Arranging Strings toward different quadrants of the sky

[Jefferson]

Just when you thought it would be safe to open a noob's solar plans.....

I am trying to put a solar system on my elderly parents home so they can have some relief from their power bills and some emergency backup for medical devices etc. I have been studying and planning for a few months (which has been like drinking out of a fire hose, but at least the water is tasty.....
I decided to work with Signature Solar since they are fairly close to home and I like that they have in-house warranty/repair etc.

My situation is somewhat challenging because we can only put panels on their garage which is not shaded by trees, but the roof planes point to the least favorable areas of the sky. (N,E.W) so I am trying to go with the highest wattage panel to provide the best energy producing/charging capacity.

The original plan was to do 32 panels (4 strings of 8) but the designer I have been working with has provided me with a wiring diagram that is somewhat confusing and uses 6 strings . I was also a little taken back that they weren't familiar with a pass through for a shingle roof into the attic, so I though I would reach out to this great group for some ideas before I pulled the trigger on this massive MASSIVE and multi-faceted project.

While I am familiar with general construction, I have always let others handle the electrical, even though I've learned a lot lately. Any advice or tips as far as string arrangement, junction box placement would be greatly appreciated. I will try to include all relative photos as well. Thank you for your time and consideration.

Roof pic^^^^^ The PV wire will pass through into the attic and travel to the opposite end of the house where we will be extending a room to house a "power shed" w/ batteries etc. 60KW of battery (2 racks of 6) and 4 inverters


Sun path relative to my general location.




82.44 x 40.86 x 1.37" actual panel size
My panel drawing. (The panels are a little larger on graph paper than their actual size)


Wiring diagram I received from the designer. ?????????????????!!!!!!!!!!!


(I'm hoping that these can be consolidated to 4 strings instead of six as they suggested) 1 string of 8 panels per inverter (which can handle up to 8000W of PV input each), plus hopefully easier install at the soladeck junction box.
I'm not sure if I have my junction box in the right location for this application either. I'm also not sure if 10 gauge PV wire is the right size for this. This has become a little overwhelming because I'm not sure I'm getting 100% best advice.


(I hope these panel specs are large enough to read)



Inverter layout. This will be connected to the 12 of the same brand EG4 batteries in 2 racks


Front of garage





Anyway, I know this might be a bit much to dump on this community, but I really didn't know where else to turn. Again, I am deeply grateful for any advice that can be given and will be happy to answer any more questions or provide relevant info. Kindest Regards, Jefferson

 

[sunshine_eggo]

I can't digest all that, and the blue and orange strings looks suspicious, but here are the rules:

1) ALL panels in a single string must be facing the same direction.
2) You can parallel strings of the same number of same model of panels on the same MPPT mostly willy-nilly without detriment.

e.g., a 6S array with all panels facing EAST could be paralleled with a 6S array with all panels facing WEST on the same MPPT. These would not interfere with each other except in EXTREME cases like multiple panels in one string are in complete darkness, i.e., you have covered them completely with cardboard.

When using multiple MPPT, things get more flexible in terms of panel count, provided you don't violate the above two rules. You could have an MPPT with a 6S2P array on it. You could have another MPPT with a 4S2P array on it. They would be completely independent of each other.

 

[Jefferson]

I can't digest all that, and the blue and orange strings looks suspicious, but here are the rules:

1) ALL panels in a single string must be facing the same direction.
2) You can parallel strings of the same number of same model of panels on the same MPPT mostly willy-nilly without detriment.

e.g., a 6S array with all panels facing EAST could be paralleled with a 6S array with all panels facing WEST on the same MPPT. These would not interfere with each other except in EXTREME cases like multiple panels in one string are in complete darkness, i.e., you have covered them completely with cardboard.

When using multiple MPPT, things get more flexible in terms of panel count, provided you don't violate the above two rules. You could have an MPPT with a 6S2P array on it. You could have another MPPT with a 4S2P array on it. They would be completely independent of each other.

Thanks for your reply and for the info. I think the blue (pyramid of 6) should be attached to the orange "L-Shape" panels that are off to the side since they are mainly facing north, As you may have noticed, the house is not exactly aligned with magnetic North.

I think I will redraw the panels with color groups as to how I think they should be arranged according to sky quadrant direction (if that makes any sense) and see what you guys think. I REALLY appreciate the input. Thanks again, and sorry for the jumbled mess of a wiring diagram.

 

[sunshine_eggo]

Do like numbers represent parallel faces and the thick arrow represent south?

