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PVwatts numbers, inserting

h2ofun

Active Member
Aug 11, 2020
3,864
947
auburn, ca
I just put my house into PVwatts and moved the direction around on a 5kw system. I guess it does not know about shading much?, but, I guess I keep learning.

Was surprised on the estimates vs direction pointed. Is this normal?

South 7,531 kWH/year
East 6,527 kWH/year
West 6,431 kWh/year
North 5,177 kwh/year

I am surprised East is so much. Even though on my roof, with my structure shading, I guess they do not know this?

I was also surprised north was as much as predicted?

Based on these numbers, I am less concerned about putting a bunch of panels on my north roofs, which is pretty much all I have left. Am I missing something?
 
I just put my house into PVwatts and moved the direction around on a 5kw system. I guess it does not know about shading much?, but, I guess I keep learning.

Was surprised on the estimates vs direction pointed. Is this normal?

South 7,531 kWH/year
East 6,527 kWH/year
West 6,431 kWh/year
North 5,177 kwh/year

I am surprised East is so much. Even though on my roof, with my structure shading, I guess they do not know this?

I was also surprised north was as much as predicted?

Based on these numbers, I am less concerned about putting a bunch of panels on my north roofs, which is pretty much all I have left. Am I missing something?
No, that sounds about right. Some people act like East/West facing panels are "better than nothing" and that North-facing panels aren't even worth installing, but all else being equal (roof pitch, shading, etc), East/West panels still generate ~85% of what South-facing panels will, and even North-facing panels will still produce ~70% of what South-facing panels will.
 
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h2ofun

Active Member
Aug 11, 2020
3,864
947
auburn, ca
No, that sounds about right. Some people act like East/West facing panels are "better than nothing" and that North-facing panels aren't even worth installing, but all else being equal (roof pitch, shading, etc), East/West panels still generate ~85% of what South-facing panels will, and even North-facing panels will still produce ~70% of what South-facing panels will.
Yes, as I say, I am learning, and was surprised, 70% is better than nothing. And with less shading, it would probably be even closer compared to my south. One of these days I will have a neighbor who will let me pay to take a pine tree that has zero value to any of us.
 
No, that sounds about right. Some people act like East/West facing panels are "better than nothing" and that North-facing panels aren't even worth installing, but all else being equal (roof pitch, shading, etc), East/West panels still generate ~85% of what South-facing panels will, and even North-facing panels will still produce ~70% of what South-facing panels will.
Yeah - the main issue with East vs. West is TOU rates. For some, West-facing is advantageous over East because production more closely aligns with peak periods. Otherwise, they are virtually identical (with East probably having a marginal advantage due to lower temps in the morning, but weather can be a bigger factor, based on location.)

And the main issue with North beyond the overall lower production is that there is an extremely large difference between summer (where it is not much worse than south-facing) and winter (where it can drop to nearly zero, depending on the roof slope.) So, depending on the goals of the system (for example, to offset your usage for the year vs. to be almost/entirely off-grid) this can present an issue.
 

h2ofun

Active Member
Aug 11, 2020
3,864
947
auburn, ca
Yeah - the main issue with East vs. West is TOU rates. For some, West-facing is advantageous over East because production more closely aligns with peak periods. Otherwise, they are virtually identical (with East probably having a marginal advantage due to lower temps in the morning, but weather can be a bigger factor, based on location.)

And the main issue with North beyond the overall lower production is that there is an extremely large difference between summer (where it is not much worse than south-facing) and winter (where it can drop to nearly zero, depending on the roof slope.) So, depending on the goals of the system (for example, to offset your usage for the year vs. to be almost/entirely off-grid) this can present an issue.
The main reason I am looking at is I assume NEM3 will get rid of retail pricing on sending energy back. I also am assuming NEM3 might charge the 11 bucks per month per KW of solar. I am assuming if I put more in now, I get NEM2, and it stays for 20 years. Now, if I knew NEM2 was going away at the end of the year, I would not be looking at adding more solar. I also have no idea if I can even get more solar approved.. So many unknowns. :(

So, I am assuming with north panels, I bank credits for winter heat pumps when these panels go way way way down. But if no banking, then would be a TOTAL waste of money. Should I roll the dice, will have to decide soon. :(
 

Ampster

Active Member
Supporting Member
Should I roll the dice
With Powerwalls you have a good hedge. Instead of rolling the dice. it would be more informative to model what the Powerwalls can do and see if the constraint is production or storage. there are several modes for the Powerwalls that would be worth understanding.

I am assuming you have good numbers for production by hour and consumption by hour.
 

h2ofun

Active Member
Aug 11, 2020
3,864
947
auburn, ca
With Powerwalls you have a good hedge. Instead of rolling the dice. it would be more informative to model what the Powerwalls can do and see if the constraint is production or storage. there are several modes for the Powerwalls that would be worth understanding.

I am assuming you have good numbers for production by hour and consumption by hour.
After a month now, I have no issues with storage, assuming I have solar. So, the issue in the off season will be solar production. Also, if I want to really heat my house next winter, and get it cold this summer, again, it is solar production. I see zero return adding anymore batteries for me.
 
Yeah, roof slope combined with latitude matters. For me being up at 47.5 degrees north, I need about a 7 kW system to roughly match your numbers using a 4:12 roof pitch (18.43 degrees). If I increase the roof pitch to 9:12 (36.87 degrees), which is what my south-facing roof is, I get a way higher spread; north-facing is about half the production of south-facing in that scenario. Yours may be a little different due to more southerly latitude; my sun angle on the winter solstice is only 19 degrees!
 

h2ofun

Active Member
Aug 11, 2020
3,864
947
auburn, ca
The North vs South difference depends a lot on roof slope. Flat roof is no difference; 12:12 slope would be a pretty big difference.

Cheers, Wayne
Yes, glad I do not have any crazy roof angles like that. Was thinking today, that if I were to build a new home, the first thing I would do is work on the roof to make it handle max solar at best direction with nice flat surfaces
 

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