g/solar • Posted by u/battery_backup_brad • 1 days ago

Tesla Powerwall 2 not charging from solar during grid outage — backup gateway config?

Installed a Tesla Powerwall 2 with Backup Gateway 2 last month. Works great during normal grid operation — charges from solar and discharges per the set schedule.

During a grid outage test, the Powerwall correctly switched to backup power. But the solar panels shut down and wouldn't produce, so the Powerwall didn't recharge from solar during the outage.

Is this a Backup Gateway configuration issue or is the solar inverter not islanding correctly?

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u/string_inverter_sarah • 1 days ago

Tesla Powerwall islanding with solar recharge is only fully supported with certain compatible inverters listed on Tesla's compatibility page. The Backup Gateway creates a micro-grid frequency reference, but the inverter has to support "grid-forming" operation to recognize it. If the inverter isn't on the approved list, you need a specific configuration change — or a different inverter.

u/solar_steve • 1 days ago

This is a common confusion: most grid-tied string inverters require a grid reference voltage to operate. When the grid goes down, they shut off per UL 1741. The Powerwall's islanding capability is supposed to provide that reference, but the Backup Gateway needs to be set to "self-powered" or "backup-only" mode correctly, and the solar inverter must be compatible. What inverter are you using? Not all inverters work with Powerwall island mode.

u/roof_mount_ray • 1 days ago

Also: the solar recharge during outage may be throttled intentionally. Powerwall limits solar input rate during island mode to match load consumption. If there's no load on the backup circuits during your test, it may appear that solar isn't charging, but it's actually limited to a very low rate. Try running a load during the test and see if solar production appears.