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Old 01-10-2020, 09:45 PM   #1
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Flat Panels

I’m getting into the design of the PV system. For version V1.0 the panels are going to be flat or nearly so. I’m going to revisit that later, but I am keeping it simple and cheaper for now. I’m going to mount 3 rows of panel longitudinally. The center is flat and the outside panels on each side are probably at 10 - 15 degrees. So my question: how much efficiency loss and I going to incur with this setup?

Thanks!

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Old 01-10-2020, 10:48 PM   #2
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Just one source, but I found this helpful:


https://www.civicsolar.com/article/s...-energy-output


I may not be understanding your system correctly, but it sounds like you're creating a 'V' shaped array (only with a flat bottom). If so, I don't think this is the best approach. If you can't tilt them all to be facing - more or less - the sun, it would be better to leave them all flat.


Alternatively, if you mean the center is flat & both sides are angled the same, then one one side or the other will likely be shading the center panels (and perhaps even the other side, depending).
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Old 01-10-2020, 10:59 PM   #3
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Originally Posted by TheHubbardBus View Post
Just one source, but I found this helpful:


https://www.civicsolar.com/article/s...-energy-output


I may not be understanding your system correctly, but it sounds like you're creating a 'V' shaped array (only with a flat bottom). If so, I don't think this is the best approach. If you can't tilt them all to be facing - more or less - the sun, it would be better to leave them all flat.


Alternatively, if you mean the center is flat & both sides are angled the same, then one one side or the other will likely be shading the center panels (and perhaps even the other side, depending).
It’s on a Thomas with a sloped roof. I went up there today with a tape and straight edge. The panels are going to have about 10 degrees of tilt either side. Not opitimal anywhere obviously. So instead of pointing them right I’m adding capacity (it’s always 4:20 somewhere) to make up for the loss in efficiency. I’m just trying to find out how close I’m going to get to optimal.
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Old 01-11-2020, 06:26 AM   #4
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A tiltable rack can double output.
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Old 01-11-2020, 10:06 AM   #5
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Check out the tiltable mounts sold on amazon for small (rv-sized) solar panels. I'm not saying to necessarily use them, but it gives you an idea how easy you can achieve the same result. You don't even have to make them tilting right away, while having the ability to add that functionality later with very little work/effort/material.


https://www.amazon.com/Renogy-Adjust...8758181&sr=8-3
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Old 01-11-2020, 10:48 AM   #6
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your panels should present a single plane surface (or parallel planes) to the sun. If you have them leaning different directions that's the same result as partial shading but with no way to get out of that shade. As mentioned, a tilt system can dramatically increase your power generation.
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Old 01-11-2020, 10:57 AM   #7
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Check out the tiltable mounts sold on amazon for small (rv-sized) solar panels. I'm not saying to necessarily use them, but it gives you an idea how easy you can achieve the same result. You don't even have to make them tilting right away, while having the ability to add that functionality later with very little work/effort/material.


https://www.amazon.com/Renogy-Adjust...8758181&sr=8-3
Thanks for the replies

I’ve found a couple youtuber posts about losing panels while driving. I don’t want to do that, so robust connections are in mind. I also don’t want to climb on the roof all the time to set panel angle. Maybe I can come up with a way to do it by standing in the emergency hatch.

For now they are going to be flat-mounted to unistrut. If I can realize 60% collection efficiency then on a 4 sun-hour day I would be able to collect 160 amp hours, which will be enough to run refrigerator, lights, and stereo with a day or two of buffer.

I’m realizing this build needs to be complete sooner than expected. Flat now, tilt later.
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Old 01-11-2020, 11:18 AM   #8
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I'm not sure what your planned configuration (parallel / series) of panels will be, but this may impact that decision. Probably be best to have each panel in a row (row being with the plane of the bus) wired in series, and each of these series strings wired in parallel with the others (so for 3 rows, 3 parallel strings). If you did it the other way around, you'd always have at least one panel out of 3 pulling down down the other two, no matter where the sun was or how you parked.
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Old 01-11-2020, 12:15 PM   #9
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Originally Posted by Danjo View Post
I’m getting into the design of the PV system. For version V1.0 the panels are going to be flat or nearly so. I’m going to revisit that later, but I am keeping it simple and cheaper for now. I’m going to mount 3 rows of panel longitudinally. The center is flat and the outside panels on each side are probably at 10 - 15 degrees. So my question: how much efficiency loss and I going to incur with this setup?

Thanks!
Google "NREL pvwatts" and you will find a calculator that will estimate production and let you see what effects various angles will produce.
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Old 01-11-2020, 12:44 PM   #10
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So my question: how much efficiency loss and I going to incur with this setup?
I've had flat mounted panels for five years. My rough numbers are 80% rated output during the summer months, 60% rated output during the winter. Both measured in the desert southwest. Lots of variables so this is just a crude rule of thumb.
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Old 01-11-2020, 01:26 PM   #11
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I've had flat mounted panels for five years. My rough numbers are 80% rated output during the summer months, 60% rated output during the winter. Both measured in the desert southwest. Lots of variables so this is just a crude rule of thumb.
Thank you!
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Old 01-11-2020, 02:10 PM   #12
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FWIW: As I plan on being very mobile in my bus and often not parked pointed in the ideal direction to accommodate tilting towards the sun, I have decided to mount them flat and "overpanel" to accommodate less than ideal orientation. With the price of panels these days it cost me less to buy additional panels than to build a tilt mechanism.

My charge controller has a function that allows me to set a maximum charge current so that, when I am in good summer sun, I don't boil my batteries.
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Old 01-11-2020, 06:01 PM   #13
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Let the current go high, just be sure to take them offline once endAmps is reached - but not until then.

Excess "free" ebergy can heat water, make icecubes or something
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