Solar roof capacity calculator
How much solar your roof can take, in kW and panels, and what that system would make and cost. Enter the roof's area or its length and width.
What your roof can take
Usable roof fits about
6.4 kW of panels
| Roof area | 800 sq ft |
|---|---|
| Usable areaAfter shade, tanks, stairs and walkways | 640 sq ft |
| Capacity the usable area takesAt 100 sq ft per kW, including gaps between rows | 6.4 kW |
| Largest standard on-grid systemLimited by your sanctioned load | 5 kW |
| PanelsAt the panel size you chose | 10 |
| Average units a monthAveraged over the year | 510 |
| Estimated installed priceOn-grid, before subsidy | ₹2,50,000 to 2,75,000 |
| PM Surya Ghar subsidyPaid to your bank after inspection | − ₹78,000 |
- A net-metered system cannot be larger than the sanctioned load. To use more of the roof, apply to PSPCL for a load increase first.
- The right size depends on your bill as well as your roof. A home in Punjab often needs less than the roof allows, because the bill is already zero once net use is under 300 units a month.
Check it on your roof
Send us a few photos of the roof and your last bill. We confirm the layout, the size your bill needs and the price.
An estimate from the area you entered. The final layout depends on the roof's direction, shade through the day and where the structure can be fixed.
Example: an 800 sq ft roof, mostly clear, 5 kW sanctioned load, 555 W panels. Enter your own figures above.
How it works it out
- Usable area is the roof area times the share you say is clear.
- Capacity is the usable area divided by 100 sq ft per kW, the planning figure every calculator on this site uses. It allows for the gaps between rows.
- The system is the largest of our standard on-grid sizes that fits both the roof and, if you enter it, your sanctioned load. On-grid sizes start at 3 kW.
- Units a month use 102 units per kW, averaged over the year after losses. See how many units 1 kW makes.
- The price is our published on-grid range for that size, and the subsidy is the PM Surya Ghar amount for a home: ₹30,000 per kW for the first 2 kW, ₹18,000 for the third, up to ₹78,000.
Prices are estimates for a first conversation, not a quotation. The roof's direction, shade and structure decide the final layout.
Questions we are asked
How much roof does a 1 kW solar system need?
About 100 sq ft of shade-free roof per kW. That includes the gaps between rows that keep one row from shading the next and leave room to walk and clean. A 3 kW system needs about 300 sq ft.
Should I fill my whole roof with panels?
Not always. In Punjab a home's bill is already zero once its net use is under 300 units a month, so a system bigger than the bill needs adds little. The roof sets the most you can fit; your bill sets what is worth fitting. The solar calculator works out the second.
Can the system be bigger than my sanctioned load?
No. A net-metered rooftop system in Punjab can be at most 100% of the sanctioned load printed on your bill. To fit more, apply to PSPCL for a load increase before the solar application.
What counts as usable roof?
Roof that gets sun for most of the day and has room for the structure. Take out water tanks, stair rooms, parapet edges and anything that throws a shadow in the middle of the day, such as a taller building next door.