The electrical system of the International Space Station is a critical part of the International Space Station (ISS) as it allows the operation of essential life-support systems, safe operation of the station, operation of science equipment, as well as improving crew comfort. The ISS electrical system uses solar cells to directly convert sunlight to electricity. Large numbers o. Each ISS solar array wing (often abbreviated "SAW") consists of two retractable "blankets" of solar cells with a mast between them. Each wing is the largest ever deployed in space, weighing over 2,400 poun. Since the station is often not in direct sunlight, it relies on rechargeable (initially ) to provide continuous power during the "eclipse" part of the (35 minutes of every 90 minute. The power management and distribution subsystem operates at a primary bus voltage set to Vmp, the of the solar arrays. As of 30 December 2005, Vmp was 160 volts DC (). It can change over.