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  • Underestimated Results of Cleaning Panels

    Last week I cleaned my 22 panels after almost a year on my roof. I've read that the power difference, if any would be negligible after cleaning under normal circumstances. Here in Northern California we had epic rainfall this spring, and I figured that would get me through to this winter. I noticed though that they were looking quite dusty. After getting on the roof and looking closer, they looked even worse, and I decided that they needed cleaning.

    Went to Lowes and got the biggest professional window squeegee they sold, an 18 inch Ettore model and the corresponding 15 foot expandable pole. I also bought a cloth window washing scrubby tool. After dragging the hose up, the normal water pressure from the hose nozzle was plenty good to wash off the dirt. And there was a great deal of dirt. More than it even appeared just by looking at them. I have hardish water in my area, so as soon as I washed the panels down a few times, I squeegeed them to remove the water and dirt. I worked from the bottom, pulling the dirt and water towards me. The whole process only took about 15 minutes to clean the entire array. Each panel was basically three swipes with the squeegee. Never needed the cloth scrubbing tool, nothing was stuck on that didn't come off with the normal water flow.

    This was all done last Wed, the 20th. Today I took a look and my readings and the increased power after cleaning is quite noticeable, as seen in the graph below. At least 4 KWh's more per day. Worth the time for sure. So I'm guessing I'm going to start doing quarterly cleanings. Lastly, I don't live near any construction or busy roads, just the normal suburbs.

    Steve



    ScreenHunter_615 Sep. 25 11.56.jpg

  • #2
    Originally posted by steveholtam View Post
    Last week I cleaned my 22 panels after almost a year on my roof. I've read that the power difference, if any would be negligible after cleaning under normal circumstances. Here in Northern California we had epic rainfall this spring, and I figured that would get me through to this winter. I noticed though that they were looking quite dusty. After getting on the roof and looking closer, they looked even worse, and I decided that they needed cleaning.

    Went to Lowes and got the biggest professional window squeegee they sold, an 18 inch Ettore model and the corresponding 15 foot expandable pole. I also bought a cloth window washing scrubby tool. After dragging the hose up, the normal water pressure from the hose nozzle was plenty good to wash off the dirt. And there was a great deal of dirt. More than it even appeared just by looking at them. I have hardish water in my area, so as soon as I washed the panels down a few times, I squeegeed them to remove the water and dirt. I worked from the bottom, pulling the dirt and water towards me. The whole process only took about 15 minutes to clean the entire array. Each panel was basically three swipes with the squeegee. Never needed the cloth scrubbing tool, nothing was stuck on that didn't come off with the normal water flow.

    This was all done last Wed, the 20th. Today I took a look and my readings and the increased power after cleaning is quite noticeable, as seen in the graph below. At least 4 KWh's more per day. Worth the time for sure. So I'm guessing I'm going to start doing quarterly cleanings. Lastly, I don't live near any construction or busy roads, just the normal suburbs.

    Steve


    have you compared this pattern to other systems nearby using PVOutput? Just to make sure this was not related to weather.

    Comment


    • #3
      Interesting. has anyone tried installing a system like this: http://www.solarpanelcleaningsystems...sidential.html

      thx
      mike

      Comment


      • #4
        Originally posted by max2k View Post

        have you compared this pattern to other systems nearby using PVOutput? Just to make sure this was not related to weather.
        I just checked the OP's zipcode (shared in an earlier post) in PVOutput, and only returned one system, which looks like it is probably his!

        Weather does appear to be a factor, with lots of clouds from 9/11 - 9/20.

        9/15, 9/17 and 9/19 are clear day comps, but it is cooler now than it was then, and much cooler than the clear days earlier in Sept.

        Peak output on 9/22 was 4769 W at 12:40 pm, temp 70.3 F.

        On 9/19, 4532 W at 12:40 pm, temp 73.9 F

        On 9/17, 4365 W at 12:30 pm, temp 79.0 F

        On 9/15, 4346 W at 12:30 pm, temp 78.4 F.

        On the other hand, using the map tool in PVoutput finds a few systems not too far away, a couple of which have similar tilt. Here is one that shows the difference between the two systems doubling after the cleaning date. Those data suggest a cleaning bump in daily energy produced of about 10%.

        Last edited by sensij; 09-25-2017, 09:11 PM.
        CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

        Comment


        • #5
          As I've written, array fouling is a very local phenomenon. I have no trouble believing you might see a 10 % + increase in output after a cleaning, although that seems maybe a bit high.

          Hard to get even dart throw estimates without before/after measurements of output without weather variable info and irradiance measurements from a pyranometer.

