A state energy official, not a scientist, once asked me, obviously puzzled,
this question: He knew that the transmission lines carried electrons into
your house, but he wondered why there was no problem with the electrons
piling up in the house, or at least the last house on the line. I started
to explain that first of all, the electric wires were double wires, and he
struck his forehead and said, "Of course, the second wire is to carry them
back."
Another state energy official, thinking about the problem of storing energy
(like solar electric energy collected during daytime hours), once came up
with this idea, which really excited him: Use the excess to lift heavy
weights (like steel bars) into the air, and retrieve their (gravitational
potential) energy by lowering them again. I did a back-of-the-envelope
calculation, which you might like to reproduce, to show him what would be
entailed in storing, say, one million Btu (approximately one billion
joules), what a house might use for heating on a cold night. He gave up on
the idea.