Updated
The Panels Do Nothing In A Power Cut
The sun is out, the array is on the roof, and the house is as dark as everyone else's.
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What's happening?
This surprises almost every new owner, and it is designed behaviour rather than a fault. A grid-connected inverter is required to disconnect the moment it loses the mains, and to stay disconnected until the supply has been stable for a set period. The reason is people rather than equipment: if inverters kept generating into a dead network, they would energise cables that engineers are working on believing them dead. That automatic disconnection, and the delay before reconnecting, is part of the connection standards every domestic inverter is built and commissioned to. So a standard solar system without storage produces nothing during an outage, and a standard solar-plus-battery system usually does the same, because supplying the house while the grid is down needs specific backup hardware that separates your circuits from the network first. If you want power in an outage, that has to be designed in — and it is normally a defined set of circuits, not the whole house.
What usually causes it?
- A standard grid-tied inverter, which must disconnect when the mains fails
- A battery installed without any backup or islanding capability, which is the common configuration
- Backup hardware fitted but never commissioned or tested
- A backup circuit that only covers selected sockets, which the household was never shown
- An inverter still in its reconnection delay after the supply returned
- Backup capability limited by the battery's output, so a shower or oven trips it immediately
Is it dangerous?
The disconnection is a safety feature protecting network engineers, and nothing should ever be done to defeat it. The genuinely dangerous version of this problem is a generator or an improvised connection wired into the house during an outage without proper isolation, which can push power back into the street. If you need power during outages, it has to be designed and installed as backup, not improvised.
Can I fix it myself?
Understand what you have before the next outage rather than during one. Check your documentation or ask your installer whether the system includes any backup function, and if it does, find out which circuits it covers and how it starts. After a cut, give the inverter time — a delay before reconnecting is normal, so an inverter that is dark for a while after power returns is not necessarily faulty. If it is still dark hours later, that is worth a call.
When should you call a solar installer?
Call a solar installer if you want backup capability added, since it needs the right inverter, a battery capable of supplying the load, and a changeover arrangement that isolates you from the network. Also call one if you were told your system has backup and it did not work in an outage, or if the inverter has not come back long after the supply returned.
What will the solar installer actually do?
- Confirm whether the existing inverter and battery are capable of supplying the house when isolated
- Design a backup arrangement covering defined essential circuits, sized to the battery's output
- Install the changeover and protection that keeps your generation off the network during an outage
- Commission and physically test the backup by simulating a supply failure
- Confirm the installation still complies with the connection requirements notified to the network operator
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