Tamil Nadu monsoon solar yield 2025-26 — real data from 340 SVN systems

**Dataset:** SVN's OMS (operations monitoring system) 340 rooftop customer sites Tamil Nadu la — Trichy 96, Chennai 84, Madurai 62, Coimbatore 48, Karur 22, Salem 18, Tirunelveli 10. Size range 2-15 kW residential + 10-50 kW commercial. Time period Oct 1, 2025 to Dec 31, 2025 (NE monsoon peak).

**Overall finding:** average yield reduction 18% vs peak summer (Feb-May). Not catastrophic — annual bill offset target still achievable, but Nov-Dec la small grid import expected. Zero-bill Q1/Q2 la over-generation credit compensate pannum.

**City-wise daily yield (units/kW/day, monsoon avg vs summer avg):** Trichy 3.8 vs 4.6 (-17%). Chennai 3.5 vs 4.4 (-20%). Madurai 4.0 vs 4.7 (-15%). Coimbatore 3.6 vs 4.5 (-20%). Karur 3.9 vs 4.6 (-15%). Salem 4.1 vs 4.7 (-13%). Tirunelveli 4.2 vs 4.8 (-12%).

**Insight — interior TN wins:** coastal cities (Chennai, Nagai) monsoon impact higher — humidity + cloud cover dense. Interior (Madurai, Tirunelveli, Salem) faster clearing, more sun breaks between showers.

**Best-performing week:** Nov 3-9, 2025. Post-cyclone Fengal clear skies + low pollution + cool temperature (panel efficiency inversely proportional to temp). Trichy peak 5.1 units/kW/day recorded — better than typical summer.

**Worst week:** Dec 8-14, 2025. Continuous NE monsoon rain, 8 straight overcast days. Chennai bottom 1.4 units/kW/day, Trichy 1.8. Battery-backed systems zero grid import (used bank), non-battery systems small daytime import.

**Cyclone Fengal impact (Nov 30 - Dec 1):** 2 days total generation loss for Chennai + Cuddalore + Villupuram cluster. No panel physical damage reported in monitored fleet (proper mounting critical — wind rating 150 km/h Waaree spec, Fengal peak 105 km/h).

**Battery-backed systems performance:** 24 sites with 5-15 kWh LFP bank — zero grid import full monsoon quarter. Battery cycles 88 in 3 months (0.98 cycles/day). Autonomy proven for 2-day continuous rain.

**Commercial site data:** 22 commercial (10-50 kW) sites. Bill offset 62% monsoon vs 88% summer. Monthly bill difference ₹8k-45k impact — customers pre-informed at install, expectation managed.

**Panel degradation check:** used monsoon downtime for panel-level IV curve testing. 3-year-old systems 4-6% degradation (within warranty spec 2%/year). 5-year-old systems 8-10%. Cleaning + inverter firmware update recovered 2-3% output.

**Actionable buyer takeaways:** (1) Design system for annual generation target, not monthly zero-bill. TN annual sun 1,650-1,750 kWh/kW — Q1+Q2 surplus offsets Q4 dip. (2) 3 kW sizing rule: monthly consumption × 0.75 = system size in kW. Larger sizing wastes capex (surplus lapses annually). (3) Battery ROI justified only if 3+ day outage frequency OR daily peak-hour savings math positive. Pure monsoon backup insufficient reason for ₹1.5L+ battery.

**Predictive insight for 2026:** IMD forecast NE monsoon 2026 above-normal (+8%). Expect similar 18-22% dip Oct-Dec. Plan year budget accordingly if commercial user — 3 months buffer working capital.

**SVN monitoring service:** all customers OMS dashboard free (mobile app) — daily generation, alerts, monthly report auto-email. AMC customers ku SLA-based response: output drop 15%+ trigger site visit within 48 hours.