The short answer
An inverter converts the DC electricity your panels produce into the AC electricity your home and the grid use. A string inverter is a single unit, usually in the loft or garage, wired to all the panels in a series 'string'. A microinverter is a small inverter fitted under each individual panel. The key difference is how they handle shade: with a basic string inverter, shading one panel drags down the whole string, whereas microinverters let each panel work independently, so a shaded panel only loses its own output. Micros also give panel-level monitoring and avoid high-voltage DC on the roof. The trade-off is that microinverters cost more and put more electronics on the roof. Power optimisers are a middle option, adding per-panel control while keeping a central string inverter.
Once you have chosen panels, the next big decision is the inverter setup. The three common options are a plain string inverter, a string inverter with power optimisers, and microinverters. The right choice depends mostly on shading and how much per-panel detail you want.
Inverter options
- String inverterOne central unit
- MicroinverterOne per panel
- Best for shadeMicroinverters or optimisers
- Panel-level monitoringMicros / optimisers yes
- Lowest costPlain string inverter
How each setup handles shade
With a simple string inverter, panels are wired in series. Current flows through the whole string, so if one panel is shaded by a chimney, aerial or tree, it acts like a partial bottleneck and can pull down the output of every panel on that string. On a clear, unshaded roof this is rarely a problem, but on a roof with shading it can cost a meaningful amount of generation.
Microinverters convert each panel's output to AC at the panel itself, so every panel operates independently. A shaded panel only loses its own share, and the rest carry on at full output. Power optimisers achieve a similar result differently: they keep a central string inverter but add a small device on each panel that conditions its output, so one weak panel no longer drags down the string.
| Factor | String inverter | Microinverters | Optimisers + string |
|---|---|---|---|
| Where it sits | One central unit | Under each panel | Central + per-panel device |
| Shade tolerance | Lower | High | High |
| Panel-level monitoring | No | Yes | Yes |
| DC on roof | Yes (high voltage) | No (AC at panel) | Yes, but reduced |
| Typical cost | Lowest | Highest | Middle |
| Units that can fail | One (accessible) | Many (on roof) | One + per-panel devices |
Indicative comparison for guidance. Sources: Energy Saving Trust; manufacturer datasheets.
Monitoring, safety and reliability
Microinverters and optimisers both give panel-level monitoring, so you can see in an app exactly how each panel is performing and quickly spot a fault or a panel that needs cleaning. A plain string inverter reports the system as a whole, so a single underperforming panel is harder to detect.
On safety, microinverters convert to low-voltage AC at the panel, so there is no high-voltage DC running across the roof, which some installers prefer. On reliability, a string inverter is a single point of failure but it is easy to reach and replace if it fails, and it typically carries a 5 to 12 year warranty with longer options. Microinverters spread the risk across many units — if one fails, the others keep working — but replacing one means roof access, and they usually carry longer warranties of up to 20 to 25 years to reflect their on-roof life.
Cost and which suits which roof
A plain string inverter is the lowest-cost option and works very well on a straightforward, south-facing, unshaded roof where all panels face the same way and behave alike. For many UK homes this is perfectly adequate and keeps the install simple.
Power optimisers add a moderate cost and are a popular middle path: you keep a single, accessible central inverter but gain shade tolerance and panel-level monitoring. They suit roofs with some shading or panels split across two orientations. Microinverters are usually the most expensive option but give the most flexibility, letting you mix panel orientations freely and add panels easily later, which can suit complex roofs.
There is no single right answer — it depends on your roof. A reputable MCS-certified installer should assess shading and orientation and recommend the setup that fits, rather than defaulting to one technology. If shading is significant, paying for per-panel electronics usually pays back in extra generation; if your roof is clean and unshaded, a simple string inverter is hard to beat on value.
Frequently asked questions
Are microinverters worth it in the UK?
They are worth it where shading, multiple roof orientations or panel-level monitoring matter. On a clear, unshaded, single-orientation roof, a cheaper string inverter performs just as well. Microinverters cost more but recover some of that through better generation on shaded or complex roofs, plus easier future expansion.
What is the difference between optimisers and microinverters?
Power optimisers keep one central string inverter but add a small device to each panel to condition its output and enable monitoring. Microinverters replace the central inverter entirely, converting DC to AC at each panel. Both solve the shading problem and give panel-level data; optimisers are usually a cheaper middle option.
Which inverter lasts longest?
Microinverters typically carry the longest warranties, often up to 20 to 25 years, matching their on-roof life. String inverters usually carry 5 to 12 year warranties and may need replacing once during the panels' life, but they are easy to access and swap. Both can be reliable; the trade-off is accessibility versus warranty length.
Sources & further reading
Figures on this page are typical UK ranges drawn from published sources and depend on your specific home. They are guidance, not a quotation or guaranteed saving.