Factor for production dip away from 180 degrees?

lasitter

Is there a rule of thumb for solar production as the panels are tilted away from the ideal azimuth? Say, for every 10 degrees off of 180, your production drops "x" percent.

I know that there are very specific tools that I can use for very precise array azimuth / tilt for a given latitude, but I figured there must be some quick and easy approximation somewhere for this ...

lasitter

OK, just talked with a vendor that confirmed that changing the azimuth is relatively insensitive as regards to optimal solar production. I don't understand it, but that's the way it is ...

zoneblue

Its actually quite a complex relationship, involving cosine theta for the literal AOI,     but then you have alteration in glass reflectance,  temp changes, an many other factors. However some of that depends on the shading and season and site related features. Its not use pointing the array due south if theres a building there (you see this with utility telemetry and public wifi solar all the time).

Your best bet is to try various scenarios in PVwatts etc to see what you get. OTOH if you are interested in the math these sites will give you more bed time reading than you can ever use in one lifetime:

http://solarpaneltilt.com/
http://pveducation.org
http://pvpmc.sandia.gov/

BB.

A couple of places you can enter information about your site/setup:

http://solarelectricityhandbook.com/solar-irradiance.html
PVWatts® Calculator

-Bill