# pvlib.iam.martin_ruiz_diffuse¶

pvlib.iam.martin_ruiz_diffuse(surface_tilt, a_r=0.16, c1=0.4244, c2=None)[source]

Determine the incidence angle modifiers (iam) for diffuse sky and ground-reflected irradiance using the Martin and Ruiz incident angle model.

Parameters
• surface_tilt (float or array-like, default 0) – Surface tilt angles in decimal degrees. The tilt angle is defined as degrees from horizontal (e.g. surface facing up = 0, surface facing horizon = 90) surface_tilt must be in the range [0, 180]

• a_r (numeric) – The angular losses coefficient described in equation 3 of 1. This is an empirical dimensionless parameter. Values of a_r are generally on the order of 0.08 to 0.25 for flat-plate PV modules. a_r must be greater than zero.

• c1 (float) – First fitting parameter for the expressions that approximate the integral of diffuse irradiance coming from different directions. c1 is given as the constant 4 / 3 / pi (0.4244) in 1.

• c2 (float) – Second fitting parameter for the expressions that approximate the integral of diffuse irradiance coming from different directions. If c2 is None, it will be calculated according to the linear relationship given in 3.

Returns

• iam_sky (numeric) – The incident angle modifier for sky diffuse

• iam_ground (numeric) – The incident angle modifier for ground-reflected diffuse

Notes

Sky and ground modifiers are complementary: iam_sky for tilt = 30 is equal to iam_ground for tilt = 180 - 30. For vertical surfaces, tilt = 90, the two factors are equal.

References

1(1,2)

N. Martin and J. M. Ruiz, “Calculation of the PV modules angular losses under field conditions by means of an analytical model”, Solar Energy Materials & Solar Cells, vol. 70, pp. 25-38, 2001.

2

N. Martin and J. M. Ruiz, “Corrigendum to ‘Calculation of the PV modules angular losses under field conditions by means of an analytical model’”, Solar Energy Materials & Solar Cells, vol. 110, pp. 154, 2013.

3

“IEC 61853-3 Photovoltaic (PV) module performance testing and energy rating - Part 3: Energy rating of PV modules”. IEC, Geneva, 2018.