Snow Covering on Solar Generators

Solar generators with relatively shallow tilt angles are often covered with snow for varying periods as the result of heavy winter snowfalls. Even a few centimetres of snow are sufficient to prevent virtually any light from arriving at the solar module surface, which means that the solar generator will hardly produce any power. The situation is even worse in cases where wet snow falls on a cold solar generator and then freezes. Figure 4.116 displays a solar generator (b = 30°) after such a snowfall involving a blanket of around 25 cm of freshly fallen snow. In such cases, relatively deep snow will not slide off modules until the temperature goes above freezing and a thaw begins, thus enabling a film of water to develop under the snow so that it can slide off. If the layer of snow has holes in it for one reason or another, the exposed portions of the solar generator warm up very quickly, thus allowing the remaining snow to melt and slide off. Light, powdery snow at low temperatures is less of a problem as it is less adhesive and is readily blown away by the wind.

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Figure 4.112 A cleaned M55 module with solar cell clouding that extended from the edges of the cells inwards and that likewise induced output loss (see Figure 4.113)

 

I-V – and P-V-Curves at Modules M55 (new and with haze at edges) at STC

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Figure 4.114 Hail damage incurred by a solar generator (top left module) © Urs Muntwyler (Solarcenter Muntwyler, Zollikofen)

 

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Figure 4.115 Hail damage incurred by a solar module. The deformation of the lower panel is indicative of the force of the hail. © Urs Muntwyler (Solarcenter Muntwyler, Zollikofen)

 

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Figure 4.116 Snow-covered solar generator at Bern University of Applied Sciences in winter (fi = 30°, snow depth around 25 cm). The leading edges of the horizontally mounted modules (see Figures 4.92 and 1.11) act as snow traps. In most such cases the snow does not slide off until the temperature reaches 0° and a film of water forms under the snow. At this tilt angle, even when a thaw sets in and the Sun shines, this kind of snow remains on the solar generator for quite some time, i. e. until the first bare patches begin appearing that allow the Sun to warm the generator to a greater extent

Shallow tilt angles, framed modules, solar tile edges and leading laminate edges prevent snow from sliding off because the leading edges act as mini snow traps. Lengthy ‘snowed-in’ periods for solar generators can be avoided using the same measures as those discussed above for reducing soiling in the vicinity of the lower module edges.

Large amounts of snow result in power loss while snow remains on the solar generator. However, it was also observed during the Bern University of Applied Sciences’ long-term solar generator monitoring projects that snow remaining in place for lengthy periods counteracts module soiling and that the snow sliding off has a de-soiling effect to some degree.

The Mont Soleil installation shown in Figure 4.44 (1270 m above sea level) enables snow to slide off the solar generator owing to the installation’s steep tilt angle (b = 50°) and glued-down laminates without leading edges; however, this only holds true if enough clearance remains in front of the solar generators for the snow to slide off – which is not always the case during snowy winters (see Section 4.5.2.1). Iln most cases the snow slides off after being exposed to direct sunlight for a few hours. To avoid blankets of snow on solar generators in high mountain areas, the solar modules should be mounted vertically (as in Figure 2.44) with 75°-90° tilt angles.

Several maps showing the duration of winter snow covering in various regions of the world can be found in Section 8.1.3.

Updated: August 8, 2015 — 2:11 pm