Need someone to check me on this Please.

[Robbober]

Been working on this going on 3 years now, getting things when i can, and reading and watching videos but would like my diagram checked. always better to be checked and corrected them to burn everything up or worse. I do have other things I am not showing like 4 new 12v LifePO4 100AH battery's that I will wire to 24v, I know should have gotten bigger ones but got them for just under $200 each brand new could not pass them up. also have inline Diode fuses that I was told are better, maybe not? Disconnect switches ex. but my concern rite now is to get the panels up and wired before the snow comes then I can work on the inside wiring and such in the shed. Please tell me anything you see wrong, I would rather know now then after its too late.

 

[sunshine_eggo]

Been working on this going on 3 years now, getting things when i can, and reading and watching videos but would like my diagram checked. always better to be checked and corrected them to burn everything up or worse. I do have other things I am not showing like 4 new 12v LifePO4 100AH battery's that I will wire to 24v, I know should have gotten bigger ones but got them for just under $200 each brand new could not pass them up. also have inline Diode fuses that I was told are better, maybe not? Disconnect switches ex. but my concern rite now is to get the panels up and wired before the snow comes then I can work on the inside wiring and such in the shed. Please tell me anything you see wrong, I would rather know now then after its too late.

That won't work. You can't parallel strings of panels at different voltages.

You can't feed the output of one array into two different MPPT.

Those panels are actually "12V" panels. You'll need at least two in series for 24V.

Simplification:

4S into each inverter. No combiner box or fuses needed.

EDIT: Make sure you charge all of your 12V batteries individually to 14.4V and again in parallel to 14.4V holding for at least a couple hours BEFORE you string them in series for 24V. It's very important that they both be fully charged and at true 100% when connected together in series for 24V.

 

[MaikaiLifeDIY]

Those panels are actually "12V" panels. You'll need at least two in series for 24V.

Where do you see from the two panel pictures he provided that they're 12V panels? Am I missing something?

 

[Robbober]

Thank You! That's why you ask 1st.
Thought they were 12v but was confused because the output power was 24v.
So will it be ok to connect the battery as they show here. I'm guessing yes but have to ask.

 

[Rednecktek]

"12v Panels" and "24v Panels" are marketing terms. When you see something saying it's a "12v panel" it means "I can produce enough power to charge a 12v system, but not enough to charge a 24v system" and likewise. Those panels have a VMP of 20v which is enough to charge a "12v nominal" system asking for 15v or so, but doesn't produce the 30+v that a "24v nominal" system will call for.

 

[OffGridForGood]

800W PV
200Ah of 24v Battery
Two 3kW Growatt inverters
WI location.
PV Watts for your location, 44 degree tilt due south reports 65 - 109 kWh per month - ie 2-3 kWh per day.
The growatts idle consumption (IIRC) is about 50W continuous and 100W for the pair x 24 = 2.4kWh per day ie all of the solar the panels can collect.
Your starting out, and learning, but this set up is not going to do much unless you drop one of the inverters/turn them on and off for using one or two. If you can let the batteries charge up for a few days, with the inverters off (they will still charge with solar) then you can plan to use the battery to run some things until these are depleted. Your battery storage is about 5kWh. Some more solar panels when you can will allow a lot more performance.

 

[MaikaiLifeDIY]

"12v Panels" and "24v Panels" are marketing terms. When you see something saying it's a "12v panel" it means "I can produce enough power to charge a 12v system, but not enough to charge a 24v system" and likewise. Those panels have a VMP of 20v which is enough to charge a "12v nominal" system asking for 15v or so, but doesn't produce the 30+v that a "24v nominal" system will call for.

That totally makes sense, I missed what he was implying by calling them 12V panels.

 

[sunshine_eggo]

800W PV
200Ah of 24v Battery
Two 3kW Growatt inverters
WI location.
PV Watts for your location, 44 degree tilt due south reports 65 - 109 kWh per month - ie 2-3 kWh per day.
The growatts idle consumption (IIRC) is about 50W continuous and 100W for the pair x 24 = 2.4kWh per day ie all of the solar the panels can collect.
Your starting out, and learning, but this set up is not going to do much unless you drop one of the inverters/turn them on and off for using one or two. If you can let the batteries charge up for a few days, with the inverters off (they will still charge with solar) then you can plan to use the battery to run some things until these are depleted. You battery storage is about 5kWh. Some more solar panels when you can will allow a lot more performance.

Nice deep dive.

Thank You! That's why you ask 1st.
Thought they were 12v but was confused because the output power was 24v.

Vmp is the number that matters. Always worth remembering 12V/24V systems need to be charged to about 14V/28V.

So will it be ok to connect the battery as they show here. I'm guessing yes but have to ask.

One battery feeding two inverters is fine, but you clearly need a lot more capacity.

 

[sunshine_eggo]

That totally makes sense, I missed what he was implying by calling them 12V panels.

If using a PWM controller, it's very important to use the correct voltage panels as PWM function by shorting the panel to the battery thus forcing the panels run operate at battery voltage. Use a 24V panel on a 12V battery with PWM controller, and you cut its output by 50%.

It's technically more than a marketing term. It's technical in origin for the above reason.

 

[MaikaiLifeDIY]

So if @Robbober has 8 of these panels he should wire then a 4s2p?

That would give him a max VOC of 97.2, for each string?

 

[sunshine_eggo]

So if @Robbober has 8 of these panels he should wire then a 4s2p?

No. Has two MPPT. Why only use one?

That would give him a max VOC of 97.2, for each string?

4S will.

From post #2:

4S into each inverter. No combiner box or fuses needed.

