Solar has gone from luxury to default in Pakistan. Net-metering approvals, panel prices that fell through the floor, and tariffs that keep climbing have made rooftop systems the standard answer to a painful bill. But most quotes still arrive as mystery numbers: so many panels, so many kilowatts, a price. The maths behind a solar quote is actually simple enough to check by hand — and checking it is the difference between a right-sized system and an expensive guess.
Sizing the system: the divide-by-135 rule
A solar system is sized against the electricity you actually use, and the rule of thumb is this: kilowatts needed = monthly units ÷ 135. The 135 comes from 30 days multiplied by 4.5 peak sun hours — the realistic daily generation per installed kilowatt across most of Pakistan. So a household using 450 units a month needs 450 ÷ 135 = 3.33, which rounds up to a 3.4 kW system. In today’s common 550 W panels that is 3,400 ÷ 550 = 6.18, rounded up to 7 panels — an installed array of 3.85 kW. The slight oversizing is deliberate: it covers inverter losses, dusty panels and winter shortfalls.
What it costs in 2026
At 2026 on-grid rates of roughly Rs. 300 per watt installed — panels, inverter, mounting, wiring and net-metering paperwork included — that 7-panel array costs about 7 × 550 × 300 = Rs. 11.55 lakh (1,155,000). Prices move with the dollar and with import policy, so treat the per-watt figure as the thing to negotiate, not the panel count. Hybrid systems with batteries run meaningfully higher per watt and belong in a different conversation: they suit load-shedding zones, shops and clinics, while pure on-grid suits homes whose goal is the bill, not backup.
The payback, worked out
Now the part everyone actually wants. At an average effective tariff of Rs. 60 per unit — check your own bill, because slabs make this vary — 450 units costs Rs. 27,000 a month. If the system offsets that usage, the payback is 1,155,000 ÷ 27,000 = 42.8 months, about 3.6 years. Everything after that is return. Over a 25-year panel life, Rs. 27,000 a month compounds to Rs. 81 lakh gross, and after the system cost the net saving is roughly Rs. 69.45 lakh (6,945,000) — before allowing for degradation, one inverter replacement and maintenance, which is exactly why honest quotes mention them.
Where solar quotes go wrong
Three things derail solar purchases. First, sizing off the sanctioned load instead of actual units — a 5 kW sanction means nothing if you use 200 units a month. Second, a flattered tariff: a quote that assumes Rs. 90 a unit to beautify the payback will not survive your real bill, so always ask which tariff the calculation used. Third, forgetting that net-metering credits offset units, not fixed charges — your bill never reaches zero, and a good installer says so upfront. Ask for the sizing maths, the assumed tariff and the expected units offset, in writing, and compare two installers line by line.
Do the maths yourself in two minutes
You can audit any quote with the solar panel savings calculator — enter your monthly units, tariff, panel wattage and per-watt cost, and it returns system size, panel count, cost, monthly saving and payback. Pair it with the electricity bill estimator to see how the same units produce your current bill, and you have both sides of the comparison: what you pay today, what you would pay after the switch. When the payback lands under four years, the decision usually makes itself.
