The Boulder 15M collect 15 watts of power from the sun, and stores power with the Escape 150 or Sherpa 50 power packs (sold separately) for use anytime. The solar panel can charge the Escape 150 in about 10 hours, and the Sherpa 50 in about 4 hours. Use the stored solar power with your USB or 12V devices. On the mountain or at the beach, the Boulder 15M goes wherever you do to help charge your power packs, to keep you connected to your digital life.