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.
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