For most manufacturers, electricity is one of the top three operating costs, and in Tamil Nadu it is billed at roughly ₹7.50–8.25 a unit for industrial connections. A factory's large sheet roof and daytime production shifts are an almost perfect match for solar. Done right, rooftop solar for a factory in Chennai pays back in about 3–4 years and then cuts power costs for two decades more.
- Best fit: factories running day shifts with large metal-sheet or RCC roofs.
- Sizing: about 80–100 sq ft of shade-free roof per kW, so a 10,000 sq ft shed fits roughly 100–125 kW; size it to your daytime load, not just the roof.
- Cost: roughly ₹30,000–50,000 per kW; a 100 kW plant costs about ₹30–50 lakh.
- Output: about 1,450 units per kW a year in Chennai.
- Payback: about 3.3–3.7 years at industrial tariffs, plus 40% accelerated depreciation in year one for eligible owners.
Why factories are ideal for rooftop solar
- Daytime demand: most production runs while the sun is up, so solar power is used on site rather than exported cheaply.
- Large, unshaded roofs: sheds and warehouses offer thousands of square feet of usable space.
- High tariffs: industrial energy charges in Tamil Nadu are well above the cost of solar generation.
- Tax benefit: owners can generally claim 40% accelerated depreciation in the first year.
- Long-term certainty: a fixed cost of power for 25 years, insulated from future tariff revisions.
- Customer and ESG pressure: many OEMs and export buyers now ask suppliers about renewable energy use.
Which manufacturing industries benefit most?
| Industry | Typical load pattern | Solar fit |
|---|---|---|
| Auto components | Heavy daytime machining, compressors, 1–2 shifts | Excellent |
| Engineering & fabrication | Welding, CNC and press loads during the day | Excellent |
| Textiles & garments | High, steady consumption; large roofs | Excellent |
| Food processing & cold storage | Refrigeration all day, peaking in afternoon heat | Excellent |
| Plastics & injection moulding | High loads, often 24/7 | Good: covers the daytime share |
| Pharma & chemicals | Continuous process and cleanroom HVAC | Good: covers the daytime share |
| Electronics assembly | Air-conditioning-heavy, mostly daytime | Excellent |
Continuous (24/7) plants still benefit; solar simply covers the daytime portion of the load, and every unit it produces is used on site.
Sizing a factory solar plant to your shifts
The biggest mistake in factory solar is sizing to the roof instead of the load. Solar saves the most when every unit is consumed on site. Surplus exported to the grid earns far less than the power you avoid buying.
| Your operation | How to size |
|---|---|
| Single day shift, Monday–Saturday | Size to your midday load; check Sunday surplus |
| Two or three shifts | Size to daytime load; solar covers the day shift fully |
| Continuous 24/7 process | Can usually use the full roof; all output is absorbed |
| Seasonal shutdowns | Factor shutdown weeks into the export calculation |
A proper energy audit uses 12 months of bills and, ideally, your hourly load data to find the size that maximises savings, not just capacity.
Savings for small, mid-size and large factories
| Factory | Plant | Units per year | Approx. savings per year | Approx. plant cost | Payback | Year-1 depreciation tax benefit* |
|---|---|---|---|---|---|---|
| Small MSME (LT III-B, ₹8.25) | 50 kW | ≈ 72,500 | ≈ ₹6 lakh | ≈ ₹20 lakh | ≈ 3.3 years | ≈ ₹2 lakh |
| Mid-size plant (HT I, ₹7.50) | 250 kW | ≈ 3.6 lakh | ≈ ₹27 lakh | ≈ ₹1 crore | ≈ 3.7 years | ≈ ₹10 lakh |
| Large plant (HT I, ₹7.50) | 1 MW | ≈ 14.5 lakh | ≈ ₹1.09 crore | ≈ ₹4 crore | ≈ 3.7 years | ≈ ₹40 lakh |
Illustrative: ~1,450 units per kW a year, all consumed on site, energy charges from the TNERC tariff order effective 1 July 2025, mid-range plant costs. *40% accelerated depreciation at a ~25% tax rate, for eligible owners; confirm with your chartered accountant. Excludes O&M (around 1% of plant cost a year) and panel degradation.
How Tamil Nadu industrial tariffs affect your savings
- Energy charge: solar directly replaces this, at about ₹7.50 a unit for HT I industries and ₹8.25 for LT III-B industries (2025-26 rates).
- Peak-hour surcharge: HT energy used from 6–10 am and 6–10 pm carries a 25% surcharge. Morning solar generation offsets part of this costly window.
