Calculator Inputs
Enter roof dimensions, solar assumptions, electricity values, and lifetime settings. Results appear above this form after submission.
Example Data Table
| Scenario | Roof Area (m²) | Panels | System Size (kW) | Annual Output (kWh) | Annual Value |
|---|---|---|---|---|---|
| Compact urban home | 54.00 | 18 | 8.10 | 10,950 | $1,730 |
| Suburban family roof | 96.00 | 34 | 15.30 | 20,880 | $3,170 |
| Shaded mixed roof | 84.00 | 24 | 10.80 | 12,960 | $1,860 |
| Open commercial section | 180.00 | 68 | 30.60 | 43,500 | $6,350 |
Formula Used
1. Roof area
Roof Area = Roof Length × Roof Width
2. Usable area after setbacks and obstructions
Usable Area = Roof Area × Usable Area % × (1 − Obstruction %)
3. Panel count
Panel Count = floor(Usable Area ÷ Panel Area)
4. Installed size
Installed DC Size (kW) = Panel Count × Panel Wattage ÷ 1000
5. Annual generation
Annual kWh = DC Size × Peak Sun Hours × 365 × Orientation Factor × Tilt Factor × Shading Factor × System Loss Factor × Temperature Factor × Soiling Factor × Inverter Factor
6. Annual energy value
Annual Value = (Self Consumed kWh × Retail Rate) + (Exported kWh × Export Rate)
7. Payback period
Payback = Installed Cost ÷ Annual Value
8. Lifetime generation multiplier
Lifetime Multiplier = (1 − (1 − Degradation Rate)Years) ÷ Degradation Rate
How to Use This Calculator
- Enter roof length and width in meters.
- Set the usable percentage for safe installation space.
- Add obstruction losses for vents, skylights, setbacks, and access paths.
- Provide module size, wattage, and local peak sun hours.
- Adjust orientation, tilt, shading, temperature, soiling, and system losses.
- Input electricity usage, rates, self-consumption, and installed cost.
- Choose degradation and analysis period for lifetime estimates.
- Submit the form to view results above, then export CSV or PDF.
Frequently Asked Questions
1. What does roof solar potential mean?
It estimates how much solar capacity your roof can hold and how much electricity that system may produce. It also values the energy, estimates payback, and shows long-term savings under your chosen assumptions.
2. Why is usable roof area lower than total roof area?
Not every square meter can take panels. Walkways, fire setbacks, chimneys, vents, skylights, and maintenance clearances reduce the space available for safe and code-friendly installation.
3. Why do orientation and tilt matter?
Panel direction and angle affect how much sunlight reaches the modules across the year. Better alignment usually improves annual output, while poor orientation lowers the generation estimate.
4. What are peak sun hours?
Peak sun hours represent the average daily solar energy equivalent to one hour at full solar intensity. They simplify local solar resource into a practical number for annual generation estimates.
5. Why are there several loss inputs?
Solar systems lose energy through shading, cable and inverter losses, heat, dirt, mismatch, and other real-world effects. Separate loss fields make the estimate more flexible and closer to practical conditions.
6. What is self-consumption percentage?
It is the share of solar electricity used directly on-site instead of exported. Higher self-consumption often improves savings when retail electricity prices are higher than export credit rates.
7. Is payback the same as profit?
No. Payback shows how many years it takes for annual energy value to recover installation cost. Profit or net savings looks beyond payback and includes value gained after that point.
8. Can I use this for preliminary project screening?
Yes. It works well for early comparisons and rough sizing. Final design should still confirm structural limits, local codes, inverter sizing, wiring, module spacing, and site-specific solar resource data.