Panel configuration for my 5th wheel build

[BretS]

Starting to look at panel configuration for my 5th wheel build and looking for input...

I will have a total of nine 210W panels. Here are the specs:

• Max Power Output(W): 210W
• Voltage MPP Vmp(V): 16.77V
• Current MPP Imp(A): 12.48A
• Voltage Open Circuit Voc(V): 19.83V
• Short Circuit Current Isc(A): 13.09A

What is best and why? Series or parallel, or combination? Trying to determine what SCCs and other components I will need. I was thinking of sets of three panels, so that I could add them as I can afford to, but not sure that will work. Thanks in advance for any input!!

**Edit: my battery is around 900Ah DIY at 12V. Total 12V system. Also, I can drop to 8 panels if that makes it work better, but can't get more than 9 up there.**

 

[MisterSandals]

What is best and why? Series or parallel, or combination? Trying to determine what SCCs and other components I will need.

You're on the right track making sure that your choice of SCC will work with you panel configuration. An odd number of panels sometimes is tough but 3S3P looks very workable.

You didn't specify a battery voltage so I will assume 12v.

Voc x 3 = 60v so that is easily solved for an SCC max input voltage.
210w x 9 = 1890w array
1890w / 12.8v = 147a charging (this might be more than your batteries can accept)

More info about your system is required (for me) to go beyond this.

 

[chrisski]

You really only have one realistic configuration:

3S3P. (60 volts and 39 amps). A Victron 100/50 will power this. About $270. After Each string of panels is combined, you lose the ability for MC4 connectors, which are rated for 30 amps, but that is no big deal. THis may work for a 24 volt system, but for a 12 volt system, you’d want a bigger SCC amps wise.
=======================
9S: (180 volts and 12 amps). Although doable, you’ll need a high voltage SCC and that’s $$. You also need to carefully calculate freezing voltage, which is higher.
9P: (20 volts and 117 amps) Way to much current coming down from the roof. I’d want at least 2/0 wire for that.
=======================
Taking away 1 panel will get you more options:

8P
4S2P
2S4P
8S

========================
Adding 3 more panels gets you more options:

12S
6S2P
2S6P
4S3P
3P4S
12P
==================
Max amps and volts really needs to be taken into account for these combinations.

 

[BretS]

You're on the right track making sure that your choice of SCC will work with you panel configuration. An odd number of panels sometimes is tough but 3S3P looks very workable.

You didn't specify a battery voltage so I will assume 12v.

Voc x 3 = 60v so that is easily solved for an SCC max input voltage.
210w x 9 = 1890w array
1890w / 12.8v = 147a charging (this might be more than your batteries can accept)

More info about your system is required (for me) to go beyond this.

Edit above with more info

 

[BretS]

You really only have one realistic configuration:

3S3P. (60 volts and 39 amps). A Victron 100/50 will power this. About $270. After Each string of panels is combined, you lose the ability for MC4 connectors, which are rated for 30 amps, but that is no big deal. THis may work for a 24 volt system, but for a 12 volt system, you’d want a bigger SCC amps wise.
=======================
9S: (180 volts and 12 amps). Although doable, you’ll need a high voltage SCC and that’s $$. You also need to carefully calculate freezing voltage, which is higher.
9P: (20 volts and 117 amps) Way to much current coming down from the roof. I’d want at least 2/0 wire for that.
=======================
Taking away 1 panel will get you more options:

8P
4S2P
2S4P
8S

========================
Adding 3 more panels gets you more options:

12S
6S2P
2S6P
4S3P
3P4S
12P
==================
Max amps and volts really needs to be taken into account for these combinations.

Edit above with more info

 

[chrisski]

I think 3S3P with a properly sized SCC may be the way to go, but you may find when you do the math, two charge controllers may end up being cheaper than one that handles everything.

At 3S3P you could see close to 120 charging amps, and that is quite the SCC.

Also, whatever you decide, leaving room on your powerboard and busbar for an additional SCC for ground mount panels.

 

[MisterSandals]

Looks like chrisski have most of the general numbers covered.

But to optimize this for YOUR use and YOUR situation...

Stepping back to look at the bigger picture, what are your expected daily usage kWh looking like? Will your usage during the day (like with AC) be greater than at night or consistent around the clock (refrigerator...)?
Will you be parking in the sun or shade or mixed? Will you be in a location that does not get a lot of sun (needs a lot of panels) or has frequent rainy days (needs a lot of battery storage)?

 

[BretS]

Looks like chrisski have most of the general numbers covered.

But to optimize this for YOUR use and YOUR situation...

