Photodiode as solar battery
I'm trying to build "Solarsound modules" http://www.ralfschreiber.com/jade/solar-sound-modul./solarsound-modul.html. However, it is quite hard to decide what to use to drain power from light - the device has to be small and give 2.5V. Are photodiodes suitable for that, or do I have to buy a solar panel? What PD or a series of them would be the cheapest solution?
Thanks a lot.