Solar Performance - June 2015

Thanks to some unseasonably sunny weather my June solar production was outstanding. At 551 kWh it exceeded the estimate for the month by about 11%, and last year's production by 21%. This was by far my most productive month since the system was installed. My use was only slightly higher (3%) than last June.

As you might expect, production was up compared to last month. My use also increased, likely due to the fans (and occasional AC) that I've been using to keep cool when the temperature climbs. 

Production started out a little low at the beginning of the month but then consistently trended above the estimate as the month went on. Part of that could be that I'm using a linear approximation for the daily cumulative estimate based on the monthly total, rather than a sinusoid that would better match actual solar exposure. June 21, the summer solstice, should be the peak.

Annual production is also trending very well for the first half of the year, about 9% above the estimate and about 7% above last year. I'm also getting close to having sold a surplus 1 MWh to Seattle City Light.

Looking at the individual panel data reveals some odd behavior. Much like previous months there's a notable difference between the West-facing and East-facing panels. However, panels 3 & 4 are noticeably under-performing their West-facing peers 1, 2, 7, and 8.

I dug into the daily data and saw that the difference is mostly due to poor performance for a few hours on just a few days during the month. I'm not sure what to make of this, since a shading problem would be consistent from day to day, and would also be unlikely given the lack of obstructions to the South and the variation in time of day. I'll have to keep an eye on these panels to see if there's an equipment failure on the way. Click any of the images below to enlarge.

Last but not least, June 30 marks the end of the incentive year for Washington's Solar Incentive Program. This program pays 54 cents for every kilowatt-hour produced using equipment that was made in Washington, and is the primary reason that solar penciled out for me. Based on my eGauge data I'm expecting to get an incentive check for about $1,800! This is in addition to the $71 worth of surplus power that I sold to City Light, and also the "free" power that I've been using for the past year. To those who doubt: solar really does work in Washington!