Looking for feedback on camper trailer PV setup concept

[CantStopTommy]

Hello,
Newbie here looking for feedback on my idea for powering an off-road camper trailer.
We're building this trailer for a planned ~6 month lap of Australia with our family of 4.

Guiding principles
- Be self-sufficient on PV alone - most similar setups seem under powered on PV and constantly require shore power and/or DCDC charging from the tow vehicle's alternator - don't want this!
- No AC loads - trying to avoid an inverter as we don't need it - i think 12v can power everything we actually need
- No dual battery setup in the tow vehicle - seems like a lot of expense that could be invested in the trailer instead

Calcs
Average Load (from my big spreadsheet)
1.05 kWh / day (88Ah/day)

Solar Power Required (assumes avg solar irradiance = 5hrs/day)
422W

Days of Autonomy
2 (Australia is pretty sunny!)

Battery Storage Required
2.1kWh (176Ah)

Required Charge Controller Capacity (assumes 500W of PV is used)
41.7 A

Planned System Specs
500W of solar panel/s
200Ah LiFePo4 battery
50A PV Charge controller (MPPT)
Lots of USB and Cigarette outlets
240V Battery Charger + extension cord for shore power if we need it (with charging profile for LiFePo4)
~500A capable jump start battery (in case we accidentally run down the start battery on the tow vehicle)


Q's for you!
- Does this setup make sense?
- Should I allow more headroom in the Charge Controller Spec in case I want (or need) to add more PV later
- If I use a nice BMS like the Overkill, do I still need a shunt to accurately monitor state of charge, etc?
- Should I build up my own battery from cells and Overkill BMS?
- If I build, are the Fortune cells worth it? (lots of corrugated dirt roads where we are going)
- What am I missing?

Any and all feedback will be much appreciated!
Cheers,
Tom

 

[John Frum]

2 kw of battery is easy to do.
For "corrugated dirt roads" I would choose battleborn batteries with interconnects make of welding cable.
In this scenario you will require a shunt.
If you are confident you can build a battery to tolerate usage model then more power to you.

433 watts / .9 conversion factor / 2 horizontal roof mount penalty = 194.85 watts into the batteries
Does that sound about right?

 

[time2roll]

If you only need two days then sufficient battery alone should get you through.

 

[chrisski]

Is your area really so sunny you don’t think you’ll go without sun for more than two days in six months? I think not wanting a charger is pretty brave.

Does your 500 watts of panels take into account the angle and any shade? My flat roof panels on the a good weather shortest day of the year produced about the watt hours what they wattage of the panels is. The biggest loss was shading from things on the roof, otherwise I would have gotten twice watt hours than the panels rated wattage. In the summer with the longer days and higher sun angle, the flat panels may reach five or six times without shading.

I think even though a 500 watts of panels may produce 30 charging amps, I think a 50 amp controller is good. I have noticed the charge controllers I run at full rating get warmer than the ones that aren’t running near max. Temps are still cool so running my 30 amp charge controller at 30 amps is slightly warm, but I wonder how this will be in the summer. For expansion, I first added additional charge controllers to each battery. This was much easier to do with space limits of my RV than try to fit solar panels on the roof.

For DC quick connections, I have found Anderson Powerpoles to be a useful disconnect. I have a couple of lighter sockets liek you mentioned, but decided against using those because they were bulky. THat of course does not apply if it comes wired from the factory with it.

 

[CantStopTommy]

2 kw of battery is easy to do.
For "corrugated dirt roads" I would choose battleborn batteries with interconnects make of welding cable.
In this scenario you will require a shunt.
If you are confident you can build a battery to tolerate usage model then more power to you.

433 watts / .9 conversion factor / 2 horizontal roof mount penalty = 194.85 watts into the batteries
Does that sound about right?

Thanks Joey,
I had a look at those BBs, great batter but very expensive for us down under ($3,600 AUD for 200Ah landed in Australia)
Do you have any thoughts on those Fortune cells that Will reviewed

They look properly tough and I'd feel confident wiring them up. Getting them to Australia is another matter though.

Re the panel sizing, i total forgot to include conversion factor and compensate for mounting them flat. I'll get that fixed up now. Thank you!

 

[John Frum]

Do you have any thoughts on those Fortune cells that Will reviewed

I like them.
Great for a smaller setup like yours.
Good match for the overkill 4s bms.
From memory they have really beefy 3/8"(10 milli-meter) terminals.
Tough cells from the reports I've heard.

 

[CantStopTommy]

Is your area really so sunny you don’t think you’ll go without sun for more than two days in six months? I think not wanting a charger is pretty brave.

Does your 500 watts of panels take into account the angle and any shade? My flat roof panels on the a good weather shortest day of the year produced about the watt hours what they wattage of the panels is. The biggest loss was shading from things on the roof, otherwise I would have gotten twice watt hours than the panels rated wattage. In the summer with the longer days and higher sun angle, the flat panels may reach five or six times without shading.

