PV wiring when in shade


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Sonic01

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Hi All,

I had a question about the best setup for an array that gets a bit of shade each day - I've done what research I can and believe I know what the best solution would be, but I'd really appreciate your opinions on this.

I've made this lovely crude drawing showing my intended array setup, as you can see 6 of the 14 panels get shaded from about 12pm onwards, it starts with just the top left corner of the top left panel on the pitched roof but as the day goes on it grows to cover most of the 6 panels at once. by about 6pm its just covering the middle 3 panels.

The obvious solution would be to remove the chimney (its not even real anymore, the stack below it inside the building has been removed) but due to local laws I can't remove it from the roof.


Now from what I've read, any shading in any series setup will ruin the performance of the whole array. I understand that doing the entire thing in parallel reduces the impact of the shading but no 48v system can work off a 30v PV array. I also read that panels are less efficient in parallel than in series as well.

Even if the shaded 6 panels are all connected in parallel with the rest of the array in series, the group of 6 in parallel will still negatively effect the rest of the string won't they?

To this effect from what I've read in other posts on here and a quick google around it seems the most efficient way is to split the shaded and non-shaded panels into 2 separate strings with their own charge controller? So for example, have the 6 shaded panels in series connected to one CT, and the other 8 panels in series connected to another CT?

I see the MPP Solar "MAX" series has 2 PV inputs, and it looks they they both have their own current inputs (18a each it says) so I'm guessing this means it has 2 CT's inside?

 

Korishan

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To this effect from what I've read in other posts on here and a quick google around it seems the most efficient way is to split the shaded and non-shaded panels into 2 separate strings with their own charge controller? So for example, have the 6 shaded panels in series connected to one CT, and the other 8 panels in series connected to another CT?
This is what I was going to suggest as I was reading the backstory. Splitting it is pretty much the best option, without going stupid expensive. The other option is that each panel has it's own micro-inverter.
MI's have their own MPPT controller to get the most out of the panel. But you're looking at spending another $100+ for each panel for a decent MI. And then you need the controller as well to convert it back to DC for charging. I think a regular Charger Controller that takes AC input would work fine here, but not entirely sure.

The other option is to raise the panels higher so they see less shade. But that might not be feasible, or legal.
 

Sonic01

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This is what I was going to suggest as I was reading the backstory. Splitting it is pretty much the best option, without going stupid expensive. The other option is that each panel has it's own micro-inverter.
MI's have their own MPPT controller to get the most out of the panel. But you're looking at spending another $100+ for each panel for a decent MI. And then you need the controller as well to convert it back to DC for charging. I think a regular Charger Controller that takes AC input would work fine here, but not entirely sure.

The other option is to raise the panels higher so they see less shade. But that might not be feasible, or legal.
Thanks for confirming, I've already emailed MPP to ask them to confirm the MAX series 2x PV inputs actually has 2x CT's behind them.

I did think about the MI approach but as you say, this adds a cost of £1400 to my install, and how would you wire the 14x MI 230v outputs to the charger, could you just connect them all in parallel to the CT AC input? I also couldn't find any kind of MPPT CT device that supports this, I'm guessing a standard 48v lithium-ion charger wouldn't work as the input wattage would be variable so you'd have to find an MPPT charger that accepts 230v AC input? I imagine even if I did find a device that supports this it would be an expensive addition to my PIP/Inverter. It also means I'd lose the monitoring I already have via Solar-Assistant.

Lastly raising the panels isn't an option sadly, due to multiple laws, plus high winds in my area.
 

Korishan

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how would you wire the 14x MI 230v outputs to the charger, could you just connect them all in parallel to the CT AC input?
You have to use an MI specific charge controller. So it's another piece of hardware.
The other option is that the MI's output to house voltage. So they are grid-tied. This allows them to work in parallel with grid voltages, and lowers current consumed on the grid side.
As long as they sense AC house voltage/signal, they'll keep working. Which means they would work on the AC output side of the other inverters.
 

