Please help to check the Solar setup

[tina2]

Hi,
Could anyone please help to check our solar setups?
Currently, our fifth wheel came with a 100W solar panel.
It uses standard MC4 solar panel cables on the roof but changes to some cheap yellow/white cable (probably only for 15Amps) into the front compartment (where the charging controller and battery are).

Now, we'd like to add another 100w x 4 solar panels and upgrade to Lithium batteries.

So here we think maybe we have two options.
Option1:
Re-do the whole wiring. I guess most people do this way, but we will have to drill another hole in the roof, sounds a little scary for a newbie. Please help to check the design to see if there's anything wrong! Especial the breaker/fuse/cable size. Thanks!!

Option2:
Reuse the factory cable and roof entry gland thing. But since the cable could hold probably 15 Amps. We use "serial" for all the solar panels to keep the current around 8.33 Amps. But for that reason, we need to get a 5x12V=60V MPPT solar charging controller. Is this feasible? Will that charge faster?

Any input would help!
Thanks

[vsheetz]

Need to check the voltage rating as well as the amp rating of the wire coming down from the roof.

A '12v panel' is typically has a VoC rating of over 20v. Array VoC is used to determine voltage spec of charge controller. Allow typically 10-15% margin for cold increase.

So with five '12v' 100w panels in series you likely need a 150v capable controller.

Consider using an even number of panels in two strings or '12v' narrow 200w panels.

Determine specifically what the exusting wire is, or replace it with proper wire.

[vsheetz]

Likely you will want to add a battery monitor.

[rarebear.nm]

A few comments,



1. When I zoom into the drawing they too fuzzy to read amp rating of anything. So no comment about that.


2. When mixing old and new panels make sure they are electrically similar in their ratings.


3. Frequently when using these smaller watt panels (100 watts) people place at pairs in series to get the voltage up. You're planning on five panels. So if you run them parallel you may end up with a rather low voltage input to the controller.


If you run them in series shading on any one panel may greatly reduce output of the entire system. In parallel configurations shading becomes a lesser issue.


4. Your roof top layout and space makes a difference in what panels you can use and thus voltages and watts.


In my case on a 5th wheeler with three large open spaces I used commercial panels, about 49 x 79" each. I ran them all parallel using #4 down haul wire to the controller. With these panels shade makes only a small difference. I park under trees and still get fully charged before noon every day.


5. I would think about adding some battery capacity into the system as well.


When I size solar I degrade it by abut 10% for systems losses, 30% for a flat install and another 10+% for weather. I never really count on more than five hours of good sun per day in many locations. Here in the southwest the sun is good most of the daylight hours on most days.

[hclarkx]

If you can fit 200W panels, you may be better off cost-wise by installing three 200W panels. The Rich Solar panels I have a a bit less than 27" x 57". Cost per watt is less than most name brand 100W panels. Fewer support brackets to deal with as well.

Yes, you can lose some production due to shade with series panels, but not enough to give up the better MPPT action you get with the higher voltage of a series system. The optimum voltage for the solar controllers I"ve looked at is about 48 volts open circuit. This makes two of the typical 200W panels (Voc of about 26 V each IIRC) an excellent choice, but three series panels with Voc total of about 75 Volts works nearly as well. The higher voltage gives MPPT controllers more "headroom" to work with when they pull voltage down to get more power in the morning and afternoon and in less than bright sun.

[tina2]

Thanks for everyone's comments,
I read it several times to make sure I understand it correctly.
We bought four of the Renogy 100W last year, the size is 42"x21".
So we prefer to use 100W instead of 200W.
Could you please check my chart to see if it is doable?
If I serial the 5 x 100 W together, what kind of MTTP charge controller should I get?
vsheetz said "150V", but you said "75 V"?

Thank you so much!

