Hybrid inverters: what they do, and when to switch

Most people ask about one when an old inverter fails. You need a new inverter anyway, so should it be a hybrid solar inverter? Here’s what a hybrid does, when it’s the right choice, and what to check before you switch.

Panels make direct current (DC); your home runs on alternating current (AC). On most UK homes a single string inverter converts one to the other, and that’s all it does.

A hybrid also manages a battery. One inverter maker calls it a single “brain” for the panels and the battery. It can:

• store spare solar power instead of exporting it all;
• run the house from the battery when the panels aren’t generating;
• charge the battery from the grid at cheap times on a time-of-use tariff;
• on some models, power a socket or some circuits in a power cut, if wired for it. See do solar panels work in a power cut?

Inverters wear out long before panels. The Energy Saving Trust advises replacing a solar inverter after around 12 years, so many systems from the feed-in tariff years are due one now. See how long do solar inverters last?

A hybrid usually makes sense when:

• the old string inverter has failed, or is 10 to 15 years old and logging faults, and you want a battery now or later: you’re buying an inverter anyway, and won’t replace it again when the battery goes in;
• you’d rather have one box, one app and one set of settings.

An AC-coupled battery is often better when:

• your inverter is young and working well, so there’s no point replacing it;
• you have microinverters, so there’s no central inverter to swap;
• you’re on the feed-in tariff and want to charge from the grid (see below).

The downsides of AC-coupling: a little more conversion loss, two inverters to look after, and more combined output for your network operator to consider.

Your FIT generation payments come from the generation meter, and Ofgem expects it to measure only electricity your panels generate.

• Changes are allowed. Ofgem says you can repair or replace equipment, or add a battery, without affecting your accreditation, as long as the installation still meets the scheme rules.
• Tell your FIT supplier. Ofgem says you must tell them when a battery is connected, when a generation meter is replaced, or when it starts measuring electricity the panels didn’t generate. Expect to send a wiring diagram, meter readings and whether the battery can charge from the grid.
• Why a hybrid needs care. The battery shares the solar inverter, so its output passes through the generation meter. Ofgem’s examples show payments can continue if the battery charges only from the panels, or if the generation meter is an approved bi-directional meter that works out the net figure itself. Where the battery charges from the grid through standard meters, its example says generation payments could not be made.
• An AC-coupled battery is usually wired in after the generation meter, so the meter still records solar only.
• Extra panels won’t earn FIT. Ofgem says extensions commissioned on or after 15 January 2016 aren’t eligible, and any change in capacity must be reported.

Ofgem’s storage guidance isn’t a legal ruling, and your FIT supplier decides on payments. Talk to them before the work, and photograph the meter reading on the day. See feed-in tariff meter readings and will a battery affect my FIT payments?

1. Testing first. We confirm the old inverter really has failed, and check the panels, wiring and fuse board.
2. A survey and a clear written quote for the route that suits your system.
3. Paperwork before the day: your FIT supplier if you have one, and a G99 application if needed.
4. The swap. The old inverter comes off and the hybrid goes on. The panels stay as they are.
5. Set-up and handover: battery settings, monitoring, meter readings and your paperwork.

Please don’t disconnect or swap an inverter yourself. The cables from the panels stay live whenever there’s daylight.

We fit hybrid inverters and batteries, and when an old inverter fails we can fit a hybrid in its place, with or without a battery. We’re a certified Growatt installer, but we look at what you have before recommending anything. We work on any installer’s system, across England, Wales and southern Scotland. For costs, see inverter repair and what a solar battery costs.

Sources: Energy Saving Trust; Ofgem feed-in tariff guidance for generators and co-location of storage guidance; Energy Networks Association (EREC G98 and G99 guides); MCS MIS 3012; inverter makers’ own guides.