History of science question - Heinlein

I've been re-reading some old Heinlein stories in which various inventions are mentioned. I'm wondering whether the suggestions are incredibly foresighted or whether scientists at the time would have known that these might come about one day.

Solar panels - ("Let there be light," 1940.)
Segways (except only one wheel) - ("The Roads Must Roll," 1940.)
Motion-activated light switches - ("The Man Who Sold the Moon," 1949.)

Any ideas?

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