building a car that proves a concept or wins a race means very little in the real world of 1-ton trucks, stop-n-go traffic, parking, freeways, 50mpg winds, rain, ice, snow, 16yr old drivers, 96 year old drivers, etc, etc. It isn't about whats POSSIBLE, it is about whats PRACTICAL and SAFE.
Ok, well it started with Ford Greenpower, which was pretty basic. Then I got involved with solar cars at uni and built one which we got road legal (with certain restrictions) in the UK. Then we built this one to race in Australia (see below, white one). Seeing what we achieved and, moreover, what some of the more experienced teams were able to do with a 2kw continuous, 5kw max setup has convinced me that there is mileage in electric cars (although I remain unconvinced by solar). One team clocked 157kph and the winners in Australia averaged 100kph over 3000km on an average of about 1.6-1.8kw.
I take your points, these were expensive vehicles to build but I wouldn't be looking to do quite such a Hi-tech job and the whole solar aspect would be cut out. I'm quite happy to compromise on space, handling (to a degree) and safety (I already accept that if I crash I'm basically done for). Fortunately the UK makes it relatively easy to get home builds legal (my runabout is an ICE trike).
What I would be planning is a lightweight spaceframe chassis (probably alloy) with two hub motors driving rear wheels and a single front wheel. Looking for a total power of about 10-15kw if I can find motors with adequate starting torque. Encapsulate the whole thing in a balsa and GRP shell (because I can't afford Nomex or carbon and don't have the facilities for anything but a wet layup). The shape of the car is inspired by one built a few years ago by Bochum and was actually designed as a potential two seater (yellow, below)
Happy to answer any questions or offer any ehlp I can.