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  • #31
    Soap, water and some scrubbing certainly gets things cleaner than just dribbling water on them. A heavy rainstorm would do just that. I try to wash mine once a year. I have a pole mounted brush.

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    • #32
      Originally posted by nate379 View Post
      Soap, water and some scrubbing certainly gets things cleaner than just dribbling water on them. A heavy rainstorm would do just that. I try to wash mine once a year. I have a pole mounted brush.
      Have you measured the difference using some quantifiable method ? I have for about 2+ years now.

      Long story short, my array fouls at a rate such that the performance deteriorates about 0.075 % to 1.0% per week if It doesn't see rain or a cleaning. A rain of some decent quantity, say, 1/4" to 1/2", will restore very roughly, about 2/3 - 3/4 of the clean performance, sort of depending on how much/how long it rains, pretty much regardless of how fouled the array is before the rain.

      I generally agree that it seems washing with mechanical scrubbing would restore almost all of the clean performance, and it may well do that.

      But, the surprising thing I believe I've found after doing mechanical scrubbing and also simple hosing about a dozen times each, and measuring before/after performance each time as well as a lot of measurements between cleanings, including hand measurements of individual panel temps from under the array on about 200 days, and a recent series of cleanings on sunny days somewhat around the dates of min. solar incidence angle as sunny days allow (31 total) to compare 3 different cleaning methods to see if one is superior to the others in terms of how clean they will get an array, is that:

      Aside from some minor scrubbing to remove things like owl skrock, I've found hosing my array from the top down 3 consecutive times such that the rate of H2O use is about 10 l/m^2 of array, a process that takes about 10 min., restores about as much of the original performance as mechanical scrubbing.

      Not only that, but at a fouling rate of ~~ 0.75 % /week, and for comparable results, at least as close I can SWAG it using a +/- tolerance of about 0.75 % on my ability to estimate the performance impairment due to fouling level, hitting the array with a hose 1X/month will probably result in an array that's over time only slightly less fouling impaired than one that's been scrubbed, and with a lot less hassle.

      As for how the fouling rate proceeds as f(time) I'm still unsure the nature of the fouling rate I'm seeing so as to be able to do a better job of estimating when best to hose the array. That is, is it a linear rate, with the rate being unchanging at a rate of ~ 0.75% -1.0%/week, or, as I continue to suspect, does it tend toward some type of asymptotic behavior that becomes more apparent after 8 or so weeks, or is it some wildly galloping function of weather and local conditions ? Or ...????

      BTW, for those wondering, The remaining water spots as a result of hosing and drip drying do not seem to impair performance compared to scrubbing, squeegeeing and hand drying to remove water spots in any way I've been able to measure.
      Last edited by J.P.M.; 09-06-2016, 09:21 PM.

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      • #33
        Originally posted by J.P.M. View Post
        Around my area - San Diego county, I look at PV arrays as I'm driving around the area and walking in my neighborhood. The last measureable rain at my house was 06/06/16, and that was only 0.03" - just enough to cake the dust on my panels. Many/most arrays I see are getting a nice and quite noticeable bathtub ring with the remainder of the panel getting pretty dusty looking.

        From a bunch of measurements I've done and continue with, as best as I can give an educated guess, my array's performance degrades approx. somewhere between 0.75% and 1.0% per week as a result of dirt buildup on the panels if they are not washed. Without rain or washing, I believe that rate starts to get asymptotic after about 6-8 weeks or so in some way I can't yet estimate, quantify or model.

        A decent rain or hosing the array down seems to restore about 1/2 to 2/3 or so of the clean array performance. So, if my array is fouled to the point of, say, a 6 % decline in performance due to dirt,
        hosing it off will probably improve the array's performance by about 3 or 4 %.

        A mostly south facing array around here will produce about 150 - 175 kWh/month per nameplate kW this time of year. 3% of that is ~ 5 kWh per nameplate (DC) kW. If in tier 4, or prime time T.O.U. that's ~ $0.35 or so per kWh --->>> approx. savings per installed kW ~ = $1.75/mo. So, for those with arrays that have seen no moisture in a few months, a few minutes with a hose and probably what amounts to less than 50 gal. of H2O, someone with a 5 kW array might well reduce their current electric bill by something like ($1.75) X (5) = ~ $8 or $9. per month or ~ 30 day billing period.

