Solar Plant Commissioning Checklist: Tests Your EPC Must Run Before You Sign Off

A solar plant commissioning checklist covers four things: a visual and mechanical inspection, electrical tests on the DC and AC sides (insulation resistance, polarity, string open-circuit voltage and short-circuit current, earth resistance), inverter and protection settings including anti-islanding, and the statutory steps of safety approval, meter sealing and DISCOM synchronisation. Sign off only when each reading is recorded against a drawing and a serial number.

Why does sign-off sit with you and not with the EPC?

An EPC contractor's "mechanical completion" is a statement about the contractor's work. Commissioning is the point where you accept a power station that will sit on your roof or land for decades. Under the CEA safety regulations of 2023 it is the owner who must keep an installation free from danger, and the same regulations expect tests to be done with instruments calibrated by a government-authorised or NABL-accredited laboratory. A test sheet signed by a licensed electrical contractor is what the supplier or DISCOM will accept. So the file you receive at sign-off is the file you will defend later, to the inspector, the insurer and the next buyer of the factory.

What does the visual and mechanical inspection cover?

Walk the plant with the approved drawings in hand, before any test instrument comes out. Regulation 121 of the CEA 2023 regulations gives a useful list of what an inspector expects to see on a solar installation:

• clear roof pathways at least 75 cm wide with hand rails for access and emergency exit, and walkways between rows for cleaning;
• cables in trenches for ground-mounted plants, and fencing of at least 1.8 metres to stop unauthorised entry;
• DC cables that are UV protected or run in UV-protected pipe, with the inverter placed at the periphery of the building and as near the panels as practicable;
• phases on the AC side and positive and negative on the DC side marked in different colours;
• a manual disconnection switch, outside the AC combiner box, that isolates the plant from the grid;
• earth strips interconnected by welding, not bolting, and an adequate number of interconnected earth pits.

Add what the regulations do not list: module damage and micro-cracks visible on a close walk, mounting torque marks, structure levelling, cable glands and sealing at roof entries, and labels that match the single-line diagram.

Which DC-side tests prove the array?

Every string needs its own record. Test polarity first, because a reversed string damages inverter inputs the moment it is connected. Then measure open-circuit voltage and compare it with the value expected from the module count and the module temperature. Measure short-circuit or operating current and compare strings of the same orientation under steady sunlight; a string that reads clearly lower than its neighbours points to shading, soiling, a damaged module or a bad connector. Measure insulation resistance of the array to earth. Voltage and insulation readings do not depend on irradiance, but current comparisons do, so record the irradiance and the time, and repeat on a clear day if clouds moved through.

Many EPC contracts name IEC 62446-1 as the reference for this documentation and testing. We have not quoted its limits here, because they belong in your contract: write the standard, the instruments and the acceptance tolerance into the commissioning clause before the test day, not after a reading is disputed.

What should the AC side, earthing and protection checks record?

The table below turns the checklist into records. If a line has no record, treat the check as not done.

How do you check the inverter, anti-islanding and grid settings?

Haryana's 2021 rooftop regulation is a good example of what a DISCOM expects, and most states ask for similar things. The system must detect an unintended islanding condition and must not feed the grid when the grid fails; applicable IEC or IEEE standards are to be used to test islanding prevention. It must have an automatic synchronising function, which an inverter may provide internally, and the inverter must filter harmonics so that voltage distortion stays within grid-code limits. If DC, flicker or harmonic content in the supply is measured above permitted values, the consumer must disconnect the plant until it is corrected. And any alternate source such as a DG set or battery must be confined to the consumer's network so it cannot back-feed the grid.

Turn those clauses into tests. With the plant generating, open the grid-side breaker and confirm the inverter stops and stays off until grid supply returns. Print the inverter's grid-protection settings and attach them. If a DG set exists, run the changeover with solar online and confirm the interlock; our guide to solar with DG sets explains what typically goes wrong. For hand-held evidence of the plant's health after energisation, see the note on thermography.

What happens at the statutory sign-off, and when should you hold it back?

Regulation 34 of the CEA 2023 regulations leaves the capacity above which a generating unit, including a renewable one, must be inspected by the Electrical Inspector to each state's notification, so the threshold differs by state. Karnataka's Electrical Inspectorate runs rooftop solar in two stages: drawing approval first, then a pre-commissioning inspection on submission of a work completion report signed by the licensed contractor and supervisor, the manufacturer's test report for the installation, the calibration report of the energy meter, current transformers and any protective relays, and a list of authorised operators. The inspector expects the owner's representative and the supervisor on site with testing instruments, defects are rectified and reported back, and the safety approval follows.

Haryana's regulation sets the DISCOM side for plants above 20 kWp: the work completion report goes to the Directorate of Electrical Safety, the inspection and safety certificate are due within seven days of submission, and the DISCOM then synchronises the plant, installs meters and issues the letter of synchronisation with the date of commissioning. Meters are jointly inspected and sealed with the consumer present. For plants above 50 kWp the same regulation asks for a check meter and data telemetry. Other states differ, so ask the DISCOM and the inspectorate for the current checklist. Our CEIG guide covers the approval itself.

Hold the sign-off if any of these is missing: a string sheet for every string, earth readings per pit, calibration certificates for the instruments used, the printed inverter settings, a witnessed anti-islanding test, the DG interlock test where a DG exists, the inspector's approval, or sealed meters. Commissioning shows that the plant works on the day. Whether it keeps performing is a separate question, answered by the guarantee and test method in your contract; see what a performance guarantee should commit to.

How Secured Engineers helps

We design the plant in-house and file the Fire NOC, CEIG and DISCOM net-metering applications in-house, so the drawings the inspector approves are the drawings the commissioning team tests against. MEPF and solar can sit under one contract, which matters when the solar plant ties into a DG changeover, an HT substation or a fire scheme. We work from our Noida (Delhi NCR) and Ludhiana offices, across 535+ projects in 18+ states, and 89.77% of our clients are repeat clients. Our testing and commissioning service also covers independent third-party commissioning of electrical systems installed by another contractor.

If you want a second pair of eyes on a commissioning scope before you sign, see our testing and commissioning service, message us on WhatsApp, call +91 70099 85817, or ask for a free proposal for your plant.