The Vistabule comes pre-wired with a Zamp/GoPower-Solar on the Side Port wired directly to the battery bank. This is perfect for connecting a regulated (charge controller equipped) Zamp/GoPower-Solar on the Side Portable Solar Panel Kit. Because the Zamp/GoPower-Solar on the Side port is wired directly to the input side of the battery it needs to be fed with regulated power to avoid damage and to properly charge the battery. A Zamp/GoPower-Power on the Side panel has its own solar controller mounted to the panels so it can output the correct charging “recipe” to the battery. Typically, solar panels that connect directly to a solar generator are unregulated and the solar controller is built into the solar generator itself. Plugging this type of panel directly into the Zamp/GoPower port may cause damage to the electrical system and will not charge the battery properly. Having a solar controller wired between the panels and the battery is needed. The controller will also need to be set for the battery type/chemistry to properly charge the battery.  https://gopowersolar.com/solar-on-the-side/