[DennisP]

Right, if you need to fully charge then plug it in. You'll do that after a road trip. But if you live somewhere sunny and typically drive 20 miles a day, you can keep it topped up by just parking in the sun.

Some will find this worthwhile, others won't. Apartment dwellers without convenient chargers might find it handy. The comment I replied to advocated doing your own energy production, and if that's what you care about, grid power doesn't really compete.