The most important thing about the flux capacitor is that it requires
1.21 Gigawatts of
power to
work its wonder.
This huge amount of power (in the form of electicity) is apparently generated by a very small nuclear reactor which uses plutonium (in the form of a red liquid, for some reason) as fuel. However, after the year 2015 we will have available to us miniaturized fusion reactors which can be fueled by any spare matter you happen to have lying around.
Alternatively, a bolt of lightning will do the trick.
What is unknown is exactly why Doctor Emmett Brown, a brilliant scientist and inventor, insists on pronouncing gigawatt as "jigawatt"*.
*Well. It appears that "jigawatt" is indeed the correct pronunciation due to the Greek origin of the prefix "giga". JUST RUIN ALL MY FUN, WHY DON'T YOU?