Recommendations for an 80 watt off road ready vehicle Solar Panel?

[4x4junkie]

Any links for my reading pleasure? :coffeedrink:

On page 61 of this .pdf are some efficiency graphs:
http://support.morningstarcorp.com/wp-content/uploads/2014/07/150V-TS-MPPT-Operators-Manual.pdf

Notice how the curve drops off sharply at the low end, especially on the 12V table (how we'd usually use it in our vehicles).
A single 100W panel hooked to this particular controller would reap little to no benefit of MPPT on a partly-mostly cloudy day.

You can see the same thing comparing the charts starting on pg 27 of this one also.

http://www.renogy.com/wp-content/uploads/Manuals/20A-30A-40A-MPPT-Solar-Charge-Controller-Manual.pdf

For some reason I'm not finding efficiency graphs in manuals for the smallest MPPT controllers (3-10 amps), however it should stand to reason their curves will likely peak at a much lower wattage than that of the above units.
I presume this is due to the rated capacity of the components in the controller (similarly you can compare a small 12VDC wall-wart to a 5A regulated DC power supply... The wall-wart will provide a small 500mA current to power a small LED lamp more efficiently than the 5A supply will).

The simple circuit of a PWM controller OTOH simply passes any amount of panel current directly through to the battery whether it's a 3A unit or a 60A unit.

 

[Rezarf <><]

Thanks everyone I have found te solar FAQ, and I have been reading up. I appreciate all the help I am starting to understand and plan accordingly,

 

[IdaSHO]

4x4Junkie, I still fail to see how that is referring to reduction of performance based upon controller size.


I may be missing something on those data sheets however.

Can you help me out? 'Cause Im not seeing it.


From where Im sitting the Conversion Efficiency Curves on those sheets have nothing to do with the capacity of the controller.

They do have everything to do with the change of efficiency and output of ANY MPPT with regards to different panel voltages.

As in, with a set system voltage, the higher the panel voltage the better.

That's always a given, and why I will always advise a a panel of higher voltage than the system voltage.

MTTP's primary benefits lies within that conversion.

 

[IdaSHO]

You can see the same thing comparing the charts starting on pg 27 of this one also.

http://www.renogy.com/wp-content/uploads/Manuals/20A-30A-40A-MPPT-Solar-Charge-Controller-Manual.pdf

Okay, in taking a closer look at this renogy sheet, I snipped the 20A controller @ 12V and the 40A controller @ 12v to look at them side by side.


here it is...

there are some differences, but for the most part I think the benefit, even for a 80-100 watt system lies int he larger 40A unit

Assuming Im reading that correctly :sombrero:

 

[4x4junkie]

If you look at the far left side of the graph, you can see the 20A Renogy unit has about a 94.75% conversion efficiency while it is operating at 20 watts of throughput (about what a 100W panel would produce on a light-medium overcast day). The 40A controller has about a 93 - 93.5% efficiency at 20W of throughput (estimating from where the line stops on the graph), and it also has a steeper dropoff as throughput goes down.
The difference between these two particular Renogy controllers isn't huge, but it is there nonetheless.
However if you look at the efficiency of the 60A TriStar unit @20W, it is quite significantly lower, at around 90%, and the curve plummets very sharply below that (again extrapolating from where the line (16.5Vmp) stops on the graph).

A small 5-10A MPPT unit OTOH is bound to have the peak of it's efficiency curve be right at about 20 watts (or maybe a slight hair above) and will remain within a few percent of that peak down to probably 10 watts or even less (it's unfortunate I'm not able to find a graph for a small unit, but it should be a logical assumption based on the relative operating power & efficiency levels of different units).


Again, I suspect it is due to the rated capacity of the components (the DC-DC converter transformer a MPPT unit uses in particular). A larger, higher power-rated transformer is going to have higher iron core losses than a smaller transformer rated for smaller power will. These iron core losses are what become a much greater percentage of the total throughput at low power levels.

 

[IdaSHO]

Gotcha. I follow ya.

Specifically for marginal solar, yes, a smaller unit looks to maintain a higher efficiency.

Though during excellent solar, that same smaller controller will loose efficiency when compared to a slightly higher capacity controller.


At least using that renogy example I posted.

As you stated, it is probably due to components.

So MFG to MFG and model to model may or may not follow this trend.

 

[broncobowsher]

Been running a 70W panel and a PWM charge controller on my ARB fridge for a couple years. All vehicle tied in as well. Even in poor light (shady trees) I have had no issues with park times in the 40 hour range. My math said I should run a 100W panel to run the fridge full time but packaging limited me to only 70W. Now that I have done it and lived with it I think it is fine. At one point I was running the fridge on solar alone (disconnected from the battery) and the compressor was running happily at 9AM in late December with the panel laid flat (not correctly aimed at the sun).

This performance is based on running in fridge mode. In freezer mode (I left it on all night once after making a grocery run) the starting battery was noticeably low in the morning. As in the lights were dim and it didn't want to start very well. Yes, I am doing it wrong, fridge tied into a single battery that also starts the truck.

If you want to run it as a freezer, you need a healthy battery and a solar panel bigger than the 70W I am using. I would say over 100W as a minimum. Ambient temps also matter. Inside a parked vehicle, parked in the sun, good luck trying to keep anything frozen. I've had times where it was lucky to even be cool inside. But that is inside a parked vehicle in Phoenix in the summer.

 

[4x4junkie]

Though during excellent solar, that same smaller controller will loose efficiency when compared to a slightly higher capacity controller.

That is why I like Morningstar's controllers. They maintain their efficiency a lot better on the higher end. My 15A SunSaver MPPT is only a bit over 1% less efficient at it's full 200W rated output as the 60A TriStar unit is at that same power level.

 

[biff]

I went to Powerfilm and got one of their seconds. They sell them at a big discount, folding or rolling. I am not sure if they can sell any of the ones they manufacture for anyone else but they are very easy to work with.

Talk to Julia Stone www.powerfilmsolar.com

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This.
I did the exact same thing.