Hybrid Inverters

What a hybrid inverter is

A string inverter with a battery port and the control logic to decide where energy should go. Instead of one box converting solar and a second box charging a battery, one unit handles the array, the battery, the house and the grid connection together.

The control logic is the point. At any moment the unit is deciding whether to send array output to the house, to the battery or to export, whether to discharge the battery to cover demand, and whether to import from the grid to charge. Those decisions are what turn a battery from a piece of hardware into a saving.

How it works

Solar arrives on the DC side through one or more MPPT inputs. A Maximum Power Point Tracker adjusts the operating voltage of the array it is connected to, hunting for the point where voltage multiplied by current is greatest, and re-checking constantly as light and temperature change. As on any string inverter, everything on one tracker shares one operating voltage, so separate roof orientations need separate trackers.

The battery connects on its own DC port. Because both the array and the battery are on the DC side, solar charging happens with a single conversion. An AC-coupled system converts DC to AC and then back to DC to charge, and loses a few per cent to that round trip.

Grid charging works the other way: the unit imports at a time you set, converts to DC and fills the battery. On a tariff with a cheap overnight window this is often worth more than the solar charging, particularly in winter.

Where it is used

New solar-and-battery installations, where fitting one unit rather than two is both cheaper and simpler. Installations where a battery is planned for a later phase but the wiring and inverter should be ready. Larger systems where the tariff control and load management matter as much as the generation.

It is less commonly the right answer as a retrofit to existing solar, because that means removing an inverter that works. In that case AC coupling a separate battery inverter usually makes more sense.

Suitability and limitations

A hybrid is the right choice when storage is part of the plan. It is the wrong choice for a household that will never fit a battery, because the extra cost buys capability that sits idle.

The commitment to think about is compatibility. The battery must come from the inverter manufacturer’s approved list, and high-voltage and low-voltage battery architectures are not interchangeable. That constrains what you can add in five years’ time, so the sensible approach is to specify against the capacity you might eventually want rather than only the capacity you are buying.

Installation implications

A hybrid needs siting near both the array cabling and the battery, which usually means a garage, utility or plant space rather than a loft. Batteries have their own temperature and location requirements, and putting the pair somewhere that suits both takes some thought at survey.

If backup during an outage is wanted, it must be designed in. That means deciding which circuits are backed up, wiring a changeover arrangement, and accepting that the backup output has a capacity limit — it will not necessarily run an electric shower or a heat pump.

The DNO position also changes. A system with storage may cross the threshold from G98 notification to a G99 application requiring approval before installation, which affects the programme.

Cost and warranty

A hybrid costs more than a plain string inverter of the same rating, and less than a string inverter plus a separate battery inverter. The comparison worth making is against your own likely path: fitting a hybrid now against fitting a string inverter now and AC coupling later.

Warranty terms for the inverter and for the battery are separate, and the battery’s terms will usually reference a throughput or cycle limit as well as a period. Both datasheets come with the written quotation.