For a 300 watt solar panel, you need anywhere between 500-1500 watt capacity inverter.However, the exact size you need will depend on the size of appliances you plan to use. Now let's discuss how you can calcula. When selecting an inverter for your solar panel system, follow a simple rule:choose an inverter with a capacity t. When picking an inverter for your 300 watt solar panel system, there are a few things to keep in mind. 1. Voltage compatibility:Ensure that the inverter is compatible with the voltage of your solar panel system. Fo. If you're planning to set up a small portable solar panel system for RVing/trips, consider investing in a portable solar power station. This is an all-in-one package that makes things simple. Just connect your solar panel to the power stati.