Design questions for a solar system

[Firetodd]

My family are avid campers who spend 50-60 days per summer at a lake. Our land at the lake has no facilities and so we “boondock” for 4-6 days at a time and generally have used portable generators. Our power needs are small as we rarely if ever have used air conditioning. We can swim or boat to cool down and entertainment can be found in front of a campfire!


I am getting a new 5th wheel camper and want to go solar to limit or even eliminate the need to fire up portable generators (the lake has rules against generators after 10pm too). The 5th wheel RV will come with a 50 watt solar panel on the roof, connected to a solar port, and run down to a cheap charge controller in the battery compartment. I plan on discarding the 50 watt panel and charge controller and putting in my own system. My hope is that the wires from the solar port are 10-12 gauge at the minimum. The RV has a 50 amp power cord….


So I have looked at a million systems and watched every video on youtube and am struggling to decide on exactly what to do. I had pretty much decided on going with a Growatt SPF3000 24V all in one, with two 24V-A123 LifePO4 batteries from bigbattery.com with 240ah of storage, and (6) 310 watt panels from santansolar.com wired in 3s2p. As the storage compartment and electrical systems are not remotely near each other, I was planning on placing the batteries and Growatt unit in the compartment and wire the AC output of the Growatt to a new boxed 50 amp outlet in the compartment. Then when I arrived at the lake, I will take the shore power cord from the RV and plug it into the outlet. I understand it would be under powered, but I really only need it to power some tvs, charge phones, and charge the separate house batteries. As I don’t use A/C, that system should allow me to eliminate the need to fire up a generator for the most part and to flip on a TV at night. But that system with shipping would be about $5000 with wiring, Victron Bluetooth shunt, and materials.


Then I went down the rabbit hole of building my own batteries. I had watched Will Prowse and others build their own LifePO4 batteries by ordering cells and a BMS and decided that I could do that! So I looked at 280 AH cells and thought that I should buy 16 cells and matching BMS unit and depending on pricing and time of shipping from Alibaba, I could cut my battery prices down $600 and increase storage to 280ah! But I worried that I’d get grade B cells or make a mistake and burn down the whole thing, plus I would need to spend money on power supplies and materials to balance and charge the units and build enclosures. So I may be back to looking at the Big Battery premade units, although I ‘m not sold on the Anderson connectors…


And then I saw the MPP LV6548. It can provide more than twice the power of the Growatt unit and provide power from solar panels even without any batteries connected! If I were to wire the two 24V-A123 LifePO4 batteries from bigbattery.com in series for 48V, I would have 120 ah of storage. The larger MPP LV6548 would also allow me to wire my panels in a 6s configuration as well. Having more power available would be nice for two reasons. One, not having the noise of a generator is nice, but even if I do this system, my in-laws will still need to fire one up to power their camper to watch tv at night in their camper. Having more power will allow me to run an extension cord to them as well. The Second reason the MPP LV 6548 appeals to me is that because the charge controller in it allows up to 250V input, I can run the solar panels in series and lower the amperage on those unknown solar wires routed down from the roof. Total price for this system is $5600.

Here are the panels: https://store.santansolar.com/product/csun-310w/

Here is the MPP LV6548 all in one: https://watts247.com/product/2-x-lv...kw-250v-mppt-bms-ul1741-listed-built-in-wifi/

Here are the batteries: https://bigbattery.com/products/24v-a123-8s5p-lifepo4-battery-box-3/

RV outlet: https://www.amazon.com/GE-Unmetered-Circuit-Protected-Receptacles/dp/B00FI6TKK2/ref=sr_1_36

My RV: https://www.rvwholesalers.com/desig...fth+wheel&brand=heritage+glen&floorplan=378fl



What do you think?

 

[snoobler]

I think you have designed a system without a concrete goal.

Step 1: How much solar potential do you have? (Link #5 in my signature, link #6 if there's not a nearby city)
Step 2: What do you want to power, how much does it use, and how long do you want to run it each day (link #1 in my signature)

Those two steps enable you to design a "perfect" solar system that will meet the needs.

