How would you regulate it? From what I've heard the leafs batteries can have anything between 300 and 400 volts on them depending on the state of charge. From what I know about charging batteries, most of the "resistance" of electrical flow comes from the voltage on the battery, not the resistance of the cells, so if you increase the voltage of the charger just a little bit, the current goes up a ton. (because you've already overcome the voltage on the battery, all that's left to slow down the current is the resistance of the cells, which is quite small) So no matter what you do you are going to need electronic switching on the charger end. So the only inverter you would save would be the one that converts the solar panel to ac. All kinds of people make those and like the previous posters have said, they have become quite efficient. Plus, I wouldn't want to trust my expensive battery to a charger I built with my limited resources and knowledge. Big corporations like Nissan have a sea of engineers working in a huge cubicle farm. surely they could come up with a better plan than I could in my cluttered garage.
2013 S model with quick charge package.
AV 30 amp level 2 EVSE, Bosch PowerMax 30 Amp EVSE, EVSE upgraded EVSE.