A low sun angle means the sun sits close to the horizon, so light hits the modules at a steep incidence angle and less of it reaches the cells. This is most pronounced at high latitudes in winter, where the sun may rise only about 2 degrees above the horizon at the solstice and give only a few hours of dim light. On tracker sites with rolling ground, terrain undulation yield losses are strongest in low sun-angle periods and tend to cluster at motor block boundaries, grade breaks and swales. Low sun angles, together with cold module temperatures, frame geometry and tracker position, affect how long snow stays on the array, which prolongs snow accumulation yield losses. Shade patterns move with the sun's position through the day and the seasons, and row-to-row self-shading grows when the sun's profile angle drops below the shading angle of the rows. Performance analyses often filter out periods of low solar elevation, because these periods add shading, self-shading and air-mass differences to the data. Exposure can be reduced by tuning backtracking parameters for each terrain zone, checking motor block sizing, and adjusting tilt or module orientation at the design stage. At snowy sites, operators can look at tracker stow, tilt or design changes where the economics justify them.
<!-- review notes
typical_power_lossConditions: Combined winter loss from angle of incidence and low light at high-latitude, cold-climate sites such as Fairbanks, Alaska, as a share of annual energy production
The loss stays small because summer insolation is much higher. For most crystalline silicon modules, angle-of-incidence losses are reported as negligible below about 60 degrees.
sec=h87 h=b622923feee6caused_by c2caused_by c4