I read that Powerwall can either be charged by solar or the grid, not both. I’m wondering why that is and what the difference would be in terms of wiring. I have an existing solar system installed many years ago. Do I need a Tesla solar inverter to charge the Powerwall with solar? Or will my existing grid-tie inverter work? As I understand it, the Tesla backup gateway should be sufficient to trick a grid-tie inverter into thinking that the grid is online. Any other considerations to keep in mind?