        Caution: before you run out with a hose: ONLY HOSE AN ARRAY WHEN THE SUN IS NOT ON IT, PREFERABLY IN THE MORNING, AND NEVER AFTER ABOUT 8 A.M. AT THE LATEST.

        REASON: THE PANEL GLAZING MAY CRACK FROM THERMAL SHOCK
        .

        Just sayin'. No guarantees expressed or implied. Your mileage may vary.

        Take what you want of the above. scrap the rest.
        You can refer to the article posted at http://www.reonenergy.com/how-often-...-solar-panels/ .. It shows clear video for cleaning and maintaining solar panels.

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        • #34
          Originally posted by Guest View Post

          You can refer to the article posted at http://www.reonenergy.com/how-often-...-solar-panels/ .. It shows clear video for cleaning and maintaining solar panels.
          Probably not bad advice and I can't disagree with too much of it. However, my experience, measurements and data indicate that for my array (and I'd make an educated guess and say others' arrays, but not everyone's) hosing without wiping is sufficient except for really caked/cooked on stuff, provided the array gets hosed about 1X/month or after 1 month without a decent rain. That is, I've been unable to detect a difference in performance improvement over rinsing and wiping then rinsing again, over simple rinsing. Added to that, if my rate of fouling is such that my array's output drops ~~ 1% per week without rain/hosing, which is about what it is, the small difference in cleanliness between simple hosing and hosing/wiping/rinsing becomes moot after a few days or less.

          And to repeat, spots from hard water content do not seem to reduce the restored performance of my array over using D.I. or distilled water in any way I can measure, and I've been looking for a difference off and on for going on 4 years. Maybe I/m wrong and/or my methods are incorrect, but That's what my experience and data are telling me.

          I'd like to see other data that would improve my knowledge of the subject.

          As for guano, I don't have much (on my array anyway) but for the most part it comes off with hosings/rain.

          Aside from that, the folks at Furnace Creek Ranch in Death valley continue to tell me they wash their 1 MW array about every 2 years to remove droppings from the large flocks of desert starlings that live on/around the adjacent golf course and it's relatively abundant water supply. But aside from that, they (facility maint.) don't seem to be worried about array performance, although I don't believe they have all they need to correctly interpret their monitored data.

          Bottom line for me: Hose the array every 4 weeks or so if it doesn't rain. Use ~ 3/4 gal./panel. Do it early before the array heats up.

          IMO, for most folks in SO CA or deserts, more than that won't improve things much.

          As before, just based on my findings. Your results may and probably will vary, but my guess is not by much.

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          • #35
            I've observed that quite a bit of dew collects on my PV panels in the early morning, which then picks up dust and dirt. My area is very dusty, so quite a bit accumulates in just a few months. Spraying by itself is not enough to get the caked on dirt off, so I purchased a wide window washer/squeegee tool with an extendable pole long enough to reach the panels in the middle of the array.
            Cleaning Tool.JPG

            The production results were pretty significant before and after cleaning. The weather was pretty much identical with clear skies all day so the primary difference should be due to the cleaning.

            Here's the side by side daily production from the day before and the day of cleaning:
            Total production 38.52 kWh vs 43.37 kWh (12.5% increase). Peak 5.16 kW vs 5.71 kW
            Daily Production Before and After.PNG


            The weekly view shows the big jump.
            Production Before and After Cleaning.PNG
            And this is with 5 of the 21 panels not cleaned. The sun was coming up and I was getting hungry so I still need to get the last 5 cleaned. There would likely be a couple more percent increase if all of them were cleaned.
            Panels Semi-cleaned.JPG
            Attached Files

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            • #36
              Originally posted by Kendalf View Post
              I've observed that quite a bit of dew collects on my PV panels in the early morning, which then picks up dust and dirt. My area is very dusty, so quite a bit accumulates in just a few months. Spraying by itself is not enough to get the caked on dirt off, so I purchased a wide window washer/squeegee tool with an extendable pole long enough to reach the panels in the middle of the array.
              Cleaning Tool.JPG

              The production results were pretty significant before and after cleaning. The weather was pretty much identical with clear skies all day so the primary difference should be due to the cleaning.

