A rooftop system has no moving parts, so customers assume it needs no care. In India that is costly. Dust from construction, roads and desert winds, bird droppings, monkeys, monsoon damp and summer heat all take their toll. Good O&M is mostly simple and regular. It protects generation (the customer's savings), safety, and your reputation, and under PM Surya Ghar the vendor has a five-year maintenance commitment.
Cleaning
Why it matters
Dust blocks light. On dusty sites, especially in north-west India, in the dry months before the monsoon, and near construction or unpaved roads, losses build up quickly between cleanings. Bird droppings are worse than dust: a single dropping can shade part of a cell and pull down a whole string's current. The only reliable way to know the loss on a given roof is to measure it: compare generation on similar clear days before and after cleaning.
How to clean
- When: early morning or evening, when modules are cool. Cold water on hot glass at noon causes thermal stress.
- Water: clean, low-dissolved-solids water. Hard bore-well water leaves a scale film that builds up over months. Some module makers specify water quality in their manuals; check.
- Tools: soft brush or sponge mop with a long handle, or a soft-bristle water-fed brush. No abrasive pads, no metal scrapers.
- No detergents or chemicals unless the module maker approves them; they can damage the anti-reflective coating.
- No high-pressure jets at seals and junction boxes.
- Never stand or walk on modules. Clean from walkways; this is why layouts must leave access.
- Safety: harness on roofs without parapets; cleaning is the most frequent reason people go onto the roof.
How often
| Situation | Typical frequency |
|---|---|
| Dusty dry season (roughly Feb–June in much of north and west India) | Weekly to fortnightly |
| Near construction, highways, cement or stone works | Weekly |
| Monsoon | Rain washes dust; clean after bird droppings and when silt dries on the lower edge |
| Post-monsoon and winter | Fortnightly to monthly |
Start with this and adjust using the customer's own before/after numbers.
Preventive inspections around the Indian year
Monthly (remote or by the customer)
- Compare generation with the expected value (below)
- Look for inverter alarms in the app
Quarterly visual walk-round
- Modules: cracks, hot spots (brown marks), delamination, bird nests underneath
- Cables: sagging, rubbing on frames, UV-damaged sheathing, monkey or rodent damage, loose conduit
- Connectors: discolouration or melting (a thermal camera finds hot connectors in seconds)
- Structure: loose bolts, rust at cut ends and welds, cracked anchor sealing
- Inverter: fan and heat sink clean, no dust blanket, display normal, no new error history
- DBs: SPD status windows, signs of heating, insects or water inside
Pre-monsoon (April–May)
- Earth continuity and electrode resistance (record and compare with the commissioning value)
- SPDs replaced if their windows show red
- Roof drains clear of structure feet and debris; waterproofing around anchors
- Cable glands tight, DB doors sealing, conduit ends facing down
Post-monsoon (October)
- Insulation resistance of each string (moisture faults show now)
- Corrosion on structure and fasteners, especially in coastal cities
- Any leaks reported by the customer; reseal before they become a dispute
- Torque check on terminals (heat cycles loosen them)
Using monitoring data
Monitoring turns the customer's app into an early-warning system.
Specific yield
Specific yield = energy produced (kWh) ÷ system size (kWp)
It lets you compare systems of different sizes, and compare a system with its own design.
Worked example
A 5 kWp system in Jaipur. The design (from your yield software) expects about 145 kWh/kWp in March, so about 725 kWh for the month.
The app shows 620 kWh for March, or 124 kWh/kWp. That is 620 ÷ 725 = 86% of expected.
What to check, quickest first: 1. Were there unusual weather days (dust storm, unseasonal cloud)? Compare with a neighbouring system if you have one. 2. When were the modules last cleaned? Look for a step-change in daily output after cleaning. 3. Is any string producing less? Many inverters show per-MPPT or per-string current. 4. Any inverter trips (grid over-voltage at noon is common in March and April)? 5. New shading: a neighbour's new floor, a tree, a dish antenna?
A system consistently below about 90% of expected, after allowing for weather, deserves a visit.
Performance ratio (PR)
PR compares actual output with what the array would make at STC efficiency for the sunlight it received:
PR = actual kWh ÷ (kWp × irradiation in kWh/m²)
With plane-of-array irradiation of 190 kWh/m² for the month, the system above gives 620 ÷ (5 × 190) = 0.65, low for a rooftop system, which typically reaches roughly 0.75–0.80. PR needs a measured or reliable irradiation figure, which homes rarely have, so specific yield against expectation is the practical tool.
Structuring a CMC or AMC visit
A good visit has a checklist, a report and a photo record: 1. Review monitoring before you go. 2. Visual walk-round, cleaning if included. 3. Tests due in this season (earthing, insulation, torque). 4. Fix small issues on the spot; quote for anything outside scope. 5. Leave a short written report with readings and photos, and send it on WhatsApp.
The report is your evidence that the system was maintained, which matters for warranty claims and disputes.
Key points
- Clean early or late, with soft tools and low-TDS water, no detergents, never walking on modules; frequency depends on local dust.
- Plan inspections around the seasons: a pre-monsoon and a post-monsoon check, with quarterly walk-rounds.
- Use specific yield (kWh/kWp) against the design expectation to spot under-performance.
- Investigate weather, soiling, string outputs, trips and new shading, in that order.
- Document every visit with readings and photos.
Check yourself
- Why should modules not be washed with cold water at noon?
- A 3 kWp system expected 400 kWh in a month produces 330 kWh. What percentage of expected is that, and is it worth a visit?
- Name three things to check before the monsoon.
Answers
- Hot glass hit by cold water suffers thermal stress, which can crack it or damage cells; cleaning when modules are cool is safer and leaves fewer marks.
- 330 ÷ 400 = 82.5%. After checking the weather, yes: it is well below 90% and needs investigation.
- Any three of: earth continuity and resistance, SPD status, roof drains and waterproofing, cable glands and DB sealing, conduit ends.