The tech said that if you had one panel that puts out 16 volts and another 17 and another 19 volts then the voltages will average and you will be wasting the potential output of the panels above the average. If I understood him right.
When you hook the panels all together, they will all be the same voltage. The MPPT controller is continually searching for the maximum power point of the panels as this constantly changes - for example by a cloud passing. Since the different panels all generally have different max power points, the controller can only look at the average of what comes in - and this may not be optimum for any of the panels (but stilll generally a benifit)
The PWM (or obsolete shunt) simply connects the panels directly to the battery - the panel voltage drops to the battery voltage. Since the panels are "constant current", i.e., the current output from them is independent of voltage, the current from each panel is simply added together. Doesn’t matter what the open circuit or max power voltage of the panel is, they will all be at the battery voltage. No tradeoff at alll to connect differnt panels in parellel.
FYI, I like MPPT controllers, just don’t think they are always the best for what most people with our trailerable boats need. My opinion is that a 20 to 40 watt panel is all these boats need unless you have special needs (such as a 12 volt fridge).
Here is an example..
Say a baseline is a 20 watt panel (use solartech as an example) and a Morningstar Sunsaver 6 (PWM) – cost is $142 for panel and $38 for the charge controller.
Then look at two upgrades on this.
1. Go to the Genasun GV-4 MPPT controller. Added cost is about $100-$38 = $62. What did you get for $62 – about 15% more current in general.
2. Keep the same charge controller, go to a solartech 30 watt panel. Added cost is $154-$142 = $12. What did you get for $12 – about 50% more current in general.
Of course the 30 watt panel is larger than the 20 and that can be very important..