A battery upgrade that became a full system rebuild

What was already there

The original system dated from the period after 2020 when solar equipment was hard to get hold of: a string inverter with an AC-coupled battery system made up of three 5kWh modules. The individual components came from established manufacturers — the problem was how the system as a whole had been designed and installed.

The newer battery equipment was not compatible with the existing modules, so the requested 15kWh simply could not be added. The old batteries also sat in the loft, and we were not willing to put more storage up there.

What the survey found

Loose DC cabling. The DC runs from the panels had been left lying across the loft rather than routed and clipped properly.

Different roof orientations on the same tracker. This was the significant one. The house has panels on four elevations, and they had been wired north with east, south with west, then combined into the inverter’s MPPT inputs.

An MPPT — Maximum Power Point Tracker — constantly adjusts the operating voltage of an array to find the point where it produces the most power. Put panels facing very different directions on the same tracker and they see completely different light through the day, which makes finding a good operating point for either of them impossible. The system could not perform the way it should.

Irregular performance. Monitoring showed inconsistent output and odd voltage behaviour, which is what prompted us to look harder at both the roof and the electrical side.

The in-roof system itself. Inspecting the roof raised concerns about how the existing in-roof installation had been fitted. After talking it through with the homeowner, we agreed to take the solar off and rebuild from the roof upwards rather than try to modify something with fundamental problems.

The redesign

Around 30kWh of storage. Rather than extending the old arrangement, it is being replaced with one modern system, installed at ground level in a dedicated location instead of the loft.

Two 6kW inverters in parallel, configured as master and secondary. That gives four independent MPPT inputs, so the north, east, south and west arrays each get their own tracker and can each run at the voltage that suits the light they are actually receiving. It is the single biggest improvement over the original design.

New 480W panels on a completely new in-roof mounting system. Rebuilding the array meant we could correct the configuration rather than compromise a new system by keeping poorly configured parts of the old one.

Why the survey mattered

This is the clearest example we have of why an existing system should be surveyed properly before anything is added to it. Had we simply connected the extra storage the homeowner originally asked for, every underlying problem — the array configuration, the cabling, the roof system — would still be there, now powering a bigger battery.

Adding storage to an older installation is not always as simple as connecting another battery. Compatibility, inverter capacity, panel configuration, cable installation and the condition of the existing system all need to be considered first.

Certification

On completion the installation will be issued with an Electrical Installation Certificate, solar PV documentation covering the array, and a Building Regulations notification.