Work out your own daytime consumption before anyone quotes you

Since February 2026, one number decides the right size of a solar system: how many units you consume between roughly 9am and 4pm. Units you consume as you generate them are worth your full tariff. Units you export are worth roughly a third of the old buyback rate. Those are two different products and only the first one justifies capacity.

Nobody can guess that number from your roof, and most quotations are built without it. Here is how to get a usable estimate yourself, before you talk to anyone.

Start with twelve bills, not one

One bill tells you almost nothing, because seasonality is most of the picture — in Punjab, summer cooling load can be a multiple of a winter month. Twelve bills give you the shape of the year, your tariff slab, your sanctioned load and whether you are paying power factor penalties.

While you have them out, check two things people miss: whether your consumption pattern has changed over the year for a reason you can explain, and whether there is a demand or maximum-demand charge on the bill separate from the units. If there is, that charge is affected by solar differently from the unit charge, and it needs to be in the calculation.

Then list what actually runs, and when

Walk the site with whoever genuinely knows the operating pattern. In a factory that is a foreman, not an owner. For each significant load, write down three things: its rating, the hours it runs, and whether those hours are inside the 9am to 4pm window.

• Motors and machinery — nameplate rating, but note that a motor rarely draws its full rating; loading matters and a badly oversized motor is its own problem.
• Refrigeration and cooling — these are the loads that peak with the sun, which makes them the best-matched consumption you have.
• Air conditioning — take the seasonal pattern seriously; a summer profile and a winter profile are different sites.
• Lighting — usually smaller than people expect, and often partly outside daylight hours anyway.
• Anything on a night shift — list it, then set it aside. It is not what your array will serve.

What this gets you in a sales conversation

You do not need a precise figure. You need enough to tell whether a proposed system is sized to your consumption or to your roof — and to ask the question that separates the two: "what daytime consumption figure did you size this against, and where did it come from?"

A quotation built from a load study will have an answer. A quotation built from roof area will not, and the way that question is handled tells you most of what you need to know about the rest of the document.

Where the estimate runs out

This method is good enough to sanity-check a quotation and bad enough that I would not design a megawatt plant on it. Duty cycles are the weak point: a machine that is "running all day" is often drawing full load for a fraction of it, and the difference compounds across a plant.

For a domestic system or a small commercial one, the estimate above plus twelve bills is genuinely sufficient. At industrial scale, where a sizing error costs millions of rupees of capacity you cannot consume, it is worth measuring properly — which is what an energy audit and load profile study is for.