Model step
Incidence-angle modifier, beam
Reflection loss of beam irradiance
Inputs used: ASHRAE b₀, AR-coated glass, module.iam_angles_deg, iam.angles_deg
What it is
Glass reflects more light as the sun moves away from perpendicular. The incidence-angle modifier is the curve that gives the accepted fraction of the direct sunlight as a function of the incidence angle. The next step turns it into factors for the diffuse light. The automatic choice, the default of the API, takes the module's own curve when the module file carries one and the Fresnel curve with an anti-reflective coating otherwise.
Options
- Fresnel, AR coating: the Fresnel equations for glass with an anti-reflective coating, tabulated at nine angles
- Module IAM profile: the incidence-angle curve carried in the module file
- Fresnel, direct: the Fresnel equations for coated or plain glass
- ASHRAE b₀: the one-coefficient ASHRAE formula
- De Soto cover: the transmittance of an anti-reflective coating and glass, after De Soto, Klein and Beckman
- Tabulated: a measured table entered on the Module tab
References
- ASHRAE Standard 93-2010, Methods of testing to determine the thermal performance of solar collectors (incidence-angle modifier)
- IEC 61853-2:2016, Photovoltaic module performance testing and energy rating, Part 2: spectral responsivity, incidence angle and module operating temperature measurements
API
iam.kind = auto | fresnel_ar | module_profile | fresnel | ashrae | desoto | tabulated