Calculator Inputs
Use the responsive grid below. Large screens show three columns, smaller screens show two, and mobile shows one.
Plotly Graph
The chart compares projected monthly production against the adjusted monthly energy target.
Example Data Table
This sample row demonstrates how the calculator sizes an array for a typical medium-load system.
| Daily Load (kWh/day) |
Peak Sun Hours | Panel Wattage (W) |
Reserve Margin (%) |
Required Array (W) |
Panel Count | Installed Array (W) |
Array Area (m²) |
Annual Energy (kWh) |
|---|---|---|---|---|---|---|---|---|
| 18.00 | 5.50 | 550.00 | 20.00 | 5,293.93 | 10 | 5,500.00 | 26.00 | 8,190.88 |
Formula Used
1. Performance ratio
Performance Ratio = Inverter × Controller × Cable × (1 − Shading) × (1 − Dust) × (1 − Temperature)
2. Adjusted daily load
Adjusted Load (Wh/day) = Daily Load (Wh/day) × (1 + Reserve Margin)
3. Required array capacity
Required Array (W) = Adjusted Load ÷ (Peak Sun Hours × Performance Ratio)
4. Panel quantity
Panel Count = Ceiling(Required Array ÷ Panel Wattage)
5. Installed area
Array Area (m²) = Panel Count × Panel Area
6. Estimated annual energy
Annual Energy (kWh) = Installed Array × Peak Sun Hours × Performance Ratio × 365 ÷ 1000
This method is practical for preliminary sizing. Final engineering should still confirm local irradiance, tilt, azimuth, wiring limits, temperature coefficients, and code compliance.
How to Use This Calculator
- Enter the site’s daily energy demand in kilowatt-hours.
- Add realistic peak sun hours for the installation location.
- Enter the intended panel wattage and system voltage.
- Input inverter, controller, and cable efficiencies.
- Add shading, dust, and temperature losses honestly.
- Set a reserve margin for growth and cloudy periods.
- Provide panel area and available roof area.
- Submit the form to view results, graph, and download options.
Frequently Asked Questions
1. What does peak sun hours mean?
Peak sun hours represent the equivalent number of full-intensity sunlight hours received in one day. It converts varying sunlight levels into a single sizing figure for energy calculations.
2. Why do losses matter so much in array sizing?
Real systems never deliver nameplate power all day. Heat, cable resistance, inverter conversion, controller losses, dust, and shading all reduce usable energy, so ignoring them undersizes the array.
3. Why is reserve margin included?
Reserve margin adds extra capacity for future loads, weather variability, seasonal swings, and equipment aging. It helps avoid systems that only work under ideal conditions.
4. Is this calculator for grid-tied or off-grid systems?
It can support early sizing for both, but it is especially useful for preliminary off-grid planning because reserve margin and detailed loss assumptions strongly affect array requirements.
5. Why does the panel count round up?
Panels are purchased as whole units, so any fractional requirement must round up. The extra capacity is usually beneficial because it offsets future degradation and imperfect conditions.
6. What if the array does not fit the roof?
You can choose higher-wattage modules, reduce demand, improve efficiency, use a ground mount, or redesign the system. Roof fit is a practical constraint, not just an electrical one.
7. Does this replace a professional solar design?
No. It is an advanced planning tool, but final design should verify local solar resource data, structural loading, electrical protection, code rules, mounting layout, and utility requirements.
8. Can I use this for expansion planning?
Yes. Increase the reserve margin or daily load to test future demand. That gives a fast way to compare present sizing against expected growth scenarios.