Help making this battery charger

[EyeB]

Hi, I saw this a while back and have been tempted to try it on my TP2. Just not exactly sure if this will harm the phone or not, shorting it or otherwise. And I'm not sure if it is worth the time, if the solar cells can get enough power into it actually charge it, not too good with this kind of electrical math.

Solar Powered Cell Phone Hack <link that I'm talking about. It's building in solar cells into back case for charging.

I mean it would be nice to leave phone face down on the desk while I'm home/work and have it somewhat charge itself. And I can do a full charge with power cord once I'm at home, if the solar cells can't provide enough for a full charge in a reasonable time.

PS: Or if anyone has done this successfully, I'd be willing to buy one for a reasonable price since I'd have to buy a spare back cover anyways to do this.

edit: to clarify why I don't just buy an extended battery is I just don't want the size it adds lol. Plus I'm not getting bad battery life on normal battery, (around 60% by end of day). Mostly looking to do this because I'm curious if it'll work