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Microinverter vs String Inverter Calculator

Compare microinverter vs string inverter cost, yield, payback and 25-year ROI for UK residential solar in 2026. Enphase IQ8 vs SolarEdge HD-Wave vs SMA Sunny Boy.

Microinverter vs String Inverter Calculator

Yield — string config
864 kWh/kWp
Yield — micro config
883 kWh/kWp
Total cost — string
£3,700
Total cost — micro
£2,160
Annual revenue — string
£846
Annual revenue — micro
£866
Micro premium
-£1,540
Annual revenue delta
£20
Payback period
0 years
25-year net benefit
£2,029
Recommended
Microinverter

What this calculator does

The tool compares the lifetime economics of two inverter architectures on a UK home PV system:

  • String inverter — one central inverter (SMA Sunny Boy, SolarEdge HD-Wave, Fronius Primo, Sungrow SG, Growatt MIN, GoodWe) handles all panels wired in a single DC string.
  • Microinverter — one small inverter (Enphase IQ8M, APsystems DS3-L, Hoymiles HMS-2000) sits behind every panel.

It outputs total installed cost in each configuration, annual generation after shading losses, annual revenue at your retail tariff, the premium for the microinverter route, the annual revenue delta the microinverter delivers, simple payback in years, and 25-year net benefit. Under 7% shading the string inverter usually wins; over 12% the microinverter usually wins.

How the math works

yield_string = annual_yield × (1 − shading_pct × 1.3 / 100)
yield_micro  = annual_yield × (1 − shading_pct × 1.0 / 100)

cost_string  = system_kWp × cost_per_kW_string_bos + central_inverter_cost
cost_micro   = n_panels × cost_per_micro + bos_per_kW_micro × system_kWp

rev_string   = system_kWp × yield_string × tariff
rev_micro    = system_kWp × yield_micro  × tariff

premium      = cost_micro − cost_string
delta_rev    = rev_micro − rev_string
payback      = premium / delta_rev
net_25y      = delta_rev × 25 − premium

The recommendation is microinverter if 25-year net benefit is positive, otherwise string inverter. The 1.3× shading multiplier on the string config matches MCS Performance Estimation 2024 guidance for unoptimized strings.

Microinverter advantages

Per-panel MPPT. Each panel runs its own maximum power point tracker, so shaded or mismatched panels do not drag the rest of the array. The MCS Performance Estimation 2024 guidance assumes a 1.25–1.35× shading penalty on unoptimized strings versus 1.0× on MLPE.

25-year warranty on Enphase IQ8 matches the typical Tier-1 panel warranty (REC Alpha Pure-R, Q CELLS Q.PEAK DUO, LONGi Hi-MO 6 all carry 25-year product warranty). String inverters from Solis, Growatt, and SMA carry 5–10-year warranties; SolarEdge HD-Wave is 12 years extendable to 25.

Module-level monitoring via Enphase Enlighten or APsystems EMA detects per-panel underperformance — a chimney shadow that drifted with foliage, a soiled lower row, a microcrack from hail — within days rather than the months it would take to notice on a string-inverter aggregate output.

G98/G99 compliance is unaffected by architecture choice; both are on the ENA Type Test Register.

No single point of failure — a dead microinverter loses one panel of generation. A failed string inverter takes the whole system offline.

String inverter advantages

Lower upfront cost for clean rooftops. A 4 kWp Solis or Growatt MIN string-inverter system costs £4,200–£5,400 fully installed in 2026 (Solar Energy UK Q1 2026 installer survey). An equivalent Enphase IQ8 system runs £5,400–£6,800.

Single point of replacement. When a SolarEdge HD-Wave or SMA Sunny Boy fails out of warranty, the swap is £1,000–£1,800 for parts and a half-day’s labour on one accessible unit. Replacing 10 microinverters individually after warranty expiry would run £2,400–£3,500 because of roof-access scaffolding.

Mature UK service ecosystem. SMA Sunny Boy, Fronius Primo, and SolarEdge HD-Wave have been in UK service since the FIT era and most MCS installers carry stock or can source within a week.

