Someone drives up to your house, cracks your Wi-Fi password, and then…

No. It’s not really possible to crack WiFi passwords these days with WPA-3. Also the overlap between electronic vulnerabilities and physical security is low. Remote vulnerabilities? Back doors? Yes, very worried. Someone coming to my house with advanced hacking tools, skills to attack my inverter? No.

This is not a problem with the solar power system per se, this is an issue with the terrible state of security in IOT and "smart home" devices. Observers of IOT have been noting for a long time the various ways a malicious person could access the devices and cause real harm.