I'm working on a small LED project for a friend's wedding - 24 LEDs that randomly come on and off to imitate fireflies. I need to make it mobile - preferably solar powered so after the wedding it could run a couple hours a night at most. I have everything figured out and working just off of USB or a 5V ac/dc converter, but I'm having a hard time wrapping my mind around the best way to make use of batteries and a solar panel. I'm a beginner here and have done a few hours of research on this, but still just can't put the pieces together.
I know my device only draws a max of 80mA - just the arduino and a couple LEDs that fade on and off every few seconds. So how do I figure out the best way to make use of batteries? If I use a 9V, does that mean the arduino steps it down to 5V and wastes voltage through heat, or does that just mean I'll be able to pull 5V longer? Is it better to get as close to a 5v source as possible, like using 6V (1.2v*5 or 1.5*4) batteries?
And if I were to go the 1.2V*5 (rechargeable) batteries route, as far as the solar panel goes, do I need a solar cell that is more than 6V, or could I use a 2V panel, just taking much longer to charge? My gut says no on this one, but I couldn't give an explanation. Since it's only on a couple hours at a time at most and with such a small current draw, I wouldn't think it would take much to charge up the batteries, but I'm just not sure! I want to make the best use of money while trying to make this as efficient as possible.
I'm sure these are simple questions for experienced folk, and it will probably click if someone can relate some of these things together for me.