The realistic daily figure
Pakistan enjoys strong irradiation, and a properly oriented, unshaded system generally produces in the region of four units per installed kW per day averaged across the year. Clear winter days can be excellent because cool panels are efficient panels; peak summer often disappoints slightly because heat reduces module efficiency.
Use the annual average when calculating savings, and expect month-to-month variation of roughly plus or minus twenty five percent around it.
What reduces output in practice
When a system underperforms, the cause is almost always in this list rather than in the panels themselves.
- Dust accumulation — in dusty months this alone can cost a double-digit percentage of output.
- Shading — even partial shade across one module can drag down a whole string.
- Heat derating — modules lose efficiency as cell temperature rises, so airflow beneath the array matters.
- Undersized or long DC cable runs causing voltage drop.
- Inverter clipping when the array is badly matched to inverter capacity.
- Orientation and tilt chosen for aesthetics rather than for yield.
How to check your own system honestly
Read your inverter's daily and monthly generation logs, not your electricity bill, because the bill mixes generation with consumption behaviour.
Compare a clear-sky day this month against a clear-sky day in the same month last year. A consistent drop of more than a few percent year on year, after cleaning, is worth investigating as a string, connector or inverter issue.
Sizing from consumption, not from roof space
Work backwards: take your average monthly units, divide by thirty, then divide by the daily units per kW figure to get the array size that matches your consumption.
Then check that your roof can physically host that array with clear access and no shading, and that your sanctioned load supports it if you intend to net meter.
Frequently asked questions
- How many units does a 10 kW system produce per day?
- As a planning figure, around forty units per day averaged over the year, with higher output on clear cool days and lower output on hazy or very hot days.
- Do panels produce anything on cloudy days?
- Yes, but substantially less. Output falls with irradiation rather than stopping entirely.
- How often should panels be cleaned?
- In dusty conditions, roughly monthly during the dry season. Cleaning is the cheapest performance improvement available to any system owner.