Sonic01

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Yeah I'll skip on the MI approach I think, it over complicates and overprices the setup.

One other thought I had, the flat roof panels are obviously a bit higher than the lowest unshaded row of pitched panels, they're also likely to be at a different angle - 15 degrees on the flat vs 35 degrees on the pitched. Do you think this will cause any big problems? I guess the roof panels being at 15 will mean the sun will have to be a bit higher for them to get full benefit, so by that time it will be hitting the lowest pitched row anyway? I'm not sure how much time it takes between the sun covering all roof panels and it covering the lowest pitched row... I'll see if I can wake up early enough to monitor that this week.
 

paddy72

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Just for curiosity: what local law prohibits to remove a chimney that isn't used any more?
Is this a special style old house that needs to be conservated as is for historic reasons or is it just because other houses in the street have the same kind of chimney?
Don't energy saving and environment protections have more priority over some old chimney regulations? Just wondering. I would really dig deeper here at your local authority than investing several 100 bucks in a special solution. I would also involve local media / press if nessecary... ;)
 

Korishan

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Don't energy saving and environment protections have more priority over some old chimney regulations?
He states that the fireplace was removed and the chimney was sealed inside. So there's no energy losses through the chimney.

If it's a case of historic reasons because of where the house is located, getting the news/media involved is gonna be pointless, it won't do anything. Same is true if where they live the Home Owners Association has the right to dictate the removal. Altho, the HOA saying they can't remove the chimney, but allows solar panels, is kinda odd if they are the ones making those provisions.
 

Sonic01

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The plot is 140 years old but its not the age that created the law, its because its a terrace row. The law says you're not allowed to make changes to a house that causes it to be structurally deviated from the rest of the terraced plot when viewed from the street level.

Installing your own solar panels and PW is also a legal grey area so I'd rather not draw unnecessary attention. There are even specific laws for flat roof installs here that mean many companies wont do them as it becomes a technical and legal minefield.

MPP Solar confirmed the MAX series has 2x CT's behind its 2x PV inputs so seems that the simple solution for me, just trying to plan the best way to wire the circuits in regards to the bottom pitched row being lower than the 5 panels on the plat roof. I imagine I'll stick with my original plan of the 6 shaded in 1 circuit and 5 roof and 3 lower pitched panels in another circuit.
 

Sonic01

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The plot is 140 years old but its not the age that created the law, its because its a terrace row. The law says you're not allowed to make changes to a house that causes it to be structurally deviated from the rest of the terraced plot when viewed from the street level.

Hence why during my restructuring I was able to fully remove the chimney from the rear of the house and give myself a nice flat roof to stick some new panels on :)

Installing your own solar panels and PW is also a legal grey area so I'd rather not draw unnecessary attention. There are even specific laws for flat roof installs here that mean many companies wont do them as it becomes a technical and legal minefield.

MPP Solar confirmed the MAX series has 2x CT's behind its 2x PV inputs so seems that the simple solution for me, just trying to plan the best way to wire the circuits in regards to the bottom pitched row being lower than the 5 panels on the plat roof. I imagine I'll stick with my original plan of the 6 shaded in 1 circuit and 5 roof and 3 lower pitched panels in another circuit.

He states that the fireplace was removed and the chimney was sealed inside. So there's no energy losses through the chimney.

It's more than just being sealed, the entire stack has been removed from inside the house. That chimney on the roof is just a facade, there's actually nothing under it, it goes inside the house about 1 meter (into a storage space under the pitched roof) and I actually had to pay for a structural engineer to calculate the weight and steel supports needed to hold the useless fake chimney up on the roof.

