Why do east facing panels really outperform west facing?

softdown · October 14

Panels follow roof contours. House is not exactly south facing. Pretty close.

Southern array performs great except for summer months. Panels at 42 degrees to maximize winter production.

East and west panels at 10 degrees. Racks were included with main south facing racks. Free.

The west panels are simply 180 degrees from east panels.

I never get more than 8.5 amps from three 5.2 amp panels at high, sunny location. West Side disappointment.

37 degrees latitude.

JRHill · October 14

Temperature. Unless they are covered with ice or snow. Then they are about the same.

Miller_Ranch · October 14

Looks like you have plenty of room for a ground mount that faces south.

softdown · October 14

For several days I had not production from the westerly panels at all. Bad MC4 connection going to the wires going to the CC. Messed around with it and got power. But unsatisfactory power.

Could a poor hand made MC4 connection be lowering production by about 50% or so?

BB. · October 15

If 3x parallel wiring, then one bad connection will kill output by 50%.

In general, a bad connection will overheat, burn the connector, and or melt the contact housing.

Connectors don't have the ability to dissipate waste heat without damage (unless current flow is very low).

-Bill

softdown · October 16

BB. said:

If 3x parallel wiring, then one bad connection will kill output by 50%.
In general, a bad connection will overheat, burn the connector, and or melt the contact housing.
Connectors don't have the ability to dissipate waste heat without damage (unless current flow is very low).
-Bill

3X serial wiring. It does seem like production is at ~50%.

~126 volts.

I could point a remote thermometer gun at the connections I would think.

JRHill · October 16

This is frustrating. Are you too old to keep doing this stuff?

A thermo gun on a hot roof during production?

BB. · October 16

I do have a typo there... Intended to type 2x for 1 open connection giving you 50% harvest...

Since you have parallel connections... Open a breaker per string or cover a couple panels, etc.. and see how much the output drops per string.... They should all drop equally, if connections (and panels) are OK.

You could also get an AC+DC Current Clamp meter and measure the current of each string -- Again looking for equal current flow if all OK.

Lastly, how do you "know" that your output is down by 50%... From what I have seen over the years (with my Grid Tied System), the "nominal" current flow is proportional to amount of light hitting panels (pretty close to actual sun--i.e., if sun is down by 50% do to clouds, shading, etc., then current is down by equal amount).

Also, need to be more specific if your are 50% of Power (Watts=V*I), voltage, or current... Seeing 50% to 70% of Watts is pretty much standard derating from "Standard" to "real life" solar performance.

Parallel strings--Then variation in voltage can change current flow dramatically (I.e., 2x strings at "normal voltage" and one string with a bad panel/shading at less than normal, and current fall dramatically).

You have a battery based system... Also array harvest is based on on both available sun, and controller "needs" (battery state of charge, loading, etc.)... Obviously, this is not a "single variable" equation.

Which is why I suggest the per string measurements of current first (by shading or current clamp meter). If all are equal current (parallel strings to a single controller), then more than likely "all is normal".

If you have one poor performing string, then you need to do things like disconnect/shad the 2x good strings, and measure voltage/current of the poor performing string. Likely lower voltage is possibly a bad panel. Near zero voltage would be a bad connection, etc. Then per panel tests (voltage/current shorted/into test load, etc.). Again looking for comparison with "known good performing panel vs questionable panel").

-Bill

cleancurrent002 · October 17

That’s a pretty detailed setup! Sounds like you’ve optimized for winter performance nicely. Any plans to tweak the west array to boost output, or are you keeping it as-is for balance?

softdown · October 19

cleancurrent002 said:

That’s a pretty detailed setup! Sounds like you’ve optimized for winter performance nicely. Any plans to tweak the west array to boost output, or are you keeping it as-is for balance?

Yes I seek to boost production from the west facing panels.
Hence the thread.

softdown · October 19

JRHill said:

This is frustrating. Are you too old to keep doing this stuff?

A thermo gun on a hot roof during production?

Maybe

Miller_Ranch · October 20

Food Dish Cuisine Pizza Pepperoni Ventricina Meat Ingredient Italian food Salt-cured meat

manzanita2 · November 5

I like Bill's suggestion that the battery may be at a better SOC in the afternoon, thus demanding less power from the PV.

Does the PV output increase if you introduce a large load in the afternoon?

By all means, test the current flow in the west PV leads to see if they are equal.

JRHill · November 5

Miller_Ranch said:

Don't toss your pizza loaded. Don't solar people know this?

Or was it a delivery?

Miller_Ranch · November 7

Mike will take care of your roof mount problems. Article Lead Image

softdown · December 12

The west facing panels are now almost useless it seems. Could be that it is because the batteries are now fully charged by ~11am. Or it could be that east and west panels perform poorly during the cold months once a certain latitude is reached. They should still be fine closer to the equatorial latitude region.

I keep seeing ~ 1 amp total from the three western panels. Almost useless. Again, the batteries are fully charged pretty early.

littleharbor2 · December 13

If your batteries are fully charged you can at least benefit From your loads being covered by the West facing panels

DanS26 · December 13

My west facing panels slightly outperform the east facing. I believe its on average weather related.

sunsolarenergy · December 23

East-facing panels usually look like they outperform west-facing ones because of how solar production lines up with real-world conditions, not because the panels themselves are better.

In most locations, mornings are cooler and clearer, so panels operate more efficiently and produce cleaner power earlier in the day. In the afternoon, when west-facing panels should shine, you often get higher temperatures, haze, or cloud buildup, all of which reduce output. Heat alone can knock a noticeable chunk off panel efficiency.

There’s also the usage and system side of it. Many systems start the day with empty batteries or higher demand, so east-facing panels immediately get “used,” while west-facing panels may be producing when batteries are already full or the inverter is limiting output.

So east panels don’t actually make more energy overall in a perfect lab scenario—but in real life, cooler mornings, weather patterns, and system limits often make them appear to outperform west-facing panels.

706jim · 3:17AM

My system has two panel banks one facing southeast and the other southwest. As you'd expect, the southeast bank does the heavy lifting on the summer but is hobbled by trees once late September arrives. A possible plan will be to reorient the southeast bank to due south as in its present orientation I don't get full sun until about 12:30pm.

Why do east facing panels really outperform west facing?

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