Enter system and site assumptions
Use the direct system size field or let module count and wattage calculate it automatically.
Core calculation model
1. DC system size: DC Size (kW) = Module Wattage × Module Count ÷ 1000, unless a direct system size override is entered.
2. Performance ratio: PR = Tilt Factor × (1 − Soiling) × (1 − Shading) × (1 − Wiring) × (1 − Mismatch) × (1 − Availability) × (1 − Temperature) × Inverter Efficiency.
3. Daily generation: Daily Energy = DC Size × Peak Sun Hours × PR.
4. Monthly generation: Monthly Energy = Daily Energy × Days in Billing Month.
5. Annual generation: Annual Energy = Daily Energy × 365 × (1 − First-Year Degradation).
Capacity factor is based on AC size, where AC Size = DC Size ÷ DC/AC Ratio. Specific yield equals annual generation divided by DC size.
Recommended workflow
- Enter either a direct DC system size or fill module wattage and module count.
- Add realistic peak sun hours for the site using local solar resource data.
- Adjust tilt, shading, temperature, and loss assumptions to match project conditions.
- Set DC/AC ratio, monthly consumption, tariff, and grid factor for deeper financial and carbon insight.
- Press the calculate button to display the result summary above the form.
- Use the CSV and PDF buttons to save the generated output for reporting.
Sample project assumptions and results
| Item | Example Value | Notes |
|---|---|---|
| Module wattage | 550 W | High-efficiency residential or light commercial module. |
| Module count | 18 | Total DC size becomes 9.90 kW. |
| Peak sun hours | 5.60 | Average daily equivalent full-sun irradiance. |
| Total net performance ratio | 79.51% | After orientation and system losses. |
| Daily generation | 44.08 kWh | Average modeled daily energy output. |
| Monthly generation | 1,322.40 kWh | Based on a 30-day billing month. |
| Annual generation | 15,960.55 kWh | First-year value after degradation. |
| CO2 avoided | 6.70 tonnes | Using a 0.42 kg/kWh grid factor. |
This sample helps validate the calculator and gives users a realistic reference scenario.
Common questions
1. What does peak sun hours mean?
Peak sun hours convert daily solar irradiation into an equivalent number of full-power sunshine hours. It simplifies energy estimation without modeling every hourly weather change.
2. Why include so many loss factors?
Solar systems rarely operate at ideal nameplate conditions. Separate losses for shading, wiring, soiling, mismatch, temperature, and downtime produce a more realistic performance ratio.
3. Should I use direct system size or module inputs?
Use direct system size when the array capacity is already known. Use module wattage and count when designing a new layout or checking the total DC size.
4. What does the DC/AC ratio affect?
The DC/AC ratio converts installed DC nameplate into approximate inverter-side AC capacity. It influences capacity factor and helps compare sizing strategies for clipping risk.
5. Is annual generation the same every year?
No. Real systems change with weather variability, equipment aging, and maintenance quality. This calculator estimates first-year production after applying the selected degradation factor.
6. How accurate is the bill offset result?
It is a planning estimate. Actual bill savings depend on tariffs, export credits, time-of-use pricing, self-consumption patterns, seasonal demand, and utility billing rules.
7. Can I use this for off-grid projects?
Yes, for generation estimation only. Off-grid system design still requires battery sizing, depth of discharge, autonomy days, inverter surge checks, and load scheduling.
8. What is specific yield used for?
Specific yield shows annual energy per installed DC kilowatt. It is useful for comparing project quality, climate suitability, and system performance across differently sized arrays.