It's a joke right? paying extra to keep something you don't even want.
 

paddy72

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If it's a legal grey area i would make sure the PV is accepted before i would invest or even install the panels ;)
If PV is allowed i would ask if it wouldn't be an option to optimize the law for PV usage if its only the chimney.
What does 'terrace row' mean? Is it a flat building with flat roof what we call bungalow in germany?
140 years is a lot and could be historically protected if the houses in the whole area look the same. Is it in GB?
Anyway - new times, new technology, new problems (ecological impact, climate change) lead to new laws...

I was not meaning energy losses from the chimney, i meant to say we have to use ecological technology to protect the climate...
If local laws prohibit or only slows down use of PV, we cant achieve a climate change.
 

Sonic01

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If it's a legal grey area i would make sure the PV is accepted before i would invest or even install the panels ;)
If PV is allowed i would ask if it wouldn't be an option to optimize the law for PV usage if its only the chimney.
What does 'terrace row' mean? Is it a flat building with flat roof what we call bungalow in germany?
140 years is a lot and could be historically protected if the houses in the whole area look the same. Is it in GB?
Anyway - new times, new technology, new problems (ecological impact, climate change) lead to new laws...

I was not meaning energy losses from the chimney, i meant to say we have to use ecological technology to protect the climate...
If local laws prohibit or only slows down use of PV, we cant achieve a climate change.

there isn't really any way the council would know I have them, they're only visible once you're on top of the 3rd floor roof and I imagine I'd have to do something pretty bad to cause them to want to inspect my roof 😅 though I think its fine if they're installed using ballast mounts as this way they're not actually fixed to the building.

140 years isnt that old for a house in the UK, listed buildings as you're thinking of are typically over 200 years old. My building isn't one of those, I'd know if it was.

These are terraced houses:


It's not a matter I want to discuss with them tbh, apart from the fact I don't have the time or the energy for that fight I'd just prefer if the government left me alone as much as possible.
 

OffGridInTheCity

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there isn't really any way the council would know I have them, they're only visible once you're on top of the 3rd floor roof and I imagine I'd have to do something pretty bad to cause them to want to inspect my roof 😅
I'm sure you've thought of this (don't mean to sound condescending) but what's the issues with raising them higher but still not visible - e.g. higher = less shadow perhaps?
And along the crazy idea track, slant them down-sun from the chimney... e.g. bad angle but less shade and somehow get a net positive?
Enjoying following your issue - forgive the crazy comments, just thinking out loud :)

I know what you mean by not wanting a fight. I put a ground array in my back yard but kept it at only 17deg rise from horizontal (not optimal) so it would not stick up or be dominate to the sight-line and annoy my neighbors. Annoyed neighbors is usually a complaint to downtown.
 
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Korishan

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Yeah, if the law states "visible from the road front", you have quite a bit of wiggle room to do solar on the roof considering they are pretty flat. You have the advantage the building is multi-story, making it even more difficult to see the roof top.
 

paddy72

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O.k. - understood the problem. 'terraced houses' would be called 'Reihenhäuser' in Germany ;-)
Yes, if it looks like this the problem is clear - i think i wouldn't mention it either :cool:

In Germany they start to enforce laws for new houses they must have a PV-panel roof of a certain wattage.
Maybe sometime they will change the law in UK too and force ppl to take away their chimneys to make room for PV ;)
 

Sonic01

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Think you guys are getting a bit mixed up, the shaded pitched roof panels are facing the road so those are the ones visible from street level. the panels couldn't be raised - they're allowed to be up to 20cm above the highest part of the roof (with chimneys excluded of course :p) and they're already at this level.

Also structure support would be an issue, winds in my area reached 200kmh this year. I'm never going to take that risk.

I already have panels up there at the moment, in the positions of the lowest and middle pitched rows, and they do perform reasonably well. since currently my PIP load is low the 1.5kw PV typically fills my PW by about 11-12am so its normally maxed out before the shading starts, but soon im integrating the whole system into my house so the load will greatly be increases hence I'm looking to optimise this issue any way I can.

