Why Did My Electric Bill Spike After Installing Solar? A Rodent Damage Case Study
If you have invested in a rooftop solar plant only to find that your monthly electricity bills are unexpectedly rising instead of dropping, your system may be suffering from a hidden "half-capacity" failure. Many modern string inverters will continue operating normally on a single healthy string without triggering a primary fault alarm on the display, effectively masking a severe DC failure beneath the modules.
This technical field report breaks down how the Avishakti Solar team investigated an unexplained generation drop at a CHS in Mulund (a 10.4 kWp plant commissioned in May 2021) and traced the root cause to extensive rodent damage.
Why does a rooftop solar inverter show "Normal" when generation is cut in half?
A common pitfall in rooftop solar management is assuming that if the inverter screen is green and showing production, the system is generating at 100% capacity.
At the Mahalaxmi CHS installation—which uses 26 Axitec 400 Wp panels paired with a 10 kW SMA string inverter configured across two independent MPPT inputs (13 modules per string)—the site initially lacked an active internet connection for remote monitoring.
After a few months of operation, the housing society noticed their electricity bills had spiked unexpectedly. When our technical team arrived on site:
The inverter was powered ON and operating in production mode.
No primary fault or error alarms were visible on the display.
The system appeared functional at first glance, but was quietly operating at only 50% output.
How do you diagnose a low-voltage DC string fault?
To understand why generation had dropped, our engineers conducted direct DC voltage measurements at the inverter input terminals.
For a 13-module string of 400 Wp Axitec modules (Voc ~49–50 V per module), the expected electrical parameters are:
Expected String Open Circuit Voltage (Voc): ~640–650 V DC
Expected Operating Voltage (Vmp): ~520–560 V DC
Measured Field Readings:
String 1 (Healthy): Operating voltage was ~545 V DC (Open Circuit Voc: ~645 V DC).
String 2 (Faulty): Operating voltage was fluctuating between ~120–150 V DC (Open Circuit Voc: ~210 V DC).
This confirmed an immediate electrical discontinuity on String 2, isolating the fault to the physical DC routing beneath that specific array.
What damage do rodents cause to rooftop solar DC cabling?
Following the abnormal voltage readings, technicians conducted a detailed visual and physical inspection under the array structure. The inspection revealed severe biological pest damage:
Exposed Live Conductors: Several sections of DC cable were completely stripped down to bare copper by mouse bites.
Compromised Insulation: Cable insulation was severed at multiple points along the routing path, creating severe leakage paths.
Component Housing Breaches: The outer protective casing of a module junction box was chewed through, exposing internal bypass diodes and connectors to atmospheric moisture.
Chewed Cable Sleeving: Standard plastic conduit sleeves had been penetrated and broken.
Because rodents frequently nest under shaded, warm solar panels, unprotected or poorly routed cables are vulnerable to bite damage, creating immediate fire risks, leakage currents, and massive generation loss.
How do you repair and rodent-proof a rooftop solar plant?
To permanently resolve the issue and restore complete electrical safety, the Avishakti team executed a multi-step corrective protocol:
Complete Cable Replacement: Stripped out all damaged DC wiring and installed fresh, high-grade, UV-resistant solar DC cables.
Junction Box Restoration: Replaced broken connectors and inspected and resealed the compromised module junction box.
Full Rodent-Proof Armoring: Encased all exposed DC cables beneath the panels inside specialized rat-protection sleeves (heavy-duty, rodent-resistant conduits) across the entire cable run.
Post-Repair Verification: Retested the system under full load. String 1 registered ~550 V DC, String 2 registered ~548 V DC, and Insulation Resistance (IR) returned to healthy parameters (>1 MΩ).
Key Takeaways for Housing Societies & Commercial Asset Owners
Inverters can lie by omission: An inverter without real-time remote monitoring will gladly run on one string while the other is dead, leaving you with hefty utility bills.
Cable protection is mandatory: Standard open cable ties under the array are an open invitation for pests. Heavy-duty rodent-resistant conduits are essential for rooftop longevity.
Routine voltage audits are essential: Semi-annual electrical check-ups catch string drops before you spend months overpaying on utility bills.
Is your solar plant delivering the savings you were promised? If your electricity bills seem higher than expected, contact Avishakti Rooftop Solar for a comprehensive Solar Plant Health Audit and proactive Maintenance and Asset Management (MAC) contract.
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