Norwegian researchers have developed a multi-pyranometer method to more accurately estimate global tilted irradiance (GTI) in the Arctic by separating beam, diffuse, and reflected solar components. Validated in the world’s northermost settlement, the approach was found to outperform conventional models in high-latitude conditions and improve PV system design for extreme environments.
A research team from Norway has proposed a new method to estimate global tilted irradiance (GTI) in the Arctic.
The approach uses measurements from a 25-pyranometer array developed by the team to reconstruct the components of solar radiation: direct beam, diffuse sky radiation, and ground-reflected irradiance. These components are then used to calculate solar irradiance for any tilt and orientation.
“Our multi-pyranometer instrument GLOB was used for the first time in the Arctic, where the sun is low on the horizon, to provide a precise picture of the solar energy potential on inclined planes,” lead author Arthur Garreau told pv magazine. “We have since also installed it at a site where a PV plant is planned in the coming years.”
The project site is located in Longyearbyen, the world’s northernmost settlement, situated roughly midway between mainland Norway’s northern coast and the North Pole. According to the researchers, conventional GTI models often perform poorly at high latitudes due to low solar elevation angles, strong snow reflectance, and reliance on empirical models developed for mid-latitude conditions.
“The Longyearbyen project will be the world’s northernmost solar PV plant,” Garreau added. “Our goal is to support project stakeholders in the design phase by providing accurate data on solar energy potential on the selected inclined plane.”
GLOB consists of 25 silicon-cell pyranometers mounted on a geometric structure, with each sensor oriented at a different tilt and azimuth to capture incoming radiation from across the sky. An additional downward-facing sensor measures reflected irradiance from the ground.
Image: The University Centre in Svalbard
By capturing irradiance from multiple angles simultaneously, the system provides a detailed characterization of incoming solar radiation. The measurements are combined using a least-squares inversion to linearly estimate the direct and diffuse components of solar irradiance. In a second, nonlinear estimation approach, the same dataset is also used to derive ground reflectivity. Once these components are determined, a transposition model is applied to calculate global tilted irradiance (GTI) for any desired surface tilt and orientation.
However, the researchers did not always rely on all 25 pyranometers. Suspecting that a higher number of sensors could introduce noise, and aiming to assess the potential for a lower-cost configuration, they tested combinations of 3, 4, 5, 9, 13, and 25 pyranometers under both linear and nonlinear processing schemes. When validated against high-quality reference data from a Baseline Surface Radiation Network (BSRN) station, the 13-pyranometer nonlinear configuration delivered the best overall performance, with a normalized root mean square error (nRMSE) of around 36% for beam irradiance and 23% for diffuse irradiance.
“We were surprised by the accuracy that a five-pyranometer setup provided,” lead author Arthur Garreau noted. With only five sensors and a linear inversion method, the system achieved an nRMSE of around 38% for beam irradiance and 23% for diffuse irradiance. The results were benchmarked against conventional decomposition models and consistently showed improved accuracy.
Using the optimal 13-pyranometer nonlinear configuration, the team then calculated GTI for Adventdalen, near Longyearbyen. The results indicate that, for monofacial systems, peak irradiance occurs at a tilt of around 45° facing south. For bifacial configurations, the highest values were found at a tilt of approximately 70°, with south and southeast orientations.
“We also found that the solar energy potential at high latitudes for bifacial planes is near-optimal across a wide range of azimuths and for inclination angles between 60° and 90°,” Garreau concluded. “This provides greater design flexibility for PV installations in harsh Arctic environments.”
The novel approach was described in “Improving solar energy estimates for tilted planes in the Arctic using a multi-pyranometer array,” published in Solar Energy. Researchers from Norway’s University Centre in Svalbard and the Norwegian University of Science and Technology have contributed to the study.
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