Concerns:

More power isn't necessarily better. An inverter burns power just by being on with no loads applied. It takes energy to make 60Hz/120VAC available at the outlet. Bigger inverters use more. That unit has a 70W idle consumption. That's 1.68kWh per day. Based on the battery you linked, just powering the inverter will consume 29% of your daily battery capacity (5.76kWh).

Solar panels in series are sensitive to shading, even partial shading. Your RV roof protrusions may partially shade portions of your panels. Partial shading of one panel will affect the entire series string of panels. The best way to deal with partial shading is to limit your series panels and favor more of them in parallel. Unfortunately, for a 48V bank, you need 3 of those panels in series, so you'd need 3S2P. In that case, I would try to have one of the strings comprised of panels that are the least likely to be shaded with the second string comprised of the panels that are more likely to be shaded.

There are cheaper RV outlets available. https://www.homedepot.com/p/Midwest...Amp-Temporary-RV-Power-Outlet-U054P/100193650

Here are some limitations of your components:

1860W of solar.

In winter, you'd probably only get about 1.86kWh of energy per day - that won't be enough to run a typical residential fridge for a day. it will barely be able to allow you to just turn the inverter on. It would take over 3 days to fully charge your 5.76kWh battery assuming you use no power at all (inverter off, lights out, etc.). In summer, you'll probably pull in about 7.44kWh/day.

Your battery can provide 5.76kWh between charges. That would allow you to run a single RV A/C for a little over 3 hours. That's it. Good news there is the idle draw of the mega inverter won't matter much over only 3 hours.

I have a 4kW Victron that powered two RVs. One RV was the "primary" where the heavy appliances got used. The second ran everything except the high current items - microwave, water heater, A/C, etc. We would occasionally use high power items, but we just checked that there was sufficient power available.

Lastly, if it runs on propane, run it on propane. Don't imagine you have sufficient capacity to run that AC/propane device on solar/batteries. For example, a 7.5cu-ft absorption fridge uses almost 5kWh per day in fair weather conditions.

I recommend you execute steps 1 and 2 and then establish a design goal. At this point, you're getting ready to drop $6500 on "hope," and I hope that I've illustrated designing on hope results in unfavorable outcomes... like an inverter that consumes 29% of your battery capacity just by being on.

 

[HRTKD]

Firetodd, is the 5th wheel electric system currently 24v? If it's 12v, then you may need to include some heavy amperage step down converters. 5th wheel trailers with landing gear and leveling systems (which yours has) often draw quite an amp load. A cheap step down converter probably isn't going to cut it. For that reason, you may want to stick with 12v. If the system is already 24v, then no worries as long as the BMS in the LiFePO4 batteries can handle the amp load.

 

[Firetodd]

Thank you for responding! I am in Colorado and only use the RV from May through August. So I may get 6 hours a day of good sun.

With my past camper, I have used a small 2k inverter generator for about 3-4 hours a day, mainly when kids needed the microwave, to watch a game Tv, or to charge some devices. I specifically spec’d a two way fridge so that I can continue to use propane for the fridge.

I hadn’t thought about shading of the panels or the draw from the all in one unit. I could go with 8 panels and go 4s2p. Additionally, I could go with the Growatt SPF3000tl LVM ES model as it may have a smaller draw and still allows up to 250volts on the solar input.

Luckily there are no trees on my spot on the lake.

@HRTKD this system would not be connected to the electrical system in the RV, but rather separate and only connected by the shore power plug.

 

[Firetodd]

The travel trailer in the picture is the one that I am replacing.

 

[HRTKD]

The solar/battery/inverter will be used only to generate AC power then?

I'm in Colorado also, south of Denver. I camp March to November currently, but hope to expand that by doing a bit more travelling down south.

 

[Firetodd]

The solar/battery/inverter will be used only to generate AC power then?

I'm in Colorado also, south of Denver. I camp March to November currently, but hope to expand that by doing a bit more travelling down south.

