Short answer
Plan about 1 kW of rooftop solar for every ₹1,000 of your monthly electricity bill. Bills of ₹500 to ₹3,499 suit 3 kW, ₹3,500 to ₹4,499 suit 4 kW, and ₹4,500 to ₹5,499 suit 5 kW.
Key Takeaways
- The simple sizing rule is about 1 kW for every ₹1,000 of monthly bill.
- A 3 kW system generates about 450 units a month and needs 300 to 400 sq ft of shade-free roof.
- A 4 kW system generates about 580 units a month.
- A 5 kW system generates at least 710 units a month and needs 500 to 650 sq ft.
- SolarSpot installs home systems of 3 kW and above.
How Do I Size a Rooftop Solar System from My Electricity Bill?
Start with your average monthly electricity bill over the last year, because summer and winter bills differ. Divide it by ₹1,000 to get a first estimate in kW, then round to the nearest standard size. A site visit then confirms the size against your sanctioned load, roof area, and shade.
Which Solar Size Matches Which Monthly Bill?
| Monthly bill | Suggested size | Roof area needed | Units per month |
|---|---|---|---|
| ₹500 to ₹3,499 | 3 kW | 300 to 400 sq ft | About 450 |
| ₹3,500 to ₹4,499 | 4 kW | 400 to 530 sq ft | About 580 |
| ₹4,500 to ₹5,499 | 5 kW | 500 to 650 sq ft | At least 710 |
| ₹8,000 and above | 8 kW and above | 800 sq ft and above | 1,130 and above |
Units vary with location, season, shade, and panel orientation. Your roof visit gives the final figure.
How Much Roof Space Does a Solar System Need?
A rooftop solar system needs about 100 to 133 sq ft of shade-free roof for every kW. A 3 kW system therefore needs 300 to 400 sq ft. An elevated structure such as the OCTASHIELD frame lifts the panels above water tanks and parapet shade, so the terrace below stays usable.
How Many Units Does a 3 kW Solar System Generate?
A 3 kW rooftop system generates about 450 units a month, or roughly 150 units per kW, under typical conditions in northern India. Output is higher on clear summer days and lower during the monsoon and winter, and yearly savings take these seasonal changes into account.
Should I Choose a Bigger Solar System Than I Need Today?
A slightly bigger system makes sense if you plan to add an air conditioner, an electric vehicle, or more family members soon. However, the system size cannot exceed your sanctioned load without a load increase from your DISCOM, so check your sanctioned load on your electricity bill first.
The Bottom Line
Plan about 1 kW of rooftop solar for every ₹1,000 of your monthly electricity bill. Bills of ₹500 to ₹3,499 suit 3 kW, ₹3,500 to ₹4,499 suit 4 kW, and ₹4,500 to ₹5,499 suit 5 kW. To confirm your size, enter your bill in the SolarSpot solar calculator or book a free roof visit to check roof space and sanctioned load.