Start with your bill, not with panels
Every rooftop solar decision starts with the same document: your electricity bill. The units you consume each month are the most honest measure of how much solar you actually need.
Panel counts and system sizes quoted by vendors are guesses until they are tied to your consumption. Two houses that look identical can need very different systems if one runs air conditioners all summer and the other does not.
That is why the calculator asks for monthly units first. It sizes the system from what you use, not from a round number a salesperson prefers.
How the calculator sizes your system
Enter your average monthly units and the calculator estimates the rooftop system size that covers that consumption. It also estimates how much electricity that system would generate.
The estimates come from your own usage figures, so they move with your bill. A household using 300 units a month gets a different answer from one using 800, and that is exactly the point.
The calculator also estimates savings and payback under 2026 net billing. Those are estimates from your units — the cost side of payback depends on vendor quotes, which is covered in the last section.
- Enter your monthly units from your electricity bill.
- Get an estimated system size and expected generation.
- See estimated savings and payback under net billing.
Net billing in 2026: the basics
Net billing is the framework under which rooftop solar works in Pakistan in 2026, set by the NEPRA Prosumer Regulations 2026 (SRO 251(I)/2026). In simple terms, your system exports extra units to the grid and those exports are credited against the units you import.
You are billed on the net difference between what you took from the grid and what you sent back. On sunny days when your panels produce more than you use, the surplus earns you credit instead of going to waste.
A net meter is what makes this possible. It is a bidirectional meter that records both import and export, and it is arranged through your DISCO when the system is installed.
What affects how much your system generates
The same panels produce different amounts of electricity on different roofs. Direction and shade matter most: panels facing the sun without shade from trees, tanks or neighbouring buildings generate far more than shaded ones.
Roof space sets the ceiling. A system can only be as big as the unshaded area available, so a small roof may cap the size no matter how many units you use.
Season and dust play a role too. Generation is higher in long, clear summer days, and dust on panels cuts output until they are cleaned. None of this changes the sizing logic — it is why the calculator gives estimates, and why a site visit still matters before buying.
- Unshaded, sun-facing roof space generates the most.
- Roof area caps the maximum system size.
- Dust and season affect output; estimates assume normal conditions.
Before you buy: get real quotes
The calculator estimates the system; it does not price it. System prices vary by vendor, panel brand, inverter brand and installation quality, so no honest tool can quote you a single figure.
Get quotes from at least two or three installers for the same system size, and compare them line by line — panels, inverter, structure, net meter and wiring should all be itemised.
Check the installer's credentials and the warranty terms on panels and inverter before paying anything. A cheaper quote with weak after-sales support usually costs more in the end than a fair quote from a reliable installer.
- Prices vary by vendor — get multiple itemised quotes.
- Compare panels, inverter, structure and wiring, not just the total.
- Check installer credentials and warranty terms first.
