Bifacial Modeling - BPOA to RMAD

[Spencer Zanardi]

Hi Everyone,

I'm looking to integrate the bifacial.power_mismatch_deline function into the model I've constructed so I can calculate the mismatch loss from the back side irradiance non-uniformity. Unfortunately, all I have is one BPOA (rPOA) sensor onsite to measure the rear side irradiance, while the example shows I'll need irradiance levels across each row in order to determine RMAD.

How can I convert a single measurement point to an RMAD value to use in the power mismatch function?

Best,

Spencer

[Echedey]

Hi Spencer,

> How can I convert a single measurement point to an RMAD value to use in the power mismatch function?

You can't. RMAD is akin to variance (or standard distribution). You need a set of values to compute a realistic value.

The main drawback I saw when documenting this model into pvlib was exactly where to source the RMAD from. There is a modelling gap to map system and weather characteristics to an usable RMAD. I propose some suggestions below, in case you can use any of them:

0. Get your hands on more sensors. Reference cells should be enough and cost-effective.
1. Put your sensor on a linear actuator - and sweep it to take measurements.
2. The implementation reference also proposes models based on standard deviation (with different forms and coefficients). I didn't find, but there may be models out there that relate system and weather to non-uniformity stdev.
3. I don't know of software you can use to model the non-uniformity, but here are some options if you want to dig deeper: pvlib.bifacial.utils.vf_row_sky_2d_integ (I've never used it, IDK if it could help to calculate rear side VFs to the sky and correct for the diffuse on each row) and this list https://github.com/protontypes/open-sustainable-technology#photovoltaics-and-solar-energy. pvlib.bifacial.power_mismatch_deline reference [1] cites the usage of "bifacialvf" and "bifacial_radiance" (sect. 3.6 Single-axis-tracking reduced-order model).

I hope to have shed some light into that issue.

Best,
Echedey.

[1]

C. Deline, S. Ayala Pelaez, S. MacAlpine, and C. Olalla, “Estimating and parameterizing mismatch power loss in bifacial photovoltaic systems,” Progress in Photovoltaics: Research and Applications, vol. 28, no. 7, pp. 691–703, 2020, doi: 10.1002/pip.3259.

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[Spencer Zanardi]

Thank you for the detailed response, Echedey! Those are definitely some useful suggestions, I will definitely look into those more

Best,

Spencer

[Echedey]

Hi again Spencer,

I've opened an issue at pvlib-python to track the implementation of a model that was described publicly this 20 Aug that models irradiance non-uniformity.

You may want to look at the issue [1] or the paper [2] - they've open sourced the model MATLAB code too.

[1] https://github.com/pvlib/pvlib-python/issues/2852
[2] M. Wild, S. Strebel, D. Anderegg, and J. Rohrer, “A general view-factor based irradiation distribution model for multi-row bifacial PV arrays on sloped and reflective ground,” Solar Energy, vol. 318, p. 115030, Nov. 2026, doi: 10.1016/j.solener.2026.115030.

To view this discussion visit https://groups.google.com/d/msgid/pvlib-python/58215b19-48a7-4bef-8898-d6631df26431n%40googlegroups.com.