These are comments from Lawrence, who recommends this Solar Shading tool for Android phones from Comoving Magnetics:
The app was $16. I thought the skyline accuracy was pretty good. They have several ways to input the skyline - one with the phone camera, which they claim is less accurate, and one that just sights down the length of the phone, which they claim is more accurate. I tried both and liked sighting down the phone.
I found the compass to be inaccurate, but that is probably more related to the hardware in my phone than the program. For surveys, I will carry a magnetic compass and put a declination number into the program which makes it read the same as a magnetic compass. The pitch and yaw (useful for estimating roof angles) readings were accurate. So with this tool you can find the roof angle, roof orientation, and shading all with the same app.
I did some tests where I just spun the phone slowly on a tabletop, and the result was a reliably flat shading profile, with just a bit of noise in it. I also did some tests at two of my arrays, and thought the profile looked pretty close to what I saw with my eye. I am confident that sighting down the phone produces a pretty accurate shading profile.
They have a section which predicts system power output, which they admit is optimistic since it does not account for weather. However, it is possible to add "monthly derating factors". A little playing around with PVWATTS vs the app, with the same size array and the same default system derating factor produced a plot of monthly derating factors that can account for local weather. Once that is done, the power output predicted by the app, vs PVWATTS, are within a half a percent or so, close enough.
I recommend the tool highly, and would compare it favorably to manual solar survey methods, and to the Solar Pathfinder. If one can take the time to calibrate it with monthly derating factors, I believe this is as good a solar site survey tool as you can find.
Lawrence Lile, PE, CEM, LEED AP BD+C, QCxP
Lile Engineering LLC
Energy Auditing, Commissioning and LEED Outsourcing