Originally Posted by hclarkx

If you can fit 200W panels, you may be better off cost-wise by installing three 200W panels. The Rich Solar panels I have a a bit less than 27" x 57". Cost per watt is less than most name brand 100W panels. Fewer support brackets to deal with as well.

Yes, you can lose some production due to shade with series panels, but not enough to give up the better MPPT action you get with the higher voltage of a series system. The optimum voltage for the solar controllers I"ve looked at is about 48 volts open circuit. This makes two of the typical 200W panels (Voc of about 26 V each IIRC) an excellent choice, but three series panels with Voc total of about 75 Volts works nearly as well. The higher voltage gives MPPT controllers more "headroom" to work with when they pull voltage down to get more power in the morning and afternoon and in less than bright sun.

[hclarkx]

The 75V I mentioned was for three 200W panels with about 25 open circuit volts each (or a bit more).

If you are looking at https://www.renogy.com/100-watt-12-v...ompact-design/ then your open circuit voltage will be five times 24.3V or about 122 volts. As such you want a 150V solar controller.

I use Epever solar controllers. They are rated 150V on the input, though a footnote says 135V above 25C, so realistically they are 135V.

With over 100V you will be losing a bit of efficiency in the solar controller, and will have more headroom than necessary for good MPPT action. However, we are talking a few percent, so not a deal killer.

[tina2]

Thank you hclarkx,
Now I understand.

Could you please help to check other than the MPPT solar controller, is the wiring correct? Like the 4AWG & 6AWG, is that enough?
And about the black block bus bar (negative cables), I saw some videos connecting it to the chassis. Should I do that as well?

Originally Posted by hclarkx

The 75V I mentioned was for three 200W panels with about 25 open circuit volts each (or a bit more).

If you are looking at https://www.renogy.com/100-watt-12-v...ompact-design/ then your open circuit voltage will be five times 24.3V or about 122 volts. As such you want a 150V solar controller.

I use Epever solar controllers. They are rated 150V on the input, though a footnote says 135V above 25C, so realistically they are 135V.

With over 100V you will be losing a bit of efficiency in the solar controller, and will have more headroom than necessary for good MPPT action. However, we are talking a few percent, so not a deal killer.

[DavidEM]

I would recommend only having four panels. That way you can wire them in series/parallel and keep the voltage in the wire down to less than 50V for best safety. Use a 100V, 40A MPPT controller such as Renogy's Rover.

David

[Nwcid]

As Dave said, using 4 panels with 2 in series and then the 2 sets in parallel will give you the best performance. Or add 1 more panel and do 3 in series then parallel those sets.

You will need to move up to a 10ga wire from your rooftop to the controller.

You also need to do larger wiring from your batteries to your inverter. A 2000 watt inverter is able to draw 167 amps at 12v. 4ga wire is only rated to 100 amps and only for short runs. You are looking at a minimum of 2/0 wire if you want to be able to use the full capacity of the inverter.

Also you should have more circuit protection. At minimum you should have a breaker/fuse near the output of your batteries for the full rated draw of wire gauge from the batteries. Any wiring coming off the positive buss bar that has a lower rating than from your batteries also needs a breaker/fuse.

Breakers/fuses protect the wiring. If they are not set up correctly, the wiring becomes the weak link, heats up and melts/catches on fire.

Here is a great resource for wiring info, https://www.bluesea.com/support/arti...r_a_DC_Circuit

[rarebear.nm]

Originally Posted by tina2

Thank you hclarkx,
Now I understand.

Could you please help to check other than the MPPT solar controller, is the wiring correct? Like the 4AWG & 6AWG, is that enough?
And about the black block bus bar (negative cables), I saw some videos connecting it to the chassis. Should I do that as well?

Yes the negative buss must be tied to a solid chassis ground like the frame. Using a #4 or larger wire.


