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Would an east facing array outperform a west facing array?

1201

1201

Solar Wizard
Joined
Feb 1, 2023
Messages
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Location
Texas
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?
 
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?
Click to expand...
Yes
According to my East and West facing arrays.
 
Strangely enough pvwatts says the West facing array will slightly outperform the east facing array??
 
While ambient plays a role, my gut says that the 80% of sunlight that gets converted into heat and raising the cell temperature is going to have a bigger influence. Yes, I think morning will outperform evening by a bit, but it doesn't seem like a ton.

Hmmm...I just checked some older models I had saved from PVWatts at my location.

Annual production of a 5kW E array: 8.85MWh
Annual production of a 5kW w array: 8.28MWh

About 7% better
 
sunshine_eggo said:
While ambient plays a role, my gut says that the 80% of sunlight that gets converted into heat and raising the cell temperature is going to have a bigger influence. Yes, I think morning will outperform evening by a bit, but it doesn't seem like a ton.

Hmmm...I just checked some older models I had saved from PVWatts at my location.

Annual production of a 5kW E array: 8.85MWh
Annual production of a 5kW w array: 8.28MWh

About 7% better
Click to expand...
Hmm. I wonder why it says West is better in my location. I wouldn't imagine it would be location dependent but it appears it is. I have a lot to learn
 
cdherman said:
PVWatts has information about cloud cover. Morning clouds in many locations occur and then burn off in the afternoon. Just a guess on my part, but valid I think.
Click to expand...
Ahh. I didn't even know about cloud cover. Very nice. Thanks for that bit of info
 
sunshine_eggo said:
While ambient plays a role, my gut says that the 80% of sunlight that gets converted into heat and raising the cell temperature is going to have a bigger influence. Yes, I think morning will outperform evening by a bit, but it doesn't seem like a ton.

Hmmm...I just checked some older models I had saved from PVWatts at my location.

Annual production of a 5kW E array: 8.85MWh
Annual production of a 5kW w array: 8.28MWh

About 7% better
Click to expand...

While those models were based on theoretical due E and due W arrays @ latitude tilt, my actual array is set to 165° vs. 180° at 29° tilt due to anecdotal claims that afternoon clouds inhibit afternoon production, so you get a little more daily juice favoring East.

Unfortunately, it's not true according to PVWatts. My 165° array produces 5.402MWh vs. 5.416MWh for a 180° array. During the summer months, I can produce up to 8kWh additional per month.
 
The real practical consideration is when do you need the power and that is usually in the morning. I have an east facing array and my system has totally recovered by 10am. This results in needing less battery. Don't know how this matters here. Majority buy batteries like women buy shoes.
 
Keep in mind that a nearly empty battery charges faster than a nearly full battery. So if your battery has been drained overnight by whatever you use at night, it would draw more power and charge faster the next morning as opposed to charging all day and then top off at the end of the day.
 
efficientPV said:
The real practical consideration is when do you need the power and that is usually in the morning. I have an east facing array and my system has totally recovered by 10am. This results in needing less battery. Don't know how this matters here. Majority buy batteries like women buy shoes.
Click to expand...
Hmm that's interesting.

Now in Texas where I live, we need that power from noon till 7pm so west might be best but I do like the idea of charging the batteries up early
 
timselectric said:
Something else to keep in mind.
Storms usually come in the afternoon/ evening.
Mornings are more often clear skies, than evenings are.
There are a lot of variables to consider.
That's why I have both, East and West arrays.
Click to expand...
Another thing I'm thinking about and i don't know how this works exactly but Ive seen vids that suggest if you are using power directly from pv it's more efficient than storing it in the battery first and then using it later

So what I'm thinking is that with a west facing array ,for example, the power is available later in the day when it's needed so it could be pulling straight from pv instead of battery, say for example at 6pm in the summer when I imagine a south facing array is already done.
This would mean some efficiency gains vs a south array correct?

Now, where I'm confused,or skeptical is this. How can battery inverter consume directly from the pv(charge controller) when the job of the charge controller is to, wait for it, charge the battery?

It's makes no sense because to my thinking the charge controller is always charging the battery and the inverter will always pull from battery, no?
 
I have a one string 3.6kW going in now at 165°/60° angled and a two string 7.2kW at 215°/60° angled array- just finished. Let’s just say, REC405 (215°) panels out performed my QCells430 (180°/45° angled) from noon on yesterday after the sun popped out. The steeper angle with the 405’s does not do well in overcast conditions like yesterday morning compared to the 430’s. I will not go with due east or west, because I have plenty of power when the sun is that far north in the sky. I need wintertime power for heat pumps. I also have a 200’ tall hill to my east.

I like southwest array for cooking dinner. My SolArk12K’s is 2% more efficient when going from PV to A/C output vs going into battery then pulling back out later.
 
