I haven't heard of the Singapore project before, that is impressive indeed.

I think the proper way to solve a problem should be smart charging, where the car chooses the cheapest energy through out the day, making much finer decision than a consumer ever could. And grid should be (it usually is) managed in such a way that lowest price corresponds to highest % of clean energy.

We could take this even further: usually the grid responds to demand and predict demand based on past patterns, but we could have a protocol for IoT devices and cars to request power they will need in the future, and ask the grid for the best time to draw power in the next X hour window.