Lean-to Shed Solar Power for Year Round Use

nicorellius

New Member
Very cool, things are getting clearer. Thank you both for the prompt replies! I really like the idea of a control box, but my understanding of these is a bit behind the curve.

One follow up:
Here's a 'combiner diagram' example for your 4 panels arranged in 2s2p + 24v Battery going thru a circuit breaker for ON/OFF. Crude/messy but hopefully get's the idea across.
I see that you are "combining" the positive and negative leads (2x of each) in the box. I was under the impression I needed MC4 Y/branch connectors for the parallel part (which would be 1x positive and 1x negative going in). Is there any advantage to doing it one way or the other? Or am I missing something else?
 

OffGridInTheCity

Solar Enthusiast
Very cool, things are getting clearer. Thank you both for the prompt replies! I really like the idea of a control box, but my understanding of these is a bit behind the curve.

One follow up:

I see that you are "combining" the positive and negative leads (2x of each) in the box. I was under the impression I needed MC4 Y/branch connectors for the parallel part (which would be 1x positive and 1x negative going in). Is there any advantage to doing it one way or the other? Or am I missing something else?
Great question!

The MC4 Y/Branch connectors would 'combine' out at the panels and 2 wires would run into the control box. The diagram has 4 wires running to the control box... with a circuit breaker on each string... and then combining.

If the distance if long (like 100-200ft) then combining at the panels saves $ / wire. But if the panels are close - then 4 wires is not big $ compared to 2 wires. For my trailer's 4 panels - the longest wire is 7 ft, so 4 wires are cheap/easy. For my house, I have the combiner box / breakers out the panels - 1 breaker for each string (30 wires) - and then 6 wires from there to the charge controllers 150ft away.

For me, I prefer running the 4 wires with a circuit breaker on each string at the control box to allow me to turn on/off each string independently (or both to disable PV power while I work on things) so I can check each string in isolation to verify it's working. If you do the 7/Branch it's all or nothing by the time it gets to the control box / PIP.

There's no wrong choice here - its just a nuance I'm sharing :)

Some people use the Y/Branch out at the panels and run the wires directly to the PIP - and don't have an intermediate control box or circuit breaker near the PIP. I (personally) prefer having a control box with breakers - at the equipment panel. If you did Y/Branch and only have 2 wires coming in - you could still do a breaker just before the PIP so that you could disable the current flow to work on things. IF you do 1 breaker, then it's easy to do 2 and have that diagnostic option on each string.

You may get other comments/advise and I do not claim 'my way' is the only or best way - just sharing a perspective from being further down the road on all this. Take it all in and choose what makes sense for you! :)
 
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nicorellius

New Member
The MC4 Y/Branch connectors would 'combine' out at the panels and 2 wires would run into the control box. The diagram has 4 wires running to the control box... with a circuit breaker on each string... and then combining.
Perfect answer, thank you. I figured this was the reasoning but wanted to confirm.

One other reason I was asking is that I'm about ready to buy solar panel wiring and if I combine with the Ys closer to the panels (which I'm not even sure is a good idea), I would run two leads from the array on the roof to the combiner and LV2424. Your method makes good sense, but would require more 10 gauge wire and connectors (not exactly 2x as much, but maybe 1.5x as much).

Here's a rough sketch I've been working on. If I don't use Y/branches, I'll need to reconfigure my shopping list ;-)

1626900600519.png
 

OffGridInTheCity

Solar Enthusiast
Yes sir - looks good. From a wire perspective - I'm sure you'll be < 10a per string. So you can go down to 14awg (15a rated) if you wanted 4 wires and keep the $ down. However - I don't know your physical setup....

One of the reasons I use 10awg is because 'PV wire' is typically UV protected whereas home 14awg (15a) Romex is not - and you want exposed wire to be fully protected. Another reason if it's a long distance (100ft or more) then 10awg running <10a or even if you combine at <20a - will have a little less power loss than if you use 14/12awg.
 
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nicorellius

New Member
I priced out 10 AWG (UV resistant, etc) for the solar wire and it's a bit more expensive than 12 AWG, but it seems the most versatile in the long run. And if there is no reason aside from a few more bucks, it seems prudent. Especially since I'm not really dealing with all that long of lengths.

@OffGridInTheCity When you say PIP, what do you mean? The LV2424? What does that stand for, acronym-wise?

I'm leaning towards starting out without a "control box" as it adds a bit of cost to the overall project (box + wires + breakers ~ $300). I've got a pretty clear picture how to do this. And I can always save up for a control box/wires/breakers and install those in phase 2. Given that, and the size of this system, what is the minimum protection I need for fuses/breakers? I guess I'm still a bit unclear on when/where to use fuses and/or breakers.

