To determine photovoltaic (PV) energy from solar irradiance, you need to consider several key factors including the amount of solar irradiance received, the area and efficiency of the solar panels, and the time over which the energy is collected. Solar irradiance, measured in watts per square meter (W/m²), represents the power of sunlight hitting the panel surface. By multiplying this irradiance by the panel’s surface area, the efficiency of the panel (as a decimal), the duration of sunlight exposure in hours, and optionally a performance ratio (to account for real-world losses like shading, temperature, or inverter inefficiencies), you can estimate the total energy output. The basic formula is: Energy (Wh) = Irradiance × Area × Efficiency × Time × Performance Ratio. If irradiance data varies over time, you would integrate or sum the energy produced over each time interval. This approach allows for a practical estimation of how much electrical energy a solar PV system can produce under given conditions.

According to the Joint Research Centre: EU Science Hub, to determine Photovoltaic Energy from Solar Irradiance, the following are the steps to be implemented:

1. Understand Solar Irradiance vs. Irradiation

Irradiance is the instantaneous solar power per unit area (W/m²), while irradiation is the accumulated energy over time (Wh/m²). PV system energy calculations typically use daily or monthly irradiation data rather than momentary irradiance, because it already integrates sunlight throughout the interest period.

2. Select Your Time Basis

• Instantaneous power (P in W): P = I(t) × A × η • I(t): solar irradiance at time t (W/m²) • A: module area (m²) • η: module efficiency (decimal)
• Daily energy (E in kWh/day): E = H × A × η × PR • H: daily irradiation (kWh/m²/day) • PR: performance ratio (accounts for losses; 0.75–0.85 typical)

3. Factor in System Parameters

4. Step-by-Step Calculation

Over a year, multiply by 365 (adjust for seasonal variation).

5. Integrate Over Time for Instantaneous Data

If you have a timeseries of irradiance I(t) (e.g., from a pyranometer):

This yields the same result as using daily H, but captures transient shading or weather effects more accurately.

6. Tips for Greater Accuracy

• Use real module temperature coefficients to adjust η for heat losses.
• Account for inverter efficiency separately if it is not included in the PR.
• Include wiring and mismatch losses (typically 2–5%).
• Validate results with post-installation monitoring data to refine the PR.

By following these steps—choosing the right irradiation data, applying module specs, and incorporating loss factors—you can reliably convert solar irradiance into expected PV energy yield.