Vertical bifacial rooftop PV systems can outperform conventional tilted monofacial rooftop PV systems across seasons in the U.K, a year-long study has found.
Research by the University of York has performed the first empirical assessment of a vertical bifacial rooftop PV system belonging to Norwegian-headquartered vertical solar specialists Over Easy Solar in a British climate. The full findings are presented in the paper “Comprehensive study of the efficiency of vertical bifacial photovoltaic systems: a UK case study,” published in the journal Scientific Reports.
The study assessed the performance of Over Easy Solar’s vertical bifacial PV system installed on the rooftop of the university’s physics tower. It encompasses 22.5% efficiency heterojunction cells and utilizes white gravel to bounce light onto the rear side of the system, something traditional panel setups are unable to utilize.
The system was monitored over a full annual cycle in 2023 and compared against a vertically-mounted monocrystalline silicon monofacial PV system and a traditional tilted monofacial PV system. Over Easy Solar’s system demonstrated a 26.91% higher output than the tilted system during the morning hours between 05:30 and 09:00 and a 22.8% higher output in the hours between 17:00 and 20:30.
Keelin Currivan, international customers solutions advisor at Over Easy Solar, explained to pv magazine how these results highlight the double peak advantage offered by vertical bifacial PV.
“While traditional tilted panels struggle with midday saturation, peaking when the grid is often full and prices are low, our vertical bifacial system shifts production to when it is needed most,” Currivan said. She added that these peaks align with residential spikes caused by demand for heating, cooking and electric vehicles, in turn reducing the need for battery storage and mitigating grid congestion.
Over Easy Solar’s vertical bifacial PV system outperformed both other test systems across the four seasons. It had a 14.77% comparative gain on the traditional tilted system in summer, increasing to 19.32% in spring, 20.27% in autumn and 24.52% in winter.
“Vertical orientation is the superior geometry for the UK and Irish climates because it is optimized for low-angle winter sun and diffused light,” Currivan explained. “Even against a vertical monofacial system, the bifacial version gains an extra 12.45% in winter, proving that capturing rear-side reflection is critical.”
On one particularly high-performance day, May 7, Over Easy Solar’s system produced 4.92 kWh, around 25.38% more energy than the tilted system across the day. The authors of the research paper, based at the University of York, add that their findings “underscore the vertical bifacial PV system’s unparalleled ability to harness solar energy efficiently, irrespective of seasonal variances.”
“Its design not only maximizes land use but also integrates seamlessly with modern architectural landscapes, adding an aesthetic value to its functional benefits,” their conclusion says. “The system’s bifacial technology, capable of capturing solar radiation from both sides, significantly boosts its energy yield, making it a potent solution for regions with variable sun exposure and reflective environments.”
Currivan added that the higher yield in high-priced months also leads to a faster payback period despite a higher initial cost. She estimated the initial costs of a vertical bifacial PV system at GBP1,200 ($1,630)/kW, compared to GBP900/kW for a traditional system. “The increased yield results in an estimated GBP1,221.13 in additional annual savings per 1,500 kWh baseline in the UK, based on GBP0.28/kWh pricing,” Currivan explained.
Over Easy Solar’s vertical bifacial system was also subject to computational fluid dynamics simulations during the testing. The system maintained negligible lift forces at wind speeds of approximately 98 kmh, which Currivan said is a critical structural advantage for high-wind coastal regions across the UK and Ireland.
Currivan told pv magazine Over Easy Solar is using the research findings to drive expansion into the UK and Irish markets. “It surprised me just how applicable these systems are to the UK and Irish markets,” she said. “In Norway and colder climates, these systems are the only viable ones because of the amount of snow, but even in this climate it’s hitting multiple key points, from seasonal gains to mitigating grid issues to giving the double peak.”
Earlier this month, Over Easy Solar installed its first rooftop vertical solar installation in the U.S. market. A previous case study analysis from the company found vertical rooftop panels are capable of outperforming conventional rooftop systems during snowy months.
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