Guide

Sizing a system from your bill

Turning rupees into units, units into kilowatts, and kilowatts into panels.

From bill to units

Your bill is not linear. Pakistani domestic tariffs are banded, and crossing 200 units in a single month moves an entire bill onto unprotected rates. Work from the unit count printed on the bill rather than the rupee total wherever you can.

From units to kilowatts

A kilowatt of well-installed panels produces roughly 120 to 135 units a month depending on your city and shading. Divide your monthly units by that figure to get the array size you need.

From kilowatts to panels and roof

At 580W a module, a six kilowatt array is around eleven panels and roughly 360 square feet of unshaded roof. Add a fifth of the array size in extra panel capacity to cover winter and dust losses, and keep the inverter about a fifth smaller than the array.