Opinions on solar panel install.

[Dave 2000]

Hi all,

I was forced to change my solar panel setup when the replacement rack for my 80 (link in sig) was not wide enough to allow the panels to fit. I have just purchased another two panels, they are slightly smaller. The plan is to fit both at the front of the rack, they will slide out forwards and lay one in front of the other over the hood.

The panel specs are as follows:

I was planning on using them both in parallel via the PWM fitted at the rear of the 80, this is then carried back to the batteries up front via heavy cables. Given that now both panels were being mounted up front, is there any worthwhile mileage in throwing out the PWM and using the MPPT type?

Obviously I was looking at the option of running the panels in series and letting the latter style controller sort the voltage out, but given the size of the system any gains may be negligible?

Your thoughts?

Regards

Dave

 

[Suprasoup]

Pwm
Current in = current out.

Mppt
Watts in = Watts out

So for a depleted battery at say 12v (~50% State of Charge)

PWM
12v x 8.9a (Imp of your panels x2 panels) = 106.8w

MPPT
12v x Xa=150w where Xa is current so 150w/12v = 12.5a

So PWM is producing only about 70% of MPPT when battery is depleted.

How about when your battery has reached Bulk Voltage? Lets say it’s 14.8v for a Standard Flooded battery.

PWM
14.8v x 8.9a =131.72w

MPPT
150w

So PWM is still producing only 88% of MPPT. Better than when the battery is depleted but still less than MPPT.

Once you’re in the Absorption stage and Float stage both PWM and MPPT are pretty much the same as those stages are current limited.

So for someone who regularly depletes his battery there are significant gains to using an MPPT controller vs a PWM.

For those that keeps their battery at a high SOC or are using solar to supplement another charging source ( your alternator) then either works.


Some other advantage of an MPPT controller.
Ability to series wire panels. Higher voltage = less loss from panel to controller
The controllers Bulk-absorption-float are usually user adjustable.
Use of higher Voltage panels I.e. grid tie panels. Cost less per watt
Higher voltage means MPPT will start charging sooner than PWM and will continue to charge later in the day as well.

That said I always recommend adding some modern battery isolator/relay before solar. Your alternator can produce more in an hr than your panels could produce all day.

Hope that helps,

Supra

 

[Dave 2000]

@Suprasoup Thanks for that, you pretty much came to the same conclusion as I had. My batteries tend to be fully charged most of the time. It is only when camping away from a hook up at night that the batteries do some work keeping the fridge working, during the day the panels will pick up the slack if I am not driving.

The PWM install has been in a few years now with zero issues other than when I camp out during winter and get a couple of very grey days, the amount the MPPT gives me may make a difference.

My other thought was to put the panels in series to help compensate with the front to rear cabling, I could use thinner wiring however, I do like the idea of keeping my present two ammeters, it would help if I had any problems.

When I originaly fitted the system I fitted a changeover relay, as soon as the ignition is switched on the solar panels are disconnected from the controller, obviously the alternator takes over charging duty, when I switch off the ignition the relay allows the panels to resume charging or maintaining the batteries.

Thanks again

Regards

Dave