1. System Architecture Basics
| Feature | Microinverter | String Inverter |
|---|---|---|
| Conversion | Each panel (or 2 panels) has its own inverter converting DC → AC on the roof. | One central inverter converts DC → AC for a whole string (10–20 panels). |
| MPPT | Module-level (each panel independent). | String-level (shared across all panels in one string). |
| Output | AC from the roof; parallel wiring to the panelboard. | DC from roof; series wiring to the inverter, then AC output at ground level. |
2. Advantages of Microinverters
✅ a) Module-level MPPT (Maximum Power Point Tracking)
- Each panel works independently, so shading, soiling, or mismatch on one panel does not drag down the others.
- Ideal if you have:
- Multiple roof orientations (east/west split)
- Partial shading from trees, chimneys, etc.
- Mixed panel models/ages in future expansion.
✅ b) Built-in Rapid Shutdown (Module Level)
- Each microinverter naturally meets NEC 690.12 / CSA C22.2 RSD (rapid shutdown) since DC is converted to AC right at the module.
- No extra shutdown boxes or optimizers needed — simpler compliance for residential & commercial installs.
✅ c) Easier to Scale or Expand
- Add panels later without replacing or upsizing a central inverter — just add more micros and tie into the branch.
- Great for modular growth (e.g., starting with 10 kW now, adding 5 kW next year).
✅ d) Granular Monitoring
- Panel-level data helps:
- Spot failed panels quickly
- Diagnose shading or degradation
- Optimize cleaning and maintenance
✅ e) Improved Safety
- No high-voltage DC runs across the roof or into the building.
- Installers, firefighters, and maintenance teams are safer since AC voltages are lower (120/240 V).
⚠️ 3. Disadvantages of Microinverters
❌ a) Higher Up-Front Cost
- Typical installed cost is 10 – 20 % higher per watt than a comparable string inverter system.
- Each micro costs more individually, and AC trunk cabling adds to BOS (balance of system) cost.
❌ b) Roof-mounted electronics exposure
- Micros live under panels on the roof → exposed to heat, moisture, and freeze-thaw cycles.
- Though rated IP67 and warranted 25 years, servicing them means going back on the roof.
❌ c) Maintenance access complexity
- If a unit fails, identifying and replacing it involves removing at least one panel.
- Contrast: a string inverter swap is ground-level, fast, and easy.
❌ d) AC trunk design limits
- Each branch has a maximum number of micros (limited by branch breaker and current).
- Large systems (like 21 kW) require multiple AC branches and a combiner/subpanel, increasing wiring complexity.
❌ e) Slightly lower efficiency (system-level)
- Microinverters typically have 96 – 97 % peak efficiency, while top string inverters reach 98 – 99 %.
- The difference is small but measurable over time.
❌ f) Harder to use for battery integration
- Hybrid (PV + storage) systems are usually designed around string or hybrid inverters.
- Microinverters export only AC; to add batteries, you need an AC-coupled system, which adds cost and complexity.
⚡ 4. Advantages of String Inverters
✅ a) Lower Cost per Watt
- Fewer components — 1 inverter instead of 15–20 micros.
- Lower BOS (fewer connectors, trunk cables, etc.).
- Excellent for large uniform arrays with consistent sunlight.
✅ b) Easier Maintenance
- All electronics are ground-mounted and easily replaced.
- Firmware updates, diagnostics, and swaps are simple.
✅ c) Better for Integrated Battery Systems
- Hybrid string inverters handle both PV and batteries (DC-coupled), enabling high-efficiency storage integration.
- Ideal if you plan to add energy storage (LiFePO₄ battery bank) later.
✅ d) Fewer AC connections
- Only one AC output to service, simpler wiring and less rooftop junction work.
⚙️ 5. Disadvantages of String Inverters
❌ a) Single-point failure
- If the inverter fails, the whole system stops producing until it’s replaced.
- With micros, only one or two panels go offline.
❌ b) Shading and mismatch losses
- A shaded or dirty panel reduces current for the entire string.
- You can mitigate this with DC optimizers (e.g., SolarEdge), but then cost and complexity rise.
❌ c) Limited flexibility for expansion
- Adding panels later may require a new inverter or new MPPT channel.
🧭 7. Practical Recommendation for You
- If your roof is complex or partially shaded, go microinverter
- If your roof is uniform, sunny, and you plan battery backup soon, go string inverter (e.g., Growatt SPH 10000TL-BH-US, SPE6000TL, SPE12000TL)