Your factory roof is probably the largest unused asset you own. The big question is how much solar it can really hold. If you want to know how much roof area is required for industrial solar, the short answer is to plan for about 100 sq ft of shadow-free roof per kW. This is the starting point for estimating industrial solar roof area, but the actual requirement for your factory depends on roof type, skylights, vents, shading and daytime electricity consumption.
This guide explains each factor, with roof area calculations for 100 kW, 500 kW and 1 MW solar plants in Ahmedabad.
Industrial Solar Roof Area per kW: The Quick Answer
The SECI rooftop solar FAQ also provides guidance on rooftop solar area requirements.The Ministry’s rooftop solar FAQ puts the need at 10 to 12 sq m of shadow-free area for each kWp. SECI’s own FAQ gives a similar figure of about 12 sq m per kW.
In sq ft, that works out to roughly 100 to 130 sq ft per kW. Most EPC companies use 100 sq ft per kW as the planning number for large industrial roofs.
| Plant size | Approx. panels (550 Wp) | Shadow-free roof (sq ft) | Shadow-free roof (sq m) | Approx. yearly units in Ahmedabad |
|---|---|---|---|---|
| 100 kW | 180 to 185 | about 10,000 | about 930 | 1.6 to 1.8 lakh |
| 250 kW | 450 to 460 | about 25,000 | about 2,320 | 4.0 to 4.5 lakh |
| 500 kW | 900 to 910 | about 50,000 | about 4,650 | 8.0 to 9.0 lakh |
| 1 MW | 1,800 to 1,820 | about 1,00,000 | about 9,300 | 16 to 18 lakh |
The yearly units use Ahmedabad’s typical output of about 1,600 to 1,800 units per kW each year. Your real figure will depend on cleaning, tilt and shade.
Solar Panel Area per kW vs the Real Roof Space You Need
Many factory owners measure their roof, divide by panel size and expect a much bigger plant. The math looks right, but it leaves out the space a plant needs to work safely for 25 years.
Why Panels Cover Only Part of the Space
A 550 Wp panel measures roughly 2.3 m by 1.1 m, so about two panels make 1 kW. That is only around 55 to 60 sq ft of glass per kW. The rest of the 100 sq ft goes to walkways, gaps between rows, edge setbacks and cable routes. The 10 sq m per kW rule already includes room for tilt, maintenance walkways and safe access. Skip these and your team cannot clean or repair the plant without stepping on panels.
Metal Sheet Roofs vs RCC Roofs: Which Needs Less Area?
Most factories in Ahmedabad’s industrial estates have metal sheet roofs. Here, panels usually sit flush on the roof slope, so there is no gap needed between rows to avoid shade. That is why a metal roof can often fit more kW per sq ft than a flat RCC roof.
On a flat RCC roof, panels sit on tilted frames facing south. Each row casts a shadow behind it, so rows need wider spacing. Plan for the higher end of the 100 to 130 sq ft range on RCC. This difference is one reason two vendors can quote very different plant sizes for the same building. Always ask which layout each quote assumes.
Roof Area Required for 100 kW, 500 kW and 1 MW Solar
Here is what each common factory plant size needs, and what changes as the plant grows.
Roof Area Required for 100 kW Solar
A 100 kW plant needs about 10,000 sq ft of shadow-free roof. In Ahmedabad, that should produce about 1.6 to 1.8 lakh units a year. This size suits small units in estates like Odhav, Vatva or Naroda. Most single factory buildings of this size can hold the full plant on one roof.
Roof Area Required for 500 kW Solar
A 500 kW plant needs about 50,000 sq ft of shadow-free roof. Large warehouses can often fit this on one roof, but factories with several buildings often split it across roofs. Splitting the plant is fine, but it adds cable runs and may need more inverters. At this size, check your connection type early, since many 500 kW plants need an HT connection.
Roof Area Required for 1 MW Solar
A 1 MW plant needs about 1 lakh sq ft of shadow-free roof, which is roughly one acre spread across your buildings. Few Ahmedabad factories have that much clear roof in one block. At this size, rules matter as much as roof area. Gujarat permits net metering for rooftop plants from 1 kW to 1 MW, so a plant above 1 MW needs a different route, such as captive rules. HT connection and transformer losses also need careful planning. We explain this in our guide on transformer losses in industrial solar plants.
How to Work Out Your Factory Roof Solar Capacity
You can estimate your factory roof solar capacity before any vendor visits. Use these four steps:
- Measure total roof area from your building plan, in sq ft.
- Subtract what cannot hold panels. Remove skylights, turbo vents, exhaust stacks, water tanks and the strip along roof edges.
- Subtract shaded zones. Remove any area shaded by taller buildings, stacks or parapet walls between 9 am and 4 pm, all year.
- Divide the usable area by 100. The result is a rough plant size in kW.