          Good info. Thank you. After monitoring daily output, weather variables, including irradiance at 1 minute intervals, and measuring instantaneous output and panel temps for 3 + years several hundred times, all with as much precision as I can manage, I believe my array's fouling is a non constant f(weather) whose a rate that seems to, at this time anyway, decrease my array's output at the rate of something like, and very approx. 0.6 - 0.8% or so per week +/- a lot when it doesn't rain. A decent rain ( > maybe 0.25" or so) will restore ~ 2/3 -3/4 of the performance lost to fouling. After a rain, or cleaning,output resumes its decline at ~ the same 0.6 - 0.8 %/ week rate until the next rain or wash.

          Something I think I'm seeing but not quite a smoking gun yet is that the rate of performance decrease for my array and location only, seems to want to become asymptotic at about a 6 - 8 % decrease from clean output after something like 10 to 12 weeks without rain.

          As for cleaning, I've done what I believe are some controlled measurements and have come to the conclusion that hosing off my array without any other measures with a hose at a rate of ~~ 0.75 gal. /panel and letting it drip dry is about as effective as washing with soap/scrubbing with soft cloth/rinsing with a hose followed by a D.I. rinse/squeegeeing, or soap/cloth scrub/ hose rinse/squeegee/cloth dry. I used each of those 3 cleaning scenarios 11 times each on 36 almost consecutively sunny days, measured input against output at the time minimum incidence angle each day as adjusted for irradiance, wind and array and ambient temp. with the result that I could not detect a measureable difference in array performance or output when adjusted for those variables of irradiance wind and panel temp. The hose rinse left water spots but those spots didn't decrease output over the more extensive and vigorous methods I described in any way I could measure.


          If I ever stop measuring fouling, I'll hose my array ~ 1X/month when it doesn't rain and accept a more/less permanent fouling penalty of ~~ 3% of performance due to dirt, but only in the A.M. when the array is cool and before much sun hits the glazing.

          Given what I think I found, I sure as hell won't pay for a cleaning service to do any panel cleaning. Seems like a rip off and another way to separate the solar ignorant from their assets.
          Last edited by J.P.M.; 09-25-2017, 09:22 PM.

          Comment


          • #6
            Originally posted by sensij View Post

            I just checked the OP's zipcode (shared in an earlier post) in PVOutput, and only returned one system, which looks like it is probably his!

            Weather does appear to be a factor, with lots of clouds from 9/11 - 9/20.

            9/15, 9/17 and 9/19 are clear day comps, but it is cooler now than it was then, and much cooler than the clear days earlier in Sept.

            Peak output on 9/22 was 4769 W at 12:40 pm, temp 70.3 F.

            On 9/19, 4532 W at 12:40 pm, temp 73.9 F

            On 9/17, 4365 W at 12:30 pm, temp 79.0 F

            On 9/15, 4346 W at 12:30 pm, temp 78.4 F.

            On the other hand, using the map tool in PVoutput finds a few systems not too far away, a couple of which have similar tilt. Here is one that shows the difference between the two systems doubling after the cleaning date. Those data suggest a cleaning bump in daily energy produced of about 10%.
            good comparison, thank you! It does seem like it made 10% difference. Now how quickly that would go back down is another interesting question.

            Comment


            • #7
              Originally posted by fresnoboy View Post
              Interesting. has anyone tried installing a system like this: solarpanelcleaningsystems.com/residential.html
              Looks like a useless scam to sell special cleaning soap and ineffectual rinse agent. Do they re-warranty the panels ? The panel mfg, if they found you sprayed soap and rinse agent, will cancel your warranty.

              Powerfab top of pole PV mount (2) | Listeroid 6/1 w/st5 gen head | XW6048 inverter/chgr | Iota 48V/15A charger | Morningstar 60A MPPT | 48V, 800A NiFe Battery (in series)| 15, Evergreen 205w "12V" PV array on pole | Midnight ePanel | Grundfos 10 SO5-9 with 3 wire Franklin Electric motor (1/2hp 240V 1ph ) on a timer for 3 hr noontime run - Runs off PV ||
              || Midnight Classic 200 | 10, Evergreen 200w in a 160VOC array ||
              || VEC1093 12V Charger | Maha C401 aa/aaa Charger | SureSine | Sunsaver MPPT 15A

              solar: http://tinyurl.com/LMR-Solar
              gen: http://tinyurl.com/LMR-Lister

              Comment


              • #8
                Originally posted by sensij View Post

                I just checked the OP's zipcode (shared in an earlier post) in PVOutput, and only returned one system, which looks like it is probably his!

                Weather does appear to be a factor, with lots of clouds from 9/11 - 9/20.

                9/15, 9/17 and 9/19 are clear day comps, but it is cooler now than it was then, and much cooler than the clear days earlier in Sept.

                Peak output on 9/22 was 4769 W at 12:40 pm, temp 70.3 F.

