[shadowpho]

8.64 joules = 2.4 mW hours. Dividing by 5v gives 0.48 mA*hrs, so you can run a 5v load for 1 hr if it takes 0.48 mA.

[gpm]

Take the easy route when it's presented like that! 2.4 mW hours is 0.1 mW days, dividing by 1 day (i.e. doing nothing / applying the "per day" part of the original units) and 5v gives you 0.02 mA.

[meatmanek]

You could also just go back to the sentence just before "8.64 joules of energy per day" and see that it produces 100 microwatts (or 0.1mW).