Does a Vertical Bifacial Array Produce More Than a Tilted One?
Summary
At high latitudes it can hold its own over a full year. NLR researchers describe east-west vertical bifacial systems as an emerging design that targets morning and afternoon output and can deliver annual yield competitive with south-tilted modules in high-latitude locations. The catch is that production models disagree two to three times more for vertical systems than for fixed south-tilted ones.
Two peaks instead of one
An east-facing side catches the morning sun and a west-facing side catches the afternoon sun, and the direct beam swaps faces at solar noon. The daily output curve ends up with two humps instead of one centered on midday. IEA PVPS lists the benefits as a wider generation window that better matches typical load profiles, very low soiling, and land between the rows left free for uses such as livestock grazing. It explains the high-latitude advantage by the large swing in solar azimuth during the summer.
Less certain estimates
NLR validated five bifacial irradiance models against field data from Golden, Colorado (40°N) and Fairbanks, Alaska (65°N), with east-west vertical, north-south vertical, and south-tilted arrays. The subhourly models landed at a root-mean-squared error of 11% to 28%, depending on site and orientation. Across more than 250 locations between 15°N and 85°N, the gap between models' predicted annual insolation ran two to three times wider for vertical systems than for south-facing fixed-tilt systems. An earlier 2024 poster from the same team traced part of the Alaska error to uncertain albedo measurements during snowy months.
So a vertical-versus-tilted comparison for one site can come out differently depending on which model produced it.
Sources
- National Laboratory of the Rockies — Vertical Bifacial Photovoltaic System Model Validation: Study With Field Data, Various Orientations, and Latitudes (IEEE Journal of Photovoltaics, 2025)
- National Laboratory of the Rockies — Validating Irradiance Models for High-Latitude Vertical Bifacial Photovoltaic Systems (PVSC52 poster, 2024)
- IEA PVPS — Bifacial Photovoltaic: Two Sides are Better than One
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