Should New PV panels Face East, West Or Both?

pabloesguapo

I'm adding another array to my off grid system.  18 panels, 6 strings of 3, into a midnite classic 150
(my third in a string of charge controllers, in "follow me" mode) .  They will be mounted on a roof,
which faces east and west.  Should I mount them all on the east side, west side, or a combination
of both?

Should I be shooting for getting my batteries to full SOC ASAP, or try for a longer "sun day" in the afternoons?  Or both?

Thoughts? 

softdown

Find information here. I think the output tends to be a little bit higher from western panels? I'd vote that a 50/50 combo would be most effective - based on my previous understanding.

As I recall this combo is quite a bit better during the summer than the winter. Fine for seasonal cabins that are not heavily used in the winter - for example.

https://pvwatts.nrel.gov/

pabloesguapo

Thanks for that resource. 

I know that E/W facing is not as efficient as South facing. I will take that hit, because roof mount is the most logical and economical use of space on the property.  For starters, location of any new south facing array would be so far from the control center, the voltage drop would be insane.

Which end of the day should I try to extend my charging time, morning or afternoon?  Is it a coin toss?  Can I put east and west facing panels on the same charge controller? 

softdown

Going from old memories here - thinking it is pretty much a coin toss on average.  East or west panels do pretty well - except during the winter. I like the fact that you have all day to harvest - it is literally better if you have enough panels I think. My panels are geared for winter time production - 45 degrees at 37N. So production is pretty weak both early and late during the summer time.

Not sure enough about the CC to even hazard a guess. I'm one of the least "electrically talented" ones here. I love to experiment - which helps keeps me active. My experiments go sideways more often than not.

The main 48 volt system though? I do not play around with that. I need reliable power for freezers and fridge. Being a prepper - have three freezers full of chicken. Just bought a new fridge yesterday - thinking of a new thread for that.

softdown

Having considered it more - if I loaded one side more than the other? I'd do the east side more - bulking takes more power than power than floating.

mike95490

It depends on your usage.  We added a array to take up the morning load of the toaster.   You might use the microwave more in the afternoon..

mountainman

It also depends on location.
 Summer here we have frequent afternoon thunder storms and triple digit temps. So east produces more.

BB.

You might also look at South East and South West orientations...

Softdown's PVWatts link above--They have an option to download hour by hour 365 Days a year solar production (based on "a real day" that is representative of the "average" days over 20 something years). So, you can do some spreadsheet experiments and see how things work out by day/season/charging vs loads/etc.

For PWM charge controllers--You can use two arrays with E/W facing without issue.

For MPPT charge controllers--They set their Vmp-array operating point (for maximum harvest) based on the present Array Temperature (hot panels, lower Vmp-array). So, the optimum harvest would require separate MPPT controllers, one for each "differently facing" array.

In practice--Not sure how much difference you would see... I am of the opinion a 10% difference is almost impossible to "measure" and "confirm" with home test gear/solar charger reports. You need lab gear, and a reference cell/panel to be better than 10% accuracy.

Some charge controllers/solar GT inverters have been seen to be 2% accuracy... And other seem to have been 6% accuracy.

-Bill

MichaelK

I my case, I let my loads decide for me.  Since my primary arrays are on rotating mounts, I can run my heavy loads from about 8:00am till about 4:00pm.  So, getting to a full state of charge in the morning is easy.  But, my primary arrays start getting shading by about 4:00pm.  I've added an additional 1000W array facing due west so I can run loads till about 6:30pm without any battery depletion.  That's important if I want to be running the air-conditioner later in the afternoon.

New_Mexico_Will

Loads being equal, I'd put more panels on the east side, just because panels are more efficient in colder weather.

706jim

I have 3 panels facing southeast and three facing southwest. This has worked well for me.