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As one may know, Tesla Powerwall 2 comes in two versions: AC (with internal inverter) and DC. This question is about the DC version which comes with this coupling diagram:

enter image description here

We know that solar panels generate DC. So, on the diagram above, what does the hybrid inverter do with DC coming from the solar panel? Can the latter not be plugged into Powerwall directly?

Also, related question: if there was no grid involved (i.e. completely autonomous system), could the inverter be DC->AC only (not hybrid)?

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Even though both battery and panels are DC, they can't be (efficiently) connected directly. For optimal efficiency, solar panels need to be loaded at an optimal point, varying current drawn and thereby output voltage (this is called Maximum Power Point Tracking or MPPT). It basically ensure maximum power by maximising IxV (=P).

The battery will require a different current and voltage, optimised for efficient charging, battery life, etc.
At such, the hybrid inverter will need to do three things:

  • Do MPPT for the solar panels
  • Provide charge control for the battery
  • Provide AC voltage to the house/grid

Lastly, the inverter will somehow 'switch' (or balance) between drawing power from the panel and from the battery, and might even charge the battery from the grid when it's empty and there no or not enough sun (not sure about this).

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  • \$\begingroup\$ Are you sure hybrid inverter does charge control for Powerwall, not Powerwall itself? \$\endgroup\$ – Greendrake Apr 11 '18 at 8:11
  • \$\begingroup\$ I'm not sure, I can't find much detail. \$\endgroup\$ – RJR Apr 11 '18 at 10:14

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