Solar Generation Calculator
Estimate daily, monthly and annual generation from a PV system using peak sun hours and performance ratio, with CO₂ savings and bill savings.
Inputs
Formula
- E_daily = kWp × PSH × PR
- E_annual = E_daily × 365
- E_year_n = E_annual × (1 − d)^(n−1)
- CO₂ avoided = E_annual × grid carbon intensity
Peak sun hours express the day's total irradiation as an equivalent number of hours at 1000 W/m², so a 1 kWp array in a 5 PSH location receives 5 kWh/m² per day. The performance ratio then removes real-world losses — temperature, soiling, mismatch, inverter and wiring — which together consume 18–25% of the theoretical output on a well-built system.
Step-by-step calculation
Daily energy
kWp × PSH × PR
19.5 kWh
Annual energy
daily × 365
7,117.5 kWh
Specific yield
annual / kWp
1,423.5 kWh/kWp
Lifetime energy
Σ annual × (1 − d)ⁿ, n = 0…24
165,696 kWh
Worked example
- 5 kWp system, 5 PSH, PR 78%.
- Daily = 5 × 5 × 0.78 = 19.5 kWh; annual = 7 118 kWh.
- At ₹8/kWh that is ₹56,940 saved and 5.05 tonnes of CO₂ avoided each year.
Assumptions
- PSH already reflects the array tilt and orientation for the site.
- PR 75–80% is typical for a well-designed rooftop system; below 70% indicates shading or losses.
Tips
- Use site-specific PSH from PVGIS or NASA POWER rather than a national average.
- Cleaning the modules quarterly recovers 2–5% of annual yield in dusty regions.
Standards & references
- IEC 61724 (performance monitoring)
- IEC 61853
Frequently asked questions
How many units does a 1 kW solar system generate per day?
About 4 kWh per day in a 5 PSH location at a 78% performance ratio, which is roughly 1 460 kWh per year.
What is a good performance ratio?
75–80% for a rooftop system and 80–85% for a well-engineered ground-mount plant. Below 70% points to shading, soiling or inverter clipping.
Does generation fall over time?
Yes — modules degrade about 0.5–0.7% per year, so output after 25 years is typically 84–88% of the first-year figure.
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