Three arrangements, and which is right depends almost entirely on your roof.
The three options
String inverter Panels wired in series into one central inverter. The standard arrangement. Cheapest. The inverter sits at ground level, in a garage or in a loft.
String inverter with optimisers Small devices on each panel condition its output before it joins the string, so one underperforming panel does not hold back the rest. Middle cost.
Microinverters A small inverter on each panel, converting to AC on the roof. Each panel is fully independent. Highest cost.
Side by side
| String | Optimisers | Microinverters | |
|---|---|---|---|
| Cost | Lowest | Middle | Highest |
| Handles shading | Poorly | Well | Well |
| Mixed roof directions | Poorly | Well | Well |
| Panel-level monitoring | No | Yes | Yes |
| Single point of failure | Yes, the inverter | Yes, the inverter | No |
| Where the electronics sit | Indoors | On the roof | On the roof |
| Replacing a failed unit | Easy | Needs roof access | Needs roof access |
| Number of things that can fail | Fewest | More | Most |
The trade-off nobody mentions
Microinverters are sold on removing the single point of failure. That is true and it is genuinely valuable: if one microinverter fails, you lose one panel’s output rather than the whole system.
The part that gets less airtime: you have now put a piece of electronics on the roof for every panel, so there are more things that can fail, and each one needs roof access to replace. That means scaffolding, which on most UK houses costs more than the part.
Neither arrangement is wrong. But “no single point of failure” and “more total failure points, each harder to reach” are both true at once, and you should hear both.
Which to choose
String inverter alone if you have a single unshaded roof face. Put the money saved into more panels or a battery.
Optimisers if you have shading, or panels split across roof faces, and you want the fix without putting a full inverter on every panel. This is the middle ground and it suits a lot of British roofs.
Microinverters if you have significant shading or a complicated layout, you want panel-level monitoring, and you are comfortable with the roof-access point above.
Questions to ask
- Why this arrangement for my roof specifically?
- What is the generation estimate with and without panel-level electronics?
- What is the warranty on the optimisers or microinverters, separately from the panels?
- If one fails in year eight, what does replacement cost including access?
- Is rapid shutdown included, and does it matter here?
If an installer proposes optimisers or microinverters on a plain unshaded south roof, ask what problem they are solving. Sometimes there is a good answer. Sometimes it is just what they always fit.