Tigo TS4-A-2F retrofit. If shade develops after install — neighbour’s extension or tree growth — Tigo optimizers can be added on affected panels for £60–£90/panel, getting most of the microinverter shade-tolerance benefit without a complete inverter swap.

2026 cost comparison in GBP

Solar Energy UK Q1 2026 installer survey, MCS database, and Checkatrade/MyBuilder benchmarks for a 4 kWp London/Birmingham/Manchester residential install:

ComponentString (Solis 4G 4 kWp)Micro (Enphase IQ8M ×10)
Inverter hardware£1,500£1,800 (10 × £180)
Balance of system£2,200 (£550/kWp × 4)£360 (£90/kWp × 4)
MLPE / optimizers£0 (string, no shade)£0 (built in)
Total inverter side£3,700£2,160

Fully-installed market benchmarks Q1 2026:

  • Enphase IQ8M + REC Alpha Pure-R: £8,200 (zero VAT 0% to March 2027)
  • SolarEdge HD-Wave + Q CELLS: £7,400
  • Sungrow SG + JA Solar DeepBlue: £6,900
  • Solis + Trina Vertex S+ (budget): £6,200

When to choose which

Choose microinverters when:

  • Shading exceeds 10% on any roof face — use the solar panel shading calculator to quantify
  • Roof has multiple orientations (E + W terrace, complex hip roof, dormer roof)
  • You plan to expand the array within 5 years (Enphase mid-life additions are simple)
  • You want module-level monitoring for SEG and warranty-claim documentation
  • The system serves a heat-pump or EV charger and minimising downtime concentration matters

Choose string inverter when:

  • One clean south-facing roof plane (typical mid-terrace or new-build), under 7% shading
  • Budget is the binding constraint
  • You accept a mid-life inverter swap (£1,000–£1,800)
  • Local installer base is limited and SMA/SolarEdge service is more available than Enphase

UK regulatory and tariff context

G98/G99 — both architectures are on the ENA Type Test Register. G98 covers single-phase systems under 16 A per phase (most domestic, up to ~3.68 kW export-limited or paired with a Solis/Growatt export-limiting relay). G99 covers larger or three-phase systems.

MCS MIS 3002 — both architectures qualify for MCS Product Certification. The system must be commissioned to MIS 3002 by an MCS-certified installer to qualify for the Smart Export Guarantee (SEG).

SEG tariffs in April 2026 range from 5.5p/kWh (British Gas Export Reward) to 27.0p/kWh (Octopus Outgoing Agile peak rate). The retail Ofgem price cap is 24.5p/kWh for April–June 2026. Net-metered self-consumption is therefore worth roughly 3–4× the average export rate, so self-consumption-maximising battery integration matters more than inverter architecture. Enphase IQ8 + IQ Battery 5P offers AC-coupled storage which simplifies retrofit; SolarEdge HD-Wave + Energy Bank gives DC-coupled storage with higher round-trip efficiency.

0% VAT on solar + battery installs runs until March 2027 under the Spring 2023 Budget — applies equally to both architectures.

Building Regulations Part P electrical safety and BS 7671 (IET Wiring Regulations 18th Edition) apply to all installations. Both inverter types are covered.

How to use this calculator

  1. Enter your system size in kWp.
  2. Enter annual yield in kWh/kWp — MCS Performance Estimation 2024 default for southern England is 950 kWh/kWp at 35° tilt south. Use the solar irradiance calculator for site-specific.
  3. Enter your retail Ofgem tariff in £/kWh — use the unit rate, not the standing charge.
  4. Set shading honestly — a single mature horse chestnut at the south boundary typically contributes 4–8% annual shading on a London terrace.
  5. Set Enphase IQ8M cost — wholesale £165–£195 in 2026.
  6. Set string inverter cost — Solis 4G wholesale £1,300, SolarEdge HD-Wave £1,500, SMA Sunny Boy £1,900.
  7. Read off the recommendation.