              Here's the side by side daily production from the day before and the day of cleaning:
              Total production 38.52 kWh vs 43.37 kWh (12.5% increase). Peak 5.16 kW vs 5.71 kW
              Daily Production Before and After.PNG


              The weekly view shows the big jump.
              Production Before and After Cleaning.PNG
              And this is with 5 of the 21 panels not cleaned. The sun was coming up and I was getting hungry so I still need to get the last 5 cleaned. There would likely be a couple more percent increase if all of them were cleaned.
              Panels Semi-cleaned.JPG
              Thank you. for the input.

              Given that you had several months worth of dirt, and that works out to about maybe 12 - 15 weeks or so, an 11% to, say, maybe 15 % or so, that fouling penalty sounds about in line with my number of ~ 0.75 - 1.0% performance loss/week due to fouling without rain or intentional cleaning. And still, keeping in mind that array fouling can be highly dependent on location and lots of other factors.

              As for the crud caking on from dew/cooling and then cooking on the next day cyclic type activity, I too have seen a fair amount of that due to copious marine layer and low nitetime radiant sky temps. that will often produce the equivalent of about 0.03"-0.05" of precip. in the Davis rain gage that's located about 4 ft. north of the array. I agree that left for several months, some mechanical means is necessary to get rid of it, most of which, for my array anyway is what seems to be what's responsible for the bathtub ring at the bottom 6" - 12" or so of the panels. But, so far and, I stress, for my experience only, hosing about every 3-4 weeks seems to also restore most array performance due to that mechanism as well, with the eye again being not necessarily the best judge of performance.

              I haven't been able to get accumulated fouling data on my array since 06/30/18 as I've hosed, mopped (with a brush identical to yours BTW), and hosed again every morning at 0700 hrs. I then measure instantaneous output and input, voltages and currents from the inverter, and a bunch of other parameters the Davis spits out 1X/minute, and get an estimate of instantaneous input and output at the minute of minimum incidence angle. That'll continue until 09/04/2018.

              Question: How do you avoid tile breakage ? Looks like they're all intact.

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              • #37
                I agree with what everyon say here. My panels has not been cleaned since installation about 3 years now. I decided to climb the roof to scrub it with simple water and a car was brush then squeegee it off a couple days ago. I definitely see improvement. The weather in the Bay area has been pretty consistent the past couple days.

                I washed the panels late morning on the 22nd and look how it improved the past two days.

                solar.png

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                • #38
                  I recently purchased a pole mounted brush for my panels and have used it twice. The first time was just with water and I didn't see a huge improvement. However, that was after about a year of not cleaning with any mechanical means (I had done a hose spray a couple of times). I think I incurred a pretty significant penalty due to ash from local brush fires, one of which caused me to evacuate (side note, monitoring my solar production remotely let me know that my house had not burned down). When looking at the panels after they dried I could definitely see that the panels were still dirty.

                  My latest clean was a couple of weeks ago and I dragged a bucket with some Dawn up on the roof with me and used that to scrub the panels down and did see a decent increase in production as a result. It looks like my peak production went up about 250W with very similar solar radiation readings. Total production went up a little over 2kWh on the day of cleaning (on my 6.27kW system). The panels looked much cleaner and definitely had a shinier appearance as compared to using just water.
                  Last edited by jasonvr; 08-31-2018, 02:05 AM.

                  Comment


                  • #39
                    Originally posted by jasonvr View Post
                    I recently purchased a pole mounted brush for my panels and have used it twice. The first time was just with water and I didn't see a huge improvement. However, that was after about a year of not cleaning with any mechanical means (I had done a hose spray a couple of times). I think I incurred a pretty significant penalty due to ash from local brush fires, one of which caused me to evacuate (side note, monitoring my solar production remotely let me know that my house had not burned down). When looking at the panels after they dried I could definitely see that the panels were still dirty.

