How to Choose the Right Capacity for Your Rooftop Solar System in India (2025 Guide)
Switching to rooftop solar is a smart decision — it saves money, reduces your carbon footprint, and gives you energy independence.
But here’s the tricky part: how do you know what capacity of solar system you actually need?
If you choose a system that’s too small, it won’t cover your needs. If it’s too big, you’ll end up spending more than necessary.
Let’s break it down step-by-step in simple terms.rooftop solar capacity
1. Understand What “Capacity” Means
The capacity of a solar system is measured in kilowatts (kW).
Example: A 5 kW solar system can generate roughly 20–25 units (kWh) of electricity per day in good sunlight conditions.
2. Check Your Monthly Electricity Usage
The first step is to know how much electricity you actually use.
- Look at your last 12 months’ electricity bills.
- Note the average monthly units (kWh).
- Example: If you use 600 units per month, that’s about 20 units per day.
3. Match Your Consumption with Solar Output
In India, 1 kW of rooftop solar generates 4–5 units per day on average.
So, the formula is:
Required Solar Capacity (kW) = Your Daily Consumption (units) ÷ 4–5
Example:
Daily consumption = 20 units
20 ÷ 4 = 5 kW system needed
4. Consider Your Roof Space
Each 1 kW solar system needs about 100 sq. ft. of shadow-free roof space.
| Solar Capacity | Roof Space Needed |
|---|---|
| 1 kW | ~100 sq. ft. |
| 3 kW | ~300 sq. ft. |
| 5 kW | ~500 sq. ft. |
| 10 kW | ~1000 sq. ft. |
Tip: Ensure there are no tall trees or buildings casting shadows on your panels.
5. Decide Between Partial or Full Load Coverage
- Full load coverage: Your system meets all your needs year-round.
- Partial coverage: The system covers part of your needs, and the rest comes from the grid.
If your budget is limited, you can start small and expand later.
6. Factor in Net Metering
With net metering, extra electricity you produce is sent to the grid and adjusted in your bill.
If your state offers this, it’s worth installing a slightly bigger system to maximize savings.
7. Plan for the Future
Think about upcoming changes:
- Adding new appliances like ACs or EV chargers?
- Planning to shift to electric cooking?
If yes, choose a slightly higher capacity to cover future needs.
8. Consult a Solar Expert
While calculations help, a professional site visit ensures accuracy. Experts measure:
- Roof size
- Sunlight availability
- Wiring setup
- Inverter type suitability
Quick Example Calculation
Let’s say:
- Monthly usage = 900 units
- Daily usage = 30 units
- In India, 1 kW solar = ~4.5 units/day
So:
30 ÷ 4.5 = 6.6 kW
You’d need around 6.5–7 kW capacity.
Key Takeaways
- Check your daily average consumption.
- Match it with solar output in your area.
- Ensure you have enough shadow-free roof space.
- Plan for future expansion.
- Always confirm with a professional.