Estimate from long-term sun data and current quotes; a site survey settles the size.
How the size is worked out
Your monthly units are divided by 30.4 to get units a day, then by the peak sun hours for your city and by the system efficiency. The answer is rounded up to the next half kilowatt, and the panel count is rounded up to cover it.
Peak sun hours are the Global Solar Atlas's long-term tilted irradiation for each city, read 6 October 2026, divided by 365. A peak sun hour is one hour of full-strength sun, so 5.1 hours means Lahore's whole day of sun adds up to that much at full strength.
| City | Peak sun hours a day | kW for 600 units |
|---|---|---|
| Karachi | 5.9 | 4.5 kW |
| Lahore | 5.1 | 5 kW |
| Islamabad | 5.4 | 5 kW |
| Rawalpindi | 5.4 | 5 kW |
| Faisalabad | 5.2 | 5 kW |
| Multan | 5.7 | 4.5 kW |
| Peshawar | 5.2 | 5 kW |
| Quetta | 6.8 | 4 kW |
| Hyderabad | 6.2 | 4 kW |
| Sialkot | 5.1 | 5 kW |
| Gujranwala | 5.1 | 5 kW |
| Bahawalpur | 5.8 | 4.5 kW |
System efficiency is 80%: of every 100 watts on the label, 80 reach your meter over a year. NREL's PVWatts model defaults to 14% losses for dust, shading, wiring, mismatch and downtime, and the inverter takes about 4% more; Pakistani roof temperatures cost a further few percent. Installers quote75% to 85%, and the atlas's own output simulation for these twelve cities reconciles to 80% within 3%.
Roof area is the glass of each panel (27.8 sq ft for a 585 W module) plus 40% for row gaps, tilt shadow and a walkway. A flat Pakistani roof with a parapet usually has it; a pitched roof facing east-west may not.
Installed cost is Rs per kW times the recommended size, with the range beside it. On-grid: PKR 120,000 to PKR 160,000 per kW, mid PKR 140,000. Hybrid with a lithium battery:PKR 180,000 to PKR 240,000, mid PKR 210,000. Those span four installers' published 2026 price pages, listed under Sources; Zero Carbon, Reon and Premier Energy quote only on enquiry, so they are not in the range.
Monthly saving values the two halves of your solar differently. Units used as they are made would otherwise have been bought at your marginal rate: the band rate from S.R.O. 279(I)/2026 for your consumption, plus this month's fuel adjustment of Rs 2.0581 and quarterly adjustment of Rs 0.5194, plus the 1.5% duty and 18% GST that ride on all three. For a 600-unit home that is Rs 53 a unit. Units exported earn the net-billing credit of Rs 8.13. Fixed charges and the TV fee stay on the bill either way.
If you start from the bill instead of units, the tool finds the units whose bill matches, for an unprotected single-phase consumer with a 1 kW sanctioned load who files a tax return. That is the common case; a protected or three-phase household should switch to units.
What changed in February 2026
NEPRA's Prosumer Regulations 2026 took effect on 9 February and replaced net metering with net billing. Under net metering a unit sent to the grid cancelled a unit taken from it, at any hour. Under regulation 14 the two are priced apart: what you draw is billed at your tariff, what you send is credited at theNational Average Energy Purchase Price, and the credit is settled against the next bill or paid out quarterly. Agreements run five years.
NEPRA's tariff determination for 2026 puts that price at Rs 8.13 a unit. Press reports in February said "about Rs 10 to 11"; the only notified figure is8.13, and the regulations let NEPRA revise it by notification, so check your first net-billing invoice. Households with a net-metering agreement signed before 9 February keep its rate and mechanism until it expires (S.R.O. 547 of 2 April), and the old agreements' price, the National Average Power Purchase Price, is Rs 25.32. Later amendments removed NEPRA's fee and its concurrence step for systems up to 25 kW, so a home system now needs only the DISCO's approval.
What this calculator cannot know
- Shading and orientation. The sun figures assume an unshaded array at the best tilt facing south. A water tank, a neighbour's wall or a north-facing pitch can cost 10 to 30% that no city average captures.
- Your real self-consumption. The 40, 60 and 80% chips are guesses at how much of your use happens in daylight. A smart meter or the inverter app will tell you after a month; nothing tells you before.
- Seasonal swing. Lahore makes twice as much in May as in December. A system sized on the annual average over-produces in summer, when the AC is on, and under-produces in winter, when it is not.
- The slab effect. Cutting your grid units from 600 to 250 moves you to a cheaper band for every remaining unit, which this marginal-rate method understates. The saving can be a little higher than shown.
- Your quote. Brand of inverter, panel, mounting and the distance to the meter all move the price. Panel output falls about 1% a year; the payback calculator allows for it.
Sources: Global Solar Atlas (World Bank / Solargis) · NASA POWER climatology · NREL, PVWatts Version 5 Manual (NREL/TP-6A20-62641) · Jinko Tiger Neo 72HL4 datasheet · Solar Citizen, solar panel price in Pakistan today · PV.com.pk, 5 kW solar system price with installation · Hajvery Solar, how much a 5 kW system costs · Pakistan Solar Traders, solar system prices 2026 · Feroze Power, 5 kW solar system price guide · NEPRA (Prosumer) Regulations 2026, S.R.O. 251(I)/2026 · S.R.O. 547(I)/2026, amendment to regulation 21 · S.R.O. 709 of 2026, fee for prosumers · S.R.O. 1330(I)/2026, amendment to regulations 3 and 4 · NEPRA national average tariff determination for 2026, as reported by The Nation · S.R.O. 279(I)/2026, residential tariff, with the July 2026 fuel adjustment and S.R.O. 1501(I)/2026
