# Solar Panel Output



## chandler48 (Jun 5, 2017)

Are you selling the power back to the utility, or storing it in a battery bank for inversion?


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## Bigjeff (Apr 16, 2021)

Selling it back to the power company


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## chandler48 (Jun 5, 2017)

Would help to know what system you had installed.


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## djlandkpl (Jan 29, 2013)

12.8 is the sum of the rated output of your panels. For example, if you have 10 panels rated at 330 watts, your system would be 3.3kw. 

Under ideal conditions, your 12.8kw system would produce 12.8 kWh in one hour. As the sun changes position, your production decreases.


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## SPS-1 (Oct 21, 2008)

The 9.9 kW seems a little low for a 12.8 nameplate system, figuring probably not many clouds in Tuscon (nice area). But I am no expert.

You might want to try putting your location and system data into PVWATTS CALCULATOR and see what it says you can produce. 

When I had a system quoted, they gave me a printout of what I should be producing during the various times of the year. When you say 12.8 kW, is that just the sum of the rated output of all the panels ? Or is that what it is expected to produce ?
Keep in mind the angle of the panel relative to the horizontal plane (i.e. your roof slope, assuming the panels are on your roof) is relevant. If you have a roof with a steep pitch, it will tend to have its power output shift towards the winter. (Always going to make more power in summer, but skewed to making a little more in summer if you have a very steep pitch, or a lot more in summer if you have a moderate pitch) I believe the common rule of thumb is that ideal pitch is equal to your towns latitude. 
Also, if your roof is not pointed exactly south, you start losing some of the potential power.


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## User02 (Sep 17, 2015)

12.8 kW of solar array in Arizona will probably produce an average of about 9 to 10 kW of power on a sunny day. The problem with Arizona solar is heat. As panels heat up, their output decreases. Here in Michigan, our problem is the low angle of the sun during the winter, but the cooler temps during the summer allow us to crank out power like crazy. 

Most solar panels will start to decrease their output as they climb past 80 degrees surface temperature.. but the decrease is small and won't be generally noticeable. As that panel's surface temperature begins to approach the 100+ degree mark, that production decrease starts to become very apparent. Even here in Michigan, when its 95 degrees outside, our 11kW system will only produce about 8kW under full sun.

This is why ground mount systems are better than roof mounts. The extra air flow around the panels helps out quite a bit.

For example, on a chilly April or May afternoon, my 11 kW system can pump out as much as 12 kW for short periods.. But in order for that to happen, we need to be in the lower 40 degree range and have some clouds to reflect extra light. 

In order for a panel to meet its rated specs, the temperatures need to be cool and the relative angle of the sun and panel need to be spot on.. and since the sun keeps moving, even the ideal conditions only last for an hour or two. 

The PVWatts calculator linked in the post above is an excellent resource for determining solar output. And when I say excellent, I mean that it is so stunningly accurate I was surprised by it.. PVWatts calculated my solar production to within 1% of what it ended up being on the first year, 3% on the second year, and 1% again on the third year. Now that's accurate. 

The catch is that the PVWatts is only as good as the numbers you plug in, so don't fudge or cheat or make assumptions.


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## Deja-vue (Mar 24, 2013)

My System (11.5 Kw) rarely hits 10Kw/h and produces between 60-70 KWh per Day in May, June and July.
Wait for December, you're lucky if you get 25Kwh per Day lol.
That's it, your System looks like it is running fine, considering your Numbers are from May or June? Like others said, the Panels aren't facing south (mine face east and west) or you have some afternoon shading or the panels aren't tilted enough. You should be happy with your production.


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## Oso954 (Jun 23, 2012)

The other thing that may cost some power production is dirty panels. 
When was the last time you washed the panels ?

Washing the panels Regularly in dry dusty climates will help maximize the power. It’s another reason to use ground mounted racks, if you have a large enough property.


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## quatsch (Feb 4, 2021)

Shopguy said:


> As panels heat up, their output decreases.


Is it worth it for anybody to make pumped-water-cooled or convection-water-cooled solar panels?
Maybe using ground temps to cool the water? Otherwise you'd need a large radiator.

If there is a hidden cost to PV panels, what is it? 
I don't have one, the salespeople asked too many questions and gave no answers. The answerman was alway "in a meeting".

BTW, I'm at 39 degrees North Latitude.


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## User02 (Sep 17, 2015)

quatsch said:


> Is it worth it for anybody to make pumped-water-cooled or convection-water-cooled solar panels?
> Maybe using ground temps to cool the water? Otherwise you'd need a large radiator.
> 
> If there is a hidden cost to PV panels, what is it?
> ...


Solar panels have gotten so cheap that even the tracking arrays are no longer worth it. Better to just install more panels.


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## Deja-vue (Mar 24, 2013)

I wash mine every 5 months or so


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## mariahardy (Dec 6, 2021)

Ensuring regular cleaning or cleaning as needed is vital for your solar system. Cleaning the panels every six months is already enough to keep them performing excellently, increase their output, and guarantee their longevity. It is best to conduct a monthly visual inspection so that you can see any noticeable dirt and grime accumulation. Another good way to determine if your solar panels need cleaning is referring to a solar system tracking app or electricity bill; this method can pinpoint any decline in production.


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