Solar radiation of average energy ~1.25 eV and intensity 500 W/m² are incident on the surface of a solar flat plate collector. What is the approximate photon flux density impinging on the surface of the collector?
1
~5 × 10²² photons m⁻²s⁻¹
2
~2 × 10²² photons m⁻²s⁻¹
3
~2.5 × 10²⁰ photons m⁻²s⁻¹
4
~2.5 × 10²¹ photons m⁻²s⁻¹