How Big a Solar Plant Does Your Factory Need

The short answer

There is no standard industrial plant size. The right capacity comes from four inputs:

Step 1: Start with 12 months of bills

One month of bills hides seasons. A textile mill's summer load differs from its monsoon load, and a packaging unit's output may follow order cycles. Collect at least 12 months of bills and look at monthly units, peak demand and power factor.

If you are not sure how to read the units and demand lines, our guide to kW, kWh and kVA explains them.

Step 2: Find the daytime share of your load

This is the step most quotes skip. Solar generates in daylight, so what matters is how much of your consumption happens then.

• A single-shift plant that runs mostly in the day can use a large share of what solar produces.
• A three-shift plant has a flatter profile, and solar covers a smaller slice of the total.
• A plant with a heavy night load may need to size for the daytime portion only, rather than total consumption.

Step 3: Check what your space allows

A plant's size is capped by what you can physically install.

• Rooftop: usable area after setbacks, shading from chimneys, tanks and neighbouring structures, roof strength and orientation. Sheet roofs and RCC roofs need different structures.
• Ground-mount: available land, terrain and the distance to your connection point.

Higher-output modules can let you reach a target capacity in less space, which matters when the roof is the limit. The roof area needed per kWp varies with module rating, roof type and layout, which is why a site survey comes first.

Step 4: Turn the target into capacity

Once you know how many daytime units you want solar to supply, the maths is simple.

Required capacity (kWp) = Annual units you want solar to supply ÷ Annual yield per kWp

Illustrative example: a plant uses 40,000 units a month in daytime hours and wants solar to cover half of that. That is 20,000 units a month, or 240,000 units a year. Divide 240,000 by the annual yield of your site per kWp to get the required capacity.

Yield depends on location, orientation, tilt, shading, module type, temperature and cleaning, which is why a site survey and a simulation beat any generic figure.

Step 5: Convert capacity into modules

Module count follows from capacity and module rating.

Number of modules = Plant capacity (W) ÷ Module rating (W), rounded up

Illustrative example: a 100 kWp plant using 600 W modules needs 100,000 ÷ 600 = 166.7, so 167 modules in practice. The final count is also shaped by how modules are strung to match the inverter, and by the layout your roof allows.

Step 6: Check the electrical side

Capacity is not only about panels.

• Inverter sizing: the AC rating of the inverters relative to the DC capacity of the panels.
• Connection and transformer: whether your existing electrical infrastructure can take the plant's output.
• Metering and approvals: the utility's requirements for your consumer category.

Connection and metering rules differ by consumer category and utility and are revised from time to time. We work from the rules in force at the time of your application.

Right-sizing is not always as big as possible

Different goals produce different sizes from the same plant:

• Lowest bill: size to your daytime load so nearly everything solar produces is used on site.
• Maximum savings from the roof: fill the usable roof, then check what happens to surplus generation under your connection rules.
• Sustainability target: size to the renewable share you want to report, which may point towards open access for the rest.

Does the commercial model change the size?

It can.

• CAPEX: you fund the plant, so size to the best return on your capital.
• RESCO / OPEX: you pay per unit consumed, so the plant is sized to what you will actually consume.
• Open access: when your roof cannot cover your needs, renewable energy from a project beyond your premises can fill the gap.

What this looks like in practice

Our rooftop plants range from 821 kWp at Artika Cotton Mills (Ramraj) in Erode, to 959 kWp at Chola Packaging and 1.3 MWp at Polyspin Exports Limited in Rajapalayam. For larger demand, we have built ground-mount plants such as the 7.8 MWp Koochur Solar Park in Krishnagiri and the 13 MWp Suvarrchit Renewable Energy plant in Tiruvannamalai. Each began with a study of the customer's load, not a catalogue size.

How Kyra sizes a plant

Our process starts with an Energy Study of your bills and load profile and a Site Survey of your roof or land. Engineering then models the layout and yield, followed by approvals, installation, commissioning, monitoring and maintenance, all with one team.

Since 2013, Kyra Photon has delivered end-to-end renewable energy solutions for commercial and industrial businesses, with 400+ projects commissioned across India.

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