Comparison of panel output in clouds vs full sun...

[TucsonAZ]

I was in the thick of it on my trip so often too busy to post but I took pictures of things along the way I thought would help others.

In this case, here's what I was pulling in from my panels during Bulk charge, same time of day, sun directly overhead, as equal as I could get things with three different set of conditions.

Setup:

1,380 watts flat mounted on the roof.
Six 230 watt panels seriesed for three banks of two.
Location was Seattle in August.
Time was between 11am and noon.
As I'm sure you can see, MidNite Solar Classic 150 charge controller.

Here's what I was pulling in with full sun:




Here's what I was pulling in with heavy cloud cover:

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Here's what I was pulling in with full cloud cover and moderate drizzle:




The two absolute worst days I had were in southern Oregon during the rain with very low cloud cover/high fog where I was pulling in about 75 watts. Also, while broken down in Concord, CA with full sun but I was parked under heavy tree cover and was pulling in about 75 watts there as well.

I never got more than 800-850 in no matter what the conditions unless I was running something at the same time, when for example I was sunning my toaster oven I would pull in about 1,000-1,100 watts if I was parked in full sun.

 

[Scott_1776]

Sounds like you need a higher output charge controller/MPPT if you're only getting 850 watts with a 1.3kW system, should be higher than that, like when you have a draw on with the toaster. Maybe some more experienced with these system can shed some light on it (pun intended). Great observations though.

 

[Canine]

That's a lot of wattage on your cottage. I understand that a panel won't perform to the full amount advertised after running through wires, inverters, etc., but the loss seems to be a bit large. Since the batteries don't need a ton of wattage as they get full, is that extra wattage going to a dump load or somewhere else? I hate to bring this up as that wasn't the subject of your post, but I bet a bunch of people reading this are also wondering about the difference in wattage, but they were polite enough not to change the subject.

If the loss turns out to be a realistic expectation for all solar setups, I will need to account for that. I thank you ahead of time for letting hijack the thread a bit for my own personal gain. Thank you!

Still, good information. It is great to see a fairly objective real effect of full sun or shade or clouds/rain.

Was that a doughnut? I hope so. There's no way that a cop is going to give you a hard time with a giant doughnut on the side!

 

[TucsonAZ]

I'm not certain of this but it was my assumption that the CC was just putting in the amps needed to get the job done. My battery bank was very rarely below 85% as you can see the SOC in the photos and it was already putting 30amps to the batteries, that's A LOT of power coming in. So my thought was just that it would make use of what it needed to get the job done, in the same conditions as the sunny photo it would drop down even more, from 800s to 200s then under 100 watts as the bank got closer and closer to 100% SOC.

When I would add a draw it would show much higher wattage coming in to cover the load and still apply the same charge to the battery bank. Never over about 1,100 watts though which for flat mounted panels that far north I thought was damn good to be putting in from 1,380 watts. Imagine if I had been using a PWM CC, I'm sure that would have really dropped the efficiency a lot!

So, in short, nothing above set off any red flags for me.

 

[66788]

This time of year you won't get maximum performance from any panel unless it is tipped up to the proper angle towards the sun.

Here in Sacramento that would be 45-55 degrees.

 

[TucsonAZ]

This time of year you won't get maximum performance from any panel unless it is tipped up to the proper angle towards the sun.

Here in Sacramento that would be 45-55 degrees.

Hence never being able to get more than about 1,100 watts out of 1,380 while in Seattle in August.

 

[sushidog]

Yes, the controller is feeding your batteries what they need, not what the panels are supplying to the controller. In full sun you were in absorption mode because that's all your batteries needed, however when there were clouds, you were in bulk charging mode, feeding more power to your batteries. Don't try to overthink things. As long as your batteries remain charged/recharge quickly you're cool.

Chip

 

[Seraphim]

Just for information: I contacted Renogy because the controller that came with the 400 watt kit stated it was Bly rated up t 360 watts. Renogy advised the max the system could do is 340 watts, within the tolerances of the controller.

That's a 15% loss.

Haven't had a sunny day here since the install so I can't do an honest comparison. Best amperage I've seen on these overcast days is 12 amps. Generally about 6-7. 2.8 amps once the batteries reached approximately a 98% level. I'm realistically expecting, in full sunlight, a max capability of of 20 amps. But, we'll see.

 

[ccbreder]

I think there was some mention above so apology if repeating. Every thing as to be the same load each time you compare panel output. Same state of charge, same load on batteries while testing, otherwise all those displays are meaning less compared to each other.
Also, can you get more than the rating of the controller even if you have many time the panel?