How string inverters work
A string inverter connects a series of panels (a "string") into a single DC input. The inverter tracks the maximum power point of the whole string and converts it to AC. Most residential UK installations use one string inverter handling all panels, or occasionally two strings on a dual-MPPT inverter for east-west splits.
String inverters are proven technology with a long track record in the UK market. They are simpler to install, typically cheaper per watt, easier for engineers to diagnose and service, and have a wide ecosystem of spare parts and warranty support. A typical residential string inverter costs £600–£1,200 including installation, with a warranty of 5–12 years.
The drawback is string-level performance: the whole string is limited by the worst-performing panel in it. If one panel is shaded, dirty, or degraded, the others operate below their individual maximum power points. The impact varies with inverter design (dual-MPPT helps with east-west splits) but is real on any complex roof or partially shaded site.
How microinverters work
Microinverters are small inverters mounted on or beneath each individual panel, converting DC to AC at the panel level. Because each panel operates independently, shading or soiling on one panel does not affect the output of its neighbours. This is called panel-level MPPT.
Microinverters also provide panel-level monitoring — you can see the output of each individual panel from an app. This makes it easier to identify a panel that is underperforming due to soiling, shading, or failure.
The main suppliers in the UK market are Enphase (IQ series) and SolarEdge (which uses a hybrid approach — panel-level DC optimisers with a centralised inverter). A full microinverter system typically costs 15–25% more than an equivalent string inverter system, and installation is more complex (more components, more connections on the roof).
When microinverters are worth the extra cost
Microinverters are most clearly worth the premium on installations with significant shading — from chimneys, dormers, adjacent trees, or other obstructions — where string-level current mismatch would materially reduce output. They are also well-suited to complex multi-plane roofs where panels face different orientations and cannot reasonably be configured into matched strings.
For a straightforward south-facing roof with no shading and panels of uniform specification, the performance difference between microinverters and a quality string inverter is small — typically 2–5% in favour of microinverters. The financial payback on the premium cost at that level of uplift is often marginal over a 25-year panel life.
Monitoring granularity is a genuine advantage of microinverters that string inverters cannot match. If early detection of panel degradation or soiling is a priority — for example in a large installation — this has real value even on unshaded sites.
Maintenance differences
A failed string inverter stops the whole system (or the affected string). A failed microinverter stops one panel. Both failures are typically covered by warranty, but a microinverter failure is lower impact and often less urgent.
The practical maintenance difference is inverter life expectancy. String inverters typically have a quoted life of 10–15 years and often require replacement once during a 25-year panel system life, at a cost of £600–£1,000. Microinverter manufacturers quote 25-year life warranties, though this longevity is not yet proven by field data (microinverters at scale are a relatively recent product).
Soiling affects both architectures equally — dirty panels reduce output regardless of inverter type. Microinverters just make the soiling impact more visible.