The cheapest easiest solution seems to be the 2 circuit 2 CT option. otherwise I'm looking at a dispute with the local council which I really don't want. I would also have to pay builders to remove the chimney and repair the roof afterwards which would likely cost around £2000, so also makes it less worth it.

It's an interesting question though, the gov here are starting to push PV heavily now so I'm wondering if their stance has/will change on this. I'm not sure how they'd approach it, they'd either have to remove or modify the current aesthetics law.
 

Korishan

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It's an interesting question though, the gov here are starting to push PV heavily now so I'm wondering if their stance has/will change on this. I'm not sure how they'd approach it, they'd either have to remove or modify the current aesthetics law.
Yeah, they are getting themselves in a "catch-22" situation. It's good that you are aware of the various regulations, even the conflicting ones, and the costs involved. You've done your homework.

winds in my area reached 200kmh this year.
😲

Another option you could do is use 2 controllers on the shaded area alone. This would split that section up into 2 zones. So as the shading starts to cover one zone, the other can still chooch at full speed until shade from the chimney starts to reach it.
Even with MPPT, shading will effect the output. So minimizing how many panels are shaded for each controller would be key to get the most of the system.
Lower wattage/voltage MPPT controllers are available for a lot less cost. So that is another option.
 

Redpacket

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Does the shade change a different times of the year?
Will your controllers run with only two panels in series? (my Victron MPPT's do nicely)
If so you could make "vertical pairs" (per diagram, not roof pitch) on the pitched roof shaded area.
This way you'd get full power per pair until the shade hit that pair.
You could pair up the rest with one slightly less idea pair (1x flat + 1x pitch roof panel).
Basically parallel all pairs, add isolation diodes if you like.
Shade panels do not pull current from sun panels (only small leakage, especially with diodes) so no harm there.
It's the current that varies from a shaded panel, not much voltage change unless in a string.

Eg something like this:
panel layout.png
 
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Korishan

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Basically parallel all pairs, add isolation diodes if you like.
Panels "should" have built in diodes for this reason. But a good idea to check either way. Good layout/idea for connecting the controllers.
 

Sonic01

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Another option you could do is use 2 controllers on the shaded area alone. This would split that section up into 2 zones. So as the shading starts to cover one zone, the other can still chooch at full speed until shade from the chimney starts to reach it.
Even with MPPT, shading will effect the output. So minimizing how many panels are shaded for each controller would be key to get the most of the system.
Lower wattage/voltage MPPT controllers are available for a lot less cost. So that is another option.

Hm yeah that's an idea, though it brings a few other problems. I'd had to run extra PV cabling from inside the house to the roof, there's additional costs of the extra CT's and cabling and lastly it means I wouldn't be able to monitor that circuit with my Solar-Assistant.

Does the shade change a different times of the year?
Will your controllers run with only two panels in series? (my Victron MPPT's do nicely)
If so you could make "vertical pairs" (per diagram, not roof pitch) on the pitched roof shaded area.
This way you'd get full power per pair until the shade hit that pair.
You could pair up the rest with one slightly less idea pair (1x flat + 1x pitch roof panel).
Basically parallel all pairs, add isolation diodes if you like.
Shade panels do not pull current from sun panels (only small leakage, especially with diodes) so no harm there.
It's the current that varies from a shaded panel, not much voltage change unless in a string.

Eg something like this:
View attachment 27461

Yes the shade will change throughout the year, tbh I'm not sure how it would sit during the winter - with the amount of sun we get in the winters it's not really worth trying to optimise usage during that period. we pretty much have to except generation will be low.

That's a clever idea, break the whole thing up as pairs, though the 48v MPP Solar PIP's only except the lowest of 120v so would need 4s minimum. that or i end up with an army of small CT's.
 

Redpacket

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The Victron units take Vbatt + 5V to start.... If they are all paralleled, you might only need one MPPT depending on total panel wattage?
 
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