The drawing shows a 2000 watt inverter. At full load, what you should plan for, and 12 volts (2000watts / 12volts = 166 amps). The #4 & #6 wire is way too small for that load. Also the 166 amps is only the inverter draw, you still must add all other 12 volts loads onto that. Just a guess I'd plan on about 2,500 - 3,000 watts. Length of wire makes a very large difference in sizing wire. Use wire amp tables like this one, many out there:


https://www.bluesea.com/support/arti...r_a_DC_Circuit


From the table even for short distances the smallest sized wire you should be using is 2/0. Much larger than the #4 you're listing.


On some equipment the wire connections may have trouble accepting larger wire sizes. You can get reducing sleeves that crimp onto he the wire and reduces it to fit say a #4 terminal. Like this:



Morris 90987 Morris Products 90987 Offset Solid Pin Terminal Connector, Compression Connector Type, 4/0 To 2/0 Wire Range



I would use the 2/0 wire for the battery connections to the buss bars and the inverter. I just buy welding wire in the desired gauge, an assortment of crimp ring connectors, some red&black triple wall, glued lined heat shrink tubing. With my 10 ton wire crimpers I get very good cables any length needed.

[hclarkx]

Pretty well covered by the posts above but I would summarize and add as follows ......

1) The 2000W inverter can draw up around 185 amps if you actually load it to 2000W. This includes an assumed 15% losses in the inverter. I.e., 2000 Watts output and 2353 Watts input (from the battery). Efficiency of some inverters drops below 85% at maximum output. So, about 185 amps at 85% efficiency and a bit more with voltage at the battery down around 12.8 Volts (battery charge low and high load on battery) and assuming lower efficiency at max power. So ideally you want wire that can carry that 185 amps or a bit more. This indeed suggests 2/0. Though I wouldn't argue with 1/0 if you don't expect to push the inverter to its limit very often or for very long. 1/0 with 90C insulation is good for 170 amps or a bit more in free air (not enclosed in conduit). I think most 1/0 welding cable is rated 105C so is actually good for over 185 amps. 1/0 is easier to work with and is readily available. If the runs are more than a couple of feet, I'd go up to 2/0 though. Use this all the way to the battery terminals.

However, there is a way to avoid 2/0 wire and reduce the amount of 1/0 needed or even avoid 1/0. My preference is to run #2 (130 amps at 90C) from each battery to the positive terminal block/bus. From there to the inverter it's a 1/0 or a parallel pair of #2. I also use a 150 amp circuit breaker on each battery at the bus largely so I can charge them individually and once at the same voltage, close them into parallel with the breakers.

2) It's best to have a two-pole switch on the line coming from the panels (one pole in the plus lead and one in the negative lead). Using one pole is common, but leaving the ground lead from the panel connected to ground at the solar controller means that a short to ground anywhere in the panel system will generate short-circuit current and some heat. If you use two poles and open both leads, it takes two shorts to have short-circuit current flow making the hazards of a short less likely. Given that the roof is probably made from insulating material and the wires from the panel likely don't go near grounded metal, I don't feel strongly about this. Those that go with opening both leads use something like this (https://smile.amazon.com/gp/product/...e?ie=UTF8&th=1).

3) With #14 gauge wire up to the panels, I would stick with five panels in series to reduce current and losses in the #14 wire. This helps offset the higher losses in the solar controller from the higher voltage.

4) #6 wire from the solar controller is fine. #8 would be adequate as well if the run is just a few feet.

5) You show a fuse between the solar controller and the battery positive bus. Some solar controllers require that the 12V side be switched on before the panel side is switched on (and panel side switched off before the 12V side is switched off). Even if the controller manual does not call for this, it is common practice and I think is a good idea for several reasons. As such, you want a circuit breaker rather than a fuse on the 12V side of the solar controller. Strictly speaking, most circuit breakers are not designed for repetitive switching, but for the number of times you will use the circuit breaker as a switch (a few hundred times), that's simply not a concern.

