diy solar

diy solar

Would an east facing array outperform a west facing array?

efficientPV said:
I figure 12 hours of night use and a couple in the morning is a long time to wait before a south and west array start producing. My refrigerator doesn't work at night so it has to recover first thing in the morning. I'm about as close as you can get to using power directly from the panels. While not a typical day, refrigerator has recovered, hot water is up to 60C by 10am when I start the dishwasher (heating element runs from array DC) and have done three loads of laundry (direct from array power with hot water from PV) by noon with battery fully charged. It has to be a good day for laundry and started in the morning because we line dry. East facing array (1/3 of total panels) in my location produces more power than the rest of the system.

It is always site dependent and based on lifestyle. We don't have commitments like work which prevent us from doing things when the sun is shining. Dishwasher has a start delay feature making it easy to run when we are away, and the hot water gets up to temperature. Remarkably low battery requirements when you get away from the I want it now mentality. On a nice day I get nearly full rated power from the east array for several hours. South facing panels is just a dated way of thinking from when panels were expensive and batteries were cheap.
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If you're like the instrumentation/analytics type of person, get yourself a battery monitor (shunt) for better visibility into the system).. In my example I use the Victron BMV-712 battery monitor, it allows to see amps, volts, watts, in-out of the gateway (the battery), and accurate SoC.

Just think of the battery as a big storage bucket, solar trying to dump into it as much as it can (when battery is low), and loads are trying to drain the bucket.

With a battery monitor, you start to get a natural feel for how the power is flowing into, out of, or skimming across the bucket (once it gets full). When the battery is full, and not many loads running, the charger (solar MPPT) ramps down and relaxes from full output state (wasted Sun).

For example, I find that if my goal is to try and keep my power at exactly 100% (once I get there), and a cloud rolls over a little bit (starts to affect production), say I decide to turn off my AC in the RV to conserve my 100%, I am now only wasting more Sun.

If my AC draws 2000w, and I leave it on instead, the cloud cover may reduce my output a bit, and maybe I'm only running a -400w deficit, it still makes sense to just leave the AC on and let it eat that 400w deficit into the battery, because I'm still getting 1600w from the Sun (not waste it, have more AC)...

Then maybe if it gets down to 95% battery (maybe is early evening and trying to keep more battery for the nighttime), I can turn off the AC then, and it will be trying to get full solar as it can from the panels to try and fill the bucket (charge the battery at full power again).

This is all more apparent on undersized system where you are trying to get all the solar you can, obviously if you have way more power than you may ever use, then one doesn't tend to worry about it or be as mindful about the power consumption, or the times of day you do various power-hungry tasks.

It's basically same like budgeting money in my eyes. The solar is like your income, the battery is like your bank account (up to the FDIC limit), the loads are like your expenditures..
 
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A lot depends on your particular location and climate.

Usually, afternoon index of refraction of atmosphere yields more IR wavelengths of light than morning sunlight with cooler atmospheric temperatures. Silicon PV cells produce most of their output from yellow to near infrared light wavelengths.

Then panel heating is also a factor. Panel heating reduces MPPT output power which is usually higher temps in afternoon sun.

Sun spectral intensity.png
 
Almost N/S metal building (170/350) with sub panel and power entrance at north end. Thinking two strings of eight panel 460s on each side (080/260) of the 5 degree sloped roof. Hoping shorter wire runs offsets some of the east side slightly lower production. PVwatts yields:

460x8 year kW Dec Jul
080 3.68kW 4.952 495 1187
260 368kW 5.051 523 1184

Or, as previous comments pointed out, add a panel to the east side strings. South side is a bifold door, tempting to put a string there and raise the door part way. Probably need to upgrade lift cables and motor/drive - save that for another day.
 
I am in San Diego County. A west facing array is better than an east facing for these reasons: Often here we have morning ocean layer that rolls in a limits sunlight. Depending on where you are located, this could burn off by 10 AM or last till afternoon. However, west facing array never has this issue. Actually too, in summer months, sun goes to north of west here, so you get most PV in long days. Best IMP is facing Southwest in San Diego if you can't face South and West with different MPPT.
 
Here in north central Texas I have been more aware of the sun this year and watched SR & SS move north in the spring and now moving back south. That seasonal movement must by why pvwatts shows the 080 facing panels a bit higher than the 280 facing panels. And the reverse for winter monthsOccasional days of Gulf low level moisture intrusion, like your marine layer, but not frequent or long term.

Tesla estimated I needed 12.8 kW but I like ~14kW for possible plug in or electric car. Pvwatts bumps that up to ~20kW. Largest demand is summer AC, just need the LP furnace blowers turning during winter.
 
1201 said:
So on paper east and west should have the same production correct? But like the heat gain through a window, east and west should have the same heat gain but west ends up having more because of higher ambient temperature.

So, since temperatures are lower in the morning(summer time) does it mean east facing panels would be cooler and produce more than west facing panels?
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Morning will have things that block the sun more than the afternoon. Consider fog/haze that has to burn off.
 
And the points go to teal95. Actually paused when using SR but thought talking about sun position and morning sun vs afternoon sun ...

Many days here start clear and, by noon, cumulus clouds (Cu's) start showing up, grow with the afternoon heat, and are gone by sundown. If the pvwatts estimate is not too far off there is sufficient reserve to meet my needs with grid backup. Plus the almost flat roof (ridge 3' higher than sides) makes east and west production less important.

Was delaying on batteries to help fund but this summer's conservation warnings increased their importance. So a longer charging time would be more useful than mid day peak.
 
Do any of y’all maintain a ratio of sorts in your arrays of differing direction?
My initial plan was 8-10 panels facing due south at 30* and 4 facing due east, 4 facing due west at 45*
The 4 east and west will be movable so I know I’ll experiment with different angles for production and maybe they ALL end up facing the same direction hah
Just curious how other people are determining how many they are putting which way
 
GOO5E said:
Do any of y’all maintain a ratio of sorts in your arrays of differing direction?
My initial plan was 8-10 panels facing due south at 30* and 4 facing due east, 4 facing due west at 45*
The 4 east and west will be movable so I know I’ll experiment with different angles for production and maybe they ALL end up facing the same direction hah
Just curious how other people are determining how many they are putting which way
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Depends on your latitude.
 
I would have the south ones set steeper than the E W ones, if you have a choice.
Also, panels are cheap so just Tetris the whole roof.
 
45North said:
I would have the south ones set steeper than the E W ones, if you have a choice.
Also, panels are cheap so just Tetris the whole roof.
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No roof to Tetris, fortunately. Which creates my dilemma. Endless options hah.

I initially thought that I should make the south array steeper but as I continue reading threads like this, debating east vs west or e/w vs south it seemed that many were much steeper when E/W due to low sun angles I presume. My assumption was if they weren’t as steep they would still retrieve light, longer, albeit non optimal angles
I guess I still have more reading to do to better grasp the logic of angle for E/W
 
How about keeping your south facing panels and putting what you'd use on your E/W sides on one of those $500 trackers?
 
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