Rooftop solar generating less than expected? Causes, cleaning and maintenance in India

If your rooftop system produces noticeably fewer units than the vendor estimated, check the simple causes first: dust on the modules, new shade from a tank, tree or building, the season (monsoon cloud and short winter days), heat that lowers output, and inverter or wiring faults visible as error codes in the monitoring app. Compare like with like: a 3 kW system may produce well under 10 units on a cloudy July day and far more in a clear March week. As an illustrative benchmark, a well-placed system in much of India produces about 3.5–4.5 units per kW per day averaged over a year. If your annual average is far below that after cleaning and ruling out shade, ask the vendor to test the strings during the maintenance period. This guide gives a step-by-step check and a maintenance routine.

Step 1: Measure properly

Use the inverter app or the inverter display to note daily generation for at least two weeks.
Compare with the export and import registers on your net meter.
Compare the same month last year if you have it.
Work out units per kW per day: daily units ÷ system kWp.

Daily units per kW (illustrative)	Likely situation
Above 4.5	Clear, cool, clean conditions
3.5–4.5	Typical good performance
2.5–3.5	Cloud, haze, heat, light dust or shade
Below 2.5 on clear days	Something is wrong: check faults, shade, dirt

Step 2: Rule out the common causes

Dust and dirt

Dust, bird droppings, leaves and construction dust reduce output. In dry, dusty months, losses can be significant if the modules are not cleaned. Clean early morning or evening, when modules are cool, with soft water and a soft brush or sponge. Avoid hard tools, detergents that leave residue, and high-pressure jets. Do not walk on modules. Hard water can leave deposits; use the least-hard water available or wipe dry.

Shade

Watch the array at several times of day. New shade often comes from a neighbour's new floor, a growing tree, a mobile tower, a new water tank or a dish antenna. Because modules are wired in strings, one shaded module can drag down the whole string. Options: trim trees, relocate the obstruction, or ask the vendor about module-level electronics.

Season and weather

Monsoon months produce much less. Winter days in the north are short and hazy. Fog can almost stop generation for days. Judge performance over a full year.

Heat

Modules lose output as they heat up. Very hot afternoons produce less than the panel's rating suggests. Raised structures with airflow help.

Inverter faults and tripping

Check the app for error codes: grid voltage too high or low, insulation faults, earth faults. High grid voltage in areas with many rooftop systems can make inverters trip around midday. Report repeated tripping to the vendor and, for voltage issues, to the DISCOM.

Wiring and connectors

Loose or burnt DC connectors, damaged cables and blown fuses cut output from whole strings. These need a technician; do not open the DC side yourself.

Step 3: Ask for a test

If output is still low, ask the vendor in writing for:

string voltage and current measurements;
insulation resistance and earthing checks;
a visual inspection for hotspots, cracked glass or delamination.

During the vendor's maintenance period this should be part of the service. If a module is defective, see solar warranty claims.

Worked example (illustrative)

A 3 kW system averaged 12 units a day in its first March and 7 units a day the next March.

7 ÷ 3 = 2.3 units per kW per day on mostly clear days: too low.
The owner cleans the modules: output rises to 9 units a day.
A walk at 2 pm shows a neighbour's new staircase room shading two modules.
The vendor rearranges the strings so the shaded modules are on a separate MPPT input. Output returns to about 11 units a day.

Lost generation over the low period: say 4 units a day × 60 days = 240 units, about ₹1,300 at ₹5.40 a unit.

A simple maintenance routine

Task	How often (illustrative)	Who
Glance at the app for daily units and errors	Weekly	You
Clean modules	Every 2–4 weeks in dry, dusty months; less in monsoon	You or a cleaner
Check for new shade	Every season	You
Check structure bolts, cable ties, conduit	Twice a year	Vendor during maintenance
Check earthing and protection devices	Yearly	Vendor or electrician
Check inverter ventilation and dust filters	Twice a year	Vendor
Compare annual units with last year	Yearly	You

Safety

Modules produce DC voltage whenever light falls on them, even with the inverter off. Do not touch connectors.
Do not climb onto sloping roofs to clean without proper safety arrangements.
Turn off and isolate the system as instructed by the vendor before any electrical work.

Back to the pillar guide: rooftop solar mistakes and official sources. Related: how many kW of solar you need, solar panel and inverter types, DISCOM inspection and net meter delays.

Frequently asked questions

Can I use a pressure washer?

Avoid it. High pressure can damage seals and coatings and may void the warranty.

My units are fine but my bill did not fall. Why?

Check that the net meter records exports and that the bill shows net units. Fixed charges also remain. See net metering vs gross metering.

Is a robotic or automatic cleaner worth it?

For a small home system, manual cleaning is usually enough. For large society systems, compare cost with the units saved.

How much output loss is normal with age?

Modules lose a small percentage each year as stated in the performance warranty. Sudden drops are not normal ageing.

Official sources

Ministry of New and Renewable Energy — technical guidance for rooftop systems
PM Surya Ghar national portal — vendor maintenance obligations
Your DISCOM's website — voltage complaints and net meter readings