Introducing the Solar Trailer Prototype #1!

There’s a new thing on our hill with an awful lot of batteries and solar panels - and it’s something I’m going to call “Solar Trailer Prototype #1” for reasons that… well… should be obvious. It’s a solar trailer, first prototype. As my wife pointed out, “You know, we have a lot of solar panels on the hill.”

Not to be too blunt, but… I mean, it’s a trailer. With solar. Woah. This particular one has most of 1000W of panel.

What’s inside? Well, mounting solar panels on a trailer isn’t terribly useful unless you can do something more productive with them, and we most certainly can. Inside, there’s a 48V battery bank of Trojan T105s (12kWh nameplate, but FLA being FLA, rather less in practice on a typical day with a high current draw), a massive 6kVA split phase inverter, a Midnite 150 charge controller, and some various other goodies to connect everything together.

The sun. It powers the trailer!

The main goal of the trailer being to power things, there are some outlets on the side. There’s a 30A generator inlet for charging in the top left, a 14-50 for powering dryers and EV chargers in the lower left, a pair of 20A 120V outlets in the middle, and a 20A/240V outlet on the far right. Not pictured here, a couple 120V inlets in the back that could, say, charge things from the backup outlets on my Sunny Boys.

Inside, the split phase inverter feeds what would be a fairly small breaker panel for a house, and is a rather larger panel for a trailer. But, done properly, everything is run in conduit and has breakers for both overload protection (the inverter can put a lot more than 20A out into a single 120V load), and for disconnection purposes.

It would be really inconvenient to have to lean over and poke the charge controller and such on the backside of the trailer from where it opens, wouldn’t it? Fortunately, we’ve got the controllers run over where you can just lift the lid and see what’s up, with full control of everything!

@Canem and I have been working on this concept for a while, and all the physical work is his. So, if you need something that looks insanely good built, ping him.

Ever since Jimmie kept rejecting my solar plans for battery backed stuff, I’ve been wanting something that would give me some backup capability for the house, that I can charge with solar, etc. My concept had been a solar trailer for a while - batteries, inverters, and some panels. Of course, I don’t work in metal (I work in wood), so I couldn’t have created anything nearly this nice. Fortunately @Canem does this kind of thing for a living, and we’re both interested in both the capabilities of a trailer like this, and the commercial potential for such. There have been some states doing less-than-great with their power grid lately, and with the whole arc of empire thing heading down, backup power seems a good market to try and enter!

This is the first iteration, which has both proved useful in service (running a sports camp a month or two ago and hopefully a movie night this week), and has proved a useful R&D exercise for what matters and what doesn’t - and, 2021 being 2020 Mk 2, of course we can’t get half the stuff that was used to build this one, like “the trailer frame.”

But the trailer is a bit over 1000 lbs, which means just about anything can tow it - including the Volt, which now has a receiver installed for the towing of “things like this.” I can charge the car from it, should I care to drag the trailer with me. I can run… well, really, just about anything from it. The welding of some later parts of this build were done with the power from the trailer. It will run damned near anything you can come up with, from the 6kVA inverter that will surge up to 18kVA for 20s (if the battery bank holds up - the bank is somewhat undersized for what it ought to be, based heavily on the fact that we couldn’t get anything and had to build around a used collection of batteries).

I beat on it today, in preparation for a movie night later this week - no good learning that the trailer’s capacity is drained 10 minutes before the end of The Princess Bride, is it? The battery bank held a C/6 load for 4.5 hours, which isn’t half bad for lead, and I got 140Ah out of the bank before low voltage cutoff triggered on a 30A load (at the battery voltage) - about 6.5kWh. Less than rated, by far, but I was also pulling a pretty good load from it, on cold batteries, and all that combines to reduce effective capacity of lead - plus, the pack has a few years service already.

Missing from photos is the 120V AC inlet that will go to a 900W battery charger, which I can feed with my office generator, should we need more power. I also don’t have the 12V subsystem installed, which will provide for phone chargers and the like.

What would you use a trailer like this for? We’ve got plenty of ideas, but I expect other people would want it to do things we haven’t considered!

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This is a beautiful piece of kit. I have no use for it, but I want one.

They’ll eventually be for sale… if we can get parts!

The second prototype is going to be a good bit smaller and even lighter, plus designed around efficient use of materials (we’re designing around minimizing waste in the sheets of material that come in).

