At this time, the Wind for Schools program suggests the use of a Skystream 3.7 turbine as it is one of the only a few SWCC certified small wind turbines on the U.S. market. This provides a considerable level of reassurance in quality and reliability. It is a residential scale turbine, so it will not make a significant impact on reducing your school’s electric consumption from the utility, but it will provide a very tangible wind energy experience for your students and the data generated can be used in numerous classroom activities. Thanks to the Colorado WAC for pulling together most of the additional information about the Skystream for your reference.
Additional notes of significance on this turbine are:
- The Skystream is a grid-connected turbine that is UL 1741 certified
- The data acquisition system for the Skystream is configured to allow connection to the OPenEI Wind for Schools Portal http://en.openei.org/wiki/Wind_for_Schools_Portal. Data from WfS Host School turbines is available for public use from this website.
- The turbine comes with a five-year limited warranty. The expected life of the turbine is 20 years.
- The turbine has an integrated inverter that is built into the nacelle so a separate inverter is not required.
- The survival wind speed is 140 mph.
- More information about the Skystream can be found at the XZERES Website.
- The Skystream is a popular residential wind turbine. It was designed in partnership with the U.S. Department of Energy’s National Renewable Energy Laboratory. The turbine generates electricity that feeds back into the electrical system of the building on the customer’s side of the electric service, so it offsets the electricity used in the building. In Pennsylvania, there is a net metering law that requires the utilities to connect up to a 3 MW renewable power supply to the grid.
- The Skystream 3.7 has a rotor diameter of 3.7 m (12 feet). At a wind speed of 29 mph, the turbine generates 2.4 kW of electric power, but it will often generate less than this as the wind is a constantly changing resource.
- Wiring for the turbine is run up through the core of the tower. The tower height recommended will depend on the local wind resource as well as the height of other elements of the landscape near the installation. It is ideal to have the turbine be at least 30 ft above the highest object (especially from the prevailing wind direction). As mentioned on the funding page, the tower height is a cost factor. This for both the tower itself as well as for the foundation required.
- The turbine is a downwind design so that the blades of the turbine are downstream from the nacelle, which is inherently better at finding the wind direction than upwind designs. The curved shape of the blade helps make this a very quiet machine.
- The inverter constantly monitors the turbine and the electrical connection to assure that the electric energy generated by the turbine synchs with the frequency and voltage of the building’s electrical system. The inverter actually draws about 5-7 watts to operate the monitoring system. Because of this, the turbine will not generate electricity when the electrical grid to the building is down. The inverter is UL 1741 certified which means that it meets UL standards for islanding protection, frequency synchronization, flicker, and the ability to withstand surges.
- The alternator includes of 42 sets of powerful rare earth magnets. The motion of the rotor within the stator generates electricity, but there is no transmission or mechanical braking required. The only moving part is the stator hub. The inverter senses the need for braking and uses the repelling action of the magnets to slow the turbine, much like the regenerative brakes on a hybrid vehicle (but in reverse). Once the winds are strong enough to get the turbine up to speed, the inverter keeps the speed of the turbine between 300 and 340 rpm.
- The blades are constructed from two halves of compression molded fiberglass. The curve of the blade helps to more efficiently capture the energy in the wind and to reduce the sound of the the blades as they move through the air.
- Because of the many features incorporated in the turbine and blade design, the Skystream emits about 45-55 dB at 50 feet from the base of the tower. Background sound level is usually between 30 and 45 dB. Because sound perception at a receptor is measured on a logarithmic scale, a perceived doubling of sound is represented by a difference of 10 dB. Much of the sound generated by the turbine is masked by the wind itself. Sound decreases significantly with distance from the source. Doubling the distance from the turbine decreases the sound level by a factor of four. For example, sound level readings at 50 feet from the turbine hub drop by a factor of 4 at 100 feet. Learn more about the acoustic measurements from the Skystream from its IEC Certification, beginning on p. 30.
- While the Wind for Schools program is willing to provide some technical assistance for schools that choose to install a different turbine, we are in a better position to assist with the fund raising, data collection, and educational integration of the Skystream. If you already have another wind turbine installed and are interested in becoming an Affiliate Program, please view the DOE’s Wind for Schools Affiliate Projects Website.