as long as i can go with a good clean energy source?
Got a running stream nearby? I'd go with micro-hydro.
As AWOL said, come back when you have a spec. Also what do you mean by "clean"? Does that mean you won't be happy using batteries? You don't want to use a cheap Chinese power supply because of their pollution record? You don't want to use an expensive US power supply because of their pollution record? You want to energy harvest from the temperature differential in your lounge room? What?