As a reference, in the LV2424 video in which Will presents the hand truck solar system, he uses a simple 125 A circuit protector between the battery bank and the LV2424 (on the positive lead). This video seems to show a system that is very similar to what I'm going for.
 

OffGridInTheCity

Solar Enthusiast
@OffGridInTheCity When you say PIP, what do you mean? The LV2424? What does that stand for, acronym-wise?
Yes. As I understand it - "MPP Solar" is the overall company. PIP is a short-hand term for *off-grid* models as apposed to hybrid models. The LV2424 is an off-grid model.

I'm leaning towards starting out without a "control box" as it adds a bit of cost to the overall project (box + wires + breakers ~ $300). I've got a pretty clear picture how to do this. And I can always save up for a control box/wires/breakers and install those in phase 2. Given that, and the size of this system, what is the minimum protection I need for fuses/breakers? I guess I'm still a bit unclear on when/where to use fuses and/or breakers.
Most jurisdictions require a fireman's quick-disconnect (an off switch or breaker) near the panels on the outside. This can act as the off switch for you to work on things on the inside in lieu of a switch near the PIP - you just have to walk outside to toggle it. For me - its much easier to have a switch(breaker) right next to the PIP.

You should also
1) Bond/ground the panels/
2) Have a surge (lightning) arrestor on the panel wires coming in https://www.solar-electric.com/mnspd600.html

But no judgements - my goal is just to share info. For me - it took some operational time for all these things - ground, lightning arrestor, circuit breakers, control box - I ignored them all until I had some operational experience and circled back on things. Perhaps the key thing at this point is to leave room for it in your setup for the future. :)

As a reference, in the LV2424 video in which Will presents the hand truck solar system, he uses a simple 125 A circuit protector between the battery bank and the LV2424 (on the positive lead). This video seems to show a system that is very similar to what I'm going for.
OK - 125a will give you 25a headroom if you overload the Inverter for very long.

The *key* thing here is to allow the max current to the LV2424 that it can use but low enough to blow if:
1) A short occurs. The PIP could melt inside ?!? (not likely) or you could touch wires - e.g. if a short occurs you want the breaker to flip before....
2) Do not allow so much current the wire will melt! If you use 2/0 wire, you could easily go much higher than 125a.

As you get this system up and running - I'm hoping you'll post a pic or 2 - it will be fun to read that you have it going :)
 

nicorellius

New Member
@OffGridInTheCity I need to remind myself to buy you a beer (or suitable beverage); your assistance has been invaluable so far. I've been building software for 15 years, so I use the StackExchange boards (StackOverflow specifically) more than any other Q&A forums. I can definitely say that my experience on this forum so far is more/equally responsive and informative than SE. This is saying a lot since those boards get millions of views regularly (50+ billion total from recent query). Big thanks to @Will Prowse, as well, for all your efforts.

Most jurisdictions require a fireman's quick-disconnect (an off switch or breaker) near the panels on the outside. This can act as the off switch for you to work on things on the inside in lieu of a switch near the PIP - you just have to walk outside to toggle it.
You should also
1) Bond/ground the panels
2) Have a surge (lightning) arrestor on the panels wires coming in https://www.solar-electric.com/mnspd600.html

But I'm not an inspector, its your DIY build, no judgements on my part. For me - it took some operational time for all these things - ground, lightning arrestor, circuit breakers, control box - to make sense. Perhaps the key thing at this point is to leave room for it

I do have an 8 foot ground rod I intend to install by the shed for proper ground. I can use this to ground whatever I need to. The surge/lightning protection I hadn't even considered, so... more research is needed. But, I agree, setting something up with room to grow is a good idea. I get the impression that best practices dictate protection at every point in the system, but also that it's common to start with the basics and implement the rest as you are comfortable doing so. I really want an operational system ASAP so I'm begining to chomp at the bit.

What continues to amaze me (as is the case with many technical projects) is that when you start to scope the project, it can seem straight forward: solar panels, charge controller, inverter, and batteries. Which might work fine in a simple use case... but of course, depending on the actual needs of your system, the scope creeps and you realize that the actual required components are more than you thought ;/

I hope to start putting this system together in the next week or so. I've got most everything either in my possession or ordered and on the way. Planning to build my own panel mounts, so we'll see how this goes. The brackets and hardware for tilted mounting seem expensive.

I'll definitely post pictures and I'm sure I'll flood this thread with plenty more newb questions!
 
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