Last edited:
1201 said:
This would mean some efficiency gains vs a south array correct?
Click to expand...
Some, yes.
1201 said:
Now, where I'm confused,or skeptical is this. How can battery inverter consume directly from the pv(charge controller) when the job of the charge controller is to, wait for it, charge the battery?
Click to expand...
in an AIO, the SCC sends power to the high voltage DC bus. The inverter pulls its power from the high voltage DC bus. It's more efficient to not go into the battery and back out.
In a separate module system. The SCC sends its power to the low voltage DC bus bars. (If installed) and the inverter pulls its power from there.
Still more efficient than going into and back out of the battery.
But there are more conversion losses.

Basically
Avoiding the charging and discharging losses is always more efficient.
 
1201 said:
Another thing I'm thinking about and i don't know how this works exactly but Ive seen vids that suggest if you are using power directly from pv it's more efficient than storing it in the battery first and then using it later
Click to expand...

Battery charging isn't 100% efficient. Lead acid can be as low as 85% average, and it's even worse in the absorption phase.

LFP charging is pretty darn efficient.

1201 said:
So what I'm thinking is that with a west facing array ,for example, the power is available later in the day when it's needed so it could be pulling straight from pv instead of battery, say for example at 6pm in the summer when I imagine a south facing array is already done.
This would mean some efficiency gains vs a south array correct?
Click to expand...

Theoretically, but not a lot.

1201 said:
Now, where I'm confused,or skeptical is this. How can battery inverter consume directly from the pv(charge controller) when the job of the charge controller is to, wait for it, charge the battery?
Click to expand...

An inverter inverts DC to AC. It's a system. Current is either going into or out of the DC system or in equilibrium.

1201 said:
It's makes no sense because to my thinking the charge controller is always charging the battery and the inverter will always pull from battery, no?
Click to expand...

Load = battery voltage dip
battery voltage dip = charger supplies more current to maintain battery voltage.

Net result = MPPT is feeding load directly and providing "float current" to the battery.

Victron MPPT run without battery once battery voltage has been established. I was shutting my system down and not really thinking about it in detail. It was in the evening, so not a lot of juice coming in. Loads were < 200W, so order didn't matter in my head. When I turned the battery switch off, I had a stupefying moment where the system was still running with the battery completely isolated. Occurred to me the system was being powered directly by the MPPT... forgot about that feature.
 
Sometimes our choices are limited.
I have a hill to my south. And my roof is East/ West.
I will be adding a South facing ground mount array, hopefully next year.
I need it for winter production. But I have to clear some trees first. As I need to get it far away from the hill.
 
timselectric said:
Some, yes.

in an AIO, the SCC sends power to the high voltage DC bus. The inverter pulls its power from the high voltage DC bus. It's more efficient to not go into the battery and back out.
In a separate module system. The SCC sends its power to the low voltage DC bus bars. (If installed) and the inverter pulls its power from there.
Still more efficient than going into and back out of the battery.
But there are more conversion losses.

Basically
Avoiding the charging and discharging losses is always more efficient.
Click to expand...
ahh. the old high voltage dc bus. Thanks for the education.

so even with a separate charge controller the inverter can pull directly from pv without the battery conversion losses or is it always pulling from battery?
 
RV10flyer said:
I have a one string 3.6kW going in now at 165°/60° angled and a two string 7.2kW at 215°/60° angled array- just finished. Let’s just say, REC405 (215°) panels out performed my QCells430 (180°/45° angled) from noon on yesterday after the sun popped out. The steeper angle with the 405’s does not do well in overcast conditions like yesterday morning compared to the 430’s. I will not go with due east or west, because I have plenty of power when the sun is that far north in the sky. I need wintertime power for heat pumps. I also have a 200’ tall hill to my east.

I like southwest array for cooking dinner. My SolArk12K’s is 2% more efficient when going from PV to A/C output vs going into battery then pulling back out later.
Click to expand...
hi. how do you calculate the efficiency and figure out that pulling from pv is 2% more efficient than from battery? thanks!
 

sunshine_eggo said:
Theoretically, but not a lot.
Click to expand...
ok, so in practice it wont overcome the lower production of facing the array somewhere other than directly south.
sunshine_eggo said:
An inverter inverts DC to AC. It's a system. Current is either going into or out of the DC system or in equilibrium.



Load = battery voltage dip
battery voltage dip = charger supplies more current to maintain battery voltage.

Net result = MPPT is feeding load directly and providing "float current" to the battery.
Click to expand...

hmm. It makes sense but i'll have to think about this a little more.
sunshine_eggo said:
Victron MPPT run without battery once battery voltage has been established. I was shutting my system down and not really thinking about it in detail. It was in the evening, so not a lot of juice coming in. Loads were < 200W, so order didn't matter in my head. When I turned the battery switch off, I had a stupefying moment where the system was still running with the battery completely isolated. Occurred to me the system was being powered directly by the MPPT... forgot about that feature.
Click to expand...
fascinating.
 
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