A real-size example
Take an engineering college using about 40,000 units a month at roughly ₹9 a unit. A 300 kWp rooftop plant makes around 36,000 units a month, and most of it is used while classes and labs are running.
| Indicative figure | |
|---|---|
| Plant size | 300 kWp |
| Cost | about ₹1.25 crore |
| Solar units | about 36,000 a month |
| Saving after network charges | about ₹2.5 lakh a month (₹30 lakh a year) |
| Payback | about 4 years |
These are screening numbers. Your bills, roof and sanctioned load decide the real figure.
What happens in the holidays
Colleges are closed for 10 to 12 weeks a year, plus Sundays. The plant keeps generating. Under TNPDCL net feed-in the surplus is exported and credited, but at about ₹3.10–3.61 a unit, well below what you pay for grid power. So we size the plant to the working-day load, not to the size of the roof.
Trusts and the depreciation question
Most private schools and colleges are run by trusts or societies. The accelerated depreciation that makes solar attractive for companies usually does not help them. That leaves two good routes: pay from the building fund and recover the cost in about four years, or choose RESCO, where a developer owns the plant and the institution simply pays a lower tariff from the first month.
What to bring to the board meeting
- The last 12 months of electricity bills.
- Roof plans and age. Repair a leaking roof before panels go on, not after.
- Sanctioned load, which caps how big the plant can be.
- Hostel hot-water needs. A solar water heater is cheaper than PV for that job.
- A clear target, such as "cut the power bill by half".
More detail on sizes and costs: solar for educational institutions.
FAQ
How much does solar cost for a school in Tamil Nadu?
Most schools need 20–100 kWp, which costs about ₹10–50 lakh before GST. Engineering colleges usually need 300 kWp to 1 MWp, about ₹1.25–4.2 crore.
Is there a solar subsidy for schools and colleges?
No. PM Surya Ghar and the Tamil Nadu ₹22,000 top-up cover homes only. Institutions save through lower power bills or a zero-investment RESCO agreement.
Will solar keep the college running during a power cut?
A grid-tied plant switches off when the grid fails. For labs, servers or hostels that need backup, add a battery system for those loads.