I came across this interesting iPhone app while reading a newsletter from a local solar panel company - good to see people making good use of the technology - Energy Matters Solar Analyser for the iPhone (as this post probably looks somewhat like an ad, I'll note I've got no connection to the company whatsoever and have no idea if they are any good or not).
The Energy Matters Solar Analyser is a revolutionary solar power site evaluation tool for the iPhone 3G, 3Gs and iPod Touch, providing full solar site analysis - and it's free! While originally designed for solar industry professionals, it's simple enough to operate that just about anyone can use it. ...
By utilizing the compass (on iPhone 3GS) and inclinometer functions of the iPhone, together with built in GPS and sun positioning functionality, the Solar Analyser can perform site evaluations in seconds. The Solar Analyser is easy to use, requiring minimal set-up time - you simply trace the skyline with the “heads up sight” and press “Analyse”.
Using the Solar Analyser's high resolution graphical display and easy to review results, you can determine a realistic estimation of the kWhr solar power that can be generated at a location, taking into account the local shading. It also supports fixed, single and dual axis tracking systems.
The Solar Analyser includes a large database of solar panel and inverter models. Select your dream system configuration and the tool will also calculate the $/month production of the site (Australia only).