Aging solar panels?

[DonTom]

Up on the Roof of my RV, I have four old 15 watt solar panels (total 60 watts) from HFT. They were installed my me in June 2009. How many watts should I expect on a normal sunny day now around 11.5 years later? How fast do they normally age, if kept clean (I just cleaned them off today with some class cleaner)

And a solar controller, I assume the PWM they use drops the charge when the battery is near full. What is a good SOC to check the output of solar (using my SmartShunt)?

-Don- Auburn, CA

 

[Mark_K5LXP]

Typical degradation is 1% per year for the first 25 years. So after 11.5 years you would expect about a 11.5% degradation.

"Normal sunny day" output depends on where you live, time of year, ambient temperature, flat vs tilted panels and matched load. Generally, in most areas of the US you get half the insolation in January than you do July. There are websites that will give you insolation tables and net monthly watts per square meter based on your zip code and historical climatological data (clouds and temp).

For a quick test a controller should be in bulk charge phase with any battery that's under 13V at whatever charge current the panels are providing.

Mark B.
Albuquerque, NM

 

[Isaac-1]

My guess is real world is a bit better than that as most brand name solar panels are warranted to 90% of their rated output after 10 years, which would make one assume that the majority of panels are still at more than 90% of rated output at 10 years. Of course it is also common for new panels out output more than their rated watts.

 

[DonTom]

Typical degradation is 1% per year for the first 25 years. So after 11.5 years you would expect about a 11.5% degradation.

Thanks for that info. But I wonder if my cheap old HFT panels are worse than typical. But probably not by much anyway.

For a quick test a controller should be in bulk charge phase with any battery that's under 13V at whatever charge current the panels are providing.

I assume that will be a higher voltage when in the lithium mode, as my new controller now is.

73, -Don- AA6GA

 

[DonTom]

Of course it is also common for new panels out output more than their rated watts.

I am very surprised by that. I thought it was very unlikely to ever have the conditions so perfect to get their rated output. Looks like things have changed a lot over the years.

I will check to see how much trouble it is to change my roof solar panels to get a bit more wattage. 60 watts of solar isn't much these days. but I did recently buy a portable fold up solar setup that I can set up outside the RV for 150 more possible watts of solar.

-Don- Auburn, CA

 

[Lou Schneider]

The Harbor Freight panels are amorphous silicon, also known as thin film panels where the active coating is essentially just sprayed onto the substrate. These tend to degrade faster than mono- or poly-crystalline panels which have thicker active layers.

 

[DonTom]

The Harbor Freight panels are amorphous silicon, also known as thin film panels where the active coating is essentially just sprayed onto the substrate. These tend to degrade faster than mono- or poly-crystalline panels which have thicker active layers.

I am not surprised by that at all. I figure the stuff from China Tools (AKA HFT) is usually as cheaply made as possible.

That info. is good to know if I shop for new panels, thanks.

-Don- Auburn, CA

 

[Isaac-1]

Historically solar panel manufacturers would grade the output of panels and sell accordingly as output would vary from batch to batch.

Lets pretend they made a 2x3 ft solar panel that was nominally rated at 100 watts, well some of these panels may only produce 90 watts, and some may produce 105 watts under ideal conditions, so these companies would sort these panels and sell them into whatever output batch they fit in, panels producing 90-99 watts are sold as 90 watt panels, 100-104 watts sold as 100 watt, and 105+ watts sold as 105 watt panels. These days quality control has improved some, and prices have dropped to the point where it is probably not worth the effort to do such sorting. So that 100 watt panel today may output 100 to maybe 108 watts if you are very lucky, and any that are under 100 watts get sold off as factory seconds.