Solar Panel Output Calculator

Photovoltaic Energy Generation Physics and Formulas

Solar photovoltaic (PV) modules convert sunlight into direct current (DC) electricity via the photovoltaic effect within semiconductor silicon p-n junctions. The electrical output of a solar array depends on the cumulative rated DC wattage of the installed modules, local geographic solar irradiance, and systemic derating loss factors that occur during real-world operation.

The standard formula for estimating daily AC electrical energy production (\(E_{\text{daily}}\)) is:

$$E_{\text{daily}} (\text{kWh}) = P_{\text{array}} (\text{kW}) \times \text{PSH} \times \eta_{\text{system}}$$

Where:

• \(P_{\text{array}}\) is the total nameplate DC rating of the solar array in kilowatts (Number of Panels \(\times\) Wattage per Panel / 1000).
• \(\text{PSH}\) is the geographic Peak Sun Hours per day (equivalent hours of full solar irradiance at \(1,000\text{ W/m}^2\)).
• \(\eta_{\text{system}}\) is the overall system derating efficiency factor (typically 0.78 to 0.85), which accounts for real-world environmental and electrical losses.

Monthly and annual solar generation are calculated by aggregating daily production across calendar days:

$$E_{\text{annual}} (\text{kWh}) = E_{\text{daily}} \times 365$$

$$\text{Annual Financial Savings ($)} = E_{\text{annual}} \times \text{Grid Electricity Rate ($/kWh)}$$

Understanding Peak Sun Hours (PSH) vs Daylight Hours

Peak Sun Hours (PSH) does not measure the total hours the sun is visible in the sky. Rather, one Peak Sun Hour represents the amount of solar radiation energy equivalent to \(1,000\text{ Watts per square meter}\) (\(1\text{ kW/m}^2\)) of direct normal irradiance received over the span of one hour (equal to \(1\text{ kWh/m}^2\)).

Geographical PSH averages vary significantly across regional climate zones:

• High Solar Resource (Southwest US, Australia, Middle East): 5.5 to 6.5 Peak Sun Hours per day.
• Moderate Solar Resource (Central US, Southern Europe, Southeast Asia): 4.0 to 5.0 Peak Sun Hours per day.
• Low/Moderate Solar Resource (Northern US, Northern Europe, UK): 2.8 to 3.8 Peak Sun Hours per day.

System Derating Factors and Energy Loss Breakdown

Solar panels are laboratory-tested under Standard Test Conditions (STC: \(1,000\text{ W/m}^2\) irradiance, \(25^\circ\text{C}\) cell temperature, Air Mass 1.5). In real-world rooftop and ground-mount installations, multiple physical factors reduce nameplate output by 15% to 22% overall: