My 2600RB solar/power upgrade plan

[SteveCF]

Hey all!

Just got our used 2021 2600RB this spring, and planning out my solar/power upgrade. I've done a ton of reading here and in other forums, and this is what I'm thinking of.

My 2600RB has the Solar Prep: 10ga "SOLAR/INV" wires to the roof and to the battery, and we have the 2-way propane fridge. We boondock at State Parks almost exclusively, so my goal is to be able to boondock for 7 days in the summer (using 12V or USB fans for cooling, and possible furnace use on cool nights), and for 3-4 days in fall (in Wisconsin, so nighttime temps in the low 30s, and heavier furnace use).

Proposed equipment:

• Victron SmartShunt 500
• Victron SmartSolar 100/30 MPPT solar charge controller
• Rich Solar 200W 24V panel (possible future expansion to 2P, or even 2S2P config if I decide to add an inverter later)
• 2 x 100Ah LiFePO4 battery with cold temp cutoff: Weize, ADCBATT, Lisuatelli
  • Locate batteries in under bed storage, directly behind my planned panel location in front pass-through storage
• Circuit breaker between charge controller and panels. I wanted to plan for a possible future 2S2P configuration, which puts me beyond the limits of the Blue Sea surface mount circuit breakers that are often mentioned (max 48V). I read some suggestions for a breaker like this. Would the 16A model be appropriate here?
  • https://www.amazon.com/C65H-DC-Low-Voltage-Miniature-Circuit-Breaker/dp/B07HG5YR77
• Circuit breaker between charge controller and battery: same as above but the 32A model?
• 2ga parallel battery cables (planning for possible future 2000W inverter)
• Obviously not a comprehensive list, need panel mounting HW, possible panel extension cables, etc.

From what I’ve read, I should not “need” to upgrade the converter to a LiFePO4-compatible model, but can rely on solar charging to get the batteries to 100% SOC. Am I off base? (I was planning to carry a small portable LiFePO4 compatible charger as a backup, or to wake up the BMS if needed.)

Also I'd love to hear confirmation/correction on my breaker type/size choices.

Anything else big that I'm missing here, or that doesn't sound right?

I'm not specifically asking the "will this meet my boondocking goals?" question because I really can't tell how much power I'm using without the SmartShunt. But in our first couple of summer outings, I was able to get about 3 days on my 100ah FLA battery, so I feel pretty comfortable that this will take care of us, and set us up well for the future addition of an inverter for small appliance (Kuerig, hair dryer, etc.) and TV usage.

Thanks for any thoughts!
Steve

[Country Campers]

First please disregard the INV on the solar/inv sticker, this was a mislabel by GD and has nothing to do with an inverter.

I would get 3 or 4 batteries now as they are not recommended to add more after the original are more than 6 months to a year old.

Next I would get a lithium compatible charger. If you have or get a generator to use on those cloudy days where solar is not producing you will appreciate the less time a generator needs to run.

If going to an inverter someday I would recommend 4/0 or double 2/0 wire for paralleling the batteries. This will come in handy with the draw from an inverter and the high charge rate from a lithium charger. It my be a little overkill but it is only a few dollars more.

Just my thoughts, others will be along with theirs.

Brian

[TucsonJim]

Your plan will work. Just plan for future growth when you layout and install your components. I always seem to find new items to add and sometimes wish I'd planned a little better on previous upgrades.

Jim

[SteveCF]

Thanks! And the fuse sizes/types make sense for this setup?

As far as battery bank capacity....we only boondock at state parks where generators are not allowed, so we need to have the necessary capacity with us (or solar to regenerate). I'll have to think a little more about what my final config might be, so the second phase might wait until next spring!

[howson]

SteveCF

The 100/30 solar controller isn't big enough for a 2P/2S configuration...unless I don't understand what you mean. To me 2S/2P means 800W of solar. 800W (at max which is rare) could generate almost 60 amps on the output of the controller. (800W / 13.6V = 58.8 amps) If my assumption is correct consider going with a SmartSolar 150/70.

I agree 100% with Country Campers recommendation to go with more batteries. If the future (possible) inverter is a 2000W, then three 100aH will work well. (Batteries are the true limitation with off-grid power. How many batteries is usually a decision driven by the space to put them and the thickness of your wallet!) Buy all three batteries now.

Nothing wrong with putting circuit breakers between the controller and solar panels, but if the wiring between the two can handle the maximum the panels can ever generate, what's the point? If the breaker is rated below the maximum output of the panels you'll deal with nuisance popping of the breaker. If it's rated beyond the capability of the panel configuration, when will it ever open?

