Earlier quoted context omitted.
> For people using their cars once or twice a week to drive 10km to do groceries this will suit them Wouldn't they be even better suited to a regular electric car, parked under a roof of solar panels? The simple flat solar roof will be cheaper to make, and be a larger useful surface. And easier to replace, will keep the weather off the car, reduces car weight, etc.
People can do both. It really just comes down to: are the solar panels worth the added manufacturing cost and weight? If it cost ten dollars and added one pound of weight almost everyone would want it. If it cost ten thousand dollars and added a hundred pounds of weight then few people would want it. The unknowns at this point are: what are people willing to pay and how much additional weight will they tolerate? And,…
"worth" here implies the third factor that you didn't explicitly mention: how much power you get off them. And "69 miles per week of charging" is pretty small, hardly worth it unless it's extremely cheap in vehicle cost and weight.
You're not wrong with the qualifiers "people using their cars once or twice a week to drive 10km to do groceries" and "some people don't own the land they park their car on" but each qualifier of the prospective customer greatly decreases the potential market size. Combined with a qualifier that they must be without good access to shared transport (so not in a big city, but not on their own land); then you might be looking at corner cases, not a viable market.