Firecrackers rarely break solar glass, but they leave three things behind: a film of soot and salts that blocks light, spent casings that shade cells, and residue baked onto the glass where hot pieces landed. Rinse the panels with clean water in the cool part of the day, lift debris off by hand, and get any mark that will not wash off checked.
What we found on one roof
These photos are from a rooftop we inspected after Diwali 2026.
How crackers affect your panels
- Less light reaches the cells. Cracker powder is mostly potassium nitrate, charcoal and sulfur, and over half of it burns to solid residue, mainly potassium salts that absorb moisture and stick to the glass. On Deepavali 2025, Chennai's PM2.5 reached 87–162 µg/m³ against a 60 µg/m³ standard (TNPCB). A Duke University and IIT Gandhinagar study found dust and air pollution cut solar output in India by 17–25% even with monthly cleaning, and the fine particles from burning block more light per gram than dust.
- Debris causes hot spots. A casing over part of a cell blocks its current. A bypass diode then skips that group of cells, cutting up to a third of the panel's output, and the shaded cell heats up.
- Baked-on residue and fire risk. Hot pieces leave residue that bakes onto the glass, like the ring in our photos. Burnt paper caught under the array or around cables is a fire risk.
What to do this week
- Check your generation. In your inverter app, compare a sunny day now with one before Diwali. A clear drop means cleaning is due.
- Stay off the panels. Work from the roof or a ladder. Do not touch cables: panels make live DC power in daylight.
- Lift debris by hand, wearing gloves, early morning or evening when the glass is cool (LONGi limits the water-to-glass temperature difference to 10 °C). Clear ash, paper and dry leaves from under the array.
- Rinse, do not scrub. Use RO or other low-mineral water: LONGi's limit is 1,000 mg/L TDS and Waaree's 1,500 mg/L, and hard borewell water can exceed both and leave white scale. Use a soft brush or sponge at normal hose pressure (LONGi and Jinko cap it at about 0.7 MPa). No pressure washer, scraper, abrasive or acid cleaner.
- Soak baked-on rings for a few minutes, then wipe gently. Never scrape.
- Call us if a mark stays, or if you see cracked glass, melted cable insulation or a burning smell. Switch off at the inverter and DC isolator first.
Free post-Diwali panel check
Send 3 or 4 photos of your panels on WhatsApp. An engineer will tell you whether a rinse is enough or the panels need a closer look. No charge.
Send photos on WhatsAppBefore next Diwali
Light rockets and aerial crackers away from roofs with panels, clear the area under the array, and rinse within a day or two. For a regular routine, see soiling and O&M in South India.
FAQ
Can firecrackers crack solar panels?
Rarely. Panel glass is toughened and passes a 25 mm hailstone test at 23 m/s under IEC 61215. Hot debris can still leave baked-on residue that needs soaking off.
Can I use soap or a pressure washer?
No. Use RO or low-mineral water and a soft brush at normal hose pressure. LONGi and Jinko cap pressure at about 0.7 MPa and rule out abrasive or acid cleaners.
How much output do dirty panels lose?
It varies. A Duke and IIT Gandhinagar study put losses from dust and pollution at 17–25% in India, with monthly cleaning. Compare inverter readings before and after a rinse.
Should I cover my panels during Diwali?
Usually not. A cover stops generation and can blow off. Clear the area under the array before, and rinse the panels within a day or two after.
Sources: Bergin et al., "Large reductions in solar energy production due to dust and particulate air pollution", Environmental Science & Technology Letters, 2017 (doi:10.1021/acs.estlett.7b00197); TNPCB, Deepavali 2025 ambient air quality survey; LONGi module maintenance manual V2.0; Waaree installation manual; JinkoSolar global installation manual (2026); IEC 61215-2:2021 (MQT 09 hot-spot, MQT 17 hail); standard black powder composition.