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Old 04-07-2015, 03:48   #1
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Low voltage vs higer voltage solar

When would higher voltage panels be better than lower voltage panels?

I'm considering 4 x 240W flexible panels. They come in 2 version, for example:

240W @ 45.5 VOC / 39.6 VMP
or
240W @ 22.8 VOC / 19.8 VMP

It's for a 24V battery, wire length between panels and charger/battery is about 40'. Planning on using MPPT controllers.
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Old 04-07-2015, 06:47   #2
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Re: Low voltage vs higer voltage solar

You will need the higher voltage panel for a 24V system - you cannot use the lower voltage version. The output of the panel needs to be higher than your charging voltage.

In general for when one has a choice, the higher voltage panel will allow use of smaller gauge wire and will give more output when used with a MPPT controller.

Lower (battery nominal) voltage panels can be used with less expensive PWM controllers, but will need larger wire to accommodate and will still not be as efficient as if used with a MPPT.

Mark
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Old 04-07-2015, 18:57   #3
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Re: Low voltage vs higer voltage solar

Would there be benefits of using low voltage panels connected in series or is higher voltage panels still better for 24V systems?

Some PV controllers can boost the voltage so low that voltage panels can be used for 24V. Is this approach worth considering?
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Old 05-07-2015, 06:16   #4
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Re: Low voltage vs higer voltage solar

Yes, used in series, lower voltage panels can be used. The final voltage must be above your charging voltage.

There is no free lunch - boosting voltage from below nominal will drop the output amperage. Doesn't make sense.

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Old 05-07-2015, 10:13   #5
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Re: Low voltage vs higer voltage solar

Unless you have clear view of the sun do not put panels in series since any shading on any panel will reduce output of the whole array.

John boor
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Old 05-07-2015, 10:54   #6
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Re: Low voltage vs higer voltage solar

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Originally Posted by John Boor View Post
Unless you have clear view of the sun do not put panels in series since any shading on any panel will reduce output of the whole array.

John boor
True.. but with 4 panels, 2 could be completely shaded and you would still be above charging voltage. I run 4 panels in series to a MPPT controller.
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Old 05-07-2015, 11:32   #7
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Re: Low voltage vs higer voltage solar

Quote:
Originally Posted by colemj View Post
Yes, used in series, lower voltage panels can be used. The final voltage must be above your charging voltage.

There is no free lunch - boosting voltage from below nominal will drop the output amperage. Doesn't make sense.

Mark
Not quite right, you can go both ways. Most controllers are buck controllers because it is cheaper, but boost controllers exist.

First example I found:
Genasun GV-Boost 105-350W Solar Boost Charge Controller with MPPT for Lithium BatteriesGenasun

How a boost converter works:
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Old 05-07-2015, 13:26   #8
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Re: Low voltage vs higer voltage solar

Yes, I understand how a boost controller works, and the OP mentioned that these exist (and also your link).

However, unless I don't understand this fully, there still is no free lunch. The voltage will be boosted at the expense of the amperage. To me, this doesn't make sense to intentionally go with low voltage panels when proper nominal voltage or higher panels exist.

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Old 05-07-2015, 14:17   #9
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Re: Low voltage vs higer voltage solar

Quote:
Originally Posted by colemj View Post
Yes, I understand how a boost controller works, and the OP mentioned that these exist (and also your link).

However, unless I don't understand this fully, there still is no free lunch. The voltage will be boosted at the expense of the amperage. To me, this doesn't make sense to intentionally go with low voltage panels when proper nominal voltage or higher panels exist.

Mark
You are %100 correct. There is no free lunch, but the resulting watts put into the batteries will be almost the same. You will loose %5-%7 in efficiency losses to the boost converter.

This would only make sense if you had old panels of lower voltage that you wanted to continue using. If buying new, then yes buy a proper high voltage panel.
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Old 06-07-2015, 19:09   #10
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Re: Low voltage vs higer voltage solar

Quote:
Originally Posted by Singleprop View Post
Would there be benefits of using low voltage panels connected in series or is higher voltage panels still better for 24V systems?

Some PV controllers can boost the voltage so low that voltage panels can be used for 24V. Is this approach worth considering?
Yes & NO. The higher voltage in series makes the MPPT charge controllers work. The OOPS is that if a shadow crosses any part of either panel, the output will plummet. Parallel with diode linked panels and sections of panels is usually more reliable.
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Old 06-07-2015, 19:30   #11
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Re: Low voltage vs higer voltage solar

Quote:
Originally Posted by Singleprop View Post
When would higher voltage panels be better than lower voltage panels?

I'm considering 4 x 240W flexible panels. They come in 2 version, for example:

240W @ 45.5 VOC / 39.6 VMP
or
240W @ 22.8 VOC / 19.8 VMP

It's for a 24V battery, wire length between panels and charger/battery is about 40'. Planning on using MPPT controllers.
Your panels need to output more than 24V with allowance for all the voltage drops in the system.

Sent from my SM-N900T using Cruisers Sailing Forum mobile app
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Old 06-07-2015, 20:35   #12
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Re: Low voltage vs higer voltage solar

Great stuff, thanks. Will go with the higher voltage panels - in parallel.
I've been offered 1.62 $/Watt for a Chinese "Sunpower".
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