Expanding My Solar

[Glamisduner]

If I could redo everything I would have used larger 200 watt panels, but that is not so easy since it involves changing the mounts. Chalk it up to lessons learned if / when I get a new trailer.

So I have 4 100 watt renology panels in series that produce about 96v peak going toa 100/50 victron mppt controller. My understanding is that I will have less power loss over the wire, and more efficiency on the mppt the closer I am to 100v without going over, it seems to be working ok, although I have seen no where near 400watts.

If I want to expand this system, I guess my best bet would be another 4 of the same panels in series, parallel to the first string. Is that correct? Wire is 10awg. so I beleive it should be ok for another 4 panels, especially considering they never produce full power anyways...

I have a rhino roof on my trailer, so I will need to have the company install the mounts and re-spray that area to keep the lifetime warranty in tact. That would be the most expensive part of the install. I need to take my trailer into the shop anyways for other issues, probably later this year.

 

[Mattb4]

96Voc is too close to the max Voc of 100v for your Victron. You might get away with it if you never see cold weather. You are unlikely to reach much more than 75-80% rating for watts.

I would suggest getting a higher rated Voc SCC if you need to do panels in series of more than 3.

 

[sunshine_eggo]

So I have 4 100 watt renology panels in series that produce about 96v peak going toa 100/50 victron mppt controller. My understanding is that I will have less power loss over the wire, and more efficiency on the mppt the closer I am to 100v without going over, it seems to be working ok, although I have seen no where near 400watts.

You're wrong except higher voltage/lower current meaning less wiring loss, but wire length and gauge are major factors. Short runs may not see significant benefit.

96Voc on a 100V controller will almost certainly exceed 100V and destroy the controller in even mild chilly weather - 15°C could do it.

MPPT are LESS efficient converting higher voltage to lower voltage the bigger the gap. Your MPPT will be most efficient at 1.5X system nominal voltage. The wire savings is real, and it usually offsets the efficiency loss converting high PV to low battery voltage. However, short runs and properly sized wires may not be significant enough to make higher voltage/lower current offset the MPPT conversion efficiency loss.

You will almost never see 400W unless you are perfectly perpendicular to the sun at high noon on 6/21 with exactly 1000W/m^2 hitting your panels and you keeping them cooled off to 25°C while they want to heat to 50°C+

Flat on a roof means you'll never see more than about 70-80% on 6/21.

If I want to expand this system, I guess my best bet would be another 4 of the same panels in series, parallel to the first string. Is that correct? Wire is 10awg. so I beleive it should be ok for another 4 panels, especially considering they never produce full power anyways...

Absolutely not.

Get two more panels and go 3S2P.

I have a rhino roof on my trailer, so I will need to have the company install the mounts and re-spray that area to keep the lifetime warranty in tact. That would be the most expensive part of the install. I need to take my trailer into the shop anyways for other issues, probably later this year.

https://www.victronenergy.com/upload/documents/Datasheet-SmartSolar-charge-controller-MPPT-100-30-&-100-50-EN.pdf

You can put up to 60A Isc on that controller meaning you can overpanel the snot out of it. I would estimate your panels Isc at 5.5A meaning you could put up to:

60/5.5A = 10.9 or 10 strings in parallel, so you could safely accommodate a massive 3S10P array of those panels on your trailer... but... you could only output 50A.

Might be worth considering adding 5 panels and going 3S3P.

EDIT: Shade, even partial shading of panels can absolutely destroy array output. Shading a single cell on a panel can cut the output by 1/3. Shading the bottom row of cells on a panel in portrait mode will cut output to 0.

 

[Glamisduner]

Hey thanks for the correction. The wire run after the last panel is 30 feet to the controller, 10awg wire.

According to specs I should not be able to exceed 100v with them all in series. It's been cold / near freezing and never happened.

Open Circuit Voltage is (Voc):
24.3V
So close to 100 but it should never exceed 100.
Isc is 5.21A

Should I still re-wire to parallel for now to increase effeciency or is the wire too long for the 10awg run? According to AI I should be good for about 30 amps, but then again AI also suggested putting the panels in series for maximum efficiency lol.

Will consider 5 more panels 3s3p if I have room, I need to check.

Roof is not completly flat.

As for shading, I meant that the more panels I add, the more chance one could get shaded, and if one gets shaded I might produce less power than just sticking with the 4 panels I have now? Sounds like impact of shading a panel with the panels split into groups of 2 or 3 in parallel, might not be as bad as shading a panel when they are in two large series arrays?

 

[sunshine_eggo]

Hey thanks for the correction. The wire run after the last panel is 30 feet to the controller, 10awg wire.

30' is certainly an argument for 2S or 3S vs. 1S, but definitely not 4S.

