What happens to solar panels during a blackout?

The typical solar buyer discovers it the hard way after install: when there's a blackout, the system shuts off even with the sun shining. Why? And how to fix it. No marketing here.

The reason: anti-islanding

By law and for the safety of utility workers repairing the grid, all grid-tied inverters have anti-islanding: if the grid disappears, the inverter disconnects automatically. Otherwise, your panels would keep feeding energy and a lineman could be electrocuted.

Solutions to keep power during outages

• Hybrid inverter + battery: switches to island mode in milliseconds
• Dedicated backup system (Tesla Backup Switch, Enphase IQ System Controller)
• Solar coupled with automatic inverter generator
• Critical-loads sub-panel: backs up only essentials (fridge, router, lights) — cheaper

Cost of adding backup

If your system is new, adding backup costs $2,500-6,000 (hybrid inverter + 5-10 kWh battery + critical-loads panel). Whole-home backup runs $7,000-14,000 with automatic transfer switch and bigger battery.

Island mode: what you can and can't do

In island mode, your system supports everything within the inverter's limit (typically 3-8 kW). That means fridge, lights, TV, router, computer. What you can't: big central AC + pool pump + electric oven at once. You must prioritise.

If buying a battery with backup, read what battery do I need and compare with solar generator vs gas generator.