A switch between the panels and controller--I totally agree. Get a switch rated for the maximum DC voltage it will "see" from the array (VoC).

There are long debates on the topic of installing a breaker or fuse between the controller and panels already on this forum. Yes, a very popular solar-related website disagrees with me. It is a fact that a breaker between the panels and controller is not "code" in an RV for our relatively small, DC-coupled systems. PV-coupled systems tied directly to the grid in a home? Absolutely code and required. Not in our rigs. If it is, GD is in violation on every RV they produce with OEM solar.

For the breaker (or fuse) between battery and controller, the typical recommendation is 25% above the maximum amperage expected. Assuming a 150/70 controller (so 70 amps maximum) that's about a 90 amp breaker (or fuse) between the controller and battery. Of course, the wiring must be capable of handling that much, too, if not more. (Don't skimp on wiring or connectors. See Will Prowse's video on YouTube on the topic. It's an old video but has excellent content.)

One other thought: keep in mind that Victron solar controllers don't start producing power until the solar (PV) is 5 volts above the battery voltage. With lithiums it's normal to have a 13.x resting voltage, so PV output must be at least 18V to start charging the battery. What is the Vmp of the panel you're considering (the normal high operating voltage)? If it's 24V, that is a relatively narrow operating window (18-24v).

I installed Renogy 100W panels and tied two in series, then six of those series configurations in parallel (so 2S/6P for a total of 1200W). Why two of the 100W panels in series? Because the Vmp is 17.7V. Two in series is 35.4V. I get excellent results since the panels start producing almost as soon as there's PV available because PV quickly exceeds the battery standing voltage.

Howard

P.S. I've delved deep into this topic on many occasions, but as in all cases on forums like this remember I'm "just a random guy on the internet". If in doubt, keep asking questions.

[SteveCF]

Thanks howson for the detailed explanation!

Yeah, I did mean a total of 4 panels, 2 series pairs paralleled....I thought that was referred to as 2S2P, but I could be wrong!

But you are right that the 100/30 controller is too small. I found the Victron MPPT sizing calculator, and when I entered the params for the RICH Solar 200W 24V Solar panel, it said I needed the 150/45 (These 24V panels actually have Vmp=37.6V and Imp=5.32V...which means I should also have no problem with the Victron solar charger startup voltage, about the same as your Renogy 2x100W in series.)

In reality, my practical thought has really been 400W anyway. I'm balancing $$ vs features, and in reality we're looking at $1500 more (at least) for inverter capability including more batteries and extra solar panels to keep them charged, plus the beefier charge controller. The more I think about it, that's not in the short to med-term plan. I'm OK with the limitation of 30A max charging at this point, with whatever functionality it will get me. (I may consider the 3rd battery up front, depending on how it fits physically for me.)


As far as the breaker/fuse between the panels and the charge controller, that has always confused me! I've also seen configs with a DC switch to disconnect the panels, but TucsonJim's "Solar 101" presentation shows a fuse between the panels and the controller. After reading further, I found this article that is the clearest thing I've read so far about fusing panels. And according to the logic in the article, I wouldn't need any fuses in a 1x200W or 2x200W config.. Based on that, I agree that a DC switch is really what I want, and a fuse makes no sense here. (That probably explains why GD would not have fuses, since their configs are all 1x200W or 2x200W panels?)

If I did I add a 3rd 200W panel (which the 10ga wiring would support, and would only be a little oversized for the 100/30 controller), then it looks like I would be just over the Max Series Fuse Rating for the panel (Isc is 5.83A, so 3x5.83 is higher than the 15A max series fuse reading). So according to the article, I would need a 15A fuse on each parallel panel. In this 3x200W config, the fuses are really about protecting the panels themselves.

Since I don't need a higher voltage circuit breaker, I would change the controller-battery breaker to use a Blue Sea or similar surface mount breaker. The 100/30 says the terminals will take 6AWG wire. So I think I could go with 8AWG wire and 35A breaker, or 6AWG wire and a 40A breaker. Does that sound about right?

Thanks again! Steve

[howson]

SteveCF -- as Will Prowse states in his video (I'm paraphrasing), power loss in a solar system due to system wiring is one of the most overlooked aspects when building a system. Bottom line: I'd put the maximum size wire the solar controller will accept regardless of what the system is expected to provide. (Larger gauge wire results in less loss due to the resistance of the wire itself.) Of course there's a point where it becomes silly--no sense installing 4/0 wire on a 200W system, but I hope you get the point.

