season panel angles

There is a very simple calculator I use here all the time:

http://www.solarelectricityhandbook.com/solar-irradiance.html

And a  more complex calculator (that allows you to pick any location by city/lat-long), and even gives you hour by hour estimates for 365 days a year:

https://pvwatts.nrel.gov/pvwatts.php

The two are probably within 10% of each other usually. Both give long term averages (~20 years) for solar data. The PV Watts output based on "real" days (each day picked to represent the average harvest for that day). Both are based on actual measurements--So clouds/marine layer/etc. are included deratings.

I probably "trust" the PV Watts more when you start playing with East/West arrays and "non-standard" angles (SolarElectric one is very quick and limited options--Great to get a quick answer for your questions though).

I am sure there are a 100 different programs and websites out there--Just have not needed to look for more. The above seem to give accurate enough results--When accuracy is something like within 10%... And realizing that these are long term average numbers and month to month or year to year, 20% variation is normal.

This also get into looking at your loads as members of two classes... "Baseline" loads that need to run 24x7 (like refrigerators, LED lighting, and perhaps a home business--Laptop computer, networking, etc.). And "Optional" loads (washing clothes, irrigation, vacuuming, irrigation, etc.). I suggest that baseline loads should be around 50% to 65% of predicted solar output (1/0.5 = 2x array, 1/0.65 = 1.54x larger solar array).

Of course, if you are willing to run a genset more often and/or are in a very sunny/cloud free climate--Those fudge factors could be a bit on the conservative side.

Solar panels are historically cheap--And last 20-30+ years... Batteries are historically expensive and last 3-5-7 years (cheap to mid-priced lead acid, >15-20 years for "forklift"). So "over paneling" is usually a good way to help keep your batteries happy and have a long life.

Also, heat kills batteries (and pretty much everything else). A very handy engineering rule of thumb... For every 10C (18F) increase in temperature (batteries: 25C/75F is "room temperature"), the life of that "thing" goes down by 1/2. At 93F, batteries age 2x faster (1/2 life).

So, keeping your batteries cool in Arizona can be a big help too (basement, earth berm battery shed, root cellar, etc.--Watch for water/flooding in below grade installations).

-Bill