Idea: Stirling-electric motor for electric vehicles?

Hey all,

Full disclosure, I'm a major Robert Murray Smith fanboy.  In a recent video, he brings up an interesting point/idea and so I thought I'd float it here for discussion.

The concept is this:
Electric cars are "good", but their motors rely on scarce and environmentally costly materials.
His question is, "why not use a near 100% efficient electric heater element to drive a Stirling engine instead?"

Full video:


Good idea/bad idea?
Thoughts, comments, discussion?

You still need a battery bank to store the electricity.  You still need to charge the batteries.  You still have every other part of the electric car

So, then you are realy asking, first, is it more efficient to:

use the electricity from the battery to turn an electric motor                                            

battery--> electromagnetic effect  (motor) --> turns which turns axle ( wheels)

or, use the electricity from the battery to make heat to turn a stirling engine motor          

battery -->electric heat element --> stirling engine (motor) --> turns which turns axle ( wheels)

generally speaking, each time you convert energy from one form to another, you have conversion losses, and a regular electric motor, electromagnetic effect, is very efficient.  Losses are due to the physical act of turning, friction, which the external heat driven engine ( stirling engine) also has.  

the second thing you are asking would be difference in materials, so rare or environmental differences.  Again, both would use the batteries, which are the main problem component.  

What is in an electric motor ?  Copper windings ?  What is the parts that you are concerned about ? Electric motors usually have no permanent magnet, as current thru coils can be used instead, or they might have a few permanent magnets.  Thare are many ways to make an electric motor, I think you do not need to have rare materials magnets, although they may be used for space/weight or other considerations. https://en.wikipedia.org/wiki/Electric_motor

a third, potential issue to compare the 2 motors, electro-magnetc or stirling effect, would have to do with suitability to drive the load.  I dont know if a stirling engine is suited or not, but that would be a consideration.  

Electric Motor
This will convert 90% of the electrical energy into mechanically energy to spin the shaft/wheel/propeller.

Alternative
Electric to Heating Element (100%)
Heating Element to Sterling (think electric hot plate heating a pot, 50%)
Sterling to Shaft/Wheel/Propeller (30%)
Total=15% efficiency (100% x 50% x 30%)

This means that you would need a battery bank that is 6times as big  (15 vs 90) for a sterling vs motor. Now lets say you were some how able to bring the heatloss from the heating element to the sterling engine down to zero for a 100% efficiency. You could now bring up the total overall efficent to 30% vs only 15%. Even then you would still need 3 times the battery bank. And battery/power plant are probably just as bad for the environment/wildlife.

Co-Generation
I do think that sterling engines would be good in a co-generation system.
In the winter about 600 therms or 17,580kWH of heat energy is used to heat the living space. If a sterling engine or really any generator was used to recoup 30% of that (5274kWH aka 5.3WWH). I would get to use the energy twice, once as electricity and then then heat after my devices convert it. I do understand that someone in Miami, FL used alot less space conditioning compared to me.

Solar Electric Production
Solar Collector Efficiency at 70%
Solar Battery Efficiency at 80%
Sterling Engine Efficiency at 30%
Total = 17% (about the same for solar panel+battery)
We get night time (24/7) electric production (similar to how hydro gives us 24hr electric production). If done right we can have the setup only extract 300W at 3am when everyone is sleeping and 10,000W at 7pm when TV+microwave+washer+etf are all on at the same time, mostly removing the need for a battery even in an off-grid setup