Let’s be honest. Nobody wakes up excited about solar panels. What factory owners want is a smaller electricity bill, and fewer headaches when the grid acts up. Solar happens to be one of the few things that can do both.

The tricky part is the size. Too small and you barely notice a difference on the bill. Too big and you’ve paid for capacity you can’t use. So before you ask anyone for a quotation, it helps to know how the sums work. They’re not hard. A calculator and your last few bills are enough.

Your bills first

Pull out 6 to 12 months of bills. Go for twelve if you can find them, since summer and winter loads are rarely the same. Write down monthly kWh, maximum demand, and the tariff you’re on.

We’ll use a textile unit as the example, using 90,000 kWh a month. Divide by 30 and that’s 3,000 kWh a day.

Now the question that changes everything: when does that power get used? Day shift only? Then solar fits nicely, because the panels make power right when the machines want it. Running through the night? Different story. You’d need batteries or some arrangement with the grid, and that changes the cost. Understanding your electricity consumption is also the first step toward reducing operating costs. Read our guide on how commercial buildings can cut their energy bills with solar to learn how solar can help businesses manage electricity expenses.

From kWh to kW

This is where most people get lost, so go slowly.

A 1 kW panel array doesn’t give you 1 kW all day. Around noon it gets close. At 8 AM it’s well under, and after sunset it’s zero. On top of that there’s heat, dust and small losses in the wiring and inverter.

To handle this, designers talk about “peak sun hours”, which is the day’s sunshine squeezed into hours at full strength. For a rough first figure in Pakistan people commonly use 5. Then they assume about 80% of the theoretical output actually reaches you.

So:

kW needed = daily kWh ÷ (sun hours × 0.8)

3,000 ÷ (5 × 0.8) = 750 kW.

Is it exact? No. A real design uses measured data for your location and your seasons. But it tells you whether you’re thinking about a 50 kW job or a 750 kW one, and that’s useful on its own.

Panel Count

Take the system size in watts and divide by the panel rating. 750,000 ÷ 600 = 1,250 panels of 600 W each.

A small catch. 750 kW is what the panels add up to (DC). Inverters have a separate AC rating, and the two don’t always match. Designers often size them a bit differently depending on your load. Leave that to them, just know it’s not a mistake when you see two different numbers in a quote.

Roof Space

Each 600 W panel covers roughly 2.5 to 3 m². I’ll say 2.7. Across 1,250 panels you get about 3,375 m² of panel surface.

Then add the stuff nobody remembers. Walkways. Gaps between rows so they don’t shade each other. Room for the cleaning crew. Whatever’s already up there: vents, skylights, tanks, ducting. Real roof area required ends up a good deal larger than the panel area.

If your roof falls short, there are ways round it. Canopies over the parking area, ground-mounted panels on spare plot space, or a bit of both. It depends on the site.

And please, check the roof itself before you get started. Weight, leaks, age. A solar system lasts 20-plus years. A roof that needs replacing in 3 will cause trouble.

Machines and shifts

You don’t need to cover 100% of your usage. Lots of factories don’t. What matters more is how much of the solar output gets used while it’s being made.

Also, motors. Big motors, compressors and chillers pull a lot more current when they start than when they’re running. That affects the inverters and the electrical design. So a decent assessment looks at your load through the day, not only the total at the end of the month. Two factories with identical bills can need very different systems.

Do you need batteries?

Maybe. If you want power after dark, or backup during outages, then yes, a battery system (BESS) is how you do it. If you mainly want to cut daytime grid usage, probably not.

Sizing is simple on paper. Backing up a 200 kW load for 2 hours? That’s 400 kWh of usable storage as a bare minimum. In practice you’d go higher, because of conversion losses and keeping some reserve.

Batteries cost real money. Run the numbers against your tariff and how often you actually lose power before deciding.

Think Ahead

New line next year? Another shift? Tell the designer now. Leaving some room in the layout and the electrical design costs almost nothing today. Retrofitting it later does.

Then there’s upkeep. Industrial areas are dusty, and dust on panels quietly eats output. Add heat and ageing equipment and a system nobody maintains slowly produces less every year. Cleaning on a schedule is cheap insurance.

Biggest array isn’t the goal. A system that works well, year after year, and pays for itself is.

About DSG Energy

The calculation above is a good starting point, but it’s only that. A proper job needs your consumption data, a site visit, a look at your loads, and the right equipment for your setup.

That’s what we do at DSG Energy for commercial and industrial sites. Textile mills, rice mills, food processing, chemical plants, other manufacturing. If you’d like your numbers checked before you decide on a size, get in touch.

DSG Energy powering industries towards a more efficient energy future. Visit DSG Energy or call 0311-1374374.

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