Hi Tracy,
I would charge the car using AC (either 120V or 240V) for a couple of reasons:
- Most EVs have on-board chargers that designed to perfectly take care of the battery regardless of state of charge (SOC) or battery temperature, a DC-DC system would have to be designed to talk to the vehicle battery manage system (BMS) and regulate the charge.
- Isolated DC-DC converters are about 87% efficient, a little better than the combination of a solar inverter and car battery charger, but not significantly better to warrant all of the work and potential risk to the battery to implement a DC-DC system.
I would definitely charge during sunlight hours if you can to improve solar system efficiency and reduce wear and tear on your home batteries.
Brian
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Brian Jensen
brian@jensenenergyresearch.com------------------------------