According to specs I should not be able to exceed 100v with them all in series. It's been cold / near freezing and never happened.

This statement isn't accurate. The voltage of panels GOES UP when temperature goes down.

Open Circuit Voltage is (Voc):
24.3V
So close to 100 but it should never exceed 100.

Nope. Again, as temperature decreases, voltage increases. The 100V is a NEVER exceed value. Period. Not by even 0.1V. It instantly invalidates the warranty, and it's likely to destroy the controller.

Since you may not believe me, here's what the NEC says when you're planning for array voltage:



That's saying take 24.3 * 4 and multiply it by 1.10 - that's 107V. POP!

When planning, it's easier to establish your upper limit, i.e., divide 100V by 1.10, and THAT's the maximum Voc array you can install, i.e., 91V. If it's colder than freezing, you need to go lower. If you travel significantly, you need to plan for your record low temperature anywhere the array might be, not just home.

It doesn't matter that it's been fine until now. You have installed an array that can destroy the controller.

Isc is 5.21A

Should I still re-wire to parallel for now to increase effeciency or is the wire too long for the 10awg run?

2S2P would be a good compromise for the existing four panels.

According to AI I should be good for about 30 amps, but then again AI also suggested putting the panels in series for maximum efficiency lol.

AI is the absolute best way to get information that sounds very reasonable and accurate, AND miss an critical piece of information that brings it all crashing down.

Please do not use AI for solar planning.

Will consider 5 more panels 3s3p if I have room, I need to check.

If you only have room for 8 panels, 2S4P would be fine.

Roof is not completly flat.

All RV roofs are flat enough to be considered completely flat with regards to PV performance.

As for shading, I meant that the more panels I add, the more chance one could get shaded, and if one gets shaded I might produce less power than just sticking with the 4 panels I have now? Sounds like impact of shading a panel with the panels split into groups of 2 or 3 in parallel, might not be as bad as shading a panel when they are in two large series arrays?

This is alleviated by fewer panels in series and more parallel strings.

Note that two strings in parallel dont' need any special fusing consideration. When you parallel 3 or more strings, EACH string needs overcurrent protection. A single 10A MC4 fuse per string should suffice.

 

[Glamisduner]

30' is certainly an argument for 2S or 3S vs. 1S, but definitely not 4S.



This statement isn't accurate. The voltage of panels GOES UP when temperature goes down.



Nope. Again, as temperature decreases, voltage increases. The 100V is a NEVER exceed value. Period. Not by even 0.1V. It instantly invalidates the warranty, and it's likely to destroy the controller.

Since you may not believe me, here's what the NEC says when you're planning for array voltage:

View attachment 269290

That's saying take 24.3 * 4 and multiply it by 1.10 - that's 107V. POP!

When planning, it's easier to establish your upper limit, i.e., divide 100V by 1.10, and THAT's the maximum Voc array you can install, i.e., 91V. If it's colder than freezing, you need to go lower. If you travel significantly, you need to plan for your record low temperature anywhere the array might be, not just home.

It doesn't matter that it's been fine until now. You have installed an array that can destroy the controller.



2S2P would be a good compromise for the existing four panels.



AI is the absolute best way to get information that sounds very reasonable and accurate, AND miss an critical piece of information that brings it all crashing down.

Please do not use AI for solar planning.



If you only have room for 8 panels, 2S4P would be fine.



All RV roofs are flat enough to be considered completely flat with regards to PV performance.



This is alleviated by fewer panels in series and more parallel strings.

Note that two strings in parallel dont' need any special fusing consideration. When you parallel 3 or more strings, EACH string needs overcurrent protection. A single 10A MC4 fuse per string should suffice.

Hey thanks for thje explanation, I thought the 24.3v was the absolute maximum voltage that they could produce. I guess I misunderstood. I will order some parallel splitters on amazon tonight.

When I get up on the roof, I'll see if there is room for 5 more panels for the future.

I think I left a few feet of extra wire in a loop after I tapped into the side of the refrigerator vent, it's going to be a pain, but I think there will be enough extra that I don't have to splice into the longer run to do a series parallel setup.
I could actually reduce the length of the run by about 8-10 ft, but then the run, after the mppt would be longer, unless I directed it straight to the battery with an additional 4awg wire. But that battery box is getting a bit full too so probably not worth the added cost.

 

[HRTKD]

For the next install, if you start with a base of Unistrut on the roof, it's easier to switch to different panels. However, the install of Unistrut takes longer than using the typical Z brackets.

My first trailer was done with Z brackets. The second install (new trailer) used strut (not actual Unistrut). The strut allowed for a lot of flexibility in the location of the solar panels. But good grief did it take me a long time. Most of this was my own fault for not using actual Unistrut.