Posted by: nik | October 12, 2013

Falling Leaves Leave Falling Production

It’s that time of year again when the leaves start to turn red and orange and brown. Then they fall from the trees and blanket the ground or the rain gutters or the the solar panels. It’s also that time of year when our daily energy harvests take a noticeable dip.  The days start to get shorter and the sun angle gets lower.  Our shallow-pitched roof is a good angle for peak summertime production, but this time of year our system under-performs compared to other steeper roofs. This is mainly because of the incident angle of the sun but it also means that snow and debris tend to collect on the panels more.  I had noticed a few oak leaves sitting on my solar panels this week but didn’t take the time to clear them off. I finally found the time today and decided to do a little experiment. Is that little oak leaf actually reducing my panel output by any measurable amount? I was quite surprised by the results.

I went out at just before 2pm, put my ladder up on the roof and took a photo of the offending leaf to document the time before I brushed it away with my long-handled squeegee.

20131012_135541

Later in the evening I logged onto the monitoring portal for the SolarEdge inverters and generated a chart for the panel in question.

Chart - leaf

As I said, I was surprised.  There was a VERY noticeable jump in production at the exact time I cleared the leaf. I really didn’t expect a small leaf to make such a big difference.

Here is another chart showing the power profile for all 4 modules in that panel

Chart - leaf - whole panel

It’s unmistakable. The green line is the leaf module. At 13:58 the power production went from 142W to 159W. That’s an increase of more than 12.65%. Over the course of the whole day that one leaf caused a loss of about 140 watt-hours or 0.14 kilowatt-hours. That’s about how much energy this computer uses over 4 hours.


Responses

  1. great research…thanks.

  2. why would a such a small leaf on such a large solar array have this kind of impact?

    • Picante, good question. Keep in mind that our SolarEdge inverter system allows us to monitor each solar module individually. The chart shows a drastic (12.65%) increase in production when the leaf is removed but that is just for a single module out of 38 total modules. Looking at the power chart of the entire system that day, you see that it is a barely noticeable increase when leaf is removed at 13:58. This SolarEdge inverter system also allows each module to operate independently of the rest of the array. With a conventional string inverter, the impact on production would be more significant. Here’s why, the shaded cell becomes a resistor and dissipates energy that is being produced in the rest of the module. The cells are wired in series to make a module and the modules are wired in series to make up the string. A typical string is 12 modules in series. With a conventional string inverter system, the impact of that small leaf would have been multiplied by 12 modules and would definitely be noticeable on the whole system.

      • So, why did you bother about the leaf, Nik?


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