                    My latest clean was a couple of weeks ago and I dragged a bucket with some Dawn up on the roof with me and used that to scrub the panels down and did see a decent increase in production as a result. It looks like my peak production went up about 250W with very similar solar radiation readings. Total production went up a little over 2kWh on the day of cleaning (on my 6.27kW system). The panels looked much cleaner and definitely had a shinier appearance as compared to using just water.
                    After no cleaning for a long time, like months, or no significant rain, I've found my array benefits from mild detergent and some elbow grease, but unless the gunk is caked/cooked on by a lot of repeated cooking/dew cycles My experience is that a simple hosing restores about 2/3 or so of the lost performance due to dirt if done, say 1X/month or so. 6 months of no rain/no cleaning takes some soap/elbow grease and a soft cloth. That observation applies to my array only, and probably similar in my neighborhood and I'd think in similar environments.

                    I sure don't doubt your reported improvement but I'm confused about your reported numbers. Your peak production went up ~ 250W. If so, what were that an instantaneous readings ? That is, assuming they were instantaneous readings, what was the POA irradiance and what was the array output before cleaning ? What were those same numbers after cleaning ? How did you determine the irradiance levels ? How far apart were the before/after readings in days ? Were the readings done at the same time of day ?

                    Thank you.

                    Comment


                    • #40
                      Reading days were consecutive - Aug 16 and Aug 17 (panels cleaned this day, early in the morning before any significant sun). Irradiance was determined based on a local weather station reporting through Weather Underground. It's not perfect, but is a decent approximation. Peak production is based on the 5 minute values reported from SolarEdge thru PVO

                      August 16 - 1:10pm
                      Peak production ~4640 W
                      Peak irradiance ~464 W/m2
                      Aug16.JPG


                      August 17 - 1:15pm
                      Peak production ~4930 W
                      Peak irradiance ~469 W/m2
                      Aug17.JPG

                      Week
                      Week.JPG

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                      • #41
                        Originally posted by jasonvr View Post
                        Reading days were consecutive - Aug 16 and Aug 17 (panels cleaned this day, early in the morning before any significant sun). Irradiance was determined based on a local weather station reporting through Weather Underground. It's not perfect, but is a decent approximation. Peak production is based on the 5 minute values reported from SolarEdge thru PVO

                        August 16 - 1:10pm
                        Peak production ~4640 W
                        Peak irradiance ~464 W/m2
                        Aug16.JPG


                        August 17 - 1:15pm
                        Peak production ~4930 W
                        Peak irradiance ~469 W/m2
                        Aug17.JPG

                        Week
                        Week.JPG
                        Thank you. Looks like you have a west of south orientation and some morning shading ? Aside from the idea that they seem to confirm that cleaning improved output significantly, I'm not sure I understand what those two top graphs are saying. Unless you've got a somewhat northerly array orientation, the irradiance numbers seem quite low. Are they POA irradiance numbers or what ?

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                        • #42
                          I'm not 100% sure on the irradiance since I don't own the weather station, I just know it is close to my home. My gut says they have some shading issues in the morning as evidenced by the sharp increase of the light green line each morning.

                          I have two orientations on my panels. Site plan is below. The glitches in my production (dark green line) in the morning are due to cloudiness/marine layer burning off.

                          SitePlan.JPG

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                          • #43
                            Originally posted by jasonvr View Post
                            I'm not 100% sure on the irradiance since I don't own the weather station, I just know it is close to my home. My gut says they have some shading issues in the morning as evidenced by the sharp increase of the light green line each morning.

                            I have two orientations on my panels. Site plan is below. The glitches in my production (dark green line) in the morning are due to cloudiness/marine layer burning off.

                            SitePlan.JPG
                            Thank you. All this is a bit off topic, but if those irradiance measurements are from some instrument that uses conventional reporting methods, then - and nothing to do with you other than a caution on using them for anything - they're screwed up. Irradiance is usually reported on a horizontal plane (GHI, or Global Horizontal Irradiance) and then, if irradiance in another orientation (such as the plane of the array, or P.O.A. irradiance), that's conventionally found by available and mostly agreed upon methods.

                            Around So.CA on those dates the solar noon GHI was running ~ 850 to maybe 920 W/m^2 or so, and not as flat a curve as shown and not apparently as shaded as shown. Mine Davis instrument measured 907 W/m^2 on 08/16 and 904 W/m^2 on 08/17 at solar noon on those days (12:52 P.M, P.D.T. both days @ my location). Hence my questioning of the graph numbers, but not your output numbers.

