It’s been a busy winter for weathermen. First, Stormageddon drenched northern California in rain. Then, Snowpocalypse buried the Northeast in snow up to two feet deep. Now, frequent storms in the Boston area have crowned the winter of 2014-2015 as one of the top 10 snowiest in the city’s recorded history. For some, wintry weather means school cancellations, flight delays and maybe even urban skiing. For solar homeowners, it may also cause worry that their solar system isn’t producing as expected. How and by how much did Stormageddon and Snowpocalypse, representing one rainy and one snowy weather event, impact solar production? That’s the question we set out to answer using actual production data collected from hundreds of Sungevity customers. (But first, a word from our lawyers: the following data has been anonymized and presented in aggregate to protect the privacy of our customers.)

We hypothesized that the data would follow these proven trends:

Now, let’s see what happened in these two examples.

Stormageddon: I Don’t Want To Miss A Rain

Stormageddon pelted California’s Bay Area with rain and high winds, with some areas seeing over 8 inches of rain. Let’s take a look at how Sungevity system production was impacted during the storm, as compared to the previous week.

Not surprisingly, 70% of Sungevity customers saw a decrease in their system production. However, the change was fairly modest: the average system produced 80% the electricity it had produced the week prior. More surprisingly, for those remaining 30% of customers who didn’t see a decrease in production, the week of the storm was actually a positive one: 157% increases, on average.

It's The Storm Of The Century Out There. How Does That Impact My Solar Production?

Table 1: Sungevity’s Bay Area System Performance During Stormageddon.

Why would rain increase solar production? Perhaps the rain cleaned the panels of dust that had built up during the long dry spell that northern California experienced before the storm. (We’ll look at best practices for cleaning your solar panels in a future blog post, so stay tuned.) Or perhaps the sun got jealous that the storm was trending on Twitter and decided to shine harder.

Snowpocalypse Now

Next, we examined solar production before and after Snowpocalypse to evaluate the impact that heavy snowfall has on our customer’s solar production. We compared Sungevity production data from four metro areas – Albany, Boston, Hartford, and Long Island – that were hit by the snowstorm and analyzed how precipitation levels impacted the amount of electricity each system generated.

The results are clear: solar production dropped significantly on the days that snow fell. At the storm’s peak on January 26th and 27th, aggregate production dropped to nearly zero in every area.

Figure 1-4: Sungevity System Performance in the Northeast During Snowpocalypse

Production also took a few days to bounce back after the storm, which presumably represents the time it took for the snow to melt and uncover the panels beneath. Production on Long Island, for example, returns to normal on January 31st, four days after the storm. But note that, in every case, production did bounce back: the data shows that many systems began producing electricity as soon as precipitation returned to zero.

The Bottom Line

It’s true: inclement weather will impact your system’s production. Snow has the most significant effect of all because it can create a physical barrier between sunlight and the solar panels. But in the end, when the clouds clear and the snow begins to melt, homeowners can expect their solar production to return to normal levels for the season.

But Don’t Worry, We’ve Got You Covered

This data demonstrates exactly why it’s important that solar companies have a robust methodology to take seasonal variation into consideration for predicting annual solar production. Almost all companies account for seasonal differences in temperature and solar radiation. Sungevity also incorporates an analysis of historical snowfall to provide an accurate prediction for our customers. And, we provide a Performance Guarantee so that our customers can have complete peace of mind, no matter the weather.

If you have already switched to solar, just remember: the low production that you experience this winter will be balanced out by the high production you will see in summer, when precipitation is at its lowest and the sun is higher in the sky. So, here’s to a sunny spring and summer!

Posted by Leslye Penticoff

Leslye is the Content and Community Manager for Sungevity. She's also an avid coffee drinker and rock climber, and serves on the Board of Directors at Margination, a nonprofit in Troy, NY.