Maybe I need more coffee this morning, but I don't understand the logic or the "why" behind the requirement stated in the linked article. Again, no claims to any special expertise on my part--obviously there must be a reason for the NEC code.

Thinking about it (as I'm typing), perhaps if I look at a panel like a section of wire it may make sense. If that "section of wire" is only rated to carry 15A, and the circuit it's being used in has the potential to generate 20A, then a fuse is required to protect that "section of wiring". That's the purpose, after all, of a fuse (or breaker)--protect wires.

Hmmm...will have to ponder this more. Thanks for response. I'm always (trying) to learn and understand.

With regards to the number of batteries and array size, consider that a rough estimate is 300W of power generation from a 100W panel per day (per Mike Sokol, an electrical guru I follow). So for the proposed 200W panel that's 600W per day. 600W / 13.6v = 45 amps. Given you're considering two 100aH batteries, a single 200W panel may have a tough time keeping up if power usage from the batteries exceeds that 600W per day guestimate.

A 400W array should almost provide the capability to recharge the batteries (assuming a 50% state of charge) in a day. A 600W array would be better IMHO if the budget will allow.

The point I'm trying to make is scale the array to the battery bank and expected power consumption. Kind of like ensuring an engine, transmission, and drive system on a vehicle are appropriate for each other. All of the parts must work together to get the desired end result. And, of course, buy the components so the system can scale with the expected end result.

Adding more batteries may not require a larger array--it will just provide more "fuel" when PV output of the array lags due to weather or other issues

Finally, if TucsonJim has a recommendation strongly consider it. He was the one that helped me when I got started on this stuff! (Good morning, Jim! )

Howard

[SteveCF]

Like you, howson n, I'm definitely still in learning mode as well! This convo, TucsonJim's Solar 101, and this forum in general have helped so much. I think I'm ready to spend some $$.

I have watched a bunch of Will Prowse videos already, and they were really helpful! (His battery teardowns and tests led me to my battery choices after he confirmed they had working cold temp cutofs!) But could you post a link to his video that talks about power loss due to wiring size? That one I haven't seen yet, and I didn't find it with a quick search this morning. Thanks!

[howson]

I'm currently out so on my phone. Not sure how to link from the YouTube app, so search for "Off-Grid Solar Buyers Guide : DC Wire and Connectors".

Another is "Off-Grid Solar Power System Comparison: Common Efficiency Losses and Bottlenecks".

[SteveCF]

Thanks! Will is awesome, so helpful. I'll be checking his wire recommendations before placing my order!

I usually watch YT videos at 1.5 speed to consume faster...but Will makes my head explode at that speed! 😄

[acoleman43]

SteveCF I didn't read all replies so forgive me if I repeat anything.

First thing I would do before you plan a system is do an energy audit. How much energy do you use each day you are boondocking. My energy audit came up just short of 3000W (this does NOT include air conditioning).

Now take this number and multiply by 3 (so you will have enough power for 3 days if your panels are not producing power for your batteries). For me this was 9000W. With 12v batteries this means I required about (8) 100AH batteries, or 800AH of energy (simple multiplication is 800a*12v= 9600W). That was double the batteries I thought I would need.

Another "rule of thumb" for solar is double the battery bank. If you have 800AH of batteries, you would do well with 1600W of solar panels (800*2=1600). I only have 1260W and wish I had more solar....especially when we want to run the air conditioner for a couple hours each day. On average our 1260W of panels will generate about 4KW to 4.5KW of energy each day......that is sunny. If it is overcast, solar yield can be less then 1KW per day. If my average energy consumption is 3KW per day but I am generating barely 1KW per day you can see the issue.

Basically you can never have enough batteries or solar panels. If possible I would double my battery bank and solar array. But my trailer just isn't big enough :(

As far as wiring/cables, oversizing is always MUCH better than under sizing. You have lower voltage drops and the temperature of the cables/wires do not exceed safe operating temperatures.

The goes for solar charge controllers and inverters. Oversizing is always much better then under sizing. I would go with the 100/70 or larger if you are planning expansion in the future. Also, watch your wire size into the solar charge controller from your solar array. It's the current that will require the larger wire size. If you keep your voltage high and current low, you will be able to put a lot of power through the 10 awg wires. I think your idea going with the 24v panels is good. The produce higher voltage and lower current. If you wire your panels in series, your current will remain low and your voltage will increase. Something to think about

Good luck. Keep us posted on the build I am anxious to see it work for you