Solar Panel Output Calculator
Calculate daily and monthly energy output from your solar panels.
Factor in panel wattage, sunlight hours, and system efficiency.
Solar panel output is the actual electricity a panel produces under real-world conditions — which is always less than the rated wattage due to temperature, shading, wiring losses, and inverter efficiency.
The Formula:
Daily output (kWh) = Panel wattage × Peak sun hours × System efficiency
System efficiency = 0.70–0.80 (accounts for all real-world losses)
Peak Sun Hours by Region:
| Region | Peak Sun Hours/Day (annual avg) |
|---|---|
| US Southwest (Phoenix, LA) | 5.5–6.5 |
| US Southeast (Florida) | 4.5–5.5 |
| US Northeast (New York) | 3.5–4.5 |
| UK / Northern Europe | 2.5–3.5 |
| Middle East / Australia | 5.5–7.0 |
| Northern Canada / Scandinavia | 2.0–3.0 |
Loss Factors:
| Loss Source | Typical Reduction |
|---|---|
| Temperature (hot climates) | 5–15% |
| Inverter efficiency | 3–5% |
| Wiring and connections | 2–3% |
| Soiling / dust | 2–7% |
| Shading | 0–50%+ |
| Total real-world losses | 20–30% |
Worked Example:
400W panel in Phoenix, Arizona. 6 peak sun hours. System efficiency = 0.78.
Daily output = 0.4 kW × 6 h × 0.78 = 1.87 kWh/day
Monthly = 1.87 × 30 = 56 kWh/month
10-panel system: 560 kWh/month — enough for a typical US home.
Practical Tips:
- Panels degrade about 0.5% per year — after 25 years, expect ~87% of original output
- South-facing panels at 30–35° tilt maximize annual output in the northern hemisphere
- Even partial shading on one panel can reduce output of the entire string by 30–80% — use microinverters or DC optimizers to mitigate this