Solar pool heating is a smart investment. Yet, partially sunny or rainy days are a challenge. If you use a manual valve to divert the water to your Enersol Pool Panels, you will need to close/open it every time temperature changes. Otherwise, you may be cooling your pool instead of heating it during a partially sunny day. It’s like using an air conditioner or furnace without a thermostat. With an auto control system, partially sunny or rainy days are no longer a problem.