How many solar panels until it catches fire?

[Solarderp]

I live off grid and have for a while now. I'm living in a trailer while I build my house. My heat, stove, and hot water will be handled by propane and my largest power draw will be my well pump, so I bought the 12000xp since it should handle my power needs into the future when I build my shop as well.

My question is with the stated 24k pv input and 28k pv over paneling. I've played around with the EG4 solar panel string sizer and I can't get to 24k watts of input. Every panel I've tried is limited by Voc or the amperage limit.
How is it possible to get the max input with available panels and stay under 480 Voc and/or 44A, let alone over panel to 28k and not fry the 12000xp?
I'm in a cold climate, so I figure the temp coefficient will never let me get the max, but I've played with the temp range as well and can't get near the max input.
Does it have to do with serier/parallel? I've been studying solar for awhile so I don't make uneducated purchases, but I'm obviously not understanding something.

As a side note, are there better brands of solar panels to have for cold climates?

 

[robbob2112]

Post your panel datasheet or panel specs with temp coefficient so it can be figured. If you can't find the coefficient the general number is to figure a 20% gain.

And yes, it is a combination of series and parallel. You can't exceed the mppt voltage by even a volt... and you can't exceed the max current listed for the panels or the max input current listed for the mppt. So you may find you need an extra mppt and charge in parallel.

 

[Hedges]

That's the limit per MPPT input. There are two inputs.

https://eg4electronics.com/wp-content/uploads/2024/10/EG4-12000XP-Spec-Sheet.pdf

MAX. UTILIZED SOLAR POWER 24000W (12000 per MPPT) MAX. RECOMMENDED SOLAR INPUT 28000W (14000 per MPPT)

 

[Solarderp]

Post your panel datasheet or panel specs with temp coefficient so it can be figured. If you can't find the coefficient the general number is to figure a 20% gain.

And yes, it is a combination of series and parallel. You can't exceed the mppt voltage by even a volt... and you can't exceed the max current listed for the panels or the max input current listed for the mppt. So you may find you need an extra mppt and charge in parallel.

The thing is, I have tried many different panels on the website. Maybe the website is wrong? Try the link and see what you get for different panels. I couldn't get to 24k or 28k without it telling me the configuration won't work. Most of the configurations for any selected panel were just series strings. Maybe 4 series/parallel configurations, if I remember correctly, and still not getting to 24k. I did the manual calculations on a few panels to confirm the website sizer recommendation, and it matched.

SolarPanelApp

eg4electronics.com

 

[Solarderp]

That's the limit per MPPT input. There are two inputs.

https://eg4electronics.com/wp-content/uploads/2024/10/EG4-12000XP-Spec-Sheet.pdf

MAX. UTILIZED SOLAR POWER 24000W (12000 per MPPT) MAX. RECOMMENDED SOLAR INPUT 28000W (14000 per MPPT)

Understood. And the website has columns for each input.

Check it out:

SolarPanelApp

eg4electronics.com

 

[Solarderp]

For my purposes, I'll be doing a ground mount and I input -5 and 105 for temp range. I fudged those numbers up and down and couldn't get to 24k with any panel on that sizing calculator.

 

[sunshine_eggo]

Maximum practical Vmp is going to be about 307V.

Assuming you build an array with 44A Isc, thats going to be about 40A Imp, so that's about 12.3kW/MPPT

With the same 307V practical limit on Vmp and 35A actual Imp, the MPPT is limited to about 10.7kW usable.

Allowing for no temperature margin, 384Vmp * 40A Imp = 15.4kW.

 

[Solarderp]

Maximum practical Vmp is going to be about 307V.

Assuming you build an array with 44A Isc, thats going to be about 40A Imp, so that's about 12.3kW/MPPT

With the same 307V practical limit on Vmp and 35A actual Imp, the MPPT is limited to about 10.7kW usable.

Allowing for no temperature margin, 384Vmp * 40A Imp = 15.4kW.

Spec for 12000xp says 35A usable, 44A short circuit.

 

[Hedges]

Understood. And the website has columns for each input.

