raydas
Solar Devotee
Posts: 166
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Post by raydas on Oct 19, 2019 13:27:04 GMT
I just noticed that Renogy now has a 300W 24V panel available. I thought, before reading the specs, wow 300W, 15A solar panel, sounds like a good deal. But, reading the specs, for the 300W panel, the panel is only 9.33A optimum output. What happened to the other 6Amps.
Since my solar setup has only a few good sun spots, I was thinking that the one 300W panel could replace my two 50W panels. The 300W having a larger size, but still smaller than 3 x 100W panels, plus less wires to contend with.
Now, my setup is a 12V system using a Rover 20A MPPT CC. I think the Rover 20A MPPT CC is a 12/24V, but does that mean that I would have to setup two 12V batteries in series, or does the CC automatically charge the battery at 12V, even though it has 24V coming in. The other thing that comes to mind, the Rover 20A MPPT CC, I think has a limit of 250W.
Does this seem like switching to a 300W panel, mean, converting my existing system?
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Post by tattoo on Oct 19, 2019 13:42:08 GMT
Man isn't this Autumn weather beautiful? I sure am glad the summer heat is finally gone...........
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Post by bupkis on Oct 20, 2019 0:10:03 GMT
Rover 20 and one 300w panel is a good match. The MPPT of the panel is 32v x 9A, the rover can handle 100v input. The controller auto recognizes your batt being 12v and goes to work transforming incoming power to charge 12v battery.
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raydas
Solar Devotee
Posts: 166
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Post by raydas on Oct 20, 2019 16:17:34 GMT
I was not sure about how the Rover CC handled that 12/24V stuff. I guess the Rover MPPT CC will get a little warm dealing with the other 12V, when it is charging a 12V battery? I guess you would have to make sure that the CC is very ventilated.
I hope the Admin has an answer for why the 300W solar panel is only ~9A output, and not ~15A like you would have with 3 x 100W panels.
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Post by bupkis on Oct 20, 2019 17:24:51 GMT
let's compare and note the obvious different sized cells! 300w = 300w
60 cells, 3 diodes, 9.33A, 32.25v, 300w (3 stings of 20 cells each)
vs
36 cells, 2 diodes, 5.29A, 18.9v, 100w (2 strings of 18 cells each) 3 in series, 72 cell, 5.29A, 56.7w. 300W 3 in parallel, 72 cells, 15.87A, 18.9v, 300w
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raydas
Solar Devotee
Posts: 166
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Post by raydas on Oct 20, 2019 17:55:23 GMT
I just did 300W/24V = 12.5A. So, it seems theoretically, the 300W panel should be able to get 12.5A. But, when you explore it in terms of cells, and diodes, you can come up with something different. Using ohms law, in this particular case, you get a misleading impression. I guess this is theory vs reality, in this case reality comes up on top.
I still might have to pursue the 300W panel, only because handling one panel vs dealing with three panels, just might be a better situation.
From a price point though, one 300W panel = 9.33A. Two 100W panels = 10.58A. 2 x 100W = $260, 1 300W = $307. Looking at this from strictly an Amps point of view, it seems like the 2 x 100W is a better deal. Now, the 300W panel does not look that appealing. This would be a much simpler decision if that darn 300W panel equaled at least 12.5A, just to justify the ~$50. Darn now when I look at from that angle, ~$50 difference...
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Post by bupkis on Oct 20, 2019 18:56:47 GMT
stop looking at amps in, it is amps out to the battery that counts with mppt (actually power out).
300w charging a 13.209v battery = 300/13.209 = 22.7A
likely senario, 300w in direct perpendicular great sun yields 270w, charging a 14.000v battery = 19A
or
200w yeilds 180w/14 = 12.8A
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Post by mediadogg on Oct 20, 2019 19:13:31 GMT
I just did 300W/24V = 12.5A. So, it seems theoretically, the 300W panel should be able to get 12.5A. But, when you explore it in terms of cells, and diodes, you can come up with something different. Using ohms law, in this particular case, you get a misleading impression. I guess this is theory vs reality, in this case reality comes up on top. I still might have to pursue the 300W panel, only because handling one panel vs dealing with three panels, just might be a better situation. From a price point though, one 300W panel = 9.33A. Two 100W panels = 10.58A. 2 x 100W = $260, 1 300W = $307. Looking at this from strictly an Amps point of view, it seems like the 2 x 100W is a better deal. Now, the 300W panel does not look that appealing. This would be a much simpler decision if that darn 300W panel equaled at least 12.5A, just to justify the ~$50. Darn now when I look at from that angle, ~$50 difference... I know I sound like a broken record, but your analysis has no basis in either fact or theory. That's why you are getting incorrect and conflicting results. Applying ohms law to to a couple of unrelated numbers is misleading only if you incorrectly believe that what you are doing makes sense. Please, please, please listen to the advice we have all been giving you. Read the specifications. Read the technical definition of what a "24V PV" actually means. It is so easy. It takes only a minute to read the Renogy specifications for the panel in question. This is a quote from here, that took me only a few seconds to discover using Google. It describes exactly the confusion that you have. It is so easy to discover this information - I really encourage you to learn to do this before posting: "Nominal Voltage Nominal voltage is the one that confuses a lot of people. It’s not a real voltage that you will actually measure. Nominal voltage is a category. For example, a nominal 12V solar panel has a Voc of about 22V and a Vmp of about 17V. It is used to charge a 12V battery (which is actually around 14V)."
