Calculator Inputs
Example Data Table
| Case | System (kW) | Sun hours | PR | Total loss | Daily kWh | Annual kWh |
|---|---|---|---|---|---|---|
| A | 5.0 | 5.0 | 0.80 | ~12% | ~17.0 | ~6,200 |
| B | 7.0 | 4.5 | 0.82 | ~15% | ~22.0 | ~8,000 |
| C | 10.0 | 5.5 | 0.78 | ~18% | ~33.0 | ~12,000 |
Formula Used
This calculator estimates energy using a practical engineering approximation:
- PkW is system size in kW (or panels × wattage ÷ 1000).
- PSH is peak sun hours per day.
- PR is performance ratio (0–1) covering real‑world system effects.
- ηinv is inverter efficiency as a decimal.
- L is combined losses: (1−tilt)(1−shading)(1−soiling)(1−wiring).
- T is temperature factor from NOCT, ambient temperature, and coefficient.
How to Use This Calculator
- Pick a sizing mode: system size or panel count × wattage.
- Enter peak sun hours and the period days you want.
- Set performance ratio and inverter efficiency from your equipment.
- Adjust loss factors for shading, tilt, soiling, and wiring quality.
- Optionally model temperature effects using ambient, NOCT, and coefficient.
- Press Calculate to view results above, then download CSV or PDF.
System sizing benchmarks
A 5.0 kW rooftop array with 5.0 peak sun hours can produce about 25.0 kWh/day at nameplate. After a 0.80 performance ratio and 97% inverter efficiency, output often lands near 19.4 kWh/day before site losses and temperature effects. Ten 550 W modules equal 5.50 kW, useful for quick panel-based sizing.
Sun hours and seasonal spread
Peak sun hours drive linear change: moving from 4.0 to 5.5 hours raises daily energy by 37.5%. For the same system, that is the difference between roughly 120 kWh/week and 165 kWh/week. Many sites see monthly swings of 15–35%, so comparing a 30‑day period with annualized output reduces seasonal bias.
Loss factor sensitivity
Losses multiply, not add. A 3% tilt loss, 5% shading loss, 2% soiling loss, and 2% wiring loss combine to 0.88 retention, meaning 12% overall reduction. Cutting shading from 10% to 5% alone can recover about 5.6% energy. Reducing soiling from 6% to 2% improves delivered kWh by about 4.3%.
Temperature derating with NOCT
Using ambient 30°C, NOCT 45°C, and irradiance 1000 W/m², estimated cell temperature is near 61°C. With a −0.40%/°C coefficient, the temperature factor is about 0.856, a 14.4% drop versus 25°C reference. At 20°C ambient, the factor rises near 0.896, adding several percent energy in cooler months.
Export and self-consumption split
If grid export is set to 40%, a 20 kWh/day production scenario yields 12 kWh/day self-used and 8 kWh/day exported. Shifting usage to daylight or adding storage can raise self-consumption and reduce peak imports. A 3 kWh/day shift cuts exports by 37.5%.
Annualized energy and carbon impact
Annual generation is daily output multiplied by 365. A steady 18 kWh/day becomes about 6,570 kWh/year. With a 0.70 kg/kWh factor, avoided emissions are about 4,599 kg/year. Capacity factor provides a check: 18 kWh/day from 5.5 kW averages 0.75 kW, about 13.6% capacity factor.
FAQs
What peak sun hours value should I use?
Use an average daily value for your location and season. If you only have monthly irradiation, divide monthly kWh/m² by days to approximate peak sun hours for that month.
Why is performance ratio separate from losses?
Performance ratio captures broad system realities like mismatch, availability, and minor inefficiencies. The loss fields let you explicitly model site-specific factors such as shading, tilt, soiling, and wiring quality.
How does temperature affect energy estimates?
Higher cell temperature reduces module power. The calculator estimates cell temperature using ambient, NOCT, and irradiance, then applies the temperature coefficient to create a derate factor.
Can I model a different billing cycle?
Yes. Set “Days in period” to 28, 30, or any custom count up to 366. The period total updates automatically while daily and annual values remain comparable.
What does capacity factor tell me?
Capacity factor compares average output to rated capacity. It helps validate results: residential solar commonly falls around 10–20%, depending on sun hours, losses, and temperature conditions.
Are the CSV and PDF downloads identical to the screen?
They include the same key results and all inputs used in the calculation. Downloads are based on the most recent successful run saved for the current session.