How to Calculate Solar Panel Output Per Day — Step-by-Step
The Daily Output Formula
Calculating daily solar panel output is straightforward once you understand the key variables:
Daily Output (kWh) = Panel Wattage (kW) x Peak Sun Hours x Performance Ratio
The performance ratio (PR) accounts for all real-world losses including temperature, wiring, inverter efficiency, soiling, and shading. A well-designed system achieves a PR of 0.75–0.85.
Understanding Peak Sun Hours
Peak sun hours (PSH) represent the equivalent number of hours at full 1,000 W/m² irradiance. One PSH equals 1 kWh/m² of solar energy received.
| City | Annual Avg PSH | Summer PSH | Winter PSH |
|---|---|---|---|
| Dubai, UAE | 5.5 | 6.5 | 4.5 |
| Riyadh, KSA | 5.9 | 7.0 | 4.8 |
| Cairo, Egypt | 5.4 | 6.5 | 4.3 |
| Amman, Jordan | 5.2 | 6.8 | 3.5 |
| Kuwait City | 5.7 | 7.2 | 4.2 |
| Doha, Qatar | 5.5 | 6.8 | 4.2 |
Loss Factors Explained
| Loss Type | Typical Range | Notes |
|---|---|---|
| Temperature | 5–15% | Higher in hot climates; depends on temp coefficient |
| Inverter efficiency | 2–4% | Modern inverters are 96–98% efficient |
| Wiring (DC + AC) | 1–3% | Minimised with proper cable sizing |
| Soiling / dust | 2–15% | Higher in desert; mitigated by regular cleaning |
| Shading | 0–10% | Depends on site; use optimisers if significant |
| Mismatch | 1–2% | Slight differences between panels in a string |
| Degradation | 0–2% | Year 1: ~1% for PERC, ~0.5% for N-type |
Calculation Examples
Example 1: Single LONGi Hi-MO 7 (590W) in Dubai
Daily output = 0.590 kW × 5.5 PSH × 0.80 PR = 2.60 kWh/day
Annual output = 2.60 × 365 = 949 kWh/year
Example 2: 10 kW System (17 Hi-MO 7 panels) in Riyadh
Daily output = 10.03 kW × 5.9 PSH × 0.78 PR = 46.2 kWh/day
Annual output = 46.2 × 365 = 16,863 kWh/year
Example 3: 20 kW System in Cairo
Daily output = 20 kW × 5.4 PSH × 0.80 PR = 86.4 kWh/day
Annual output = 86.4 × 365 = 31,536 kWh/year
Seasonal Variation
Daily output varies significantly by season. In Dubai, a system that produces 3.0 kWh per panel in June may only produce 2.0 kWh in December — a 33% seasonal swing. Always design your system based on annual average rather than peak summer output.
How to Verify Your Calculation
Use the Global Solar Atlas (globalsolaratlas.info) to look up the specific yield (kWh/kWp) for your exact location. For the UAE, typical specific yields range from 1,600–1,800 kWh/kWp per year.
Frequently Asked Questions
How much electricity does a 590W LONGi panel produce per day?
In Dubai (5.5 PSH, 80% PR), a 590W LONGi Hi-MO 7 panel produces approximately 2.60 kWh per day, or about 949 kWh per year.
Why is my solar system producing less than calculated?
Common causes include higher-than-expected soiling (clean panels regularly), partial shading, inverter clipping, or a performance ratio lower than assumed. Monitor your system daily to identify issues early.
Does solar output change with seasons?
Yes, significantly. UAE summer output can be 30–50% higher than winter due to longer days and higher sun angle. However, extreme summer heat partially offsets this advantage through temperature losses.
Frequently Asked Questions
How much does a 590W LONGi panel produce per day?
In Dubai (5.5 PSH, 80% PR), approximately 2.60 kWh per day or 949 kWh per year.
Why is my system producing less than calculated?
Common causes: soiling, partial shading, inverter clipping, or lower performance ratio. Monitor daily to identify issues.
Does solar output change with seasons?
Yes. UAE summer output can be 30–50% higher than winter, though extreme heat partially offsets gains through temperature losses.
