The Solar Charging Optimization Module is an external maximum power point tracker (MPPT) and when installed properly, actively monitors and optimizes the energy source to maximize power input, resulting in up to 40% faster charge times, especially from solar panels. Compatible with Yeti X and Yeti Lithium Power Stations 1000W and up. Compatibility Note: All Yeti X Power Stations feature integrated MPPT charging. For the X line, Yeti MPPT Module is only recommended for additional solar input capability. NOT compatible with X line power supplies, only compatible with Yeti LI power supplies. Usage Note: The YETI LINK EXPANSION MODULE and YETI LITHIUM MPPT SOLAR CHARGING OPTIMIZATION MODULE use the same expansion bay therefore they are unable to be used at the same time.