What Percentage of My Solar Panels Should Face West?


I read the recent study from the Pecan Street Research Institute that has the Solar Industry buzzing. It makes a surprisingly good argument for facing solar panels toward the west in many grid-tie configurations. In fact, the California Energy Commission approved a new $500 incentive for west-facing solar panel installations and Arizona Public Service is working on a similar benefit program for it's sheep, opps, I mean customers. There are allot of variables to consider and I am still crunching the numbers for my pending design in Arizona. In the meantime, the report does not give any indication of the percentage of solar panels that should be facing south, west, or both.

So, does anyone have any suggestions for solar panel orientation that would be the best overall financial compromise in this situation?

My system is planned to be 60 300-watt panels. I have an unobstructed view of the south and enough land to install the whole array on the ground. However, there is a large hill to the southwest that would slightly effect the efficiency of this location, but a much better westerly view on my two-story home (and no good southern exposure on the roof). I envision installing solar panels in both locations and just need help in the best way to split up the panels.

Dr. Z.


  • softdownsoftdown Solar Expert Posts: 2,989 ✭✭✭✭
    PVWatts seems to be good about telling you what output you will get from what configuration.

    My suspicion is that a lot more installations could be made if sheep, I mean people accepted a western faced configuration.
    First Bank:16 180 watt Grape Solar with  FM80 controller and 3648 Inverter....Fullriver 8D AGM solar batteries. Second Bank/MacGyver Special: 10 165(?) watt BP Solar with Renogy MPPT 40A controller/ and Xantrex C-35 PWM controller/ and Morningstar PWM controller...Cotek 24V PSW inverter....forklift and diesel locomotive batteries
  • westbranchwestbranch Solar Expert Posts: 5,183 ✭✭✭✭
    West facing panels will give you an extended production period, but it will also lower the total output of the entire array.... just depends when you want the power, how much and for how long,, to each his own... no right answer as it depends...
    KID #51B  4s 140W to 24V 900Ah C&D AGM
    CL#29032 FW 2126/ 2073/ 2133 175A E-Panel WBjr, 3 x 4s 140W to 24V 900Ah C&D AGM 
    Cotek ST1500W 24V Inverter,OmniCharge 3024,
    2 x Cisco WRT54GL i/c DD-WRT Rtr & Bridge,
    Eu3/2/1000i Gens, 1680W & E-Panel/WBjr to come, CL #647 asleep
    West Chilcotin, BC, Canada
  • BB.BB. Super Moderators, Administrators Posts: 30,184 admin
    My summer power cost/pays around $0.30 per kwh for non to 6pm (Monday thru Friday).

    Off peak is around $0.09 power kwh.

    So, for summer, Afternoon production is worth about 3x the morning production.

    Winter, peak is $0.12 and off peak is $0.10 per kwh... so am vs pm is not a big difference.

    My array faces south east because of my house orientation. ... so I have less pm production. But still get most of my power credits during summer afternoons.

    Pv watts does have an hour by hour output. You can put this into a spreadsheet and do some what if comparisons.

    Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset
  • CALLDCALLD Solar Expert Posts: 230 ✭✭
    In some locations, particularly coastal locations near cold oceans, morning fog can be a prevailing weather phenomenon. In this instance it makes sense to have your array facing slightly towards the west, perhaps 45° from the meridian.
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