- Demand charge: the HT demand charge (₹608 per kVA a month) depends on your maximum demand and is not significantly reduced by solar. A credible proposal says so.
- Revisions: tariffs are revised periodically; an inflation-linked adjustment was due from July 2026, so solar's value rises when tariffs do.
For the full tariff table and financing comparison, read commercial & industrial solar in Chennai: cost, ROI and process. For metering and approvals, see TANGEDCO solar rules and regulations.
Factory roofs: metal sheet, RCC and more
| Roof | How solar is mounted | Check first |
|---|---|---|
| Metal sheet (trapezoidal or standing seam) | Rails or clamps on the sheet profile, with minimal or no drilling | Purlin strength, sheet age and corrosion, fixings |
| RCC terrace | Tilted or elevated galvanised structures | Waterproofing, slab condition, access routes |
| Asbestos or very old sheets | Usually replace the roof before installing | Roof replacement cost and timing |
| Limited roof space | Carports over parking, or ground mounts on open land | Land use and foundation design |
Every design in Chennai should be cyclone-rated for the city's 50 m/s basic wind speed and use hot-dip galvanised steel. See solar in Chennai's monsoon and cyclones.
Own it, finance it, or buy the power?
| Model | Upfront cost | Lifetime savings | Depreciation benefit |
|---|---|---|---|
| CAPEX (own the plant) | Full | Highest | Yes |
| Term loan / MSME loan | Margin only | High (minus interest) | Yes |
| RESCO / OPEX (buy the power) | None | Moderate | No (the developer owns it) |
| Group captive / open access | Equity stake or none | Moderate, with grid charges | Depends on structure |
Not sure which suits you? Compare providers by model in our guide to the top solar EPC contractors for factories in Chennai.
Installing solar without stopping production
- Survey and audit during normal operations.
- Structure and panel installation on the roof alongside production, with permits, lifelines and safety barricades.
- Electrical tie-in to your panel during a short, planned shutdown, often scheduled on a holiday.
- Testing, inspection and commissioning with TNPDCL and, where required, the Electrical Inspectorate.
- Monitoring and O&M with minimal disruption: scheduled cleaning and remote performance tracking.
Industrial areas we serve in Chennai
Arka works with manufacturers across Chennai's industrial belts: Ambattur and Thirumudivakkam (MSME estates), Guindy, Sriperumbudur and Oragadam (auto and electronics), Irungattukottai, Maraimalai Nagar and Chengalpattu, Padappai and Gummidipoondi, along with factories elsewhere in Tamil Nadu.
Frequently asked questions
Is rooftop solar worth it for a factory in Chennai?
For most factories with daytime operations, yes. At Tamil Nadu industrial tariffs of about ₹7.50–8.25 a unit, a well-sized plant typically pays back in about 3.3–3.7 years and keeps saving for 20+ years more, with 40% accelerated depreciation available to eligible owners.
How much solar can my factory roof hold?
Roughly 1 kW per 80–100 sq ft of shade-free roof. A 10,000 sq ft shed can typically hold about 100–125 kW, but the right size depends on your daytime load as well as roof space.
How much does a solar plant for a factory cost?
About ₹30,000–50,000 per kW in 2026, so roughly ₹20 lakh for 50 kW, ₹1 crore for 250 kW and ₹4 crore for 1 MW at mid-range prices. Larger plants cost less per kW.
Can a 24/7 factory benefit from solar?
Yes. Solar covers the daytime share of a continuous load, and because the plant runs around the clock, every solar unit is used on site rather than exported.
Will solar damage my factory's metal roof?
Not when installed correctly. Panels are mounted on rails or clamps fixed to the sheet profile, usually with minimal drilling. The roof's purlins and sheet condition should be checked first, and very old or asbestos sheets replaced before installation.
Does solar reduce my factory's demand charge?
Not significantly. Solar replaces the energy charge, while the HT demand charge depends on your maximum demand. Savings estimates should be based on the energy charge.
How long does it take to install solar at a factory?
A 100–250 kW plant typically takes several weeks of execution after approvals. Most work happens alongside production, with only a short planned shutdown for the electrical tie-in.
Get a solar proposal for your factory
Share your electricity bills and roof details, and Arka Solar Energy's engineers will send a plant design sized to your shifts, a generation estimate, and an ROI model with CAPEX, loan and RESCO compared.
Figures are indicative and based on 2025-26 TNERC industrial tariffs and typical Chennai generation. Your savings depend on your load profile, roof, equipment and financing. Arka Solar Energy is an industrial and commercial solar EPC company in Chennai.