 

[Jefferson]

Do like numbers represent parallel faces and the thick arrow represent south?

View attachment 111135

The numbers you have added represent the general directions of NSEW, but if you look at my panel drawing with magnetic N representation and compass, you'll see it's a little offset. And yes, the arrow you drew represents true South, Hope that answers your question. Thanks again!

 

[sunshine_eggo]

I was trying to establish if the faces labeled #1, #2, #3 and #4 were all the same pitch and facing, i.e., are all faces labeled #1 parallel to each other?

 

[Jefferson]

I was trying to establish if the faces labeled #1, #2, #3 and #4 were all the same pitch and facing, i.e., are all faces labeled #1 parallel to each other?

Sorry, they are all the same facing, but the pitch on the tiny roof area by the garage that has the "L-shape" 2 panel config is at a steeper pitch. You can probably notice it from the photo of the front of the garage. Hope this helps.

 

[sunshine_eggo]

These are the areas I would be looking at bounded by red lines:



Additionally, note that the EG4 inverters are going to consume about 350-400W continuously. That's almost two of the 12 batteries you have. Additionally, about 2000W of panels will be dedicated to replenishing the inverter's consumption. In other words, you will only have the capacity of 10 batteries for actual loads, and you won't be able to use the first 2000W of your array for loads.

That's the hidden cost of these "cheap" inverters. They're costing you an additional $3K in batteries and about $1K in PV you can't use.

Given the very unfavorable orientation and shading conditions, I would be looking at massively over-paneling as much as possible. If you have a sensible surface for a panel, put one there.

I suspect that winter production is going to suffer substantially.

 

[wattmatters]

Find some good local installers of PV systems and get multiple quotes.

I think you are better to stick with quality grid tied inverters like Fronius, SMA etc, or probably should be considering an Enphase microinverter system. If going with a string PV system then choose a hybrid version of a grid tied inverter or go with an AC coupled battery system with an Enphase PV system.

 

[Jefferson]

These are the areas I would be looking at bounded by red lines:

View attachment 111160

Additionally, note that the EG4 inverters are going to consume about 350-400W continuously. That's almost two of the 12 batteries you have. Additionally, about 2000W of panels will be dedicated to replenishing the inverter's consumption. In other words, you will only have the capacity of 10 batteries for actual loads, and you won't be able to use the first 2000W of your array for loads.

That's the hidden cost of these "cheap" inverters. They're costing you an additional $3K in batteries and about $1K in PV you can't use.

Given the very unfavorable orientation and shading conditions, I would be looking at massively over-paneling as much as possible. If you have a sensible surface for a panel, put one there.

I suspect that winter production is going to suffer substantially.

Wow! Firstly, THANK YOU for investing the time to map out the rooftop and analyse the situation. Secondly, I had no idea about the inverter consumption. They conveniently failed to mention that. I guess it's back to the drawing board for me. This may not even be feasible at all with the amount of trees that surround the house.
Since I don't have an optimizer setup, any amount of shading is going to knock that entire string down, judging from my limited knowledge.

I figured if I could get 12,800W over the garage (conservatively) and then have that knocked down to about 9kw with the 65-85% efficiency due to the orientation of N,E,W in the sky, that I might be doing ok, but now I'm going to have to seriously re-think the whole thing.

Seriously, thank you for your generosity of time and knowledge. I'm still reeling from the info you shared, but I'm still grateful.

 

[sunshine_eggo]

Wow! Firstly, THANK YOU for investing the time to map out the rooftop and analyse the situation. Secondly, I had no idea about the inverter consumption. They conveniently failed to mention that. I guess it's back to the drawing board for me. This may not even be feasible at all with the amount of trees that surround the house.

Note that I assumed they were 6kW 48V units. If they are 3kW units, they'll burn about half.

Since I don't have an optimizer setup, any amount of shading is going to knock that entire string down, judging from my limited knowledge.

It's not that bad. Panels have internal bypass diodes where a shaded panel/portion of a panel is essentially taken out of the circuit allowing the rest of the string to perform well. Optimizers

I figured if I could get 12,800W over the garage (conservatively) and then have that knocked down to about 9kw with the 65-85% efficiency due to the orientation of N,E,W in the sky, that I might be doing ok, but now I'm going to have to seriously re-think the whole thing.

N facing arrays will get almost nothing in the winter.

You can quickly simulate a single facing array here:

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

It can't factor in shading, but it does factor in the last 30 years of weather data for the location.

