Answer
A solar commissioning protocol is the fixed order of checks you run before and after first power-up: paperwork, visual inspection, earth continuity, polarity, string voltage and current, insulation resistance, inverter start-up, grid checks, a performance check and handover records. IEC 62446-1 (UL 62446-1 in the US) describes the tests and records.
Commissioning is the last chance to find a wiring fault while the crew is still on site. A good protocol runs the same checks in the same order on every job, so nothing is skipped and every result is recorded.
Last updated: November 2026
Get design data ready for your commissioning pack
String maps, single line diagrams and equipment lists are easier to produce when they come from the design. Bring a project to a guided demo and see how SurgePV outputs them.
Book a DemoChecking cost first? See the SurgePV pricing page.
This page covers the test methods. For a tick-list to carry on site, use our solar commissioning checklist.
Which standard to follow
The IEC webstore says IEC 62446-1:2016 defines the information and documentation to hand to a customer after a grid-connected PV system is installed. It also describes the commissioning tests, inspection criteria and documentation expected to verify safe installation and correct operation. The IEC also sells a consolidated edition that includes Amendment 1 (2018).
In the US the standard is published as UL 62446-1, approved by ANSI on 20 October 2022, as an adoption of IEC 62446-1 with US national differences. UL’s scope says it is written for grid-connected PV systems that do not use energy storage, and not for hybrid systems, although it adds that many clauses may still apply.
The standard is paid. We do not copy its limits here. Where this page says “limit from the standard,” read the table in your copy of the standard, your local electrical code and the equipment manuals. NREL’s O&M best-practice guide also tells owners to apply IEC 62446 (it cites the 2009 edition).
The test sequence in one line
Paperwork, visual check, earth continuity, polarity, string voltage, string current, insulation resistance, inverter start-up, grid and protection checks, performance check, monitoring, handover.
Master test table
| Test | Instrument | What you compare it with | Limit |
|---|---|---|---|
| Earth continuity | Low-resistance ohmmeter or continuity tester | Every metal part is joined to the earthing system | Limit from the standard and local code |
| Polarity | Multimeter or PV tester | Correct sign on every string and every connector | No reversed string |
| Open-circuit voltage (Voc) | Multimeter or PV tester | Module datasheet value, corrected for module temperature, and the other strings | Limit from the standard. Strings in the same array should read alike |
| String current (Isc or operating current) | PV tester or other instrument rated for DC string current | Datasheet value, corrected for irradiance, and the other strings | Limit from the standard. Strings in the same array should read alike |
| Insulation resistance | Insulation tester (megohmmeter) | Minimum value for the system voltage | Test voltage and minimum from the standard and local code |
| Inverter and grid checks | Inverter display, multimeter, power quality meter | Utility connection terms and the inverter manual | Utility and manual |
| Performance check | Irradiance sensor, energy meter | Expected energy from the design model | Method and limit agreed in the contract |
We do not list numeric limits because the standard is not free to read and we cannot check them here. Do not use a number from a blog post, including this one, as a pass or fail limit.
Key Takeaway
The order matters as much as the instruments. Do the DC tests before you close the inverter, and take every pass or fail limit from the standard, your local code and the equipment manuals.
Before you test
Bring these to site
- As-built single line diagram (SLD), a simple drawing of how the system is wired, and the array layout
- String map that shows which modules feed which input
- Datasheets for modules, inverters and mounting
- Permits and the utility approval
- Instrument calibration records
- Manufacturer manuals
For the design side, see our guide to electrical single line diagrams.
Make a punch list
Walk the array before you test. Write down every unfinished item with a photo and a location. Mark each one critical (a safety risk), major (it blocks testing) or minor (it can wait). Do not energize with a critical item open.
Pro Tip
Take a photo of every test label, instrument display and string number as you go. When a record is questioned at handover, the photo settles it.
Work safely
Follow the lockout and tagout rules of your company and your local law. Keep DC and AC isolators open and locked while you work. Wear the protective gear your safety rules require. A qualified person must lead any step that energizes the system. A string of modules is live in daylight, so treat every DC conductor as live.
Visual inspection
Look before you measure. Check:
- Mounting: rails, clamps, torque marks, flashing and sealing at roof penetrations, and ballast on flat roofs.