Stepping back to look at the bigger picture, what are your expected daily usage kWh looking like? Will your usage during the day (like with AC) be greater than at night or consistent around the clock (refrigerator...)?
Will you be parking in the sun or shade or mixed? Will you be in a location that does not get a lot of sun (needs a lot of panels) or has frequent rainy days (needs a lot of battery storage)?

So, that's part of what is making this hard for me. The answer to most of those questions is yes... because I don't stay in any one place, or even type of place, I am trying to find out what is most universal setup. I do have a generator for backup if conditions aren't optimal for a period of time, but I am hoping that won't be too often.

I do have a residential fridge, so that is 24/7. I want to be able to run the one A/C unit, but would expect that to be needed most when in the full sun.

 

[BretS]

I think 3S3P with a properly sized SCC may be the way to go, but you may find when you do the math, two charge controllers may end up being cheaper than one that handles everything.

At 3S3P you could see close to 120 charging amps, and that is quite the SCC.

Also, whatever you decide, leaving room on your powerboard and busbar for an additional SCC for ground mount panels.

When I put 3S3P of these panels into the Victron MPPT calculator, it tells me to use a 150/100 SCC. The Nominal PV Power at 12VDC is 1450W for that SCC. So, does that mean I am over-paneling by 440W? Is that too much to leave on the table? I'm very new to all of this, so I just don't know. I'm thinking that is not too much based on not having perfectly sunny days, shading, panel efficiency, etc. Here are the stats on that SCC:

• Rated Charge Current 100A
• Nominal PV Power at 12VDC 1450W
• Nominal PV Power at 24VDC 2900W
• Nominal PV Power at 36VDC 4350W
• Nominal PV Power at 48VDC 5800W
• Max PV Short Circuit Current 70A
• Data Communication Port VE.Direct
• Maximum PV Open Circuit Voltage 150VDC
• Peak Efficiency 98%
• Self Consumption 12v less than 35mA 48V 20mA

 

[MisterSandals]

So, does that mean I am over-paneling by 440W? Is that too much to leave on the table?

Your panels will be flat on your roof so you may not be as over paneled as the numbers show.

The Victron 150/100 is a great product. I think you're on the right track with that.

 

[HRTKD]

An alternative is 4s and 5s, using two separate solar charge controllers. I'm not sure there is an advantage to this. It requires double the number of wires to be run into the RV. But it eliminates the need for fuses and Y connectors or a combiner box on the roof.

 

[chrisski]

So, does that mean I am over-paneling by 440W?

I don’t think you’ll be overpaneled, because as mentioned, the flat roof. I think you’ll be perfect sized.

One of the sets of panels I have on my roof is 600 watts, and I should see 36 amps from these panels, but the most I’ve seen is 25 amps, or about 70% production. This is also only for a couple hours before noon and a couple hours after noon, and outside that window charging amps climbs from 0 an hour or so after sunrise and before sunset.

This output really changes based on angle of the sun. So in the winter the noon sun is lower in the sky than summer, and summer output could be higher, but my charging requirements in the summer are less than the winter, so I have been done charging between 9 am and 10 am In the summer. In the winter, where I use up to 5X as much energy, I am done between 1 pm and 3 pm.

Because of this, I don’t expect your panels to “clip” at 100 amps, even though they have the potential to produce 120 amps. If they do clip I don’t think it will be for very long and only in the summer months.

If this clipping does become a problem, you can keep 6 of these panels on the 150/100. 6 of these panels can produce 90 amps tops, and you can add a 100/30 or 100/50 to take advantage of the other 30 amps the panels are producing.

PVwatts would give you a pretty accurate production by month of what your panels can delver per day.

For loads, my biggest AH user is my propane heater electric fan at 6 amps, and that may use class to 100 ah on a short, cold winter day. Other than that, my loads are a couple of minutes like a 55 amp coffee maker, for 3 minutes, or 155 amp microwave for two minutes a serving.

THere’s a few other things that I can’t power by solar because I just can’t get enough panels on my roof to run the item, never mind charge batteries to keep them running overnight. If I were to use my electric water heater, its a 1500 watt element, so I’d expect 140 amps for up to an hour. A single air conditioner would cost me around 150 amps when running it, and in AZ it runs non-stop all day long. If your intent is to run these high amperage items, you really need to consider a 24 volt or 48 volt system.

 

[willo]

Don't forget that you can use multiple SCC to divide and conquer if you need to.
The victron mppt calculator page is handy for figuring out what can work for you. You can put in your panel info and play with the wiring options.

Issues to consider:
In cold conditions, you'll see a higher voltage from the panels - so if you leave like a 20% buffer on your voltage rating and you should be pretty safe. This is why you'll see higher voltage controllers spec'd.

With higher voltages, you can use lighter wiring - this is pretty helpful. Keep in mind what wire gauge you're going to run.

You can also play with it to determine what voltage you want. I happily use a 24v myself.