Question about wiring 12V panels to a 24V grid tie inverter

[Travis76]

Hi,

I have a couple questions and I'd like to thank anyone who offers their insight in advance. I'm planning on building a small home on my land in the next year or so, and for the time being, I wanted to install a small system where I'm living now. I'm most concerned with reducing my electric bill.

Here's what I'm working with:

(32) Sunman E-Arche SMS105M-2X12 mono-si flexible panels
Rated Maximum Power 105 W
Current at Pmax 8.27 A
Voltage at Pmax 12.7 V
Open CIrcuit Voltage 15.4 V
Maximum System Voltage 600V
Maximum Series Fuse Rating 20 A

SolarEpic Smart Grid Tie Inverter YC-B101
1000W
DC Input: 20-45VDC
AC Output: 115VAC(90-140)

Cantex 8X8X5 PVC Junction Box (Empty)

100 Amp Shut Off

(Don't think I'll need this for now, but I included it just in case)
EPEVER Tracer 4210AN MPPT Charge Controller
Voltage 12/24V/LI
Current 40Amp
Max PVoltage 100V
Max PV Input Power 520 W 12V 1040W 24V

I realize that the equipment I have isn't the best, especially the grid tie inverter. However, I want to get the most life out of it that I can and I was wondering how many panels/watts I can safely connect to it?
Do you recommend that I purchase branch connectors or a combiner box and if so, which one do you recommend?
Since the grid tie inverter operates at 20-45VDC, how should I wire the panels together for best results?
The distance between the panels and the wall socket (to plug in the grid tie inverter) is about 15ft. What wiring will I need?

[sdold]

Hi Travis and welcome to solar panel talk.

The problem with "plug-in" grid-tie inverters is that they can be dangerous and can also cause trouble with insurance and the power company. It doesn't appear that the inverter is UL 1741 listed for use as a grid-connected inverter. You didn't give your location but this would violate electrical codes in nearly all of the US, so a fire might not be covered by insurance. Not being listed means it likely won't be approved by your power company since it hasn't been proven safe for workers on the lines during power outages. This "bootleg" installation can get you in hot water with the power company if they catch you backfeeding power without an agreement. Even if they don't notice, it might actually cost you money as you may be charged for power regardless of direction of flow, depending on the meter.

That's one of the more powerful "plug in" grid tie inverters I've seen, and can put 8A on the circuit you've plugged into that is not protected by a breaker. Therefore you could have up to around 23A flowing through a branch circuit protected by only a 15A breaker, without that breaker tripping, so there's a real fire hazard there. If it were me, with all of these negatives, I would abandon this plan. A few dollars a month savings on the power bill just isn't worth it.

See what others here say, but if it was me I'd cut my losses and sell everything and then look into building a good, approved system for the new home if your power company allows it and rates and availability of net metering favor doing so. Solar equipment is getting cheaper and you might be surprised at what good stuff costs if you haven't priced equipment in a while.

Again, welcome.

[Travis76]

I appreciate the input, and my family's safety is priority number 1, so I'll follow your advice. If I wanted to set up a small 24V off grid battery backup system for my shed, using some of my panels and the 40A MPPT charge controller listed above, along with two 12V 100 AH marine batteries, how many panels do you recommend that I use and what's the best way to wire them?

[Markyrocks69]

I appreciate the input, and my family's safety is priority number 1, so I'll follow your advice. If I wanted to set up a small 24V off grid battery backup system for my shed, using some of my panels and the 40A MPPT charge controller listed above, along with two 12V 100 AH marine batteries, how many panels do you recommend that I use and what's the best way to wire them?

I concur with sdold on many points. I will however say that it looks like that inverter does have some kinda island protection. That was the first thing i thought of that it came with it's own suicide cord, but apparently it must not be live b4 you actually plug it. I'd say that the safest way to hook this up would probably to backfeed a breaker in it's own subpanel? Just seems like alot of effort for... this. But as was said the power company would be very upset if you used this ect.

As far as the above question it would really depend on what the nominal voltage of charge controller.

But I mean seriously 1000 watts? That's about enough juice to run a couple lights and maybe an alarm clock radio. It would be much easier to just buy a 1000 watt inverter that connects to a cigarette lighter in your truck and just run an extension cord when the power goes out. What your describing sounds like way to much effort for very small reward that could be had in much easier ways. Also that being said this inverter won't (or shouldn't) work if the grid is out, hence island protection

[inetdog]

I concur with sdold on many points. I will however say that it looks like that inverter does have some kinda island protection. That was the first thing i thought of that it came with it's own suicide cord, but apparently it must not be live b4 you actually plug it. I'd say that the safest way to hook this up would probably to backfeed a breaker in it's own subpanel? Just seems like alot of effort for... this. But as was said the power company would be very upset if you used this ect.

As far as the above question it would really depend on what the nominal voltage of charge controller.