Check it out:

SolarPanelApp

eg4electronics.com

I'm having same problem with that calculator. I can do 2x 7s2p Qcell 580W for 16240W, but if I make that 7s3p for 24360W it says too many watts.

At that point I would ignore it and do the 7s3p. Have already established voltage is OK, and I can see current is OK too.

 

[Solarderp]

I'm having same problem with that calculator. I can do 2x 7s2p Qcell 580W for 16240W, but if I make that 7s3p for 24360W it says too many watts.

At that point I would ignore it and do the 7s3p. Have already established voltage is OK, and I can see current is OK too.


View attachment 259841

You are right, sir. It looks like the EG4 sizing calcutlator is limiting by watts instead of Voc. I got the same thing you did by changing to 7s3p. Thank you for educating me.

 

[Hedges]

I think it is limiting you to whatever can be done with 2p, so higher current it allows higher watts.
Using SolarEver 450W (Imp: 14.970) I got it to 21600W.

If you do 3p, you should have fuse per string. Or breaker, should be non-polarized (or maybe 3 ganged would provide protection even for polarized.)

If your strings have different orientation you could over-panel more because they don't peak at same time.

 

[Solarderp]

O

I think it is limiting you to whatever can be done with 2p, so higher current it allows higher watts.
Using SolarEver 450W (Imp: 14.970) I got it to 21600W.

If you do 3p, you should have fuse per string. Or breaker, should be non-polarized (or maybe 3 ganged would provide protection even for polarized.)

If your strings have different orientation you could over-panel more because they don't peak at same time.

On some panels, it will give 3p as long as it's under the 24k watts. I must have done more than two dozen panels from the drop down. I understand about the different orientation, but that wouldn't account for the 28k over paneling claim, would it? Because the thresholds don't change.

 

[Hedges]

We don't think there is a particular technical reason for an overpaneling limit. Max Isc, maybe (perhaps just if connected backwards, current through a clamping diode.)

What I think would be useful is to target Vmp at nominal, or voltage for maximum efficiency if documented somewhere.

"NOMINAL MPPT VOLTAGE 320 VDC"

Efficiency of 99% vs. 98% in MPPT operation means half as much power dissipation, half as much temperature rise. Which should help with longevity.

Some brands actually publish curves. All I find in EG4 manual is:

"MAXIMUM EFFICIENCY (MPPT) 99%"

 

[Solarderp]

Agreed. That's why I was pretty much nailed down on the Solarever panels you mentioned. Voc cold max at 390 per string, Vmp at 300 per string, and claiming 25% bi facial gain for 22,500 watts for 4 series strings. Seems simplest and probably more power than I can use for a while.

 

[Hedges]

Consider how you might later put all those panels on one MPPT (with multiple orientations).
In a few years if you want more power, you won't find the same model, so expect to get a different model for the other MPPT.

But 22.5kW is a fair amount. I'm putting in a couple systems with around 15kW.

"My heat, stove, and hot water will be handled by propane and my largest power draw will be my well pump"
Is that referring to future house?
Try to make use of electric for heat as well, e.g. an electric water heater as batch pre-heater.
And similar for furnace.
Any heat you get from surplus PV is energy you don't need to buy as propane.

I added an electric duct heater downstream of gas furnace, manually switch between them.
Some members use mini-split and were heating just with that at least during mild sunny fall weather.

 

[Solarderp]

Consider how you might later put all those panels on one MPPT (with multiple orientations).
In a few years if you want more power, you won't find the same model, so expect to get a different model for the other MPPT.

My plan is to set up my system and then buy another 12000xp for a backup since I won't need the power of two of them.

"My heat, stove, and hot water will be handled by propane and my largest power draw will be my well pump"
Is that referring to future house?
Try to make use of electric for heat as well, e.g. an electric water heater as batch pre-heater.
And similar for furnace.
Any heat you get from surplus PV is energy you don't need to buy as propane.

Yes, the house I'm building now. I've already considered this. I have an electric dryer and stove to use during the summer so I don't waste propane even though, by my figures the propane only adds up to $150/ year. And I'm going to buy a 24k mini-split from SS to cool and supplement infloor heating.