Somebody has almost certainly quoted you a solar payback figure by taking your monthly bill, dividing it by your units, and multiplying the answer by whatever the panels will generate. It is the standard method. It is also wrong, and it will overstate your savings by a third.
We work on industrial rooftops across Karachi and Port Qasim, and the single most useful hour we spend on any project is the one where we read twelve months of bills properly. Here is what we look for, so you can look for it too before anyone quotes you a number.
Your fixed charges will not move, no matter how much solar you install
Open a B3 industrial bill and find the line marked Fixed Charges. On a mill we assessed recently it read PKR 1,347,783 for a single month. That figure is calculated from maximum demand — the highest load your site drew during the billing period — and it has nothing to do with how many units you consumed.
An on-grid solar system reduces the units you buy. It does not reliably reduce your maximum demand, because your peak can occur at night, during a cloudy hour, or at a moment when the whole plant starts together. So the fixed charge stays where it is.
On that mill, fixed charges were roughly 11% of the bill. Any calculation that treats the full bill as reducible overstates the saving by that much before it makes a single other assumption.
The average rate is not the rate that matters
Divide the bill by the units and you get the average rate. On the same mill that came to PKR 32.88 per unit in one month and PKR 46.22 in another — a 40% swing between two months at the same site.
The number that actually matters is the marginal rate: what you stop paying for the next unit you do not buy. Once you strip out fixed charges and account for how the slabs are structured, that mill’s marginal rate came to PKR 27.47 per unit.
Solar displaces units at the marginal rate, not the average rate. The gap between those two numbers was the difference between a payback of 1.5 years and a payback of 2.5 years on the same system.
The average rate is what you paid. The marginal rate is what solar saves you. Any proposal that uses the first number instead of the second is not a proposal, it is a brochure.
Check whether incremental relief is in play
Since December 2025, SRO 2409(I)/2025 has allowed a reduced rate on incremental industrial consumption. On a site that has grown its load, most units can end up billed at that lower incremental rate rather than the standard slab.
That is good news for your operating cost and slightly awkward news for your solar payback, because the units solar displaces are cheaper than they would otherwise be. It does not make solar a bad investment. It does mean a proposal built on standard slab rates is describing a bill you no longer have.
Peak and off-peak matter more than people admit
Solar generates during the day. In K-Electric’s structure, daytime is off-peak and the evening window is peak. So an on-grid array never displaces a single peak unit.
Whether that matters depends entirely on your shift pattern. On one mill we looked at, only 4,098 of 178,397 units in a month fell in the peak window — 2.3%. Solar covering nothing but off-peak was a non-issue. On a site that runs hard in the evening, the same design would leave the most expensive units untouched, and the answer would have to include storage.
You cannot know which case you are without reading the bill.
What to ask for before you sign anything
Ask any installer quoting you for a commercial or industrial system to show you four things: your fixed charges, your marginal rate after those are removed, the split between peak and off-peak consumption, and twelve months of data rather than one representative month.
If they cannot produce those four numbers, they have not read your bill. They have read your bill total, which is a different thing entirely.
Ideal Power Solutions has installed over 24,000 kW across Karachi and Sindh since 2018. Send us one recent bill and your sanctioned load and we will tell you what your site actually needs.
