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Old 06-03-2019, 05:05   #1
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Help me choose between 2 solar panels

Hi,

I have limited space for solar panel, therefore I narrowed my search to panels with suitable dimensions.
Which one would you choose of these two?
I guess Vmp 16.5v panel would be more effective with PWM regulator while 18V may benefit from MPPT? Correct me if I am wrong.

Option 1:
Phaesun Sun Peak SPR 100W
30 cells Monocrystalline
Vmp 16.5V
Imp 6.06A
Voc 19.8V
Isc 6.5A
http://www.produktinfo.conrad.com/da...COMP_de_en.pdf

Option 2:
Victron Energy 80W
36 cells Polycrystalline
Vmp 18V
Imp 4.44A
Voc 21.6V
Isc 5.06A
https://www.victronenergy.com/upload...-Panels-EN.pdf

Thanks!
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Old 06-03-2019, 05:49   #2
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Re: Help me choose between 2 solar panels

If I recall my most recent research monocrystalline panels are generally higer efficiency and maintain that for longer than polycrystalline cells.
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Old 06-03-2019, 06:47   #3
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Re: Help me choose between 2 solar panels

I would always choose mono panel, but they hate shading.
I would always choose the higher wattage panel for the same space.
I would always use a MPPT controller, but be careful with Victron MPPTs needing a +5v differential between panel voltage and battery voltage. Meaning they won't start charging until this +5 threshold is met.
I would consider getting two panels and wiring in series to jack up the voltage, thus smaller wires from the panels can be used. Also, I really like the Victron Smart MPPTs. Good value, good product and great app to see real time power output and previous 30 days.
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Old 06-03-2019, 07:02   #4
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Re: Help me choose between 2 solar panels

Unfortunately, the 30 cell panels are really too low in voltage for a 12v battery system. A Vmp of 16.5v sounds fine, but once it is derated for real world output rather than the STC (standard test conditions), the voltage will be dropping too low (especially in hot climates) to efficiently charge a 12v battery. It will work, but there are better choices.

It is a pity the 80w panel has considerably worse efficiency at 14.2% vs 18.5% for the 100w panel (meaning the 100w panel is considerably smaller per watt) and has a worse temperature coefficient (meaning in the real world the 100w panel will produce more than the extra 20w would suggest).

The ideal would be a 36 cell panel with similar characteristics to the 100w panel. I would keep looking there should be better choices than a 100w panel with a voltage that is too low, or an 80w panel that is rather old technology and not very effficient in modern terms.

You are correct that the 100w 30 cell panel has too low a voltage to benifit from the conversion inherent in MPPT controllers.
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Old 06-03-2019, 11:23   #5
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Re: Help me choose between 2 solar panels

Check the installation manual of the Phaesun, they are made with back contact cells and might be n type cells. I did not see the manual on their site, but check to see if one pole must be grounded or if a floating system is ok. Some n type cells need the negative to be grounded to avoid degradation, some don`t.
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Old 08-03-2019, 00:01   #6
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Re: Help me choose between 2 solar panels

Thanks everybody for your advice!
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Old 08-03-2019, 04:29   #7
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Re: Help me choose between 2 solar panels

I would go for the higher watts and not even think about poly/mono (I don't know which I even have) and I would get the MPPT controller regardless.
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Old 08-03-2019, 04:54   #8
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Re: Help me choose between 2 solar panels

Quote:
Originally Posted by sailorboy1 View Post
I would go for the higher watts and not even think about poly/mono (I don't know which I even have) and I would get the MPPT controller regardless.
That was also my undestanding, mono vs poly does not make so big difference. The only problem with above mentioned 100W panel was its low output voltage in my opinion. Made me think that MPPT controller may not make max power out of it (Victron MPPT needs voltage +5V above battery level to start operating).

I finally decided to buy 2pieces 40W panels with slightly higher output voltage
https://www.ebay.co.uk/itm/122614640051
Vmp 20.2V
Imp 1.98A
Voc 23.9V
Isc 2.1A
I can experiment with those in parallel and in series, to see how they perform with Victron MPPT. They have less amperes on paper but hopefully more volts will compensate that with MPPT
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