Example: A factory has a 60,000 sq ft metal roof. Skylights take 6,000 sq ft, shade from a boiler stack takes 4,000 sq ft, and edges and walkways take 5,000 sq ft. That leaves 45,000 sq ft, so the roof can hold about 450 kW.
For a faster first number, try our solar estimate tool. A site survey will then confirm the real layout.
What Reduces Rooftop Solar Space on Ahmedabad Factories
The rooftop solar space requirement is rarely the problem. The usable part of the roof usually is. These are the items that cut usable area most often on factory roofs:
- Skylights and fragile sheets. Panels cannot sit on them, and workers need safety mesh nearby.
- Turbo vents and exhaust stacks. These block space and can cast long shadows in winter.
- Taller buildings and water tanks. Any shade on part of a panel string lowers output for the whole string.
- Walkways and lifelines. These are needed for safe cleaning and repairs and should never be cut.
- Split roofs. Several small roof blocks at different heights lose space at every edge.
Shade is the most costly mistake. Shade on part of a panel can make that section heat up and burn out over time, and that damage is not covered by warranty. A proper shade study checks the roof across all seasons, not just the day of the visit. Ahmedabad’s dust also matters. Panels can lose 15 to 25% of output if left dirty for long periods. Plan water points and walkways so your team can clean every row.
Can Your Factory Roof Carry the Weight?
Roof area means nothing if the roof cannot carry the load. A rooftop solar plant weighs about 30 to 60 kg per sq m, which is too heavy for asbestos roofs. Metal roofs need a case-by-case check by an expert.
Ask Raynex Powre Solution to check purlins, sheet thickness, rust and old leak points before any layout is drawn. Mounting also differs by roof type: RCC roofs use chemical anchors with sealed caps, while metal roofs use seam clamps or screws with sealing washers.
If your roof is old, fix or replace the sheets first. Panels last 25 years or more, and taking them off later to repair the roof costs time and money.
Rooftop Solar Space Requirement vs Your Actual Load
A big roof does not always mean you should fill it. The right plant size comes from your daytime use, not just your roof area.
Gujarat rules allow HT and EHV consumers to set off captive solar units only between 7 am and 6 pm on the same day. If your plant makes more than you use in that window, the extra units may earn you much less than you expect.
Your connection also matters. Depending on location, Ahmedabad factories deal with either Torrent Power or UGVCL, and each has its own process. Check your sanctioned load and DISCOM rules before fixing the plant size.
The best plan matches three numbers: usable roof area, daytime load and DISCOM limits. Our industrial solar team checks all three in one survey.
Not Enough Roof? Your Options
If your roof is too small for your load, you still have options.
- Solar carports. Raised frames over parking or loading bays add space and give shade at the same time.
- Ground mount solar. Spare land at your site or nearby can hold a larger plant with easier cleaning. See our ground mount solar page for how it works.
- Open access. Large users can buy solar from a plant elsewhere under state rules.
Many factories start with the roof and add ground mount or open access later as their load grows.
Conclusion: Measure the Usable Roof, Not the Whole Roof
The 100 sq ft per kW rule gives you a quick starting point. The real plant size comes from usable roof area after skylights, vents, shade and walkways, checked against roof strength and daytime load.
Metal roofs often fit more kW than RCC roofs, and many factories in Ahmedabad have more usable space than they think. Others find that a smaller, well-placed plant saves more than a bigger one.
Want to know what your roof can really hold? Book a free roof and load survey with the Raynex Power Solution Ahmedabad team, or call +91 90332 32512. We will send a roof layout, a shade report and a plant size that matches your load.
Frequently Asked Questions
How Much Roof Area Is Required for Industrial Solar per kW?
Generally, around 100 sq ft of shadow-free roof area is required per kW of industrial solar capacity. Depending on the roof type, panel layout, shading and maintenance access, the actual requirement can range from approximately 100 to 130 sq ft per kW.
How much roof area is required for 500 kW solar?
About 50,000 sq ft of shadow-free roof. Factories with several buildings often split the plant across two or more roofs.
Can solar panels go on an asbestos roof?
Generally no. Asbestos roofs cannot safely carry the weight of a rooftop plant. The roof usually needs to be replaced with metal sheets first.
How much water does a factory solar plant need for cleaning?
A common guide is 35 to 40 litres per kWp each month, with water below 500 ppm TDS. A 500 kW plant would need about 17,500 to 20,000 litres a month.
Can I install a 1 MW rooftop plant under net metering in Gujarat?
Gujarat’s net metering covers rooftop plants from 1 kW up to 1 MW. Larger plants need other routes, such as captive rules, so check with your EPC company early.
Why do two vendors quote different plant sizes for my roof?
They often assume different layouts, panel wattages or setbacks. Ask each vendor for a roof layout drawing and a shade report so you can compare like for like.