solar panels in parallel

I have a 120W folding solar panel (monocrystalline I think) which I run through a Morningstar regulator mounted near the battery. I also have a new 60W flexible amorphous panel which came with its own little regulator. My question for the solar gurus on this forum (who I read with great interest for they have taught me much) is this: can I hook both these panels up via their own regulator to the battery in my camper trailer in parallel? I was thinking of throwing the light foldable one on the roof and chase the sun with the hard glass panels. The glass panels produce more current in full sun, but in low light, the amorphous panel is good.
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Reply By: Dennis Ellery - Sunday, Mar 31, 2013 at 22:54

Sunday, Mar 31, 2013 at 22:54
It won’t do any harm to connect them together and they will most likely run in harmony.
But if there is a conflict between the two regulators – one will take control and supply full current and the other will back off thinking the battery is fully charged.
Connect them in parallel, and then it you have the equipment, monitor the current being supplied by each panel – this will tell you if they are both sharing the work.
AnswerID: 507936

Reply By: The Bantam - Monday, Apr 01, 2013 at 13:13

Monday, Apr 01, 2013 at 13:13
Sorry but I personally think its going to be a waste of time.

We simply know very little about how each regulator is designed and how they will interact.

If either of the regulators are anything more than the most basic & crude type any smarts will be lost or the two regulators may resent each other very much..who knows what the result could be.

If the regulators where both simple set point regulators that took no feed back from the battery, and where not effected by backfed voltage from the other all may well work.

If the regulators contain any multi stage charging smarts.....the regulator is looking for a direct and exclusive relationship with the battery to work well...otherwise the regulator may be confused and overcharge, under charge, shut down, fail to work or even die.

very likley efficiency would suffer more than could be gained.

as for paralelling the two panels before the regulator.......well the two pannels will have completly different characteristics.

If the two panels where identical or even different sizes with a similar characteristic, there is a reasonable expectation they would paralell up fine.

if the two panels contaned or where used with anti backfeeding diodes, the expectations that they would run in paralell before the regulator are reasonable.....but not otherwise.

even then if one pannel is at a higher voltage than the other, the lesser pannel will contribute nothing, because its back feeding diode will be reverse biased.

If we consider one regulator may be Maximum power point tracking......if it was the case the regulator will not be able to track the maximum power point of two different panels with two different characteristics, thus efficiency would suffer.

It may be possible to run the two panels together.....but do you have the instruments or the knoweledge to know if you have gained anything or that things react badly under some circumstance, you may well have gone backward, perhaps even have something fail.

Serioulsy, leave it alone.

AnswerID: 507961

Reply By: Dennis Ellery - Monday, Apr 01, 2013 at 14:56

Monday, Apr 01, 2013 at 14:56
I have a common Pulse Width Modulate regulator – the manual states that it is protected against a higher voltage at the battery terminals (this is different to reverse polarity protection). I have run it in parallel with other voltage sources such as the car alternator and PWM battery chargers without damage. When the battery is heavily discharged both sources contribute but as the voltage rises, one takes the lead over the other. Yours may not perform the same but there is no way of knowing what is going on unless you measure the amperage from each source.Check your manual as to whether or not your regulator is suitable for connecting to a battery being supplied by another source – normally the car alternator.
AnswerID: 507964

Reply By: Yabbo - Monday, Apr 01, 2013 at 18:04

Monday, Apr 01, 2013 at 18:04
Thanks for the replies. I thought that each panel producing different voltages might cause the regulators to have issues. I have a clamp meter so I will hook them both up and see what happens to the current from each panel. Nothing like some field testing. You can't have too much data!
AnswerID: 507974

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