My prize entry needs a solar charged battery back to power the sensor and transmitter I'm placing in front of my house. Rather than spending a whole lot of time finding domestic suppliers of small photovoltaic panels and trying to spec a nicad or nimh battery pack, I decided to buy a "60 LED Solar Security Light" from Harbor Freight just a few miles from here. The list price was $32.99US, but it was on sale, plus I had a 20% off coupon so it ended up costing me about $20.00US. I doubt that once you consider shipping, I could have bought a solar panel and battery back for less than that. What's more, I ended up with a big LED panel and a motion detector module for use in future projects.
Here is the video of my tear-down and analysis of the light:
The photovoltaic panel and battery pack are going to work great for my project. I think I will duplicate the single-diode "charging circuit": It just can't get simpler than that. Next up, code for the transmitter.