A good installation follows a fixed order. Each step makes the next one easier and safer, and nothing gets connected before it is ready to be tested. The order also controls the main hazard: the PV array becomes live the moment modules are wired in daylight, so electrical connections come late, and the final connection to the inverter comes last of all.
Below is the sequence for a typical 3–10 kW system on an RCC roof, with notes for tin sheds.
1. Material check
Before you unload, compare the delivery with the bill of materials and the approved design: - Module make, model and wattage match the design and the DCR/ALMM paperwork; serial numbers recorded - Inverter model and rating; cable sizes and lengths; structure members and fasteners (SS 304 for module clamps where specified) - Look for damage: cracked glass, bent frames, crushed boxes, wet cartons
Photograph labels and serial numbers now. They are needed for the portal and for any warranty claim.
2. Layout marking
Mark the structure positions on the roof using the approved layout: - Keep the setbacks: from parapets (wind and access), from the roof edge, and walkways for cleaning - Check shade-free zones again on site: water tanks, staircase rooms and neighbours' buildings - Mark leg positions avoiding existing waterproofing joints, drain outlets and the slope towards drains - Confirm the azimuth with a compass (allow for local magnetic declination, small in most of India)
3. Anchors and structure
On RCC roofs
- Chemical anchors: drill to the specified diameter and depth, clean the hole thoroughly (blow, brush, blow), inject from the bottom, insert the threaded rod with a twist, and do not load it until the curing time given by the anchor maker for the current temperature has passed. In summer heat this is often short; in winter it is longer.
- Mechanical anchors: only where the design allows, at the specified edge distance and spacing.
- Check the slab: hollow, cracked or thin slabs need the structural engineer, not more anchors.
- Waterproofing: seal around every anchor and base plate with a compatible sealant or as the waterproofing contractor specifies. Many leaks blamed on solar come from unsealed anchor holes.
Erect columns and rafters, level and square them, then fix purlins (rails). Tighten bolts to the specified torque only after the frame is aligned.
On tin sheds
Fix mini-rails or clamps into the purlins, not just the sheet, with self-drilling screws and EPDM-sealed washers. Check the purlin size and condition first; rusted purlins are common on old sheds.
4. Earthing and bonding
Install the earthing system now, while access is easy (see module 6, lesson 5): - Dig and set electrodes, with inspection chambers and test links - Run the bonding conductor along the structure and connect each row - Bond to the building's main earthing terminal - Measure each electrode's resistance before connecting it to the system, and record it
5. Mount the modules
- Carry each module with two people, holding the frame.
- Place clamps within the clamping zones shown in the module installation manual. Clamping outside them can void the warranty and lets the glass flex in wind.
- Use the correct end clamps and mid clamps for the frame height, and tighten to the torque in the manual.
- Keep a consistent gap between modules for thermal expansion.
- Bond each module frame to the structure using the earthing holes with serrated washers or approved clips.
6. Wire the strings
- Follow the string plan: which modules form which string, and to which MPPT they go.
- Connect module to module with the module leads. Make the last connection of each string at the end that will go down to the DCDB, and leave that end disconnected and capped.
- Crimp MC4 contacts with the proper tool, push until they click, and pull-test each one.
- Run each string's + and − together (small loop area), clip to the structure, and take them in UV-rated conduit to the DCDB.
- Label both ends of every string cable: "S1+", "S1−".
7. Inverter, DCDB and ACDB
- Inverter location: shaded, ventilated, out of direct rain, at a height for reading the display, with the clearances in the manual. A north-facing wall or an indoor wall near the main DB is ideal. Never inside a closed metal box on the terrace.
- Mount the DCDB near the inverter (and an extra SPD near the array if the run is long).
- Wire the DCDB with isolator open and fuses removed. Leave the final DC connection to the inverter open.
- Wire the ACDB and the inverter's AC terminals, with the MCB open.
8. AC to the main DB
- Run the AC cable to the main distribution board on the consumer side of the meter (module 6, lesson 4).
- Install the generation meter if required.
- Make the final connection at the main DB with the main switch off, and keep the ACDB MCB open.
9. Labels and tidy-up
Labels are part of the installation, not decoration. Typical labels: - On the DCDB and inverter: "Solar DC: live in daylight", string identifiers, Voc - On the main DB and meter: "Dual supply: solar inverter connected"; isolation points - Shutdown procedure near the inverter - Earth pit labels with resistance and test date
Collect every offcut, cable tie end and screw from the roof. Metal swarf left on a roof rusts and stains, and on a tin shed it rusts through the sheet.
10. Test, then connect DC
Run the tests in lesson 3 (polarity, Voc, insulation resistance, earth continuity) before the DC is connected to the inverter. Only then insert fuses, close the isolator and power up in the order in the inverter manual (lesson 4).
Worked example: a two-day plan for 5 kW
| Day | Crew of four | Output |
|---|---|---|
| Day 1, morning | Material check, layout, drill and inject anchors | Anchors curing |
| Day 1, afternoon | Earth pits; structure erected and levelled | Frame ready |
| Day 2, early morning | Modules mounted and bonded | Array complete |
| Day 2, late morning | Strings wired, Voc noted, cables to DCDB | Strings ready |
| Day 2, afternoon | Inverter, DBs, AC run, labels, tests, power-up | Running (export after net meter) |
On a summer job, plan module lifting for the early morning, when the roof is cooler and the wind usually calmer.
Key points
- Mechanical work first (material check, layout, anchors, structure, earthing, modules), electrical work after.
- Clean anchor holes, respect curing times and seal every penetration.
- Clamp modules only in the manufacturer's clamping zones and bond every frame.
- Leave each string's last connection open until tests are done; connect DC to the inverter last.
- Label everything and clear the roof before leaving.
Check yourself
- Why are module strings left disconnected from the DCDB until testing?
- What three things must be done before injecting a chemical anchor?
- Give two reasons for choosing a shaded, ventilated inverter location.
Answers
- So each string can be tested on its own (polarity, Voc, insulation) and because the strings are live in daylight; the final connection is made safely with the isolator open.
- Drill to the correct diameter and depth, then clean the hole (blow, brush, blow) before injecting from the bottom.
- Heat makes inverters derate output and shortens component life; rain and sun damage enclosures and displays.