Normally, no A standard solar system shuts down when the grid goes down, even in bright sunshine, and even if you have a battery.
People find this out at the worst possible moment, so it is worth understanding before you buy.
Why it happens
It is a safety requirement called anti-islanding.
If the grid fails, engineers may be working on the lines. A house still pushing electricity out would put power onto lines they believe are dead. Inverters are therefore required to detect a grid failure and disconnect within a fraction of a second.
It is not a flaw. It is a deliberate protection and your installer cannot disable it.
Having a battery does not change it by itself
A common and expensive misunderstanding. A standard battery installation is still grid-connected and still shuts down with the grid.
For a battery to power your house in an outage, the system needs additional equipment that physically separates your house from the grid before supplying it.
What backup requires
An inverter with backup capability Not all have it, and it must be specified at the outset.
A changeover arrangement that isolates the house from the network before the battery starts supplying it.
Usually a dedicated backup circuit Most domestic backup arrangements power a selected set of circuits rather than the whole house: lights, sockets in key rooms, the fridge, the router. Running everything including an electric shower and an oven is a much larger and more expensive proposition.
Additional cost and additional installation work How much depends on the equipment and on how your consumer unit is arranged.
Deciding whether you need it
Probably worth it if:
- You are rural, or on a part of the network with frequent or long outages
- Someone in the house relies on powered medical equipment
- You work from home and an outage costs you money
- You have a freezer full of something you cannot replace easily
- You are already having a battery, so the increment is smaller
Probably not worth it if:
- You are in a town with a reliable supply and outages measured in minutes
- The cost would be better spent on more panels or more storage
Most of Britain has a fairly reliable supply. This is a real feature with a real cost, and for many households it is not the best use of the money.
What backup will and will not do
Will keep selected circuits running from the battery while it has charge, and on some systems recharge from solar during the day so it can run again that evening.
Will not run your whole house indefinitely, or power high-demand items unless specified for it. Check the power output in kW of the backup arrangement, not just the battery capacity. A battery with plenty of stored energy but limited output cannot run an electric shower.
What to ask
- Does this system provide backup in a power cut? If not, what would it cost to add?
- Which circuits would be backed up?
- What is the maximum power output while in backup?
- How long would it run typical household load?
- Does it recharge from solar during an outage?
- Is the changeover automatic, or does somebody have to do something?
- Does backup affect the battery warranty?
Raise this before quotes, not after. Retrofitting backup is more expensive than including it.