- Dust and bird droppings can cut output noticeably between cleanings, especially in dry, dusty months
- A fixed module cleaning system (pipes, valves and nozzles) makes regular washing quick and safe
- Track the performance ratio monthly; a falling ratio is the first sign of a problem
- Thermography and string-current checks find hot spots, failed bypass diodes and loose connectors early
- Earthing resistance and lightning protection should be tested every year, before the monsoon
Why O&M decides your return
A solar plant's return comes from the units it generates over 25 years. Losing even a few per cent of output every year to dirt, tripping inverters or failed strings adds up to years of lost payback. Good operation and maintenance (O&M) protects that output, and keeps the plant safe.
Module cleaning: how, how often and with what
| Method | How it works | Suits |
|---|---|---|
| Manual with hose and brush | Crews wash with water and soft brushes | Small plants; sites with easy, safe access |
| Fixed module cleaning system (MCS) | A permanent HDPE or uPVC pipe network with valves and hose points across the array | Rooftop and ground plants of any size; fast and safe |
| Robotic cleaning | Waterless or low-water robots run along the rows | Large, uniform utility plants |
Cleaning frequency depends on dust, rain and bird activity: often every one to two weeks in dry, dusty months and less in the monsoon. Use soft or demineralised water where possible, never abrasive tools, and clean in the early morning or late afternoon so cold water does not hit hot glass.
The maintenance schedule
| Frequency | Task |
|---|---|
| Daily / remote | Check inverter status and generation on the monitoring portal; investigate alarms |
| Weekly to fortnightly | Module cleaning (more often in dusty months); visual check for damage and shading |
| Monthly | Compare generation with expected; calculate performance ratio; check string currents |
| Quarterly | Inspect DC and AC connections, cable trays, glands and labels; clean inverter filters and vents |
| Half-yearly | Thermographic (infrared) scan of modules and boards; torque check on terminations |
| Yearly, before monsoon | Test earth-pit resistance, lightning arrestors and surge protection; check structure bolts and corrosion |
Reading the numbers: performance ratio
The performance ratio (PR) compares what the plant actually generated with what it should have generated for the sunlight it received. It strips out the weather, so a falling PR points to a plant problem: dirt, a failed string, an inverter derating, or shading from new growth. Track it monthly and act when it drops.
Common faults and what causes them
- Hot spots on modules: cracked cells, failed bypass diodes or persistent shading; found by thermography.
- Low string current: a loose MC4 connector, a damaged cable or a dirty or shaded row.
- Inverter trips: grid voltage excursions, insulation faults (often moisture in junction boxes) or overheating.
- Earth faults after rain: damaged DC cable insulation or water ingress; test insulation resistance.
Want a module cleaning system or an O&M plan for an existing plant? We install and service both.
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Sources
This guide explains public policy in plain language for planning purposes. Rules, rates and deadlines change: confirm the current position with the notifying authority, your DISCOM and your tax adviser before you commit. Last checked 11 Oct 2026.
About the authors. Arrays Ingenieria is an ex-servicemen-led solar EPC and installation & commissioning company working Pan-India, from Assam's tea estates to industrial rooftops. Our story · Our projects
