Extreme Winter Weather Hurts 2015 European Solar Performance

Snowy winter weather
Naomi Stringfield
Marketing Manager
Wind and Solar Energy 

Earlier this year harsh winter conditions across Europe stranded thousands of motorists, saw the Alps' heaviest snowfall in 50 years, and caused widespread property damage. These extremes also led to headaches for the owners and operators of solar projects across the continent.

​These unusual conditions caused the majority of Europe to experience solar irradiance levels 5-10% below normal, negatively impacting energy production. They also created a range of operations and maintenance challenges including snow removal and the assessment of panel efficiency following damage from hail and high winds.

EU solar performance anomalies, Q1 and Q2 2015.
EU solar performance anomalies, Q1 and Q2 2015. 


Vaisala regularly maps global solar irradiance in order to analyze the impact of short-term weather variations on solar project performance. Our 2015 Q1 and Q2 European Solar Performance study reveals significant deviations from long-term average irradiance across the continent. In doing so, it highlights a clear requirement for project operators in many of Europe's largest solar markets to regularly evaluate and address plant performance.

Looking at the root causes of this variability, Europe's harsh winter was probably the result of a mass of cold air in the middle of the Atlantic Gulf Stream. This large-scale weather pattern featured stubborn areas of high pressure over Scandinavia for much of the winter, funneling cold air into northern and eastern Europe while forcing a majority of the storm systems down across southern Europe.

This was especially true during the second half of the first quarter, where an active storm track delivered days of rainfall to southern Europe and caused windstorms Mike and Niklas to sweep across western and central Europe. The latter storms brought hurricane-force winds, killing at least nine people and causing widespread damage.

Germany, the clear E.U. solar leader with over 39 GW of installed capacity, was significantly impacted during the entire first half of the year by below normal irradiance.

Italy, France, the U.K., Spain, and Belgium — other markets with a high concentration of solar projects — also saw reduced production due to harsh weather, which was only intensified by a delay in the arrival of warm, dry spring conditions, a common occurrence in years with above average snowfall.

However, these five countries recovered in the second quarter with irradiance levels 5-10% above average, brought on by a high pressure system build up over northwestern Europe. This caused many countries to see sunnier than normal conditions while Spain and much of the Mediterranean experienced record warm temperatures.

Despite improved conditions in the second quarter, the U.K still saw rainfall 31% above average in May while damaging winds, hail, and even isolated tornadoes swept across Germany in late April and May.

This type of weather analysis is essential for understanding in the short-term whether a project is performing as it should be, based on the available resource. It also allows both distributed and utility-scale generators to effectively deploy maintenance and repair crews when problems - such as inverter issues or heavy snow load on panels - reduce production when resource data clearly show the sun was shining.

Not only does extreme weather necessitate a robust understanding of the root causes behind production deviations; it also makes it even more critical for operations and maintenance teams to make wise budgetary decisions and anticipate the kinds of weather coming their way.

For example, with the aid of forecast data feeds and specialized sensors that evaluate snow and ice, these teams can make a more informed decision on whether it is prudent to send out crews for snow removal. After all, if warmer weather or heavy rain will clear snow naturally or if another heavy snowfall is expected, hiring costly manual labor to remove it the day before is not money well spent.

The important lesson to learn from the first half of 2015 is that, while there is little we can do to change the weather, we can minimize its impact to our projects and balance sheets by better understanding it and anticipating future weather conditions. As we enter the fourth quarter and winter approaches again, taking proactive steps to mitigate the performance impact of extreme weather needs to be high on the agenda for European solar operators.​​

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