Solar Production – Recently disMAYed

Man… Doesn’t it seem like we have gotten a lot of rain lately?  In fact, from a solar production point of view, it feels like the month of May was a wash – literally!  That is how we felt at Rayah Solar, so we did what we do, we ran an analysis of the past and current solar production.  We compiled the production outputs from our customers and compared the following factors over the last four years; 1) Yearly Outputs, 2) Q1 Outputs, 3) Q2 Outputs, and 4) Month of May Outputs.

Research Overview

Please note, we choose to only use data since 2014 since any prior data did not include panel level monitoring. Yes, we have been using panel level monitoring since 2014!  We were one of the first to do so. Solar systems without panel level data were not chosen because there were too many potential variables. Also, we excluded systems that had inconsistent monitoring data (i.e. internet connection issues, etc).

Historical Results

In the last four years, we found that 2016 was the most productive year for solar production, but not my much. 2016 produced about 5% more power than 2015, and about 7% more power than 2014.  I find 2015 very interesting because as many of us may remember, we had a boatload of snow in February of 2015. In fact, some of our installations had almost no solar production that entire month. This variable goes to show that one bad month of weather, does not always reflect in a down year for solar.

Since we are less than halfway through 2017, we wanted to examine some data points to determine where we stand 5 months into the year.  The results are quite interesting. Looking at the first quarter of 2017, we did well. In fact, from a solar production point of view, only last year’s winter was better. And as some us might remember, as snowy as it was in 2015, it was equally “un-snowy” (I know that I made up that word) in 2016. So, in terms of solar production, we did very well this past winter.

Analyzing Q2 of 2017, we start to see a different story.  Extrapolating out a full quarter (April, May, and June), based on current solar production levels, we found that we are nearly 6% below our Q2 averages. When we dial down the data, even more, we found out that the month of April was a little low, but the real issue was our cloudy and rainy May.

2017 Dis-MAY-ed

Across the beautiful State of Massachusetts, our average solar installation produces about 1,094 kWh in the month of May.  Please note, this is the average of residential installations only. Any system may produce more or less power based on your system size and site conditions. So far in 2017, the same sample produced on average 841 kWh.  This is about 24% less than average. So, that is low! But let’s keep in mind February of 2015 where, some sites had no solar production, but over the course of the year, they actually produced more power than 2014. How could that happen? The answer is a bit ironic, 2015 had an excellent May. In fact, solar production in May of 2015, was about 20% higher than 2016.

The following chart (Figure 1) depicts typical Solar Production throughout the year.  You will notice a production flow, resembling a bell curve, hitting our peak solar production in June, July, and August. Basically, solar production builds up until August, until we see a pretty sudden drop off in production.


Here in Figure 2, the blue represents 2016, and green, 2017. You will see that instead of an increase in power from April to May, there was, in fact, a decrease (Please note, Figure 2 only shows 8 days of 2017 June production).



Blue Hill Observatory

Although we have hundreds of solar installations, we wanted to compare our data to local weather data. According to a recent report published by the Blue Hills Observatory and Science Center in Milton MA, they said May was generally “Cooler and Wetter than Average.”  When we dug deeper into their data, we found out there was about 26% less “Solar Radiation” this May than the previous four years. So, this confirmed both our speculations (of a rainy May) and own data.

What does this mean for 2017?

What does a dreary May mean for our total solar production of 2017?  We referred that questions to the old timers at the Farmer’s Almanac. For starters, they had predicted that “April and May will be slightly cooler than normal, with above-normal rainfall.”  Good job Farmer’s Almanac for hitting that nail on the head!

For the summer, during our peak performance months, the Farmer’s Almanac predicts, “Summer will be cooler than normal, despite hot periods in early to mid-July and mid- to late August. The north will have above-normal rainfall, with near-normal rainfall in the south.” This is a mixed bag.  Cooler temperatures are actually GREAT for solar panels, as heat reduces solar efficiency (remember it’s the light that causes power, not the heat).  It also means that if you’re in southern MA, you have a better chance of offsetting your May losses, than northern parts of MA.

Ultimately, only time will tell if 2017 turns out as a down solar year.  However, I would like to put this discussion in perspective. Solar systems are meant to produce power for at least 25 years.  We have some systems now (like the SunPower system on my house), that has a 40-year expected lifespan.  And in that timeframe, yes, we will have some down years, and of course, some great years.  I think getting nervous over one bad month or even one subpar year misses point.  So, let’s sit back, relax, and grow old basking in the comfort that our long-term savings are as predictable as the sun rising each day.


Written By Brad Stoler – Solar Consultant – Rayah Solar

P.S. Our solar systems all come panel level monitoring, so we will know if there is ever something fishy going on (aka, a system malfunction). If so, we will be on top of it.



  1. Farmer’s Almanac:
    • April and May will be slightly cooler than normal, with above-normal rainfall.
    • Summer will be cooler than normal, despite hot periods in early to mid-July and mid- to late August. The north will have above-normal rainfall, with near-normal rainfall in the south.
    • September and October will be cooler than normal, with near-normal rainfall.


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