What is the impact of snow on solar panels in Alberta (a study)
Alberta’s snowy northern climate sometimes gets a bad rap when it comes to solar. In the past, it’s been estimated that snow causes a 20-30% decrease in annual solar energy production. But, how much does snow actually affect solar and is it enough that we should be cleaning snow off the panels?
NAIT’s Alternative Energy Program set out to put this issue to rest with a five-year study with some startling findings.
What is the impact of snow on solar energy production and should we be cleaning snow off panels in the winter?
A solar array consisting of 12 solar panels was installed on an unshaded NAIT campus building. The solar array was arranged such that a pair of solar panels were placed at angles of 14°, 18°, 27°, 45°, 53.5° and 90° to represent common roof angles.
Immediately after a winter storm, the snow was removed from the left panels only, leaving only the right panels to gather snow. During the first four years of the study, the left panels required 24 snow clearings per year on average.
Result 1: roof angle effects are modest
The first outcome of the study was how the angle of the solar panels affects annual electricity production. The graph below is calibrated to show how the annual electricity production at common roof angles compared to the solar panels mounted at Edmonton’s latitude.
The optimal angle for solar production corresponds to the latitude of their location, which is the reason that 53.5° (the latitude of Edmonton) yielded the highest electricity production. As the mount angle flattens, it becomes less optimal for electricity production. However, the flattest roof angle (14°) only produced 13% less than latitude which is not enough to be concerned about.
The vertical panels, which are meant to replicate a wall-mounted system, produced 23% less than the rest since they are poorly positioned to take advantage of Alberta’s long summer days when the sun is high in the sky.
Result 2: actual energy loss from snow is less than we thought
The primary outcome of the study was how snow affects electricity production at different mount angles. The results of this test are shown in the graph below.
As expected, the 90° panels saw very little snow loss since almost no snow was able to build up the vertical surface. The higher the angle, the easier the snow slides down the surface of the solar panel. The lower angle solar panels allowed the snow to accumulate much easier, leading to more energy losses.
The big surprise was that the snow never caused more than a 5% loss in electricity production annually. A far cry from the previous industry standard of 20%.
The logic behind this conclusion is that since we have such long days in the summer, a large percentage of annual solar production happens when the ground is clear of snow anyway. The snowiest time in Alberta coincides with very short daylight hours, so the lost production from snow has a small impact on overall annual electricity production.
A possible underestimation?
It should be noted that NAIT’s snow array is a suboptimal representation of a typical residential rooftop solar installation. The NAIT array was installed on top of a school building with a flat roof, whereas a typical residential solar installation would sit flush with an angled roof. This means that the NAIT array would experience more wind buffeting, and therefore less snow buildup, than a solar installation on a house. The extent of this difference is not known, but snow losses slightly higher than what was found by this study should be expected with a residential solar installation.
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