International Solar Alliance · Rooftop solar
Rooftop Solar Calculator
Find out how large a solar system your roof can take, how much of your electricity it can cover, what it saves you each month and how soon it pays for itself.
Your home or building
Four figures, one minute
Your latest electricity bill has the monthly use and amount. All results are monthly averages, in US dollars.
Roof area free for panels *Shade-free roof only. 1 kWp of panels needs about 100 sq ft (9.3 m²).
Behind the numbers
How it works
- Roof to system size. As a rule of thumb, 1 kWp of solar panels fits on 100 sq ft of roof.
- System to generation. Each kWp generates the country’s daily solar output (Global Solar Atlas) for 30 days a month.
- Sized to your use. The system is the smaller of what the roof takes and what covers all your use.
- Savings and payback. Solar units are valued at your own electricity rate (bill ÷ use); the payback is the system cost over the yearly savings.
The calculator is for standalone rooftop systems. The average installed cost per watt varies with supplier and site; the values are an average of the sources below.
Country data and sources
| Country | Sunshine kWh/kWp/day | Cost USD/W |
|---|---|---|
| BangladeshSolar Panel Price in Bangladesh - Solar Tech Bangladesh | 3.798 | 0.97 |
| BeninIRENA, Renewable power generation costs in 2024 | 4.209 | 1.10 |
| BhutanTariff Determination Regulation 2025 (Bhutan) | 3.934 | 0.53 |
| Côte d'IvoireIRENA, Renewable power generation costs in 2024 | 3.984 | 1.10 |
| CubaCuba recurre al sol ante apagones: cost of a domestic PV system | 4.533 | 2.50 |
| EthiopiaIRENA, Renewable power generation costs in 2024 | 5.126 | 1.10 |
| FijiFiji packages - Solar Hub NZ, Fiji & Pacific | 4.024 | 2.80 |
| GhanaIRENA, Renewable power generation costs in 2024 | 4.083 | 1.10 |
| KiribatiTaken as for Fiji (Oceania) | 4.794 | 2.80 |
| SomaliaIRENA, Renewable power generation costs in 2024 | 4.939 | 1.10 |
Solar output: Global Solar Atlas.