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Post by tattoo on Oct 20, 2019 19:31:41 GMT
I know I sound like a broken record, but your analysis has no basis in either fact or theory. That's why you are getting incorrect and conflicting results. Man it's a waste of time trying to explain anything to him........
I had a guy tell me this years ago and I have found it to be so true many times........
A guy drops a quarter while waking home from the show the other night...... He's under a street light looking and looking....... A friend walks by and he ask him what he's doing........ He tells him he dropped a quarter three houses up and I'm trying to find it........... His friend ask him why aren't you looking where you dropped it? The guy tells him because the light is better here.........
Some people won't listen to sound advice and they think they know better than anyone.......... So why argue? ? ? ?
Some people have to learn things the hard way............
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raydas
Solar Devotee
Posts: 166
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Post by raydas on Oct 20, 2019 20:24:27 GMT
Thank You bupkis for your clear, cogent, and terse responses. I like your style!
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Post by tattoo on Oct 20, 2019 21:20:48 GMT
Thank You bupkis for your clear, cogent, and terse responses. I like your style! Now you thank him............. What was wrong with his first explanation since it was basically the same as the second and the third.......... It was just worded differently..........
Thank you for finally listening to him..............
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Post by mediadogg on Oct 20, 2019 21:24:57 GMT
I know I sound like a broken record, but your analysis has no basis in either fact or theory. That's why you are getting incorrect and conflicting results. Man it's a waste of time trying to explain anything to him........
I had a guy tell me this years ago and I have found it to be so true many times........
A guy drops a quarter while waking home from the show the other night...... He's under a street light looking and looking....... A friend walks by and he ask him what he's doing........ He tells him he dropped a quarter three houses up and I'm trying to find it........... His friend ask him why aren't you looking where you dropped it? The guy tells him because the light is better here.........
Some people won't listen to sound advice and they think they know better than anyone.......... So why argue? ? ? ?
Some people have to learn things the hard way............
It is just hard for me to resist attempting to help or teach, when I see a younger person make the same mistake over and over, as I have been a teacher for some years. I realize that it rarely results in popularity. So it does not bother me to be ignored and I don't need to be complimented or thanked. I will attempt to do the "right thing" and live with the consequences. And every now and then, sometimes even months or years later, a student will thank me for it, and they realize that I was not trying to be antagonistic or offensive - there would be no reason to be actually. There is an old story about the value of teaching a man to fish vs feeding him a fish every time he got hungry. Once the man learned to fish, he was independent and self-sufficient, and could then even share with others - and so the knowledge and wealth would spread.
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Post by tattoo on Oct 20, 2019 22:00:22 GMT
It is just hard for me to resist attempting to help or teach, when I see a younger person make the same mistake over and over, as I have been a teacher for some years. A school teacher? WOW Your a way better man than I am.......Seriously........ I couldn't be a school Teacher or a school bus driver....... I will leave it at that to why.........
The difference in being a School Teacher and a member on here is you get paid to teach school we don't get crap to be here to TRY and help people....... I'd be willing to bet you wouldn't teach school for free would you? No matter how much you like helping kids.........
When I was younger when I had my business I taught several guys how to paint and restore cars....... They are doing very well now......... But they listened to me, I didn't have time to explain to them several times why something is done a certain way.......
The guy that taught me about cars was good but I listened to him and I didn't argue with him about the way he was doing things........ When I went out on my own I did things differently but I learned a LOT from him by LISTENING and not running my mouth.........
I am really glad the OP has opened his eyes no matter the reason......... Hope he stays that way............
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Post by tattoo on Oct 20, 2019 22:07:29 GMT
There is an old story about the value of teaching a man to fish vs feeding him a fish every time he got hungry. Once the man learned to fish, he was independent and self-sufficient, and could then even share with others - and so the knowledge and wealth would spread. I agree, But while your trying to teach them how to fish, they keep leaving the pond to go play ball. What is your reasoning then to keep teaching them how to fish?
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Post by jsb2000 on Oct 20, 2019 22:36:08 GMT
I agree, But while your trying to teach them how to fish, they keep leaving the pond to go play ball. What is your reasoning then to keep teaching them how to fish? Because you'd rather that he not keep trying to fish with a baseball bat? (It's rarely effective and scares the fish away for everyone.)
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