                On 9/19, 4532 W at 12:40 pm, temp 73.9 F

                On 9/17, 4365 W at 12:30 pm, temp 79.0 F

                On 9/15, 4346 W at 12:30 pm, temp 78.4 F.

                On the other hand, using the map tool in PVoutput finds a few systems not too far away, a couple of which have similar tilt. Here is one that shows the difference between the two systems doubling after the cleaning date. Those data suggest a cleaning bump in daily energy produced of about 10%.
                Those of us who have pyranometers and a weather station - you, I and others - and who know their instruments' output understand that weather and irradiance data can vary more than it may appear they do, and can be responsible for at least several % variance in output under what appear to the senses to be identical conditions. Without on site weather and irradiance data, and some idea of panel temps. as a result of that weather, estimating performance deterioration from panel fouling is speculation. I believe I understand your reasoning here. And while logical and sensible, it's not a smoking gun. Neither are the results of my measurements - far from it - but I bet my barrel is warmer. Even then, and with all attention to detail I take pains to establish with my measurement protocols, it's still an estimate.

                Looking at daylong outputs from the OP's site or other close by sites is nice, especially if it fits the sought conclusion, but it's still little more than anecdotal. I'd suggest keeping that in mind.

                Still, and as I wrote, given what seems the highly variable nature of array fouling and the mechanisms that seem to influence fouling and fouling rates, as well as what the OP reports as the length of time since the last cleaning, a 10 % performance loss due to fouling that the OP suggests doesn't seem out of the question. Seems maybe a bit high, but I'm not there. But neither are the supporting data or numbers strong enough to back up the 10 % claim a bit better. Hell, for all I/we know, given the lack of data, that array's performance might be 15 % or more off from fouling.

                As to Mike's comment of a scam - maybe, but if so it's a softer sell than I'd expect or I've seen in the past.

                On cleaning, I'll still stand by my findings that simple hosing at a rate of ~~ 3/4 gal. of tap water/panel - and that's it - no soap, magic or otherwise, no scrubbing, no D.I./distilled water rinse gets things as clean as necessary as any other method, especially considering that the most thorough cleaning in the world will begin fouling as soon as cleaned at the same rate as an array that gets 75 - 90% of the dirt removed by a hosing. As a practical matter, after about 3 weeks after cleaning, either will show about the same performance reduction from fouling. Save your money and hose the array.

                That hosing is about as effective as necessary, or that more involved methods my not be worth the extra effort for what I've measured as little/any extra cleanliness may seem counterintuitive, but that's what I measured as described in prior posts. If my data and measurements are representative of some form of reality that is common, that might mean that simple hosing may suffice to keep things clean enough, and as a side bennie might help eliminate the need for, or maybe help blow a hole in the cleaning scams,

                Fouling rates and the nature of the dirt vary, sometimes a lot. Still, I've got data that suggests my stuff fouls at a rate that seems quite variable at times but somewhat steady at ~ 0.6%-0.8% per/week performance loss without rain, with that rate tending to decrease asymptotically beginning at ~ 10 weeks +/- some if it doesn't rain. While I believe fouling rates and mechanisms that cause the fouling are quite site and location dependent and variable, I also suspect my site and location are reasonably typical, whatever that means.

                Comment


                • #9
                  Originally posted by fresnoboy View Post
                  Interesting. has anyone tried installing a system like this: http://www.solarpanelcleaningsystems...sidential.html

                  thx
                  mike
                  Yea, that looks like a scam.

                  Comment


                  • #10
                    Originally posted by J.P.M. View Post

                    Looking at daylong outputs from the OP's site or other close by sites is nice, especially if it fits the sought conclusion, but it's still little more than anecdotal. I'd suggest keeping that in mind.
                    Yes, I'm comfortable with the distinction between an anecdotal "data suggest" vs "prove". I was actually seeking to prove the OP's hypothesis was false, and had written the first half of my post anticipating that I would be able to find PVOutput data that would show other systems had behaved similarly, or at least close enough to explain a good portion of the difference. There are several sites in the vicinity of the OP's system with very good data correlation, and the OP's is a clear outlier in only the period from Sept 21 onward.

                    It isn't proof, but there is enough there for me to cautiously agree that the OP achieved something close to the claimed energy gain from cleaning.
                    CS6P-260P/SE3000 - http://tiny.cc/ed5ozx

                    Comment


                    • #11
                      Originally posted by sensij View Post

                      Yes, I'm comfortable with the distinction between an anecdotal "data suggest" vs "prove". I was actually seeking to prove the OP's hypothesis was false, and had written the first half of my post anticipating that I would be able to find PVOutput data that would show other systems had behaved similarly, or at least close enough to explain a good portion of the difference. There are several sites in the vicinity of the OP's system with very good data correlation, and the OP's is a clear outlier in only the period from Sept 21 onward.