Here's a 5kW Array tilted 20°N:



The "solar radiation" column is the number of solar hours you get, i.e., take the 6.57 in July and multiply it by 5kW. That's 32.9kWh of energy produced per day on average by a 5kW array. However, December takes a hit and drops to 7.7kWh of energy per day on average.

The winter sun in the southern hemisphere is coming in at about 73° angle.

The right column is the monthly kWh produced factoring in DC-AC conversion efficiency. For July, 733/31 = 23.6kWh/day

 

[Jefferson]

Find some good local installers of PV systems and get multiple quotes.

I think you are better to stick with quality grid tied inverters like Fronius, SMA etc, or probably should be considering an Enphase microinverter system. If going with a string PV system then choose a hybrid version of a grid tied inverter or go with an AC coupled battery system with an Enphase PV system.

Thanks Watt, they had talked to a couple of local companies which gave them quotes from 35 to 40,000 bucks with no battery backup. The reason I liked these inverters so much, (other than price) was that they were considered off grid, but they have transfer switches inside that flipped over to grid power when the power demand exceeded the capacity of the solar setup and would charge the batteries with AC.

I never wanted to get into a "grid-tied system" because the power companies make you jump through all sorts of hoops and they supposedly buy whatever minimal power you may put into the grid at wholesale prices, but then charge you retail for whatever you use from them. the savings or payoff was minimal. I wanted to give my elderly parents a chunk of cash and they could get a small loan for the rest and have a manageable setup.

Either way, the roof orientation is the same, and we would have no real power unless we built some giant ground based array or somehow attached it to the southern facing property line fence,

I've got a good construction guy who built that garage addition and can handle the panel install and a good electrician that can do all the wire management, so I'm not dealing with a large cumbersome company with a lot of overheard who is going to rip my head off price wise and I can still get the job done correctly. I'm currently looking at less than $37,000 with 60KW of battery backup plus install which would be minimal compared to having a solar company do it. Plus no permits and colonoscopies from the "authorities" if you know what I mean.....

 

[Jefferson]

Note that I assumed they were 6kW 48V units. If they are 3kW units, they'll burn about half.



It's not that bad. Panels have internal bypass diodes where a shaded panel/portion of a panel is essentially taken out of the circuit allowing the rest of the string to perform well. Optimizers



N facing arrays will get almost nothing in the winter.

You can quickly simulate a single facing array here:

PVWatts

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations

pvwatts.nrel.gov

It can't factor in shading, but it does factor in the last 30 years of weather data for the location.

Here's a 5kW Array tilted 20°N:

View attachment 111177

The "solar radiation" column is the number of solar hours you get, i.e., take the 6.57 in July and multiply it by 5kW. That's 32.9kWh of energy produced per day on average by a 5kW array. However, December takes a hit and drops to 7.7kWh of energy per day on average.

The winter sun in the southern hemisphere is coming in at about 73° angle.

The right column is the monthly kWh produced factoring in DC-AC conversion efficiency. For July, 733/31 = 23.6kWh/day

That's a very useful tool! You'd think a "solar designer" would have access to that when estimating a system for customers. It's going to take me a bit to understand how to apply it to our specific equipment but I will pursue it since I have come this far. I have to admit I was drawn in by the Will Prowse (sp?) EG4 server rack battery and inverter videos..(not that he was misleading or anything) It just looked like a fairly simple clean setup.
Thank you again for all your help!

 

[cs1234]

Plus no permits and colonoscopies from the "authorities" if you know what I mean.....

It's risky to do roof mounted panels without permits/inspections and ul listed equipment. Your parents homeowners insurance will likely not cover anything if something happens. You might also get fined by the various AHJ's for not following the rules.

 

[Jefferson]

It's risky to do roof mounted panels without permits/inspections and ul listed equipment. Your parents homeowners insurance will likely not cover anything if something happens. You might also get fined by the various AHJ's for not following the rules.

I understand and appreciate you bringing that up. They are not incorporated into the city of Austin but the job (if done) will be in complete compliance with fire and electrical code. The last thing I want to do is catch their house on fire.... What is an "AHJ"?

 

[cs1234]

I understand and appreciate you bringing that up. They are not incorporated into the city of Austin but the job (if done) will be in complete compliance with fire and electrical code. The last thing I want to do is catch their house on fire.... What is an "AHJ"?

Authority Having Jurisdiction.

Travis or Williamson county probably have rules and or permits required for roof mounted solar and connecting inverters into your home electrical panel. Following fire code and electrical code is good, but without those permits, if anything happens, including somebody getting hurt, you're parents are on their own legally and financially.

