I found some information on how much energy an electric eel can theoretically produce for an hour, but not per day. Thanks to this excellent answer from dtrades and my own research.
Apparently, electric eels can produce up to 860 watts, at up to 1 amp, with 1ms pulses and up to 500hz, with older/longer eels being able to produce a more stable output. That would theoretically make for a 50% duty cycle, with square waves, but will be something more like a 25% duty cycle when we average the pulses (if I'm not mistaken).
River Monsters S03E06 Electric Executioner claims they can produce a shock for "over an hour," I'd like to find more definitive data on their potential length of shocks. I did see a video of an electric eel being bitten by a reasonably sized gator, and shocking into into unconsciousness or death after 40~45 seconds, so I would believe they could keep it up for an hour, especially since they can still shock even eight hours after death.
So, all that together, suggests that an electric eel could theoretically produce 215 Wh, after one hour. It might be too exhausted to keep that up.
Of course, that is the most ideal result for one hour. What the average eel will manage, averaged over a day, is much harder to say. Still, I'm skeptical they are only capable of less than 1 Wh, and I'd figure a result in excess of 215 Whs would be more likely, under ideal conditions.
They also, as an aside, have to be careful to not electrocute themselves and stop their own hearts, and they have to take care not to electrocute each other. The father will keep his fry in his mouth, and signal them as to where they should go to be safe, when he performs a shock.
For those reasons, if you did use electric eels for power, you'd have to be careful how you contained them, so they had enough space to not electrocute themselves or each other.