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                            • #44
                              JPM has done lots of write-ups on this topic and my case is more of a worst case example. The water line that I ran the 400' down to the solar system is also on a water line used for irrigation and I had a cracked pipe near the pump house that force me to turn off that water line after the last snow in early May. So starting in mid May I have not hosed down the four arrays. No rain since early May, and we had two massive fires close enough to cover everything with ash - the Ferguson fire was the worst. Low humidity and no dew left me with an amazing layer of gunk on the panels. I finally fixed that water line and just this morning hosed it all down. Wish I had my phone with me - what an amazing video of brown water it would have been. No scrubbing - just hosing. Really want to be careful with that ash - it does a number on car paint if you rub it before getting the majority gone from a water spray so I'm just hosing only.

                              Initial numbers for today compared to Mon-Wed with same clear skies and similar temps is just a tad under 9.5% higher. Today is the same temp as Wed but a bit cooler than Mon and Tues. When the day is done I will see where I end up. I really can't imagine those panels being more dirty than they were, so this seems to be in line with the lower numbers JPM has so carefully reported. At least for my system, I feel that I can safely say that dust/ash/pollen gunk is under 10% in a worst case and matches the under 5% ish I has seen previous when more regular hosing.

                              Comment


                              • #45
                                Originally posted by tyab View Post
                                JPM has done lots of write-ups on this topic and my case is more of a worst case example. The water line that I ran the 400' down to the solar system is also on a water line used for irrigation and I had a cracked pipe near the pump house that force me to turn off that water line after the last snow in early May. So starting in mid May I have not hosed down the four arrays. No rain since early May, and we had two massive fires close enough to cover everything with ash - the Ferguson fire was the worst. Low humidity and no dew left me with an amazing layer of gunk on the panels. I finally fixed that water line and just this morning hosed it all down. Wish I had my phone with me - what an amazing video of brown water it would have been. No scrubbing - just hosing. Really want to be careful with that ash - it does a number on car paint if you rub it before getting the majority gone from a water spray so I'm just hosing only.

                                Initial numbers for today compared to Mon-Wed with same clear skies and similar temps is just a tad under 9.5% higher. Today is the same temp as Wed but a bit cooler than Mon and Tues. When the day is done I will see where I end up. I really can't imagine those panels being more dirty than they were, so this seems to be in line with the lower numbers JPM has so carefully reported. At least for my system, I feel that I can safely say that dust/ash/pollen gunk is under 10% in a worst case and matches the under 5% ish I has seen previous when more regular hosing.
                                Thank you for the info.

                                IMO, you did the right thing by hosing as much of the fouling layer(s) off before any abrasion or rubbing.

                                Just to reiterate, never get an array wet when the array is warmer than the air temp. or when the difference between the panel temp. and the water temp. is more than maybe 20 F. or so.

                                Don't hit a hot panel with cold water. (or a cold panel with hot water)

                                As for how much your performance suffered from fouling, every application/location will most likely be different, even from the one next door. That the ~ 10% figure you report seems in line with what I might SWAG seems reasonable makes little or no difference to reality, but still that does seem in line with my experience, particularly if some asymptotic character of the rate of increase as f(time) has any relevance to your situation/location.

                                One thing I've noticed with my array: dew points close to the ambient temp. can be either good or bad for my array's fouling. If the array is very clean, a heavy dew, or marine layer that causes a lot of condensation to from on the array will tend to do little that will affect performance, maybe a bit to the good. However, if the array is less than clean, I believe a general characteristic I've found is that a high dew point or air that's close to saturation will most often tend to cause any dust/stuff on the array to mud up and then tend to run down the panels (somewhat) with the result that a bathtub ring forms on the bottom 12" or so of each row on panels, and what doesn't run down the panels tends to stay put and cake up all the way up the panel, blocking sunlite (more fouling_) and also acting as a wick that traps more moisture and more dust.

                                I'm still hanging my hat on an approx. fouling rate that results in a 1%/week deterioration in output over the clean condition for my array. Yours and other arrays will behave differently, but I' not be surprised if that 1%/week number was pretty common for suburb/rural locations.

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