Using string inverters, and that many panels, the likelihood of something happening to the wiring and getting DC ARC faults increases significantly. Especially if your electrician/construction contractors aren't experienced with solar / high voltage DC work. Search the forums here for discussions on DC ARC faults.

You should also be wary of any plumber/electrician/roofer/hvac contractor that are willing to perform major work without permits. Their industries are regulated by rules they themselves often helped create and require permits for a variety of reasons. Why are they willing to do work without following the rules for you?

It's one thing to have an apprentice/journeyman plumber replace an existing hot water heater without a permit (as a side job to their regular employment) vs having a massive brand new solar system installation installed without permitting by an an electrician/roofer as a side job with no insurance coverage.

 

[Jefferson]

Authority Having Jurisdiction.

Travis or Williamson county probably have rules and or permits required for roof mounted solar and connecting inverters into your home electrical panel. Following fire code and electrical code is good, but without those permits, if anything happens, including somebody getting hurt, you're parents are on their own legally and financially.

Using string inverters, and that many panels, the likelihood of something happening to the wiring and getting DC ARC faults increases significantly. Especially if your electrician/construction contractors aren't experienced with solar / high voltage DC work. Search the forums here for discussions on DC ARC faults.

You should also be wary of any plumber/electrician/roofer/hvac contractor that are willing to perform major work without permits. Their industries are regulated by rules they themselves often helped create and require permits for a variety of reasons. Why are they willing to do work without following the rules for you?

It's one thing to have an apprentice/journeyman plumber replace an existing hot water heater without a permit (as a side job to their regular employment) vs having a massive brand new solar system installation installed without permitting by an an electrician/roofer as a side job with no insurance coverage.

All valid points that I completely agree with. My understanding from a neighbor who had a grid tied rooftop install done was that you did not have to pull permits. We had planned to have a licensed electrician do all the wire management and then have a master electrician inspect our work before we had the city come out to disconnect the meter and then have him connect the the whole contraption to the grid, (if that makes any sense) Thanks for the explanation!

 

[wattmatters]

The cost of rooftop solar PV installations is the USA is insane. I really don't know why it's so expensive there.

A 32 panel system, in the vicinity of 12-13 kW, installed on a home rooftop in Australia by licensed experienced solar professionals with full approvals from all relevant authorities using quality panels and inverters would cost circa US$7000 - US$10,000, with the upper price being an Enphase set up. Add maybe $US1,000-1,500 for a complex two storey roof.

I can see why people in the USA look at these off-grid systems instead.

The reason I liked these inverters so much, (other than price) was that they were considered off grid, but they have transfer switches inside that flipped over to grid power when the power demand exceeded the capacity of the solar setup and would charge the batteries with AC.

Just be aware that amount of utility power you can pass through these inverters has a limitation.

And you have learned you'll need to account for quite a decent amount of self consumption, so you'll need a decent chunk of PV capacity and storage just to cover for that.

e.g.
My little cheapy 48 V 4 kW off-grid inverter consumes ~45 W most of the time.
My 3-phase 10 kW grid-tied Fronius inverter overnight consumes <1 W.

I never wanted to get into a "grid-tied system" because the power companies make you jump through all sorts of hoops and they supposedly buy whatever minimal power you may put into the grid at wholesale prices, but then charge you retail for whatever you use from them. the savings or payoff was minimal.

Regulatory requirements obviously vary throughout the world. As to tariffs, we have similar. But because of the massive cost difference in installation, solar PV here makes very good financial sense. Grid tied battery systems not so much. They are still way too expensive by a factor of about three to make rational financial sense.

 

[cs1234]

Regulatory requirements obviously vary throughout the world. As to tariffs, we have similar. But because of the massive cost difference in installation, solar PV here makes very good financial sense. Grid tied battery systems not so much. They are still way too expensive by a factor of about three to make rational financial sense.

Don't worry, either the cost of batteries will go down, or the price of grid electricity will go up until it make sense.

 

[wattmatters]

Don't worry, either the cost of batteries will go down, or the price of grid electricity will go up until it make sense.

The cost of quality grid tied battery systems permitted to be installed on our grid has not fallen over the past five years, indeed they have gone up.

I'm not hold my breath that such systems will drop to less than 1/3rd of their current price any time soon.

Off-grid DIY, that's different.

As to energy prices, perhaps but in Australia we are a little more insulated from some of the more outrageous energy price changes going in say Europe. It's not been great but nothing like in the UK.

Plus all that happens is the value of exported energy all goes up, and what makes batteries viable is the import-export tariff differential.