is intentionally oversized, allowing a wind smith to service the machine in cold weather while protected from the elements. Mott concedes that packing advanced big-turbine technology into a smaller 100 kW package results in a more expensive turbine, but points out that off-grid turbines are competing with power prices that are far higher than grid-connected turbines, often around $0.20-0.30/kWh. He argues that the higher reliability in cold climates makes wind more attractive for this speciality market. "It's a very specialised machine," he says.
NPS is currently testing a prototype in Vermont with funding support from the National Renewable Energy Lab, the National Aeronautics and Space Administration (NASA) and others are scheduled to install a demonstration model in Kotzebue, Alaska, next year. Later, they hope to develop a simplified version for warmer climates and for the distributed generation market.
South pole biosphere
Meantime, the concept of off-grid wind power has taken on a new meaning since NASA, the US space agency, raised the idea of using winds on Mars to generate electricity on the planet (Windpower Monthly, June 1999). To test the feasibility of the scheme, NASA has been running an HR3 model from Northern Power Systems for a self-contained "biosphere" at the South Pole with co-funding from the National Science Foundation. The biosphere simulates the kind of quarters Mars explorers would need to live in. Since solar power would be blocked by Mars' red dust-and since launching a plutonium reactor from Earth is hazardous-wind is seen as a potential power source for human habitation. The Antarctic test was to see how well mechanical wind turbines could withstand temperatures as low as -80 degrees C. The experiment has been such a success that intallation of multiple Northwind units is on the cards. The HR3, or "high reliability" 3 kW turbine, has been in production since 1980. According to Mott, it may be the longest running production model in the wind industry. Over 300 have been sold, usually as part of a hybrid system with diesel or solar generators.
Atlantic Orient Corporation of Norwich, Vermont, has installed ten turbines in Kotzebue, Alaska, using their workhorse 15/50 turbine as part of the Turbine Verification Program being run by the US Electric Power Research Institute and Department of Energy (Windpower Monthly, July 1999). The 15 meter, 50 kW (at 11.3 m/s) turbine was developed as part of NREL's Advanced Wind Turbine program and 35 are now deployed in the US, Morocco, Canada, Scotland, Russia and Greece, says the company.
The 15/50 is designed for maximum utility and is relatively stripped down. It has no nacelle and a hub made of a single piece of cast iron. Recent improvements include an electromagnet to control the tip brakes, fed by a rotary transformer that transfers power to the blades.