                      It isn't proof, but there is enough there for me to cautiously agree that the OP achieved something close to the claimed energy gain from cleaning.
                      Understood and mostly agree. I believe we're on the same page.

                      Comment


                      • #12
                        I am thinking abut cleaning my panels and seeing if I get any increase. Is it safe to just spray them with a hose and use a squeegee like the op did? Is there a risk of getting shocked? Better to do it in the early morning I would assume?

                        Comment


                        • #13
                          Originally posted by BFW577 View Post
                          I am thinking abut cleaning my panels and seeing if I get any increase. Is it safe to just spray them with a hose and use a squeegee like the op did? Is there a risk of getting shocked? Better to do it in the early morning I would assume?
                          I've cleaned my array many times, one period was every morning at 0630 hrs. over 70 consecutive days. Another was 36 consecutive days with various soap/scrub/rinse/wipe/buff schemes. lots of other times as well. I'm alive to tell the tale. Do it in the A.M. before the sun gets very high to help avoid thermal shocks to the glazing.

                          Since you probably don't have instrumentation for weather and irradiance measurements next to your array, for the best probability of getting a better guess at how much your array's output has decreased due to fouling, I'd suggest hosing on a day after a day of clear skies and with the day of hosing having a forecast that's as similar to the prior day as possible to the prior day in terms of being clear, and having the same temps. and winds.

                          Then, observe the array's output on both days, before and the day of cleaning, at the same time of day, at around solar noon, or post your zip code and your array's tilt and azimuth, and if you plan on doing this soon, I'll get you an approx. time of min. incidence angle on your array. Whatever time you use, make it the same clock time both the day before and the day of cleaning. What you get by dividing the first day's output by the second day's output and subtracting that quotient from 1 will be an very rough estimate of your array's fouling as a % of the clean performance.

                          The reason for consecutive days of the same weather and clear skies is that the output will vary by probably a 1% or so due to irradiance differences and about 0.5 % per degree C. of panel temp. diff. between days. That panel temp. will vary mostly with the irradiance level and wind vector which is why it's important to get data on consecutive days that have as close to the same weather regime as possible. Using day long output is much less accurate and tends to muddy the waters. The "quasi-instantaneous" method I describe will get rid of that day long smear in the output. Just do it on two days when the weather is as similar as possible.

                          Comment


                          • #14

                            Thanks for all the replies and research noted above. This board has some very intelligent people for sure and I love to learn from each of you. Below is a little chart using Weather Underground data. I was looking for any other clues. The only thing I notice of note is the recent weather has a been a bit cooler. Averaging the best pre-cleaning days (in yellow), which I am assuming was clear skies equates to 32.28 KWh per day. Post cleaning (in blue) the average is 36.20, so as noted by someone above, a 10% increase. Although the average temp for these comparisons was 89 degrees to 77 degrees.

                            The good and bad news is that we are expecting temps to again creep back into the low 90's, so I'll have some more data later this week. Maybe some of the difference post cleaning is coincidental temperature variance. I will report back though.

                            And I didn't even think about getting shocked. Dope! See, I'm not as smart as you all for sure...
                            ScreenHunter_616 Sep. 26 11.09.jpg

                            Comment


                            • #15
                              Originally posted by steveholtam View Post
                              Thanks for all the replies and research noted above. This board has some very intelligent people for sure and I love to learn from each of you. Below is a little chart using Weather Underground data. I was looking for any other clues. The only thing I notice of note is the recent weather has a been a bit cooler. Averaging the best pre-cleaning days (in yellow), which I am assuming was clear skies equates to 32.28 KWh per day. Post cleaning (in blue) the average is 36.20, so as noted by someone above, a 10% increase. Although the average temp for these comparisons was 89 degrees to 77 degrees.

                              The good and bad news is that we are expecting temps to again creep back into the low 90's, so I'll have some more data later this week. Maybe some of the difference post cleaning is coincidental temperature variance. I will report back though.

                              And I didn't even think about getting shocked. Dope! See, I'm not as smart as you all for sure...
                              I think sensij suggested reasonably reliable estimate for the possible improvement- if your system is on PVOutput just pick some other nearby with similar orientation as a reference and compare difference in production over time. Since both of you will be affected by the same weather your curves will be moving in synch. The day you cleaned your panels would change this difference and the change will remain constant afterwards still tracking the other system in parallel. If sensij is correct that he picked your system for comparison then this method clearly shows 10% improvement. You could also use it to see how new clean state sustains over time and when do you want to repeat the procedure.

                              It might get confusing if the other system owner also decides to clean his

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