For full project economics combine this calculator with the solar inverter size calculator, the solar string sizing calculator for DC sizing, and the solar panel degradation calculator for long-term yield.

Common mistakes

  • Comparing string-without-optimizers to micro. If your roof has any shade, you need to either price Tigo optimizers (£60–£90/panel) into the string quote or accept the shade-loss penalty in the yield input.
  • Forgetting the mid-life replacement. If you keep the system 20+ years, the string inverter is likely to need one out-of-warranty swap.
  • Over-estimating shading. SunEye or HelioScope shade analysis routinely measures 2–4% annual shading on systems homeowners perceive as moderately shaded.
  • Ignoring local installer ecosystem. A premium microinverter system in a rural part of Scotland with limited Enphase service is a worse deal than an SMA string system with a strong local base.

Sources

Frequently asked questions

Are microinverters worth the extra cost on a UK home solar system?
For a typical 4 kWp London semi-detached with 7% annual shading, Enphase IQ8 hardware costs about £1,800 over a SolarEdge HD-Wave or SMA Sunny Boy string inverter — but recovers an extra 2–3% of annual yield, worth roughly £25–£35 per year at the 24.5p/kWh April 2026 Ofgem cap. Payback runs 50+ years, longer than the warranty. Once shading climbs to 12–15% on chimney-shaded terraces or wooded sites, the math flips: micros recover 5–7% extra yield and the premium pays back in 12–18 years. Use the calculator to test your own roof — under 7% shading the string inverter wins on lifetime cost.
Do microinverters meet G98 or G99 grid connection requirements?
Yes. Enphase IQ8M and IQ8P are both type-tested to G98 (16 A per phase, single-phase domestic) and G99 (over 16 A or three-phase). APsystems DS3 and Hoymiles HMS-2000 also carry G98/G99 type-test certificates. Your installer files a G98 notification (most domestic systems) or G99 application (commercial or large array) with the DNO — Western Power Distribution, UK Power Networks, SSEN, Northern Powergrid, SP Energy Networks, or Electricity North West — listing the inverter model number. The DNO checks the inverter against the ENA Type Test Register. As long as it is on the register, the connection is straightforward.
How does the MCS Microgeneration Certification Scheme treat microinverters?
MCS-certified installers can install microinverter or string-inverter systems interchangeably as long as the inverter and modules carry an MCS-listed certificate. Enphase IQ8, SolarEdge HD-Wave, Fronius Primo, SMA Sunny Boy, Sungrow SG, and Growatt MIN all hold MCS Product Certification. The system must be commissioned to MIS 3002 and registered on the MCS database to qualify for the Smart Export Guarantee (SEG) tariff. There is no MCS distinction in compliance for the two architectures; the difference is purely economic.
Which performs better in shading — microinverters or string inverters?
Microinverters win clearly on shaded UK roofs (chimney shadows, dormers, neighbouring trees, terrace-house party walls). A string inverter loses 5–15% of the entire string for every 10% of single-panel shade because of current-limiting. With per-panel MPPT (Enphase IQ8 microinverter or SolarEdge HD-Wave with Power Optimizers on every panel) only the shaded panel itself loses output. The MCS Performance Estimation 2024 update applies a 1.25–1.35× shading penalty to string-inverter systems and a 1.0× penalty to MLPE systems — almost identical to the 1.3× / 1.0× ratio used in this calculator.
What does this calculator assume?
It assumes a 25-year operating life, fixed annual yield (no degradation), constant Ofgem retail tariff (no escalation), no battery, no SEG export premium versus self-consumption, no inverter replacement during the string-scenario life, and no warranty risk premium. For granular analysis on shaded UK roofs run the calculator twice — once at your portfolio-average shading and once at your worst-roof-face shading — to bracket the upside. Pair the result with the [solar inverter size calculator](/en-gb/calculators/solar-inverter-size-calculator/) and the [solar string sizing calculator](/en-gb/calculators/solar-string-sizing-calculator/) for the full DC-AC design.

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