Shops, offices, clinics, schools, warehouses and small factories use most of their electricity in daylight, on a higher tariff than homes. That makes rooftop solar work very differently for a business. Here is how to size a commercial system, what it costs, how the tax benefit replaces the home subsidy, and what payback to expect.
Start from your monthly units (kWh) on the bill, averaged over 12 months. Then use the same rule as the calculator:
Sized this way, a system produces about 78% of your units over a year, after real-world losses from heat, dust and the inverter. For a business that uses most of its power in the day, that is close to the sweet spot: almost every unit generated is used on site. If a large part of your use is at night (a cold store, a 24-hour hotel or a night shift), size down to your daytime load, because night-time units cannot come from the panels without batteries. Check your sanctioned load too: net metering stops there (Step 3).
Figures use 5.5 peak sun hours (Delhi, Maharashtra), Mono PERC panels at about 19.5% efficiency, and the calculator's sizing rule. "Roof to plan" adds walkways and gaps between rows: 80–100 sq ft per kW.
| Monthly units | System size | Panel area | Roof to plan | Units per year | Typical user |
|---|---|---|---|---|---|
| 1,500 | 9.1 kW | 502 sq ft | 730–910 sq ft | ~14,250 | Clinic, small shop |
| 3,000 | 18.2 kW | 1,005 sq ft | 1,460–1,820 sq ft | ~28,500 | Office floor, restaurant |
| 6,000 | 36.4 kW | 2,009 sq ft | 2,910–3,640 sq ft | ~57,000 | School, showroom |
| 10,000 | 60.7 kW | 3,351 sq ft | 4,860–6,070 sq ft | ~95,050 | Small factory, hospital wing |
| 20,000 | 121.3 kW | 6,696 sq ft | 9,700–12,130 sq ft | ~1,89,940 | Warehouse, mid-size plant |
| 50,000 | 303.1 kW | 16,731 sq ft | 24,250–30,310 sq ft | ~4,74,610 | Large factory |
In a sunnier state the same units need fewer kW, and in a cloudier one more. Rajasthan, at 6.5 peak sun hours, needs about 15% less capacity than this table. Kerala and West Bengal, at 4.5 hours, need about 22% more. For panel counts, see how many solar panels do I need.
For commercial roofs, the calculator starts from a benchmark of ₹52,000 per kW, then takes 6% off from 25 kW, a further 5% from 50 kW and a further 4% from 100 kW. With Mono PERC panels and the net meter, that works out to about ₹52,500 per kW at 20 kW, ₹49,000 at 40 kW and ₹44,500 at 100 kW. Real quotes depend on the roof structure, the panel and inverter brands, and the distance to your meter, so get two or three quotes.
Accelerated depreciation. Solar power generating systems used in a business are in the 40% depreciation block for renewable energy devices. From 1 April 2026 this is under Section 34 of the Income-tax Act, 2025, which replaced Section 32 of the 1961 Act with the same rate and written-down-value method. If the system is in use for fewer than 180 days in the financial year it is installed, only half the rate (20%) can be claimed that year. Commissioning by the end of September keeps the full 40%.
The calculator shows the year-one benefit as 40% of the system cost × a 30% tax rate, about 12% of the cost, and subtracts it from the price. Your real saving depends on your tax rate and regime, and on whether you have enough taxable profit to use it, so confirm it with your chartered accountant.
Under the Electricity (Rights of Consumers) Rules, net metering is available up to 500 kW or your sanctioned load, whichever is lower. Above 500 kW, systems generally move to gross metering, where all generation is sold to the DISCOM at a fixed rate. Your state's regulations set the details: some cap total solar on a distribution transformer, some use net billing instead of unit-for-unit credit, and the national rules allow commissions to apply ToD tariffs to rooftop solar prosumers. Since a 2024 amendment, systems up to 10 kW need no technical feasibility study; larger ones get the study within 15 days. Our net metering guide covers the rules in detail.
Your sanctioned load or contract demand is on the bill. If the solar system you want is bigger, the DISCOM application for the higher load usually has to come first.
These are outputs from our calculator's Earn from Surplus Space → Commercial roof mode with: Maharashtra (5.5 peak sun hours, ₹3.06/kWh export rate), Mono PERC panels, net metering capped at 100% of sanctioned load, and 90% of the output used on site. The commercial tariff is entered as ₹10/kWh, and again as ₹8/kWh to show the minimum 20% solar-hours ToD discount.
| Business use | System | System cost | Year-1 depreciation saving | Units per year | Year-1 savings at ₹10 | Payback at ₹10 | Payback at ₹8 |
|---|---|---|---|---|---|---|---|
| 3,300 units/month | 20 kW | ₹10.5 L | ₹1.26 L | 31,317 | ₹2.91 L | 3.2 years | 3.9 years |
| 6,600 units/month | 40 kW | ₹19.6 L | ₹2.35 L | 62,634 | ₹5.83 L | 3.0 years | 3.7 years |
| 16,500 units/month | 100 kW | ₹44.5 L | ₹5.34 L | 1,56,585 | ₹14.57 L | 2.7 years | 3.3 years |
Self-consumption decides the return. The same 40 kW system with only 50% of its output used on site (for example, a business closed at weekends with a light daytime load) saves ₹4.09 L a year at ₹10/kWh instead of ₹5.83 L, and payback stretches from 3.0 to 4.2 years (5.0 years at ₹8). Every unit exported earns ₹3.06 instead of saving ₹10.
Payback here is the calculator's simple measure: cost after the year-one depreciation saving, divided by year-one savings. It does not include financing costs, and it uses the calculator's assumptions of 3% yearly tariff rise and maintenance of 1% of the cost a year (also rising 3% a year) in the 25-year view.
If you have more roof than daytime load, the surplus space guide explains the economics of exporting the rest.
In the calculator, choose Earn from Surplus Space → Commercial roof, then enter your roof area, sanctioned load, daytime use and your own commercial tariff per unit.
Open the commercial solar calculator →