View Full Version : What's best parallel or serial?
June 11th, 2008, 21:56 PDT
I purchased two identical 5W solar panels and need advise if I should wire them parallel or in series. I use a 60 W 5 Amp charge controller at the outlet. If in series how works the wiring - to + before the charge controller? Thyanks for advises.
June 11th, 2008, 22:16 PDT
Too many variables to give you a series/parallel answer...
Type/model of battery (i.e., Amp*Hour rating, charging voltage, type, etc.)
Charge Controller (need input voltage/output voltage ratings)--seems to be a 12 volt controller?
Solar panels... Need Vmp (Voltage, maximum power)...
If above 15 volts--you would probably wire in parallel for best power.
If 7.5-14 volts, you would wire two in series....
If the Vmp voltage is lower, then you would need to wire more in parallel so that you can get the output voltage above ~15 volts--and not exceed the input voltage of the charge controller.
If the battery is too large (say car sized storage battery)--then a pair of 5 watt panels will just be trickle chargers.
Ideally, you would want the the charge current to be around 10% of the AH rating of the battery (or 5%-13% or so of battery's 20 hour AH rating will work OK).
Obviously, 5-10 watts of solar panel is not going to generate very much power in a day (maybe 10-20 watt*hours or 1-2 Amp*hours at 12 volts per sunny day--Amp*Hour = 1 amp for 1 hour, or 0.1 amps for 10 hours, etc.).
Very rough estimate--there are many variables that will change the exact amount of power available...
June 14th, 2008, 19:36 PDT
The panels generate 5 Watt 17 Volts and the charge controller is rated to 60W 5 Amp max. The battery is a common Marine deep cycle 12 Volt type. If you suggest parallel are the two cables from both panels connect to the same +- input connections?
June 14th, 2008, 22:00 PDT
In your case, two 5 watt @ 17 volt panels would be wired in parallel... The current will add and the voltage will stay at 17 volts...
The size of the solar panels is quite small--and is pretty close to just being enough to trickle charge the battery.
For example... If the battery is an 80 AH battery -- and you discharge it by 50% (maximum recommended) or use 40 AH of capacity...
And the panels output about 10watt/17volts=0.59amps...
40AH/0.59amps=68 hours of sun.
That would take, during the summer, about 2-3 weeks to recharge the battery. And, if it was discharged below 75% State of Charge (i.e., you used more than 20 AH or 25% of the available charge)--the battery will have been damaged because it was "stored" so long below 75% of capacity (sulfate begins hardening within hours if the battery is below ~75% state of charge).
So--if this is just for maintenance charging of the battery while a boat/RV is in storage--will be OK... But that is about it.
Wayne from NS Cana
June 15th, 2008, 0:25 PDT
It's unfortunate that many sellers lead purchasers to believe great things can be done with these small panels. The reality is that in many cases, about all they can do is keep up with the normal self discharge rate of the batteries they are hooked to. Thus, in this case, unless the battery is very tiny, there is no need for a charge controller at all. In fact you could well be better off without it, due to it's small drain on what little power that is available, and the resistance it may offer to that charge.
"BB" is right on the mark with his post.
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