Irradiation onto inclined plane

The global irradiation onto the inclined plane $E_\text{GTI}$ (Global Tilted Irradiance) results to:

$$ E_\text{GTI} = E_\text{BTI} + E_\text{DTI} + E_\text{RTI} $$

The direct radiation to the horizontal $E_\text{BHI}$ (Beam Horizontal Irradiance) can be calculated from the geometric conditions (cosine) over the elevation angle of the $\gamma_\text{M}$ to the inclined plane to the direct radiation to the inclined plane $E_\text{BTI}$ (Beam Tilted Irradiance).

For more information on reflected radiation onto the inclined plane $E_\text{RTI}$ (Reflected Tilted Irradiance), see Calculation > Irradiation > Ground reflection.

For the calculation of diffuse irradiation onto the inclined plane $E_\text{DTI}$ (Diffuse Tilted Irradiance) the following models are available:

Hay & Davies (Default model)

In previous versions of PV*SOL® only this model was available

Hay, J. E., & Davies, J. A. (1980). Calculation of the Solar Radiation Incident on an Inclined Surface. In Proceedings of First Canadian Solar Radiation Data Workshop. Toronto.

Liu & Jordan

Liu, B. Y. H., & Jordan, R. C. (1960). The interrelationship and characteristic distribution of direct, diffuse and total solar radiation. Solar Energy, 4(3), 1–19.


Klucher, T. M. (1979). Evaluation of models to predict insolation on tilted surfaces. Solar Energy, 23(2), 111–114.


Perez, R., Seals, R., Ineichen, P., Stewart, R., & Menicucci, D. (1987). A new simplified version of the perez diffuse irradiance model for tilted surfaces. Solar Energy, 39(3), 221–231.


Reindl, D. T., Beckman, W. A., & Duffie, J. A. (1990). Evaluation of hourly tilted surface radiation models. Solar Energy, 45(1), 9–17.