[nine_k]

It's a bit like nuclear fusion power.

Working prototypes have been demonstrated decades ago. Something that would be viable economically is a whole different kettle of fish. With fusion power, it's not reached yet. With electric cars, it's only starting to emerge on mass markets.

[starbeast]

I don't know where you get that idea. The current problem with fusion is not that it isn't economic, it is that it is not yet at the stage where it produces excess power that can be used.

The electric cars 100 years ago were functional as a form of transport.

[nine_k]

I tried to express the imperfection of the comparison by saying "a bit like".

Both nuclear fusion producing energy and an electric car capable of driving some distance were demonstrated long ago. At that moment, neither was economically viable compared to alternatives (both based on combustion). Both remained in that non-viable state for decades. Electric cars seem to have crossed the border of viability in certain niches; fusion power still has not.

[starbeast]

Fusion power has not yet reached ignition, without that it is not just uneconomic, it is not working period. - https://en.wikipedia.org/wiki/Fusion_energy_gain_factor

[NikolaeVarius]

They were functional, but gasoline cars quickly became much cheaper/much faster/and had greater range.

Also with highways, gasoline cars could make do with less infrastructure required to actually use them.