But I mean seriously 1000 watts? That's about enough juice to run a couple lights and maybe an alarm clock radio. It would be much easier to just buy a 1000 watt inverter that connects to a cigarette lighter in your truck and just run an extension cord when the power goes out. What your describing sounds like way to much effort for very small reward that could be had in much easier ways. Also that being said this inverter won't (or shouldn't) work if the grid is out, hence island protection

The power port (cigarette lighter socket) in most cars and trucks is limited to 10A or at most 20A and is deenergized when the ignition is off. That would allow at the very best a 200W inverter to be used.
Regarding 12V panels, they are far more costly per watt than higher voltage "grid tie" panels. As long as you use an MPPT Charge Controller the panel voltage can be much higher than the system battery voltage.

[Markyrocks69]

The power port (cigarette lighter socket) in most cars and trucks is limited to 10A or at most 20A and is deenergized when the ignition is off. That would allow at the very best a 200W inverter to be used.
Regarding 12V panels, they are far more costly per watt than higher voltage "grid tie" panels. As long as you use an MPPT Charge Controller the panel voltage can be much higher than the system battery voltage.

Ok then buy one that you connect right to the battery terminals....

[Travis76]

I will however say that it looks like that inverter does have some kinda island protection.

Yes, it does have island protection. It won't operate unless it detects a grid.

But as was said the power company would be very upset if you used this ect.

I'm averaging 2000 KWH a month. Without zeroing out or backfeeding the grid, do you think the power company would detect a small system like this?

But I mean seriously 1000 watts? That's about enough juice to run a couple lights and maybe an alarm clock radio.

Yeah, 1000 Watts is relatively insignificant, but even if I could lower my electric bill $20 a month, it adds up over the years. Plus, if it works well, for $100 I could always add another grid tie inverter. I bought 32 of these panels at auction for $600, and I was hoping to put some of them to use.

Also that being said this inverter won't (or shouldn't) work if the grid is out, hence island protection

In an emergency situation, if you remove the grid tie inverter from the grid, I've heard that you can trick the inverter's island protection with a couple small batteries and a pure sine wave inverter. Don't know if that information is accurate though.

[ButchDeal]

I'm averaging 2000 KWH a month. Without zeroing out or backfeeding the grid, do you think the power company would detect a small system like this?

It is illegal, the utility is the smallest of your concern, they can disconnect you permanently and/or give you a fine.

In an emergency situation, if you remove the grid tie inverter from the grid, I've heard that you can trick the inverter's island protection with a couple small batteries and a pure sine wave inverter. Don't know if that information is accurate though.

There are a lot of (stupid) things that people say on the internet. This is a very dangerous thing and NO it will not work. You can do it correctly with a LARGE bimodal inverter that is designed for it and a large battery, but NOT with a small off grid inverter and battery. It will not work, if you did get it to work your small battery would be the dump for your large grid tie system for a few seconds and the smoke would get out. Luckily grid tie inverter are smarter than this and will not sync to one.

[Travis76]

Illegal, fire risk, note taken. Since the plug n play grid tie inverter is a no go, I'd like to build a small off-grid battery back up system for my shed. Not sure how many panels I should use or the best way to connect them. Not sure if I need a combiner box or if branch connectors would be sufficient. A wiring diagram would be greatly appreciated.

Here's what I already have for this project.

PowerDrive PD3000 / 3000 Watt inverter

Two 100 AH deep cycle / marine batteries - If recommended, I could add to or upgrade the batteries.

100A safety switch

100A LCD energy meter

Cantex 8X8X5 PVC Junction Box (Empty)

(32) Sunman E-Arche SMS105M-2X12 mono-si flexible panels
Rated Maximum Power 105 W
Current at Pmax 8.27 A
Voltage at Pmax 12.7 V
Open CIrcuit Voltage 15.4 V
Maximum System Voltage 600V
Maximum Series Fuse Rating 20 A

EPEVER Tracer 4210AN MPPT Charge Controller
Negative Grounded
Voltage 12/24V/LI
Current 40Amp
Max PVoltage 100V
Max PV Input Power 520 W 12V 1040W 24V

[Mike90250]

From your list of things, I'd use 3 of your 12.7v panels in series, which would produce 38.1Vmp @ 8A It will be very close to 50Voc, so make sure your charge controller can handle 50 or 60V

A true (not counterfeit) MPPT controller will down-convert this to about 14.5v @ 20A for charging the batteries in ideal conditions. In cloudy weather, you will not get much at all

Depending on your loads, the solar may or may not be able to completely recharge the batteries in one day

If you used 24V battery, you could install a pair of 3 panels in parallel 3S,2P for your array and harvest twice the power, but you would need a 24V inverter

And then you should always put fuses on the cables near the battery to prevent a short circuit from starting a fire. This page has a chart

https://lugsdirect.com/WireCurrentAmpacitiesNEC-Table-301-16.htm

that says what safe amps through a wire are.