6) With your diagram, you are depending on the battery BMSs to open for a short-circuit between the battery terminals and the MPPT breaker, the house 12V breaker and in the inverter or wire to the inverter. The BMS is reliable, but nothing is 100% reliable. Ideally one has some backup to the BMS. It's increasingly common to use a Class T fuse on each battery (close to the terminal) or on the pair of batteries. A Class T fuse is very fast and limits current to the short-circuit as will the BMS by opening is a few hundred milliseconds (before current can reach its peak of thousands of amps). I don't feel strongly about this.

7) Add a circuit breaker between the positive bus and the inverter. This can be a 200 amp circuit breaker or a 12V switch like you show near the battery. You don't really need a circuit breaker here if you are okay with depending on the BMSs to disconnect the batteries in case of a short-circuit in the inverter. I personally use a 250 amp circuit breaker that is backup to the BMS and functions as a switch to disconnect the inverter when needed (say, for trouble shooting).

8) Also, inverters have large capacitors on the input that draw a huge amount of current when the inverter is switched on after sitting disconnected for a while. This is quite a shock to the capacitors and can even cause the BMSs to disconnect. It's common practice to use a 12V switch between the positive bus bar and the inverter and bridge that switch with a resistor or a light bulb to charge up the capacitors slowly (over a second or two) before closing the switch. You can just touch resistor leads to the two switch terminals before closing it. I didn't do this for my 900W inverter (but do it on my recently added 2000W inverter). If you jump that breaker/switch with a piece of copper wire to charge up the capacitors, you will understand immediately why hitting the caps that hard can't be good for them (you will see quite an arc). However, the master 12V switch near the batteries will tolerate this capacitor current surge and provide disconnection of the inverter for storage, so I wouldn't argue strongly against your current plan here.

9) You show an 80 amp circuit breaker on the #6 line to the RV 12V fuse panel. This should be a lower rating to protect the #6 wire. It's likely your 12V loads never get above about 30 amps, so a 50 amp circuit breaker would be preferred. I use a 40 and it has never opened.

I need to go now, but will try to update your sketch with my thoughts later.

[twinboat]

Originally Posted by hclarkx

Pretty well covered by the posts above but I would summarize and add as follows ......

1) The 2000W inverter can draw up around 185 amps if you actually load it to 2000W. This includes an assumed 15% losses in the inverter. I.e., 2000 Watts output and 2353 Watts input (from the battery). Efficiency of some inverters drops below 85% at maximum output. So, about 185 amps at 85% efficiency and a bit more with voltage at the battery down around 12.8 Volts (battery charge low and high load on battery) and assuming lower efficiency at max power. So ideally you want wire that can carry that 185 amps or a bit more. This indeed suggests 2/0. Though I wouldn't argue with 1/0 if you don't expect to push the inverter to its limit very often or for very long. 1/0 with 90C insulation is good for 170 amps or a bit more in free air (not enclosed in conduit). I think most 1/0 welding cable is rated 105C so is actually good for over 185 amps. 1/0 is easier to work with and is readily available. If the runs are more than a couple of feet, I'd go up to 2/0 though. Use this all the way to the battery terminals.

However, there is a way to avoid 2/0 wire and reduce the amount of 1/0 needed or even avoid 1/0. My preference is to run #2 (130 amps at 90C) from each battery to the positive terminal block/bus. From there to the inverter it's a 1/0 or a parallel pair of #2. I also use a 150 amp circuit breaker on each battery at the bus largely so I can charge them individually and once at the same voltage, close them into parallel with the breakers.

2) It's best to have a two-pole switch on the line coming from the panels (one pole in the plus lead and one in the negative lead). Using one pole is common, but leaving the ground lead from the panel connected to ground at the solar controller means that a short to ground anywhere in the panel system will generate short-circuit current and some heat. If you use two poles and open both leads, it takes two shorts to have short-circuit current flow making the hazards of a short less likely. Given that the roof is probably made from insulating material and the wires from the panel likely don't go near grounded metal, I don't feel strongly about this. Those that go with opening both leads use something like this (https://smile.amazon.com/gp/product/...e?ie=UTF8&th=1).

