Commissioning is the bridge between installation and operation. Done thoroughly, it catches wiring errors, protection relay misconfigurations, and underperforming strings before the system goes live. Done poorly, it results in warranty claims, nuisance tripping, and performance losses that quietly compound for years.

Phase 1 — Documentation review (before any power-up)

Before touching a single switch, verify that the design matches what was actually built. Discrepancies found here are free to fix; discrepancies found after energisation are expensive.

Document checks

  • As-built single-line diagram matches installed wiring
  • String layout plan matches actual module positions on roof
  • Equipment list: serial numbers of inverters, batteries, meters match delivered items
  • Grid connection agreement and approved protection relay settings from utility
  • Earthing and bonding schedule: all mounting frames and cable trays
  • Cable sizing schedule: DC strings, AC output, battery DC bus
  • Rapid shutdown device locations confirmed (if required by local code)

Phase 2 — Pre-energisation electrical checks

All checks in this phase are performed with the AC main breaker open and DC isolators open. Safe to perform with a multimeter, clamp meter, and IR camera.

Module and string checks

PV string verification

  • Open-circuit voltage (Voc) of each string ± 5% of calculated STC Voc (adjusted for ambient temperature)
  • Short-circuit current (Isc) of each string ± 3% — isolate other strings first
  • Correct polarity on every string combiner input
  • No measurable voltage between positive or negative string and earth (insulation integrity)
  • DC cable insulation resistance: ≥ 1 MΩ per IEC 60364-7-712
  • Connector torque: all MC4 or equivalent connectors fully latched, no unmated pairs
  • Module frame bonding continuity: < 0.1 Ω between frame and earthing busbar

AC wiring checks

AC-side verification

  • Inverter output cable phase sequence correct (L1, L2, L3)
  • AC main breaker rating matches inverter maximum output current
  • Neutral and earth separated correctly at the main panel (TN-S or TN-C-S per local standard)
  • Anti-islanding protection relay installed and settings match utility approval
  • Revenue-grade energy meter installed on correct measurement point
  • Emergency stop / rapid shutdown accessible and labelled

Battery checks (if hybrid system)

BESS pre-energisation

  • Battery state of charge ≥ 20% on delivery
  • Battery DC bus polarity confirmed before connecting to inverter
  • Battery DC cable insulation resistance ≥ 1 MΩ
  • Battery management system (BMS) communicating with inverter via CAN / Modbus (check inverter display)
  • Battery cabinet ventilation clear, temperature within operating range
  • Fire suppression and thermal runaway protection confirmed active

Phase 3 — Energisation and inverter startup

Energise in sequence: DC first, then AC. Follow the manufacturer's startup procedure exactly — for Sungrow inverters, the commissioning wizard in iSolarCloud walks through each step and logs the output.

Startup sequence

  1. Close DC string combiner breakers one by one — verify MPPT input voltage on inverter display matches calculated Voc
  2. Close main DC isolator — verify no DC earth fault alarm
  3. Close AC main breaker — inverter should enter "Grid detection" mode
  4. Wait for inverter to pass grid voltage and frequency checks (typically 30–120 seconds)
  5. Inverter enters "Normal" or "Grid-connected" mode and begins power production
  6. Verify active power output on inverter display and monitoring system — should be > 0 W if irradiance > 300 W/m²

Inverter startup verification

  • No fault codes or warnings on inverter display
  • Grid voltage within ±10% of nominal on all three phases
  • Grid frequency within ±1 Hz of nominal
  • Power factor > 0.95 (or per utility requirement)
  • AC output current balanced across phases (within 5% for three-phase systems)
  • Remote monitoring portal receiving data from datalogger
  • Anti-islanding test passed (contact utility to initiate, or use test relay)

Phase 4 — Performance verification

Performance verification should be carried out at irradiance ≥ 700 W/m² to match STC efficiency curves. Record all results in the commissioning report.

Performance ratio (PR) baseline

The performance ratio is the key acceptance metric. Calculate as:

PR = (Measured AC output kWh) ÷ (Installed kWp × Irradiance in kWh/m²)

A new system should achieve PR ≥ 0.78 at commissioning. Values below 0.75 indicate a wiring, shading, or soiling problem that should be investigated before handover. Values above 0.85 at STC irradiance indicate excellent installation quality.

Performance verification checks

  • Measure irradiance with calibrated pyranometer or reference cell
  • Record AC output power from inverter at ≥ 700 W/m² irradiance for ≥ 15 minutes
  • Calculate PR and compare to design value
  • Thermal imaging of all string combiner boxes — no hot connections
  • Thermal imaging of inverter AC output terminals — within normal range
  • Individual MPPT channel power balanced — no string producing < 80% of expected
  • Zero export or export limit verified if required by utility (check at inverter and at meter)

Phase 5 — Handover documentation

The commissioning report is a legal and warranty document. Keep a copy on file and provide the original to the customer.

Handover package

  • Signed commissioning report with all measurement results
  • As-built single-line diagram (stamped by licensed engineer if required)
  • String layout plan with module serial numbers
  • Inverter warranty registration confirmation
  • Monitoring system login credentials and training record
  • O&M schedule: cleaning intervals, inspection frequency, BESS cell balancing schedule
  • Punch list of any items requiring follow-up, with responsible party and due date

Common commissioning failures