Solar Inverter Replacement

The component most likely to need changing

An array of panels sitting still on a roof degrades slowly and predictably. The inverter is doing something quite different: switching at high frequency, all day, every day, in a box that gets hot, in a location that is often the hottest part of the house.

That is why the inverter is normally the first significant replacement in a system’s life. It is not a sign that anything was done badly. It is the nature of the component.

Confirming it is actually the inverter

Before anything is ordered, we establish that the inverter is the fault and not the messenger. A unit reporting an insulation fault is frequently reporting a genuine problem in the array. A unit that will not start on damp mornings may be responding to water in a rooftop isolator. A unit showing no display at all may have lost its AC supply.

Replacing an inverter that was telling the truth about a DC-side fault gets you a new inverter reporting the same error.

Matching the replacement to the array

The array is fixed, so the inverter has to fit it. Three numbers govern the choice.

• Maximum input voltage. Panel open-circuit voltage rises as temperature falls. The string voltage on a cold, bright winter morning is higher than its nameplate figure, and it must stay below the inverter limit with margin. This is the calculation most often skipped, and exceeding it damages equipment.
• MPPT voltage range. The inverter tracks the array’s maximum power point within a window. A string sitting near the bottom of that window on a hot day will underperform even though nothing is faulty.
• Input current and MPPT count. An array split across two orientations needs two independent trackers. Putting east and west strings onto one input costs generation every day of the year.

Where an old array has an awkward string count, reconfiguration is sometimes possible. Where it is not, the replacement is chosen around the array rather than the array around the replacement.

Where optimisers complicate things

Systems with power optimisers or microinverters are less flexible. Optimisers communicate with a specific inverter family over the DC cable, so a replacement generally has to come from the same manufacturer. Where that manufacturer no longer makes a compatible unit, the choice becomes removing the optimisers entirely — which means roof access and a re-examination of the shading that justified them — or replacing them alongside the inverter.

We check what is on the roof before quoting, because this changes the cost substantially.

Like-for-like, or a hybrid

A like-for-like replacement restores the system to what it was, at the lowest cost, in the shortest time.

A hybrid replacement does the same and adds a DC battery input for later. If storage is a possibility within the next few years, this is usually the better sequencing: you replace the inverter once instead of twice. The trade-off is a higher price now and a tie to the battery range that manufacturer supports.

Notification and recommissioning

Capacity is what the network operator cares about. A replacement of similar rating does not change the declared capacity of the installation. A larger unit might, and where it crosses the 16A per phase threshold — around 3.68kW single phase — it moves from a G98 notification to a G99 application requiring approval before the work, not after.

Once fitted, the system is recommissioned properly: strings tested, insulation resistance measured, protection settings confirmed, monitoring reconnected and set up on your phone, and certification issued for the work. We also make sure the new unit is registered in your name with the manufacturer, which is the step most often forgotten and the one you need if it fails.