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When looking for some MPPT solutions for a solar car, one of the things I have considered were these wonderful small "Solar Optimizer" modules provided by SolarEdge. However, they are clearly intended to be connected to their SolarEdge household inverter, which is different from our application (to connect the MPPT's directly to a battery pack)

Is anyone aware how the SolarEdge power optimizer system works? Is there some sort of AC data signal superimposed on the power rail for digital communication the power rail feeding the inverter? Or are these individual "power optimizer" modules simply dependent current sources which provide a constant-power output (current output drops as the output bus voltage increases) which feed a line of undefined voltage? (That is to say, the bus voltage will be defined by the inverter, which draws the current necessary to effectively shunt-regulate the bus voltage)

If it is the latter, and the solar optimizers can support an acceptable range of output bus voltages (from 96 V to 135 V for a 32S lithium battery pack) then I would imagine it would be possible to simply connect the optimizer directly to the battery pack. However these are big ifs, and I am not certain on exactly how their system works. Does anyone have insight on this or if there is some flaw in my reasoning?

With more research and watching the promo videos on how to install their system, it appears these MPPTs will not be suitable since they output a relatively low voltage with low output impedance, and are designed to be strung together in series.

Given that they only provide 1V until connected to the proprietary inverter, I would guess there must be some sort of AC signal superimposed on the DC connections as I feared. Either that or perhaps once they detect some load they then begin providing a higher fixed DC voltage. If anyone has a suggestion on another unit, that would be great.

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Yes, there is a flaw, an MPPT tracker can regulate the voltage and current, but most are designed for fixed loads. Lithium ion batteries have charging curve, whatever is feeding voltage and current needs to be able to provide a constant current, then constant voltage, which I doubt the solar edge is programmed to do.

enter image description here

Source: Battery University

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  • \$\begingroup\$ Yeah, I understand lithium batteries charge using a CC-CV charging curve, however most solar car builds simply connect MPPTs directly to the battery, and <i>rely</i> on the BMS (Battery Management System) to cut off the charge once the maximum voltage is reached. It is by no means ideal but that's what most teams do. Since the idea behind an MPPT is to maximize power, it will charge the batteries as fast as it can (constant power) which does mean lower cell voltages will result in higher charge currents. \$\endgroup\$
    – Power Max
    Commented Feb 6, 2018 at 17:34
  • \$\begingroup\$ The ideal MPPT / optimizer IMHO should have a compliance voltage and current, so that the voltage and current stay within specified limits, at the cost of no longer tracking the MPP, of course. I have yet to find an adequate off-the-shelf solution. \$\endgroup\$
    – Power Max
    Commented Feb 6, 2018 at 17:37
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Yes, there is a serial communication superimposed on the output of the solaredge optimizer, to the inverter or SMI. If the inverter is disconnected it outputs 1V, but you can buy from Ali also unlocked optimizer, without communication.

I am also interested to connect the battery directly on solaredge, but:

  • the optimizer works as current source, so it won't limit the voltage, thus overcharging the battery
  • I didn't see any user to have connected it directly to the battery, so not sure if it's safe

The best solution would be to hack the optimizer to limit the max. output voltage - CV. The rest is OK, since the solaredge is a buck/boost MPPT converter, very robust and relatively cheap for such quality product.

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