Planning out solar shed w/ Travel Trailer

[offgridaaron]

Hi all, I'm in design mode for my little acreage I'm planning on putting a travel trailer on. Apologies if this has been asked and answered, I've been spending weeks researching this stuff and it can be a bit overwhelming at times trying to lock in each aspect.

I'm thinking of doing a 48v system, with a decent size panel array (thinking 8x 445w Canadian Solar panels) and some lifepo4 batteries.

What I'm thinking of doing is beside the RV build a small shed that will house the solar gear and batteries. I'm planning to have insulated panels that I can slide into this shed come fall to really insulate around the batteries, and do a heating pad to keep the batteries above 0C in the colder northern Canadian winters. I do hope to use the trailer in the dead of winter as a place to crash after a day of ice fishing. And then come spring I'll pull the panels and allow more airflow and cooler temperatures in this shed.

What my big question is right now is how i wire the 12v stuff. What I was envisioning is plugging an inverter into the shore power plug to power 120v from solar. I'd disable the converter in the trailer because there wouldn't be the traditional 12v battery in the trailer anymore, just the lifepo4 48v bank. What my initial thought was take a 48v to 12v dc-dc thing, like victron or the cheap ebay/amazon one (although I'm scared of cheap electronics starting a fire) and wiring that from the 48v battery bank to the two battery leads that are at the front of the trailer that you would have bolted to the trailer battery (but again, no actual battery there)

What I *think* I'm learning is running a 48 -> 12v dc-dc converter without a battery there will cause electrical issues or not provide enough power for slides or furnace fans? I also thought of just doing the shore power plug and using the built in converter, and since there is no trailer battery hooked up, the charge part of that wouldn't function. But I also think I read that is a issue and the converter is more planned to trickle charge a battery, and the 12v gear in the trailer expected to run off the battery, not that converter.

I guess in my situation where my solar system is outside of the trailer, with no actual trailer battery planned, what would be my best solution for good 12v power? I think enough stuff runs off 12v I want it to be as robust as possible. The furnace fan uses 12v and is important in winter, and I think the fridge is better on 12v than 120v?

 

[sunshine_eggo]

What my big question is right now is how i wire the 12v stuff. What I was envisioning is plugging an inverter into the shore power plug to power 120v from solar. I'd disable the converter in the trailer because there wouldn't be the traditional 12v battery in the trailer anymore, just the lifepo4 48v bank.

Why? The additional 12V is a small bit of redundancy, and it really simplifies things... simply plug into shore power. That's what I do. You're describing my system except my little shed is a 40' shipping container.

I have the system in the container and I plug my unmodified 5th wheel into a 50A power pedestal.

What my initial thought was take a 48v to 12v dc-dc thing, like victron or the cheap ebay/amazon one (although I'm scared of cheap electronics starting a fire) and wiring that from the 48v battery bank to the two battery leads that are at the front of the trailer that you would have bolted to the trailer battery (but again, no actual battery there)

No thanks.

What I *think* I'm learning is running a 48 -> 12v dc-dc converter without a battery there will cause electrical issues or not provide enough power for slides or furnace fans? I also thought of just doing the shore power plug and using the built in converter, and since there is no trailer battery hooked up, the charge part of that wouldn't function. But I also think I read that is a issue and the converter is more planned to trickle charge a battery, and the 12v gear in the trailer expected to run off the battery, not that converter.

Possibly. They have zero surge capability, and you'll have to way over-size them... easier to just leave the battery and converter running.

I guess in my situation where my solar system is outside of the trailer, with no actual trailer battery planned, what would be my best solution for good 12v power?

Wouldn't you like the redundancy of the trailer 12V to run the furnace if there's a problem with the power system?

I think enough stuff runs off 12v I want it to be as robust as possible. The furnace fan uses 12v and is important in winter, and I think the fridge is better on 12v than 120v?

You MUST run your fridge on propane. They burn an INSANE amount of 120V. 4-5kWh for a typical 7.6cu-ft unit. You'll need a meager bit of 12V for the propane thermostat/valve.

I have relied on the Trailers' 12V system MANY times when having issues, troubleshooting or modifying the power system. In fact, one of the 5th wheels 12V system powers the modem/router and the blink cam module. That way I don't lose my meager DSL if I lose 120VAC.

 

[offgridaaron]

Awesome, thanks so much for the detailed response! That all makes sense to me, and I like your approach which is what i'm after too, not modify the trailer to the point its hard to resell or hook up and take camping elsewhere.

I think I was overthinking it thinking that there would be a super significant power loss going inverter -> shore -> converter -> 12v, but I bet I'm just overthinking that.

I think I'd still re-route the house battery to the shed for winters so it can get in the insulated heated area but thats easy. As I start getting further along in the planning and such I'll post back some drawings and thoughts. Fun to share these ideas, and really fun to hear opinions and tweaks.

thanks sunshine_eggo!

 

[sunshine_eggo]

There is a notable efficiency loss going DC-AC-DC. 75-80% efficient typically, but ultimately, your 12V loads are likely a very small portion of you're overall system, and it's a very small price to pay.

Lead acid don't actually mind the cold. They mind being used as starter batteries and require different charging parameters when cold (higher voltages). Simply disconnecting it and letting it sit in the cold is more than sufficient to maintain it while you're away. The cold slows the loss of charge. AGM will lose about 1%/month and flooded will lose about 10-15% per month.

You didn't list it, but I suspect you're looking at some of the lower end/low cost MPP Solar, EG4, Growatt, etc. units. Something to watch for on those is idle power consumption. They're pretty high. For every 3000W of inverter output power, count on 40-50W of idle consumption. 6000W inverter would burn 80-100W. That's all the time even if no loads are active. Make sure you factor that into your design. A 6000W inverter that burns 100W consumes 2.4kWh of juice per day. That's nearly 50% of the capacity of a $1500 EG4 48V 100Ah battery. It also means that the first 500W of your PV is going to replace that consumed energy and isn't available for your loads.

 

[offgridaaron]

Ah ok, good tip on the lead acid, I'll look more into those.

Yea I'm still parts shopping and planning. I may wind up with a MPP or Growatt for costs and ease to get started, with the plan and dream to go more robust down the line. Phew that is a lot of idle consumption to account for. I think having a remote kill switch for the inverter (which I don't think the growatt has, not sure about MPP) would be key, and only flick it on when necessary.

I think a few key things I want to hit is enough potential power to run the tv for a bit, charge a cell phone, and allow generator charging. I do not want to have a generator, but one of the goals of buying this lil acre lot is its really close to a lake and its pretty well treed. My dad is getting on and very frail and I think only has a couple years at most left where I can get him out. As a kid he lived in the bush, and he keeps talking about going for a fish, but without having a base camp, we're struggling to get him out. He can do an hour or so and then he really needs a bed. My thought is if I can get him there, its really well treed so it'll feel like he's in the bush again, even though its only an acre, and we can get a couple very short trips down to the lake front, let him do a few casts, and then get him comfortable back in the trailer again. So if its a ridiculously hot day, it'd be nice to cycle the AC on for 5 minutes, even if its generator assisted, and just give him a bit of relief as he's falling asleep. Or if he's having a really off day, and not getting off the couch, let him use the TV for a bit.

When its just me or my friends going , our power needs are pretty small. Some lights here and there, the pump to wash our hands, and otherwise we'll be out having a fire or exploring the area.

Like I mentioned I do also want to use it in the winter ice fishing, so there will the furnace and potentially some space heaters then.

Thanks again for the replies. As I kind of narrow down what I'm planning to order I'm going to post back a plan and diagram.