hanschristian avatar image
hanschristian asked

Optimal RV Solar Panel set up in combination with MPPT requirements

I have a question in regards to the setup of my solar panels (12V, 600W) and the Victron 150/70 MPPT charger on my RV. The MPPTs manual does NOT recommend for a 12 V electrical system a parallel panel setup that leads in my case to a MPP voltage of 18V. In the RV world it is widely recommended to set up the panels in parallel to avoid the negative impact of shading. Is Victron’s recommendation entirely based on the power losses/ or need for high cross sections in the wiring ? Or is there an additional performance loss due to a higher inefficiency of the MPPT. I could imagine that due to the smaller gradient between PV voltage and Supply voltage the MPP algorithm is less effective in finding the optimum.

MPPT Controllers
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2 Answers
JohnC avatar image
JohnC answered ·

Hi Hans. What you *may* be suffering from here is the deep & ingrained mindset of travellers experienced with pwm cc's. And that's fair enough, that's how you'd do it. And some may have even have derived that experience from cheap 'pseudo-mppt' junk.

Note Victron mppt's have a 5V 'start margin', so the early-morning Vbat of (say) 12.3V will need 17.3Voc for it to kick away. Then it will drop to a 1V difference once established.'s then Vbat vs Vmp. If you ever get to experience true and expensive mppt from some other-branded kit, the clicking relays for an hour at the crack'o'dawn might suggest the Victron approach is well considered.

Poor light at dawn, dusk & heavy cloud will reduce Voc and Vmp. Series'd panels will kick you off earlier, run later & clouds will become less of an issue. By all means try it both ways.

I've shelved expensive kit myself for Victron. And then followed recommendations that 'went against my grain'. I was wrong, my grain has learnt a little since..

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Kelly Lipp avatar image
Kelly Lipp answered ·

Very old post but thought I would update/clarify for others seeking similar answers...

In the case of Victron 100 series charge controllers I would opt for a series parallel configuration for 12V panels. Wire two or more panels in series and then wire other identical strings in parallel keeping overall voltage less than 100V. If you are using 24V panels I would probably do the same thing but with only two panels per series string. For RV applications rooftop space is the key limiting factor in the number of panels possible. If you can get an even number of panels, follow my advice above. If you wind up with an odd number of panels (to maximize total solar capture) then you may find yourself stuck with an all parallel configuration. This is not bad! Just not as efficient, perhaps, as a series/parallel config would be. I like to maximize the number of panels if I can or need to (in order to get batteries charged!) so sometimes I end up with an odd number of panels.

Keeping the voltage from the panels to the charge controller (mounted very close to the batteries) as high as possible helps to reduce the voltage drop due to wire resistance losses to a minimum. The key is the voltage delivered to the batteries by the charge controller must get sufficiently high to correctly charge the batteries.

In addition, MPPT works well when it has nice voltage/current options delivered from the panels. The affects of shading are also minimized in this configuration.

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