Photovoltaics in winter: what should you consider? Candlelight dinner and barbecue in the snow. Are these the winter alternatives for owners of a photovoltaic system or is the solar power yield sufficient even in the cold season?
Photovoltaics and the four seasons
In US, an average solar panel generator system delivers around three-quarters of its yields in summer and spring. The rest is spread over autumn and winter. In summer you can really benefit from a photovoltaic system if it diligently generates electricity on the roof. After all, the plant achieves the best yields when the sun shines brightly for hours. But when the cold season is approaching and the days are getting shorter, many wonder what the photovoltaic output will be like. How efficient are the solar modules? Can a snow load on the system pose a hazard? We give you a brief overview of photovoltaics in winter.
Does a photovoltaic system generate electricity at all in winter?
A photovoltaic system (PV system) produces its greatest yields when the sun is at its strongest, or when it can use plenty of it – i.e. in the summer months. Nevertheless, a PV system “functions” at any time of the year, even in winter, regardless of the lower position of the sun and fewer hours of sunshine with a lower yield of electricity. In some areas, such as in the mountains, with many hours of sunshine and intensive solar radiation, the yields from photovoltaics in winter are also considerable. In general, the following applies: the steeper the angle of the small solar panels, the better use can be made of the low-lying sun in winter and the sunbeams that hit the ground more flatly as a result. There is no risk of the modules failing in the cold.
Adjusting the angle of inclination: A little is always possible
At 60 degrees, the sun’s angle of incidence is much steeper in summer than in winter at 20 degrees. In the case of pitched roofs, however, the angle of inclination is always predetermined, because the modules are usually installed parallel to the roof. In order to compensate for a roof pitch that is too flat, there are special elevation systems made of metal that make it possible to change the modules according to the desired pitch.
However, such traverses are often not worthwhile from a purely economic point of view. Here you should compare the additional costs with the additional yield in winter. If you have a flat roof, you can basically set the optimal angle of inclination for the winter months by elevating the modules, but then you have to be careful that this does not cause any shading of the rows of modules behind. To do this, the distances between the individual rows of modules must be increased, which is not always possible for reasons of space. But even when standing up, it is advisable not to lose sight of the costs and benefits.
What is the efficiency of a photovoltaic system in winter?
The temperature has a significant influence on the efficiency of solar cells. The efficiency of solar cells decreases with increasing heat. Conversely, this means that the efficiency of a photovoltaic system increases the colder it is. As a result, yield increases by about 4 percent for every 10 degrees Celsius decrease in temperature. Due to the current flow, the temperature of a solar system reaches 25 degrees Celsius and above even on cold winter days. Temperatures of up to 70 degrees Celsius are possible during normal operation in the summer months. It is therefore not unusual that on a cold but sunny winter day the production of electricity is sometimes even higher than on a hot August day.
The sun supply fluctuates
According to Statista GmbH, an average of 110 hours of sunshine were measured in February 2021. The long-term average of 72 hours of sunshine was thus far exceeded. In January 2021 we only enjoyed 30 hours of sunshine. The sunniest month of 2020 was April with 294 hours of sunshine, followed by July with 230 hours. The sun shone for an average of 1,900 hours last year. Of course there are regional differences.
The orientation and thus the yield depend on the use in the season
On a cloudy winter day, a PV solar panel system (an complete solar system consists of solar panel, charge controller, 12v lithium ion battery, inverter, and other accessories ) generates around 0.5 times its nominal output. On a clear summer day, however, it is 7 times as much. This means that a 100w solar panel produces around 0.05 kilowatt hours (kWh) of solar electricity in winter and 0.7 kilowatt hours (kWh) in summer. If you consider that the winter months only account for 30 percent of the annual production of solar power, the question arises to what extent it makes economic sense to align the PV modules with a view to the cold season.
For example, if you live in an area that is less sun-drenched with many cloudy autumn and winter days, it makes more sense to optimally align your photovoltaic system for the summer days with a view to the annual yield. The situation is different with a holiday apartment or mountain hut that is only used in winter. Here it is worth adjusting the angle accordingly in order to achieve optimum efficiency in winter with an angle of 55 degrees. Given the position of the sun in our latitudes, the usual orientation in US with an angle between 30 and 35 degrees is a good compromise solution for both summer and winter. In general, an acceptable electricity yield can be achieved with a photovoltaic system in the period from October to February, when it is often cloudy and hazy.
Does snow on the modules limit the photovoltaic output in winter?
Heavy snowfall over several days is usually not an issue for most Germans. Exceptions are the regions in the east and south of the country. In addition, climate change is showing its effects: winters are getting warmer. But if there is snow on the modules, that’s not a problem either. Snow-covered solar systems reduce the yield only slightly. If your house is 1,000 meters above sea level or higher, the reduction in yield is between five and eight percent. If it is lower, it is only about one to four percent. This is so low that system owners need not worry. The sunlight manages to penetrate a snow cover of up to 15 centimeters, so that the solar modules can catch it and convert it into electricity.
Removing snow from pitched roofs
The snow usually slides off quickly on pitched roofs. This happens all the faster when parts of the solar module are exposed and heat up, causing the snow to melt. Targeted removal of the snow is therefore usually not necessary. The snow that slides down from the roof of the house is important for homeowners: The snow guards should be attached below the solar module field.
If you want to remove the snow from the system in a targeted manner, this is best done from the roof window with a telescopic rod. Under no circumstances should a snow shovel or broom be used, as you could scratch or damage the solar panel kits for home.
The situation is different on flat roofs. Here only experts should remove the snow who are trained to pay attention to their safety and not to damage the PV system or the roof.
Is there a risk of the roof collapsing due to the snow load on the PV system in winter?
It is unlikely that the roof will collapse due to excessive weight. Even when planning your photovoltaic system with an expert, the regional snow loads are included in the development and implementation in order to avoid possible cracks in the modules or in the substructure.
If you want to be on the safe side, you can protect yourself against the costs of snow pressure damage by taking out an additional module in your home building insurance or photovoltaic insurance.
What should be considered with the storage in order to use photovoltaics in winter?
In general, you should be aware of your electricity needs – both in summer and in winter. Ultimately, when planning a photovoltaic system, this affects its performance as well as that of the solar storage tank.