Eclipse vs regular panel

I'm trying to decide which panel to install on my Subaru.  I'm using a Rover 20A charger with Optima Yellowtop AGM battery and the choice is between Eclipse RNG-100MB or the regular RNG-100D-SS.  It will be mounted between the crossbars of a Prinsu roof rack.

Based on the specs, the Eclipse is slightly more efficient, but that doesn't justify the large increase for me.  ($175 vs $101 on Amazon).  I also prefer the shape of the regular one, longer and skinnier, as it leaves more spare room on my rack.  But a friend told me the Eclipse performs significantly better in partial shade, which is a very important factor when I'm camping.  They both feature two bypass diodes, so I'm not sure what the difference might be.  So I bought both panels to compare.  Unfortunately the results are inconclusive.

I put both panels side by side on a sunny day with no clouds.  I connected each panel one at a time to the Rover and turned on all my accessory lights to put a constant load on the battery.

I used a paper booklet about 6" x 8" and placed it in various positions around the panels, doing the same on each.  I measured panel voltage and charger output, waiting for the numbers to stabilize after each adjustment.  With the MPPT controller, I don't think voltage really matters, but I recorded it anyway.  I think it's the current that matters.

Then I tried smaller obstructions of a lotion bottle and a 750mL water bottle, and a few scraps of wood scattered randomly.

With the larger obstructions of the paper booklet, the Eclipse performs better, sometimes by a significant margin and sometimes by a very small margin.  But with the other tests, the Eclipse is sometimes worse.

So based on all of this, I can't tell how much difference there will be, on average.

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  • what matters is watts, the controller is supposed to find the mppt which is the combination of v & a or max watts. the IV curve is always changing and the controller is supposed to sweep the panel from time to time to determine where the max harvest is, then max power input is transformed to charge the battery.  It just doesn't matter cuz much of the time the controller will be limiting power output as to not over volt the battery, ie only the power needed to keep the battery @ absorption voltage is not produced. If float ever happens even more power is not produced to keep the battery at float (of course extra loads can use this excess power in which case it is produced to power the load).

    sprc conditions IV curve attached.

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  • I think the I-V curve you're talking about is at the output of the panel. I used a clamp ammeter between the charger and the battery, as this is the best way I could think of to measure how much useful power is actually going into the battery.
  • if batt voltage was fairly constant, controller in bulk, then comparing charging amps is appropriate.

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