The performance of photovoltaic systems (PV) in northern conditions has been measured at the University of Oulu, Finland with two research infrastructure comprised of a total of 40 solar panels, including a unique panel carousel system on the roof of the Linnanmaa campus for research purposes.

In northern conditions, solar power generation is significantly affected by seasons, the sun’s altitude, geographical location, temperature, and snowfall. The impacts were examined with solar panels installed in different directions and tilts on the roof. Measurements of solar photovoltaic production data were collected every 15 minutes since August 2021, as part of Vinay Shekar's doctoral research data.

Empirical research on solar photovoltaic generation in northern latitudes has been relatively limited compared to temperate regions. However, in recent years, it has been steadily growing, with a focus on topics such as energy loss due to snow, performance in cold climates, and economic viability. Oulu is located at about 65 degrees north latitude.

“Our research provides important information for optimising the performance of solar power in northern regions. The results can also be utilised, for example, in urban planning, zoning and construction to maximise solar energy production,” says Professor Eva Pongracz from the University of Oulu. She reminds that also EU wants to unlock the vast, underutilised solar generation potential of rooftops. According to the EU Solar Energy Strategy, by 2026, the installation of rooftop solar energy will be compulsory for all new public and commercial buildings with a useful floor area larger than 250 m² and eventually in all new residential buildings.

The best panel directions on the roof are southeast and south, following towards the east, and the best tilt angle is 28°

All the 40 solar panels used in the roof laboratory are monocrystalline Si panels, of which 12 panels were installed on the roof at a tilt angle of 23°-46° and 12 vertically on the wall at a 90° angle, all oriented towards South. This infra is used to assess the impact of tilt angle. The solar panel carousel system has 16 panels: eight tilted at 40° and eight are vertical. The tilted and vertical panels were oriented in all eight cardinal and intercardinal directions. This system is used to assess the impact of azimuth on generation. There is no similar carousel of panels in research use anywhere else.

“The measurement data indicate that, to maximise the yield for the whole year, it is best to install rooftop solar panels facing southeast or south. The second best direction is east because of the sun's path, and the third best direction is southwest”, says Shekar. The researchers base their recommendations on an overall annual review.

“Based on our previous research, we also recommend a lower tilt angle of 28° instead of the standard 43-48° angle recommendation for tilted panels", assures doctoral researcher Shekar. This angle minimises shading and optimises annual yield slightly, by 3 percent, when compared to 45° angle.

Many are interested in the effect of solar reflection (albedo) from snow on solar panels. "It indeed has energy potential and is worth exploring the specifics," confirms Shekar. “During the snowy spring in March–April, vertical, south-facing wall panels were able to produce as much energy as they did in June–July, even though the daylight hours are much shorter”.

However, throughout the year, south-oriented 28° tilted roof panels produced 20 percent more energy than the 90° angle wall panels. The long summer days also caused spikes in energy production; the panels generate more than half of their yearly production during May–July.

“Focusing on the low-tilt, summer-optimized installation is likely the best solution to optimise the total production for the year. We also do not recommend a hybrid installation approach, like installing some panels in different orientations," Pongracz summarises.

Solar panel measurement data has been published, and the latest results are currently in scientific peer-review to confirm them. “They demonstrate the orientations with the highest economic value and suboptimal orientations in northern conditions, which provide crucial insights into implementing solar PV cost-effectively under the EU solar mandate”, says Shekar.

Dataset Empirical results (generation and value) from a unique Fixed Multi-Azimuth (Carousel) Solar Photovoltaic infrastructure based in the Arctic was published in September 2024.

Read a previous study: Experiences from seasonal Arctic solar photovoltaics (PV) generation: an empirical data analysis from a research infrastructure in Northern Finland

Water, Energy and Environmental Engineering research at the University of Oulu