Did Netherlands Covid-19 lockdowns affect the performance of solar systems

On March 15, the Dutch PM announced that “All schools, cafes, restaurants and sports clubs will be closed in the Netherlands to stop the spread of coronavirus.” 3 months of hard lock down that most of us would happily forget followed. As we find ourselves starting to emerge from a second lockdown and starting to see light at the end of the tunnel it’s a good time to go back and see if we can find some positives from a difficult time.

It is reasonably well established that the natural environment benefited from a reduction in human activity during lockdown periods across the globe. Two of the most known examples are the clearing of the canals in Venice (some say the return of birdlife was also a result, but any one who has been to St Mark’s square knows there are plenty of birds in Venice!) and the reduction in pollution over Wuhan.

But what about the more direct impact on solar systems in the Netherlands? The graph below shows a clear increase over the 5yr and 30yr averages for the lockdown periods.

Impact of Dutch lockdown on irradiance

Graph 1

Irradiance overview Netherlands

Graph 2

The irradiance levels in April and May increased on the 30yr average by 29% and 24% respectively. These values are at the extremes at what would be expected based on normal variation in weather conditions, but are theoretically possible. It is worth noting that the combined irradiance of April and May achieved in 2020 has not been exceeded since records began in 1983! Statistically these sunlight levels could be considered a 1 in 50 year event.

As the lockdown began to ease at the beginning of June the irradiance levels returned to their long term averages, which in our opinion provides further evidence that the lockdowns did in fact contributed to higher irradiance levels throughout the Netherlands.However, while the data certainly suggests a direct impact, the natural variability makes it difficult to conclusively state that this is caused by the lockdowns.

Irradiance variation is widely misunderstood and the effects on performance under-estimated.


Graph 2 shows that during the boom years of Netherlands solar, irradiance levels have consistently been above the long term averages.

When an expected yield is provided for a system in design phase a long term average of irradiance is used (more on P50 andP90 later). Over the past 5 years actual irradiance has been 10% above historic levels in the Netherlands, the logical expectation is that system performance should be over achieving the expected yields provided pre-build by 10%.

It is difficult to predict future trends in irradiance, clearer skies obviously have a positive impact, but there are also much larger climate and weather affects that influence these trends. A return to historic averages, or even lower, are very likely within the SDE timeline of projects being built. When this happens, we expect a lot of rooftop asset owners will discover their systems, they thought were doing well by meeting expectation are actually underperforming, and have been ever since installation. 

For larger ground mount systems and the largest industrial rooftops with owners who are solar professionals, pyronometers are used to measure on site irradiance and monitor relative performance, but these level of sophistication remains quite rare for the majority of SDE projects.

The Autarco way


At Autarco, all of our performance metrics are based on actual irradiance data that we receive in 15min intervals for all of Europe. Using the digital twin in Helios, this irradiance data is used to generate true expected values (or retrodicted for the nerds). This Delivers a true base line for performance (referred to as Energy Performance Index (EPI) and ensuring all our systems are generating at optimal levels. It’s just one more example of how we use the power of data and digitilisation to deliver on our promise; “Solar made simple. Performance made certain”