Inverter Strategy
String vs Microinverter vs Optimiser — Commercial Solar UK
Three competing inverter architectures dominate UK commercial solar in 2026. Each has different strengths. Choosing the right one depends on shading, fault tolerance, scale, and lifecycle cost.
3 architectures
Compared
£0.05–£0.18/Wp
Cost range
3–25%
Output gain on shading
10–25 yr
Warranty range
UK commercial solar inverter architecture splits three ways: classic string inverters, MLPE (module-level power electronics) systems using DC optimisers, and microinverter systems. Each has distinct cost, performance, and lifecycle profiles.
1. String Inverters
Architecture: Multiple panels wired in series form a "string". 1–4 strings feed into a single inverter that converts the combined DC to AC. Most common for unshaded commercial installs.
- Brands: SMA, Huawei, Sungrow, Solis, Fronius, GoodWe
- Cost: £0.05–£0.08 per Wp inverter cost
- Warranty: Standard 5–10 years; extendable to 20
- Lifespan: 10–15 years typical
- Best for: Unshaded commercial roofs, ground-mount, large flat warehouse roofs
- Weaknesses: If one panel in a string fails or shades, the string output drops to the lowest-performing panel. Single point of failure for the string.
2. DC Optimisers (MLPE)
Architecture: Each panel has a small DC-DC optimiser fitted at module level. Optimisers feed a central string inverter but each panel can be tracked individually.
- Brand: SolarEdge (essentially the only player in commercial scale)
- Cost: £0.10–£0.13 per Wp combined optimiser + inverter
- Warranty: 25 years on optimisers; 12–25 on inverter
- Best for: Partially-shaded sites; sites where panel-level monitoring is required for service contracts; complex roof geometries
- Strengths: Per-panel monitoring, mitigates shading losses, easier fault diagnostics
- Weaknesses: Higher initial cost; more components to fail; SolarEdge inverter quality has been variable over recent product cycles
3. Microinverters
Architecture: Each panel has its own AC inverter directly under it. No DC string at all — each panel is independent and outputs AC directly to the grid bus.
- Brand: Enphase (essentially the only mass-market commercial player)
- Cost: £0.13–£0.18 per Wp
- Warranty: 25 years
- Best for: Heavily-shaded sites; small-medium commercial (under 50kW); installations needing maximum fault tolerance
- Strengths: Highest fault tolerance — single panel/microinverter failure does not affect rest of system; per-panel monitoring; no high-voltage DC on the roof (safety advantage)
- Weaknesses: Highest cost per Wp; more components per kW = statistically more potential failures; limited brand competition
Side-by-Side Comparison — 100kW Commercial System
- String: ~£8,000 inverter cost; 95% peak system efficiency on unshaded roofs; partial shading reduces output 15–25%; single failure point per string.
- DC Optimiser: ~£11,000 combined cost; 93% peak system efficiency; partial shading reduces output 5–8% only; per-panel monitoring + fault isolation.
- Microinverter: ~£15,000 inverter cost; 94% peak system efficiency; near-zero shading penalty; full per-panel monitoring + fault isolation; safer roof DC architecture.
What We Specify and Why
- Default for unshaded commercial (>100kW): string inverters (SMA / Huawei / Sungrow). Lowest cost, mature tech, well-understood failure modes.
- Shaded sites or complex roof geometries: SolarEdge optimisers — per-panel performance recovery on partial shade.
- Small commercial / safety-critical (NHS / schools): Enphase microinverters — best safety profile (no high-voltage DC on roof), best fault isolation, best monitoring.
- Ground-mount and utility-scale: string or central inverters — economics dominate.
Frequently Asked Questions
Which inverter type is best for commercial solar?
Depends on the site. Unshaded large commercial roofs use string inverters (lowest cost). Shaded or complex sites use DC optimisers (SolarEdge). Small/medium installs and safety-critical sites use microinverters (Enphase).
Are microinverters worth the extra cost for commercial?
On heavily-shaded sites or installations requiring per-panel fault tolerance, yes — the 5–25% output gain plus monitoring/safety benefits typically justify the price premium. On unshaded large commercial roofs, string inverters deliver better economics.
How often do solar inverters fail?
String inverters: 0.5–2% annual failure rate, with most failures concentrated in years 8–15. Microinverters: 0.05–0.15% annual rate but more units per system. DC optimisers: 0.05–0.1% per unit. Plan an inverter replacement at year 10–15 for string-based systems.
What is the best string inverter brand for UK commercial?
SMA, Huawei, and Sungrow lead UK commercial-scale string inverters in 2026. SMA has the longest UK service track record. Huawei and Sungrow offer competitive pricing with strong technical performance.
Can I mix microinverters and string inverters?
Generally no — at system design level, you commit to one architecture. Mixing creates monitoring fragmentation and design complexity. Some hybrid retrofits exist but greenfield installs use one architecture per array.
Related Guides
Ready to Reduce Your Energy Costs?
Join hundreds of UK businesses already benefiting from commercial solar. Get your free site survey and quote today.
MCS Certified | 25-Year Warranty | Nationwide Coverage