3) With #14 gauge wire up to the panels, I would stick with five panels in series to reduce current and losses in the #14 wire. This helps offset the higher losses in the solar controller from the higher voltage.

4) #6 wire from the solar controller is fine. #8 would be adequate as well if the run is just a few feet.

5) You show a fuse between the solar controller and the battery positive bus. Some solar controllers require that the 12V side be switched on before the panel side is switched on (and panel side switched off before the 12V side is switched off). Even if the controller manual does not call for this, it is common practice and I think is a good idea for several reasons. As such, you want a circuit breaker rather than a fuse on the 12V side of the solar controller. Strictly speaking, most circuit breakers are not designed for repetitive switching, but for the number of times you will use the circuit breaker as a switch (a few hundred times), that's simply not a concern.

6) With your diagram, you are depending on the battery BMSs to open for a short-circuit between the battery terminals and the MPPT breaker, the house 12V breaker and in the inverter or wire to the inverter. The BMS is reliable, but nothing is 100% reliable. Ideally one has some backup to the BMS. It's increasingly common to use a Class T fuse on each battery (close to the terminal) or on the pair of batteries. A Class T fuse is very fast and limits current to the short-circuit as will the BMS by opening is a few hundred milliseconds (before current can reach its peak of thousands of amps). I don't feel strongly about this.

7) Add a circuit breaker between the positive bus and the inverter. This can be a 200 amp circuit breaker or a 12V switch like you show near the battery. You don't really need a circuit breaker here if you are okay with depending on the BMSs to disconnect the batteries in case of a short-circuit in the inverter. I personally use a 250 amp circuit breaker that is backup to the BMS and functions as a switch to disconnect the inverter when needed (say, for trouble shooting).

8) Also, inverters have large capacitors on the input that draw a huge amount of current when the inverter is switched on after sitting disconnected for a while. This is quite a shock to the capacitors and can even cause the BMSs to disconnect. It's common practice to use a 12V switch between the positive bus bar and the inverter and bridge that switch with a resistor or a light bulb to charge up the capacitors slowly (over a second or two) before closing the switch. You can just touch resistor leads to the two switch terminals before closing it. I didn't do this for my 900W inverter (but do it on my recently added 2000W inverter). If you jump that breaker/switch with a piece of copper wire to charge up the capacitors, you will understand immediately why hitting the caps that hard can't be good for them (you will see quite an arc). However, the master 12V switch near the batteries will tolerate this capacitor current surge and provide disconnection of the inverter for storage, so I wouldn't argue strongly against your current plan here.

9) You show an 80 amp circuit breaker on the #6 line to the RV 12V fuse panel. This should be a lower rating to protect the #6 wire. It's likely your 12V loads never get above about 30 amps, so a 50 amp circuit breaker would be preferred. I use a 40 and it has never opened.

I need to go now, but will try to update your sketch with my thoughts later.

Basing inverter cabling on how much amps they can carry based on insulation temps isn't the only factor.

You need to look at voltage drop. A 120 volt system with a 5% voltage drop is survivable.

In a 12 volt solar, and inverter system, a 5% voltage drop is a severe drop and will effect the system.

[hclarkx]

Originally Posted by twinboat

Basing inverter cabling on how much amps they can carry based on insulation temps isn't the only factor.

You need to look at voltage drop. A 120 volt system with a 5% voltage drop is survivable.

In a 12 volt solar, and inverter system, a 5% voltage drop is a severe drop and will effect the system.

Like I said, "If the runs are more than a couple of feet, I'd go up to 2/0 though." But, I should have added parenthetically "to limit voltage drop."

Also, we are talking lithium batteries here, not lead-acid. Higher battery voltage and less battery voltage drop under heavy load. The extra voltage of lithium makes voltage drop a rare issue.