Solar Panel 30W with cable. As a general rule, you will need 10 watts of power for each output joule of your fence energizer. For example: 3-joule energizer = 30 watt solar panel. PER WEB:Recent improvements in efficiency and new lower costs have made powering your fence with solar power affordable and easy. Simply match the size of the solar panel with your energizer.Our Solar Panels have a rugged aluminum frame, polycrystalline panel and approximately 18" cable. Five year manufacturers warranty.