- Modules: cracked glass, damaged frames, loose clips. For cell damage, see solar panel microcrack prevention.
- DC cables: sunlight-resistant cable, neat routing, no contact with sharp edges, strain relief where needed.
- Connectors: fully mated, clean and dry. For crimp quality, see MC4 connector crimping best practices.
- Boxes: sealed, correct fuses, correct cable size.
- Earthing: continuous conductors and bonding across rail joints.
- Labels: every isolator, breaker and box labeled, and the main panel directory updated. Check the rapid shutdown label if your code needs it. See the glossary entry on rapid shutdown.
DC tests
Do the DC tests in order, and do not energize the inverter until they pass.
Earth continuity
Measure from each metal part to the earthing point. Record the value and the instrument. Paint on a rail can hide a bad bond, so check the bare metal at each bonding point. For more, see equipment grounding.
Polarity
Check polarity on every string before you connect it to anything. A reversed module or connector is easy to find now and costly to find later.
Open-circuit voltage
Open-circuit voltage is the voltage of a string with no load. Measure each string and write down the module temperature and the irradiance. Compare the value with the datasheet, corrected for temperature, and with the other strings. A string far from its neighbors points to a wiring fault, a missing module or a shaded string. Voc is higher when modules are cold.
| Reading | Possible cause | Action |
|---|---|---|
| Near zero | Open circuit, blown fuse, disconnected string | Trace the string and check connectors |
| Lower than neighbors by about one module’s voltage | A missing or reversed module, or a bypassed group of cells | Check polarity and module count |
| Higher than expected | Two strings wired in series by mistake | Check combiner box wiring |
| One string differs from the rest | Shade, dirt or module mismatch | Inspect the string |
String current
Short-circuit current changes with sunlight, so measure on a clear day, note the irradiance and compare strings measured at the same time. Use an instrument rated for the voltage and current of the string. Never short a string with test leads.
Insulation resistance
Insulation testing checks that the DC conductors are isolated from earth. It finds nicks, damp and damage that could cause an earth fault or a fire. Use an insulation tester at the test voltage the standard sets for your system voltage. Test with the string disconnected from the inverter. Test dry modules: damp can give a low reading. If a string fails, find and repair the fault. Do not just retest.
Inverter start-up and grid connection
Follow the manufacturer’s procedure.
- Check settings first. The grid voltage and frequency ranges, the anti-islanding settings and the protection settings must match the utility’s terms.
- Close the DC side. The inverter should show a DC voltage close to your own Voc reading.
- Close the AC side. The inverter will wait for its synchronization delay, which comes from its grid settings.
- Check output. Look for error codes. Check voltage, frequency and output power against what you expect. Check that the production meter counts.
Record the readings. If the utility requires a witness test, schedule it before the visit.
Anti-islanding
Anti-islanding is the inverter function that stops it feeding the grid when the grid goes dead. It protects utility workers. Ask for the inverter’s certificate and follow the utility’s rules for proof. Do not try to test it by cutting live grid connections yourself.
Performance check and post-commissioning validation
Performance ratio (PR) compares delivered energy with what the system would deliver at its nameplate rating. NREL’s weather-corrected performance ratio report writes it as:
PR = sum of measured AC energy / sum of (module nameplate power x plane-of-array irradiance / 1,000 W/m2)
The sums run over the test period. Irradiance is measured in the plane of the array, in kW/m2, with 1 kW/m2 as the reference.
NREL says PR changes with the season, by as much as plus or minus 10% in the studies it cites. A PR measured in winter and one in summer can differ a lot. So write down the test period, the sensor, the temperature correction and the pass level in the contract before you test. We do not give a target PR here, because it depends on the site and the method. See the glossary entry on performance ratio.
Figures come from the IEC webstore listing, the UL Standards listing and the NREL weather-corrected performance ratio report, all linked above.
Cut rework between design and handover
When the design names every string and inverter input, test records map cleanly to the string map. See how SurgePV’s electrical workflow support and BOM output work together.
See It in a DemoChecking cost first? See the SurgePV pricing page.