 

[MaikaiLifeDIY]

So for just the panels, to help visually illustrate, this would be ideal. I know this doesn't address the other concerns, but one piece at time is usually easier to digest for me anyways.

 

[Robbober]

So for just the panels, to help visually illustrate, this would be ideal. I know this doesn't address the other concerns, but one piece at time is usually easier to digest for me anyways.

View attachment 173677

This is how I am understanding it also but will still put a Disconnect on both of them and save combiner box for future use.

 

[sunshine_eggo]

This is how I am understanding it also but will still put a Disconnect on both of them and save combiner box for future use.

You will almost certainly want substantially more PV for a 6kW split phase system, so you'll likely need it in the future. That appears to be a 4 into 1, so you'll need one for each MPPT if you go over 3P.

 

[OffGridForGood]

Knowing the loads would normally be the starting point. (what are you trying to run?)
Then you would work out how many PV panels to collect that energy on average per day, allowing for inverter idle and losses.
Then you would pick the inverter(s) to supply the loads, and the max peak (starting) current that may be required.
Then plan the batteries to store daily solar collection, #days of rain or cloud, etc
Two Growatt 3kW inverters can together output 6kW and they can be set up to supply both 120 and 240 loads if this required. A 6kW system is a good size for many average household items including Lights computers, TV's, kettles and coffee makers, toasters and such (but not electric dryers, 40-gallon HWT's, Ovens, EV chargers generally, although you could run some of these for a very short time.)

Until you have more PV it may be better for you to either:
1. shut off the inverters when your not using them, say overnight generally, to reduce the idle consumption.
2. use only one inverter for now, connect all the PV you have to this one inverter - per the manual attached (page 10) you can have PV input up to 80A keep the voltage near 100vDC ideally. (WI)

 

[Robbober]

@OffGridForGood To start with I will not have much on it
4- 13w each LED Flood lights on motion censers =52w
10- 14w each LED Light Bulbs =140w (not on all the time, not all at the same time)
some outlets for hand tools in the shed and charger for drill battery pack. ?watts
and a 7 cu ft. Chest Freezer, 250kWh/year will attach tag
This was going to be my test for the system and monitor everything then add other things and add more battery's and PV as I can.
I will not be off the grid but the idea is to help with power a bit and to have some power if the grid is down, I do have a 9000w generator if power goes out but then you have the gas and noise thing. Not sure what way to go at this point, Have to think about it.

​

 

[sunshine_eggo]

@OffGridForGood To start with I will not have much on it
4- 13w each LED Flood lights on motion censers =52w
10- 14w each LED Light Bulbs =140w (not on all the time, not all at the same time)
some outlets for hand tools in the shed and charger for drill battery pack. ?watts
and a 7 cu ft. Chest Freezer, 250kWh/year will attach tag
This was going to be my test for the system and monitor everything then add other things and add more battery's and PV as I can.
I will not be off the grid but the idea is to help with power a bit and to have some power if the grid is down, I do have a 9000w generator if power goes out but then you have the gas and noise thing. Not sure what way to go at this point, Have to think about it.

Let's just say 2 hours per day per light:

52W*2h = 104Wh/day
140W*2h = 280Wh/day
250kWh/year/365 days/year = 685Wh/day
100W for 24 hours = 2400Wh/day (this is the power consumed by the inverters themselves).

3469Wh/day

As you can see, the inverters themselves account for over 60% of your consumption.

3469Wh/800W = 4.33 hours /day



The red months mean you'll fall short most days during those months - requiring grid or generator backup.

You have 5120Wh of battery capacity, which gives you about 1.5 days of power without charging.

If you're just doing this as an experiment, and you have cash to burn, great. Have fun.

It makes a lot more sense to get a cheap, small Giandel 2000W 24V inverter that only burns maybe 10-20W. Now you only need 1429Wh/day.

1429Wh/800W = 1.78 hours meaning on average, you'll produce sufficient PV to more than meet your loads, though inclement weather will eat into battery capacity.

5120Wh/1429Wh = 3.58 days of power without charging.

Less money results in more capability due to far less waste.

 

[OffGridForGood]

Here is another way to look at it, using an analogy:
Say you put a 500Hp engine into a car you are building from scratch. This engine is brand new. {like your twin 3kW inverters}
Now you need a gas tank so you use one from a lawn tractor and it is max capacity of five gallons. {like your battery bank}
Now you put 1/2 gallon of gas in the tank {like the solar PV you have}

can you run the car? it has an engine, a gas tank and some fuel in the tank right?
Sure you can run this car, but not far, the tank has so little fuel in it.
You can add some more fuel - ie let the PV collect for a few days with the inverters off (they will still control charging) and try to fill the small tank (battery) but you can quickly see the engine size and requirements are completely out of scale with the size of the tank (battery) and the amount of fuel in it (capacity of the PV collection). The components don't really match. And like your actuall PV set up, if the engine was started and left to run for awhile, it would completely use up the available gasoline, just sitting there ready to drive, without doing any (or much) actual driving.

So you can switch the inverters off to avoid some of the standby idle,
you could take one inverter offline for now, and keep it for later when more PV and battery is online.
you could (as @sunshine_eggo said, and get a smaller inverter to go with the PV and battery you have - like putting a smaller engine in the car example - so it's idle draw is lower. switch it on to run some stuff, and switch it off when not needed.
Just a few options. Hope you work with it, and grow it over time.

 

[MaikaiLifeDIY]

@OffGridForGood , I liked your post and it's such a great analogy. Nice work!

 

[OffGridForGood]

@OffGridForGood , I liked your post and it's such a great analogy. Nice work!

Thanks!