Insights
- The short answer is that the weight of the PV system itself puts little strain on the roof compared to the snow load, since the solar photovoltaic system normally weighs only 20 kg per m2. If you have a PV system on a roof that is newer than 2003, snow on the roof is rarely something to worry about,” says Kjetil Laupsa Steine, Head of Deployment at Sunday Power.
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If you have a commercial building where snow accumulates on the roof in winter, you may be wondering if your roof can withstand solar cells in addition to the snow load. In this article, our experts and collaborators answer everything you need to know about snow loads, solar cells and maintenance.
Snow can be both light and really heavy. It has everyone known at as seagulls snow. Fresh snow in many cold degrees can be light as a spring, while wet Easter snow can be very heavy. In addition, mild weather and rain can make the snow even heavier.
- The rule of keeping in mind for the weight of snow is 100-200-300-400 kg per m3, says Simon Hugo Haugen, Consultant Construction Engineer and Head of Department, Rambøll. Light snow weighs 100 kg per m3. Normal snow can weigh 200. Heavy snow weighs 300, and soaked snow or packed fox snow can weigh 400 kg per cubic meter. Snow exposed to mild weather and rain can weigh double this again, and water we know weighs up to 1000 kg per m3,” says Simon.
Compared to the weight of snow loads, solar panels don't weigh that much. The panels weigh only 20 kg per m2, so they load the roof little compared to a lot of snow load. As a building owner, it is wise to be aware of what the overall tolerability is. Older roofs can withstand less weight and less snow, and we divide the roofs into three different time periods to assess the need for snow shoveling:
Roofs newer than 2003
Roofs from this period should be designed to rarely need shoveling (on average every 50 years). The roof should withstand 4.0-4.5 kN/m2 (kilo-newton per m2) of snow, which corresponds to about 2 meters of normal snow. As a building owner with a roof that is newer than 2003, you can usually not have to worry about shoveling snow.
For roofs older than 2003, we have obtained RIB (Consulting Engineer Bygg) to assess the load-bearing capacity of the roof and establish a snow shoveling routine.
Thanks from 1980-2003
If you have solar panels on a roof from this period, you should make arrangements for the need for snow shoveling, and some municipalities also require documentation of a snow shoveling routine. This can be done by creating corridors between the rows of panels in order to effectively remove snow. The roofs of this period are designed to withstand a snow amount of 2.5 - 3.5 kN/m², which corresponds to about 1.2-1.7 meters of normal snow.
Roofs older than 1980
The roofs from this period can withstand a snow load of 1.5-2.0 kN/m² which corresponds to 0.7 to 1.0 meters of normal snow. For these roofs, a good snow shoveling routine is important, and the solution is often to reduce the installation capacity in order to be able to make room for good walkways between the panels.
Also read: 9 Things to Consider When Considering Solar PV Plants on Commercial Buildings
If the amount and weight of the snow begins to endanger the panels or the roof and you need to remove snow, it is important to be gentle with the panels.
- Use a soft broom or rubber swab, avoiding scraping or metal objects. As soon as the panels have little enough snow for the light to activate them, heat from the panel will remove the last remaining snow,” says Kjetil Laupsa Steine of Sunday Power.
For the roof, by the way, it depends on the substrate of the roof. Anything from snowblower to shovel or leaf blower can be applicable. Make sure you don't damage the roof itself, and leave a thin layer of snow if you want to be sure. Remember that snow shoveling should always take place in consultation with the building operators.
The good news is that cold weather produces higher power for the solar panels. High temperatures can reduce the efficiency of the panels, and the solar cells actually produce at their best at a temperature of minus 5 degrees. Reflection from snow can also increase the radiation on the panels and can make one produce more electricity. However, if the panels are covered with snow, no electricity will be produced. Although cold weather can boost the effect, the angle of the sun in winter will limit production as most solar installations are designed to maximize output throughout the year and not just the winter months. In addition, short days cause production to be limited. Snow removal for the power generation part can thus have limited effect, especially during the darkest winter months.