Optional checks for larger systems
An I-V curve tracer measures a string across its whole voltage range and can show mismatch, shade or a failing bypass diode. A thermal camera can show hot cells and bad connections under load. Use both when the system is large, when a string fails other tests, or when a lender or insurer asks. Take thermal images in strong, steady sun and avoid glare from nearby surfaces.
Monitoring and metering
- Check that each meter and sensor reads correctly and has the right scale.
- Check the monitoring portal against the inverter display.
- Name every inverter and string in the portal to match the string map.
- Set alerts for no production, low production and communication loss.
- For commercial sites, ask the customer’s IT team who owns the network connection.
Handover documents
IEC 62446-1 sets out the information a customer should receive. A typical pack has:
- As-built SLD and array layout
- Test records with date, instrument and tester
- Equipment datasheets and settings
- Warranty papers
- Operation and maintenance manual
- Utility approval
- A signed commissioning report
Give the customer a short walk-through of the isolators, the monitoring and who to call.
Common problems
| Problem | Where it shows up | What to do |
|---|---|---|
| Loose or damaged connector | Low or zero string voltage or current | Re-make the connection |
| Reversed polarity | Polarity test | Fix before connecting |
| Damp in a box or cable | Low insulation resistance | Dry, repair and retest |
| Wrong inverter settings | Start-up or grid checks | Set to the utility’s terms |
| Shade or mismatch | A string differs from its neighbors | Inspect and, if needed, change the layout |
| Missing records | Handover | Fill the gap before sign-off |
Good commissioning starts with a good design. To see how solar design software produces the string map and electrical outputs this protocol relies on, book a demo.
Sources
- IEC webstore, IEC 62446-1:2016 and IEC 62446-1:2016+AMD1:2018 CSV
- UL Standards, UL 62446-1
- NREL, Dierauf, Growitz, Kurtz, Cruz, Riley and Hansen, Weather-Corrected Performance Ratio (NREL/TP-5200-57991, 2013)
- NREL and partners, Best Practices for Operation and Maintenance of Photovoltaic and Energy Storage Systems, 3rd Edition
Frequently Asked Questions
What is a solar system commissioning protocol?
A commissioning protocol is the set order of inspections, electrical tests, performance checks and records that show a PV system is safe, installed as designed and ready to run. For grid-connected systems without batteries, IEC 62446-1 describes the information to hand over, the commissioning tests and the inspection criteria. In the US it is published as UL 62446-1, an adoption of the IEC text with US national differences.
What does IEC 62446-1 cover?
The IEC says IEC 62446-1:2016 defines the information and documentation to hand to a customer after a grid-connected PV system is installed. It also describes the commissioning tests, inspection criteria and documentation expected to verify safe installation and correct operation. UL’s page for UL 62446-1 says it is written for grid-connected systems without energy storage and not for hybrid systems, although it adds that many clauses may still apply. The limits and acceptance values are in the standard itself, so read your copy.
What tests are part of solar commissioning?
Typical tests are earth continuity, polarity, open-circuit voltage and current for each string, insulation resistance, inverter start-up and grid checks, and a performance check. Larger or complex systems often add I-V curve tracing and thermal imaging. Use the order and limits in IEC 62446-1, your local code and the equipment manuals.
What is performance ratio (PR) in solar commissioning?
Performance ratio is the energy the system delivers divided by the energy it would deliver if it turned sunlight into power at its nameplate rating. NREL writes it as the sum of measured AC energy divided by the sum of the module nameplate power times plane-of-array irradiance divided by 1,000 W/m2. PR changes with the season by as much as plus or minus 10%, so agree the method and the season in the contract.
What is anti-islanding and why does it matter?
Anti-islanding is the inverter function that stops it feeding power into the grid when the grid loses power. It keeps the system from energizing a dead part of the network, where utility workers may be working. Ask for the inverter’s anti-islanding certificate and follow the utility’s rules for proof and witness testing.
What documents do you hand over after commissioning?
Hand over the as-built single line diagram and array layout, the test records with instrument details, equipment datasheets, warranty papers, the operation and maintenance manual, the utility approval and a signed commissioning report with the date and the tester’s name. IEC 62446-1 sets out the information a customer should receive.
Where this fits
This article is part of SurgePV's Solar Installation hub, which works through the topic from first principles to the decisions a project team actually has to make.