I think even though a 500 watts of panels may produce 30 charging amps, I think a 50 amp controller is good. I have noticed the charge controllers I run at full rating get warmer than the ones that aren’t running near max. Temps are still cool so running my 30 amp charge controller at 30 amps is slightly warm, but I wonder how this will be in the summer. For expansion, I first added additional charge controllers to each battery. This was much easier to do with space limits of my RV than try to fit solar panels on the roof.

For DC quick connections, I have found Anderson Powerpoles to be a useful disconnect. I have a couple of lighter sockets liek you mentioned, but decided against using those because they were bulky. THat of course does not apply if it comes wired from the factory with it.

Thanks Chris!
Great input. yeah i was being too optimistic regarding the real world output of the panels. Even a small amount of shading can kill our output, especially if you've wired the panels in series. One thing I omitted from my original post is my plan to mount the solar panels. Idea is to use the full top rack of the camper trailer, so shading from my things shouldn't be a problem, they will be mounted flat... Also, we'll sometimes be parked up in shady areas, so being able to move the panels off the roof and tilt them appropriately would be a good idea. I'll add some sort of quick release for the panels and extension cables to allow them to be setup away from camp.

Regarding the loads, very few are actually essential, we've done 2 week trips before with xero power, so we know how to throttle our usage to stay within our supply. (one reason why easy system stats and SOC readings are important to me)

Finally it was pretty far down the post, but I do plan to be able to charge the batteries with 240v when we have access to mains power. Just going to use a standard battery charger that supports LiFePo4.
No plans for DCDC charging off our alternator though. Is that the charger you were talking about?

 

[CantStopTommy]

I like them.
Great for a smaller setup like yours.
Good match for the overkill 4s bms.
From memory they have really beefy 3/8"(10 milli-meter) terminals.
Tough cells from the reports I've heard.

Yeah, they do look like strong terminals, but I still cringed a bit (lot when I saw Will using an impact driver on them!

 

[Rocketman]

The biggest challenge for solar on RV’s is the roof space. Getting it to fit. While looking at 500w - usually people think of 5 100w panels, but don’t overlook 3 200w panels or 2 360w.

As for the fortune cells - I love them except for the price. There is a supplier of them at driving distance to my old house, I was making a 50ah portable 12v battery w/8 25ah fortune cells. So I dropped by to pick them up. While I was there I looked at the 60ah and 100ah cells that were in stock. I LOVE them! But they were too expensive for the battery on my MotorHome. I installed 272ah Lishen cell.

Good luck

 

[CantStopTommy]

Thanks Rocketman! Yeah, I'm planning on having nothing else up there at all. (more space + no chance of shading cells with my gear)
Space available on rack will be about 6ft x 6ft square, so should be able to fit plenty of PV.

Yeah I definitely have some battery envy looking at those Fortune cells. That said, one of the key features I like about them are the top and bottom plastic protectors with holes for clamping them together (and terminal covers). I probably could 3D print my own versions of this style of design and use other more readily available cells. My poor printer would be running for days on end, but it might be a viable solution for me.
How'd you find the battery build process btw?

 

[Rocketman]

I enjoyed building the batteries. I have done a write up on both builds - but I am not very good at documenting stuff. The 1st one is with the 25ah fortune cells.

Small Portable Battery - Show & Tell.

Well I finished my 12v 50Ah LiFePo4 small portable battery. I will be using the battery in my Jeep and for camping. It has eight 25Ah Fortune cells from electriccarparts.com and an Overkill BMS. I started to play with the batteries with my Batrium BMS in this thread: BMS...

diysolarforum.com

Batrium Watchmon Install

Hello everyone, I have a 2000 Monaco MotorHome, I will be installing eight 272ah Lishen LiFePo4 cells making a 2p4s 12v 500Ah (useable) battery. My two largest loads are a Victron MultiPlus 12/3000 inverter/charger and the engine "Boost" if my chassis battery gets low. For the BMS I chose a...

diysolarforum.com

Another idea on solar - if possible figure out how to tilt your panels. You get LOTS more power in the winter w/tilted panels. My guess is you would get more in the summer too.

 

[CantStopTommy]

Look like fun builds! and really well documented too! (imo)
Yeah I like that idea re tilting, ideal fixed angle for Sydney is ~33deg which if I could tilt the panels to (and get the right azimuth) would get me a nice bump indeed.
Thinking hat engaged...

thx!

 

[chrisski]

No plans for DCDC charging off our alternator though. Is that the charger you were talking about?

I was talking about a DC to DC charger; however, your plan to charge off 240 volts is valid.

I do not have a DC to DC charger for the alternator. I am able to charge through shore power either at a campground through 120 volts or by taking a generator out and Hooking to shore power. I’ve only had the camper out for a couple of weeks so far, but have not had to charge.

I also like your idea about disconnecting the panels and putting some on the ground. I have a portable array that has less watts of panels, but produces more power than the roof panels.