Every factory owner has heard “solar pays for itself in three years” from someone selling solar. Here is the actual arithmetic, with the assumptions visible, so you can check it against your own electricity bill.
Start With What You Pay Today
Industrial and commercial consumers in Gujarat typically pay ₹7.5–9 per unit all-in once demand charges, fuel surcharges and duties are counted. Take a unit running a 500 kW connected load through day shifts: a monthly bill of ₹8–12 lakh is normal. That is the number solar attacks.
The Worked Example: 500 kWp on a GIDC Shed
Generation. In Gujarat’s sun, a well-built rooftop plant produces roughly 1,450–1,550 units per kWp per year, call it 1,500. A 500 kWp plant therefore generates about 7.5 lakh units a year. That figure already includes monsoon months; June to September produce 40–60% of peak, and any honest annual estimate bakes that in.
Value. If your plant self-consumes that power at ₹8 a unit, the behind-the-meter model, where solar directly offsets what you’d have bought, that’s ₹60 lakh a year of avoided purchase. Self-consumption is the whole game: surplus exported to the grid is compensated at a fraction of retail rates, so we size systems to your daytime load, not your roof area.
Capex. At 2026 prices, quality C&I rooftop installations in Gujarat land around ₹2.2–2.6 crore for 500 kWp depending on structure complexity, inverter topology and evacuation work. Take ₹2.4 crore.
Simple payback: 2.4 crore ÷ 60 lakh = four years. And that’s before tax treatment.
The Accelerated Depreciation Kicker
Solar assets qualify for 40% accelerated depreciation under the Income Tax Act. For a profitable company in the ~25% bracket, that’s roughly ₹24 lakh of tax deferred into year one on our example plant, which typically pulls effective payback into the low threes. Your CA can confirm how it applies to your company.
After Breakeven: Twenty-One Years of Margin
Panels degrade slowly, around 0.5% a year on quality modules. From year four to year twenty-five, the plant produces power at an effective cost of just the O&M contract: cleaning, monitoring, inverter service. That works out to well under ₹1 per unit. Every tariff hike your DISCOM announces after that is someone else’s problem.
What Can Go Wrong (and How It’s Avoided)
- Dirty panels. Gujarat dust can quietly eat 10–15% of generation. Budget for a cleaning cycle every two to three weeks; it’s the highest-ROI maintenance in industry.
- Weak structures. Cyclone-season gusts don’t negotiate. Insist on wind-load calculations for your specific site, not a copy-pasted design.
- Optimistic generation claims. If a quote assumes more than ~1,600 units/kWp/year for a fixed rooftop in Gujarat, someone is selling you a spreadsheet, not a power plant.
- Under-sized cabling and protection. The cheapest place to cut corners, and the most expensive place to have cut them.
The Bottom Line
For a Gujarat factory buying power at ₹8, a properly engineered rooftop plant returns its cost in three to four years and then produces near-free power for two decades. Very few capital investments on your shop floor can say the same.
Grow Energies’ founding partners have delivered rooftop, industrial and utility-scale solar across Gujarat. Send us a recent electricity bill and we’ll return the same worked example with your numbers in it.