Math

I feel silly.

Work equals force times distance.

Given Roger's 100km and 10 tons we'll try a constant force slightly more
than gravity (F=ma or Fg=10 tons * 9.81m/s2) We'll approximate g at 10
and constant, which is not correct, but gets us in the right ballbark. Thus:

W = 100 000 m * 10 000 kg * 10 m/s²
W = 1E5 m * 10E4 kg * 10 m/s²
W = 10E10 kgm²/s²
That's 10E10 joules, or 10E4 MJ (which already is a unit of energy) Divided by
3600 seconds, that yields
2.8MW-hours... or 28MW-hours at the 10% effiecieny you mentioned.

Interestingly, my wife is just designing a 20MW power plant for an industrial
installation.