Minecraft day = 20 minutes
20 ticks/second
60 seconds/minute
60 minutes/hour
24 hours/day
Basic IC2 solar panel gives 1 EU/t during day and none during night
1*20=20 Eu/S
20*60= 1200 EU/Min
1200*20=24000/MC day
Assuming you are on a server, there are 24 hours * 60 mins/hour in one real life...