UL certified the Skystream's inverter.. This is the first UL certification for an inverter that is built into a small-scale residential wind generator (10 kW or less). Electric utilities require UL certification for all inverters that feed power into the electric grid. The inverter inside Southwest Windpower's Skystream was granted UL certification for compliance with standard UL1741 / IEEE1547 after passing a series of tests. UL tests include anti-islanding, automatic power export cessation in response to grid variations, moisture immunity, electrical hazard risk elimination, safe operation during electrical surge, elevated temperature operation, and safe design and construction. UL certification helps improve the safety of the electric grid and also the safety of electrical line workers in times of grid failure, repair and maintenance.