The inverter converts the DC your panels produce into the AC your house uses. It is the component most likely to need replacing during the system’s life, and it is where one decision can cost you real money later.
The decision that matters
If there is any chance you will add a battery, fit a hybrid inverter now.
A hybrid inverter handles both solar and battery. A standard solar inverter does not. Adding a battery to a system with a standard inverter means either replacing the inverter or adding a second separate one, both of which cost more than the difference would have cost at the start.
The extra now is modest. The cost of doing it twice is not. Given that 92% of UK batteries go onto properties with solar, and that most people who do not fit a battery initially consider one later, this is worth taking seriously.
See hybrid systems.
Types
String inverter One central unit, panels wired in series. Standard, cheapest, works well on a single unshaded roof face. Accessible at ground level or in a loft, so replacement is straightforward.
String inverter with optimisers Adds panel-level conditioning for shading or multiple roof faces.
Microinverters One small inverter per panel, on the roof. No single point of failure, but replacing one needs roof access. See microinverters.
Hybrid inverter A string inverter that also manages a battery. See above.
Sizing
The inverter does not have to match the panel capacity exactly. It is common and sensible for the inverter to be slightly smaller than the array, because panels rarely produce their full rated output in British conditions. That is called oversizing the array and it is normal.
What to check:
- The inverter’s rated AC output in kW
- Whether that output affects your grid connection route. The 3.68kW per phase threshold applies to what you can push to the network. See grid connection
- Whether export limiting is being used, and at what level
- The number of MPPT inputs, if panels are split across roof faces. One input per face is the clean arrangement
Where it will go
Inverters are usually fitted in a loft, a garage or a utility space.
They make a low hum and they generate heat. A loft is acceptable for an inverter, unlike for a battery, but it needs ventilation and it will be a hotter environment, which shortens the life of the electronics.
Ask where it is going and why A garage or utility room is generally kinder to it than a loft, and much easier to reach when it needs replacing.
Warranty and replacement
Inverter warranties are typically shorter than panel warranties, which tells you something about expected life.
Ask:
- What is the warranty, and can it be extended?
- What does a replacement cost, including labour?
- Is the manufacturer’s UK support real?
- If it fails, how quickly can it be replaced? The system generates nothing while it is out
Monitoring
The inverter is usually what reports your generation. Worth checking:
- Is monitoring included, and is there an ongoing subscription?
- Does it need a permanent internet connection?
- Can you see panel-level data, or only the total?
- What happens to the monitoring if the manufacturer discontinues the app?
Monitoring you will actually look at is how you notice a fault. A system that quietly stops producing and is not spotted for six months costs real money.