I’m in Arvada and “camp” near Fort Collins! Yes, I am only using to generate AC.

 

[snoobler]

Thank you for responding! I am in Colorado and only use the RV from May through August. So I may get 6 hours a day of good sun.

With my past camper, I have used a small 2k inverter generator for about 3-4 hours a day, mainly when kids needed the microwave, to watch a game Tv, or to charge some devices. I specifically spec’d a two way fridge so that I can continue to use propane for the fridge.

I hadn’t thought about shading of the panels or the draw from the all in one unit. I could go with 8 panels and go 4s2p. Additionally, I could go with the Growatt SPF3000tl LVM ES model as it may have a smaller draw and still allows up to 250volts on the solar input.

Luckily there are no trees on my spot on the lake.

@HRTKD this system would not be connected to the electrical system in the RV, but rather separate and only connected by the shore power plug.

Flat panels on a roof are somewhat compromised, so you won't get optimal sun, but 5 hours is probably very do-able, so that would get you 9.3kWh. Even if you needed 100% of your 2kW generator, 3-4 hours is only 6-8kWh, so your solar is beyond that, and you can probably get by on your battery.

I haven't factored in any inefficiencies. Assume 85% efficient for anything AC powered and 75% for anything 12VDC powered.

 

[snoobler]

I’m in Arvada and “camp” near Fort Collins! Yes, I am only using to generate AC.

Here's how your 1.86kW array would perform in Ft. Collins:



May: 276/31 = 8.9kWh/day
June: 279/30 = 9.3kWh/day
July: 267/31 = 8.6kWh/day
Aug: 239/31 = 7.7kWh/day

It factors in AC inefficiency, so the above would be usable AC energy on a daily basis.

 

[Firetodd]

Thank you @snoobler ! I’m thinking I will work on figuring out the layout plan to get 8 panels in the 4s2p configuration. And I’m pretty sure I like the Growatts 3000 ES model.

 

[Firetodd]

I will still have a generator and can fire it up if needed, but this does look promising.

 

[HRTKD]

Firetodd, if you want to avoid shipping on panels, there is a place in Denver that I bought my panels from. 320w panels for $180 each. Brand new. Look up CEDGreenTech.com.

Is that camping spot North Poudre Reservoir? I've fished in a few spots near there.

 

[Firetodd]

Yes it’s one of the 15 North Poudre Reservoirs - but this thing has almost no fish.

 

[HRTKD]

The one in the area that I did well at was Douglas Reservoir. I caught a few nice Trout there. That reservoir also has Walleye. But without a boat, I wasn't going to catch Walleye.

The plan you have is interesting. It's a good way to not have to rip up the existing system. It may not be as efficient, but it's probably going to be easier.

 

[Firetodd]

Ok, I will be building a 48v 280 ah battery with 16 cells and an overkill bms to increase energy storage. I will also be using 8 panels as well.

 

[Firetodd]

Here is my design layout:

 

[Firetodd]

I will be leaving the second MPPT input on the LV6548 for a future ground mount. I understand from reading other posts that the Blue Sea battery switch may not be appropriate for a 48v battery system and will be researching my options. Other than that, how does the system look?

P.S I understand that the LV6548 wont supply both phases to my outlet box. I will be running a jumper to the second bar in the panel as Will did in his latest trailer build.

 

[HRTKD]

Looks good. The fuse between the two solar strings isn't necessary. With only two strings a fuse isn't required. It looks like you have combiner box. Will it have circuit breakers?

 

[Firetodd]

I had planned on just using this switch for solar shutoff, because I would have inline MC4 fuses. Here is the switch: https://www.amazon.com/gp/product/B07C8VF2J8/ref=ox_sc_act_title_3

 

[HRTKD]

I had planned on just using this switch for solar shutoff, because I would have inline MC4 fuses. Here is the switch: https://www.amazon.com/gp/product/B07C8VF2J8/ref=ox_sc_act_title_3

That would work. I think the rating you used for the fuse is higher than it should be. Maybe a 15 amp fuse instead.