I went up on my ladder today and noticed a good thick film of dust on the panels. Only 2 months on the roof and it looks like I will have to spray them every 2 months. With the power washer the dust came off right away. Hardly any rain here in Socal so I will have to keep my eyes on them


Fred

Yep, I've got a hairy 2 story roof, I try to stretch out to about 5 months. Plain water seems to OK on it, and I did not notice a large increase last time I washed them.

Anyone ever had issues (failed panels, water in junction boxes, warranty claims or claims refused) with spraying water on the panels in the heat of the day?

Just for good engineering practices, I would tend to want to do it early in the morning or late in the evening to avoid thermal shock. Although it is not near as fun to get soaked when it is cool out.

Since nothing is in the panel instructions/specs. (that I have seen), when you wash should not be a problem.

I too have to get out a big ladder for our 2nd story installation--getting too old for this type of risk--Now if I can convince my wife that motorcycles are safe (yea, right)...

-Bill

"Just for good engineering practices, I would tend to want to do it early in the morning or late in the evening to avoid thermal shock."

gee, you don't suppose rain wouldn't give a thermal shock to the pvs now do ya? how about hail or sleet on a nice hot day? i thought i had said something about this on naws' forum. i would do it to lower the temp on the pvs as you'd get them cleaned and cooler allowing more power.

I got up there around 1pm, it was warm but windy also. Didn't feel or notice any heat coming off the roof top.


Fred

In our area we don't get rain on 100 degree days, or hail, or sleet. Water out of the hose on a hot day (again in my area) is probably closer to 55 degrees--rain would be at ambient air temperature (what ever that was on any particular day. Hail does not have thermal transfer as it usually bounces off the panels, and sleet, I would assume, would again be near ambient (i.e., cold) temperatures.

I have learned on my double pane windows that spaying cold water (to wash the dust off) on a hot day (with windows facing the sun) can break the internal seal and just suck the water right inside.

Years of testing electronics and disc drives--thermal cycling and thermal shock was a great way for doing accelerated life testing and testing to failure. High rate thermal cycling was also used by high end electronic manufacturers to test before shipment (instead of simple elevated temperature burn-in).

-Bill

bill,
my point is the pvs should handle it just fine as i could also cite a 30 degree f late spring day someplace that's cloudy and all of a sudden the sun comes out very intensively around solar noon. solar guppy has lots of rain and probably has seen many a day with 90+ temps and then sudden cold rains that are cold from being very high in the atmosphere. most have seen scenarios equalling or exceeding this in most parts of the country. the pvs should take it or most pvs would be prone to failure from thermal shock nearly everywhere as there isn't anyplace that doesn't have conditions that would not introduce a thermal shock to the pvs from the weather that could equal or exceed the conditions of your garden hose washing off the pvs in 100+ degree f temps. a garden hose to me is no different than anything mother nature will typically dish out.
guppy,
have you ever had the glass crack from thermal shock(not hail impaction forces) on any of your pvs?

I have a panel that had a bad solder tap joint, was brown spoting the tedlar ... with one of the down pours the tempature change fractured the glass. Now this is NOT normal tempatures, as the bad connection was probably a few hundred degrees, but tempered glass can fracture due to fast tempature changes

I have washed all my arrays with soap/water and tap hose and never had an issue, but usally don't do this is the peak heat as its just to damm hot on the roof!

Cracking the glass is not the only issue that I could foresee...

Simply the issue of a hot panel, cold water. Glass contracts quickly, solar cells with thermal mass and the mass of the backing contract much slower. Delamination (glass/cell and/or cell/bus and/or cell/backing) and drawing of water into delaminations and other nooks/crannies are my main concerns.

But that is why I ask. These type of issues would show up with somebody who has seen a large number of installations/panels. A an installation of 20 panels is not a statistically definitive sample.

-Bill

I had a panel that had to get replaced, did your "brown spot" look like this?
http://www.wind-sun.com/smf/index.php?topic=1920.msg15018#msg15018
( image in in the post )