Robert,
Thank you for taking the time to write and for the input. As things get sunnier (in what use to be sunny FL) I will certainly incorporate your suggestions. Up on the roof, I used an pyrometer and inclinometer every 15 minutes to record an average irradiance. The recordings were made before and after cleaning. Minimal and Max readings were 640 and 680w/m2 respectively.
I only measured from the vantage point of the 11 modules facing south. Big mistake! I should have taken the time to measure the irradiance of the modules facing East and West pre and post cleaning. Even though I cleaned all the modules in the array, without a measurement of irradiance for the East and West modules I can't justify any changes in their power. Still with no significant change in irradiance, south facing panels ( the ones that were measured), showed the greatest gain in current, 1.4A to 7.89A. At least for these panels, is it not safe to conclude that their increase in power particularly current is a function of the cleaning?
Thanks
John
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John Eftimiades
Videographer/Thermographer
Skyview Thermography and Media Services
jefti@yahoo.com------------------------------
Original Message:
Sent: Mar 04, 2021 10:18 AM
From: Robert Foster
Subject: Dust, dirt and solar panels
Hi John,
Module soiling generally accounts for about 1 to 5% drop in performance depending on rainfall frequency. Soiling averages about 2% per month without rainfall.
In some places with lots of aerosols (e.g., Abu Dhabi) soiling can be compounded as the aerosols cling to dust particles and then glue down dust to the module glass and make it much harder to clean. I have seen some systems in this situation with accumulated dust with a ~50% drop in performance, but again this is not common.
There may be some other issue with your system. Most likely this 4x power output was due to increase of irradiance across all 3 of your sub-arrays which are oriented to different cardinal points. Depending on the type of inverter you have, your lowest sub-array output can bring down the output across the entire system. As the sun gets higher in the sky your overall system output could dramatically increase.
You should measure module back temperature and POA irradiance and then normalize power production taking these changing factors into account.
Best regards
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Robert Foster
Assistant Professor
New Mexico State University, College of Engineering
Las Cruces NM
rfoster@ases.org
Original Message:
Sent: Mar 04, 2021 09:09 AM
From: John Eftimiades
Subject: Dust, dirt and solar panels
Most definitely. I did a simple experiment measuring irradiance and output both before and after cleaning. The entire test was done in about 40 minutes with the irradiance essentially unchanged. I saw a 4 fold increase in power, mostly through current but slight improvement in voltage. If your curious:
https://youtu.be/BgrZycaUZKA
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John Eftimiades
Videographer/Thermographer
Skyview Thermography and Media Services
jefti@yahoo.com
Original Message:
Sent: Feb 19, 2021 02:55 PM
From: Harlan Sager
Subject: Dust, dirt and solar panels
I live in hot and dry and dusty southern Nevada. Have not had any significant rainfall in almost a year.
Do I need to wash my panels and if so what should I use to clean them? Have had my system since 2012 and am seeing about 10% drop in annual KWHRs.
Appreciate feedback.
Thanks
Harlan