cleaning panels

Answer, Cold clear weather and a dual axis tracker.
Panels rarely put out full rated power. Warm or hot PV cells produce less voltage than cold cells.
The angle of the panels to the sun will have a direct affect on the current the panels put out. A dual axis tracker is about the only way to get maximum output all day. Nowadays solar panels have become so cheap that the more cost effective thing to do is take the money you'd spend on a dual axis tracker and buy more solar panels.
As to pollen, either dry mop the panels, if accessible, or wash them. Note, it takes quite a bit of dirt/pollen to have more than a negligible affect on power output.

Thanks for the quick response. Dual Axis Tracker would not work well in our Florida environment. Much too much wind. We just added 29 S-energy 360w panels to supplement our system. Have total of 37.1 kw at this point. Old (1 year old) panels have distinct grey appearance compared to new panels. Considering foam cannon with bio-degradable soap to clean panels, perhaps bi-annually.

Performance will never be as good as the day of startup, and it will rarely, if ever be => STC rating.

However, on your cleaning question: PRELIMINARYSTUFF: AFTER USUAL SAFETY PRECAUTIONS, DO NOT POWER WASH ! ALSO, NEVER SPRAY WATER ON A WARM/HOT ARRAY ! CLEAN IN THE MORNING BEFORE THE SUN GETS TOO HIGH.

After a long period of no cleaning, mild soap like "Dawn", etc. and a soft cloth on a long pole of the type used to clean windows will work just fine. Then rinse with a hose. Do not use abrasive cleaners or chemicals. They will PERHAPS damage the ARC coating on the glazing. Elbow grease only. For sap/pine resin, etc, some solvent may be necessary but go slow and try soap first ,and in spite of the temptation, never use a blade. And - it goes without saying - DO NOT WALK/PUT WEIGHT ON A PANEL.

I've got a lot of data from 4+ years of a lot of measurements of performance under very clear skies and rates of fouling under various conditions and cleaning scenarios. Long, boring story. Abstract of some of what I think I've found with respect to performance and dirt on my array:

1.) Removing hard water spots w/a D.I. etc. rinse or special treatments after washing makes no measurable improvement in an array's performance over a hose/tap water rinse, at least that I've been able to observe/measure. That is, before/after cleaning incremental performance improvement is the same whether or not there are hard water spots left on an array. Skip the D.I. cost/hassle. The eye is a poor indicator of array performance as f(water spots).

2.) Array fouling rates are all different depending on location and climate. For example, the dirt on an array next to a freeway (with probably a lot of tire dust for example) is not the same as dirt in my neighborhood. Or, my array's fouling characteristics are different than the big array in Death Valley at Furnace creek, at least according to the data the folks there have shared with me (FWIW, they commercial clean their MW array every 2 years and don't worry about dust/guano) Their array fouling rates seem to be asymptotic at ~ 7-10 % of clean performance, but IMO, their monitoring is poor.

3.) I'm probably a pretty typical suburban location. FWIW, without rain, my array's performance deteriorates ~ 0.75% -1.0% per week as it fouls up. Your rate may be similar or more variable. In the absence of rain or cleaning, I believe my rate of fouling may also tend to be asymptotic as f(time), but weather has not allowed me to do much with that, and I've not seen anything in the literature that discusses the matter.

4.) After a good cleaning as described above, I've found a simple hose rinse at a rate of ~ 3/4 gal./panel with no wiping restores ~ 3/4 or so of the clean performance of my array. So, after 4 weeks of no rain, if my performance penalty from fouling is, say, 4 %, I might get the performance back up to 99 % or so of clean with a 5-10 minute or so hose rinse, or close to 100% with a trip up to the roof, and 45 minutes with water/soap/elbow grease. When I'm not measuring clean performance etc. by daily deep cleaning, I rinse w/ a hose after 4 weeks of no rain and accept an average 2-3 % fouling penalty.

5.) A moderate /decent rain, say, maybe 0.25 in or more precip. restores ~ 2/3 - 3/4 of the performance lost to fouling.

6.) Guano penalty depends on guano size. House finch drops do not seem to impair array performance. The big owl skrocks, etc. might have some measurable effects on performance, but I've not been able to measure such effects. Still, I'm very happy cows don't fly.

Bottom line: If your situation is somewhat/sort of like mine, clean the array 1X/yr. or so w/ soap and a cloth, and then rinse 1X/month or 4 weeks or so after a decent rain or since the last rinse. I'd skip commercial cleaning all together. Unless you're disabled, it's usually a rip off.

Wow!, large system. I wouldn't mess with it, being that large but you'd probably be surprised at how little pollen, dirt, dust affect the output. If you had two identical panels, side by side, the only difference being one was cleaned and the other dirty the output would be very close. When looking at the array from a very shallow angle, basically looking across the glass it can look pretty bad when dirty. I see the same type thing when looking out across the hood of my truck. I'm not advocating, not cleaning your panels, just saying it really has minimal affect till the fouling gets bad. Now, bird poop, that's another story, it can severely affect output if allowed to get out of hand.

I wash my panels right at dawn, while they are still wet from dew, and before they get hot. I loft water from a garden hose and just spray them down. Weight of falling water is good enough.

Don't wash hot panels, ever see a cracked car windshield with just 1 zig zag crack - thermal stress

I always arrange for shade ( clouds ) to cool the modules, before washing my pv ( rain ).

Yes. the performance will fluctuate as per the climate and it would not be as perfect as before.

Fill your bucket with clean water and add a small amount of soap. Rinse solar panels with clean water to clear away loose dirt. Use soft scrubber and soapy water from the bucket—or mixing sprayer—to gently wash the surface of the panels. Rinse solar panels with clean water from the hose a second time.

As long as the brand of soap is approved by the panel Mfg. you don't want to ruin the edge seal on the panels with unapproved soap, and a hose end sprayer is ok, but not a pressure washer

I would definitely just start by hosing them (early morning as mentioned) and see how much that cleans up.

After they dry up, if you can still see a heavy haze on them, I found that using a wide brush with long very soft bristle mounted on a pole, and alternating with spraying water does the job.
I only had to do that once so far, after the fire season last year when there was a significant layer of soot and dust on the panels.

I never had to use soap, but may be because I never left things go too bad

However, unless you live somewhere with high amounts of smog, dust, dirt or sand blowing around, solar panel cleaning is generally not necessary. In most cases, occasional rain will be enough to naturally and safely keep your solar panels clean and free of debris that could lower production. Otherwise, you can go to https://www.totalclean.co.uk/ which takes care of the total cleaning of the office and obviously the panel cleaning. I always turn to them when dirt accumulates on the panels and in the office and my people can not help me =)))

I guess another reason to let the rain do the work is if the array is high up on the roof and hard to reach

Here in North Texas we have a lot of dust in the air, plus everything else like pollen. It tends to cling to my panels and doesn't readily wash off even during heavy rain. I bought one of those telescope sticks plus window cleaning attachment. I usually wait until we have mild to moderate rain. I don't like to waste drinking water for this. Also, our tap water has a high mineral content and could leave spots on the panels. I use a little bit of dish soap and then clean the panels from the ground. The rain washes it clean rather quickly. This is easy at my one-story ranch. Output improves about 5-8%, depending on thickness of dust layer. Certainly noticeable.

Has anyone found a cleaning solution that can be sprayed on and cleaned off without needing to scrub the solar panels? A few of my panels are very hard to reach and it would great if there was l foaming chemical solution or something eco friendly that can be sprayed on, let it sit, and then sprayed off. I have what looks like tree sap or something sticky on a few of my panels.