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Very nice! How much extra range can you get in the EV vs the extra drain of towing?

I’ve had a surprising number of people ask if you could buy a “spare battery” to extend the range of an EV, though that’s probably not the intended purpose here.

Also, what about LIFEPo prismatic cells? I did receive the LIFEPo cylindrical cells I ordered recently and they seem high quality.

I’m not sure. I haven’t really towed it very far yet, and I expect the added drag probably about negates the added battery, though that’s partly due to an undersized battery bank in the trailer. We couldn’t get the stuff we wanted, because it simply wasn’t in stock anywhere, so it’s got a smaller bank than might be desired.

I still think power trailers for an EV make sense, but literally nobody has an EV you could use them with. You could build something lower and more aerodynamic with a spare 100kWh, if you wanted, just… not cheap.

Thermal concerns for an outdoor trailer. They’d have to be heated in the winter.

Battleborn makes some heated LFP 12V/100Ah batteries, but they’re not cheap - a bank comparable to $1500 in lead would cost $8k.

How are you heating/cooling the cells?

Can you hypothetically plug it into your main panel, say, using ?

And maybe going from the main array somehow into the power inlet?

Future thoughts - slideouts-on-rails? Sound be easy enough to do a 3 layer system (one forward, one aft) or a 5 layer one (left and right). Maybe powered sun tracking with a linear actuator or three? Maybe raising up the batteries a touch so if there’s liquid inside there’s some drain room?

It will work with any setup of inlet/transfer switch one might have. Such a system would never know the difference if there’s a solar-trailer or a gas generator plugged into it.

It’s being considered. It will not be simple. It is what amounts to a full-extension drawer slide capable of holding a 55lb solar panel extended cantilever 72 inches or more. Then a sort of box structure to contain it all, and some supports that fold-out to secure everything in the wind.

Not un-doable, but certainly an engineering challenge.

There’s plenty of truck drawer slides to that spec or higher.

If you come across any shoot me a link. I got stuck trying to find much beyond the ~50-60" range.

I’m not - that’s part of why we’re using flooded lead acid. They don’t require thermal management.

This is more or less my office system, on wheels, with a lot less panel.

Especially for Gen 2, they’ll be light enough you can just rotate them manually. Any sort of sun tracking stuff adds a ton of moving parts and complexity.

The intent is that liquid never gets inside. If it’s got an inch of water sloshing around, though, the inverter is the bigger problem, not the batteries. They’re in plastic shells.

Yeah, I’ve been tempted by one of the 12V/100Ah Battleborn, since they’ve been on sale. Not the heated one though, but I’m going to hold off for the moment. I’m actually looking to get a small travel trailer I can tow, which I’ll wait until I get that and evaluate everything before going for Battleborn. My lady got 2x200W solar and full setup, great wiring job, a Battleborn 100Ah 12V, Victron charge controller and RV battery monitor (basically this but with 2 solid, roof mount 200W panels that can be cantilevered if sitting somewhere for a while for better angles for charging).

Although the temperature concerns…depends where in the world you are :stuck_out_tongue: However, for a general purpose, yeah, good FLA just makes sense in that case. Of course, overheat might be a worry during the summer. I wonder if it’s worth adding a 12v soffit fan vent, although you’d need to figure out a way to make it water tight, or auto-sealing when not needed or moisture is detected or something.

Looks like you do have plenty of room to double or more the battery if you wanted to though, but for a prototype nothing wrong with using the used batteries since you already had them around.

Overheat isn’t a worry either. If you get FLA hot, you shorten their lifespan a bit, but it really only starts adding up if they’re overheated for hugely long periods of time. For most batteries, lifespan is rated at 25C, and every 10C over or below halves or doubles livespan - so a 10 year battery, at 35C, will have half the life, and that battery at 15C will have double the life. Out here, at least, it hasn’t been a big deal. Remember, they’re a lot of lead. Thermal mass is significant.

Remember, the most common place for lead acid batteries is under the hood of a car…

However, the trailer is currently missing a “charging vent” - the intent is to use one of the outputs on the controller to run an intake fan when the battery voltage is over the gassing voltage, to help drive hydrogen out some vents that also aren’t yet installed. So I just crack the lid if it’s charging hard, and equalize with the lid wide open.

Easily. The trailer was designed for the L16 size batteries, so twice the capacity or so, but we just couldn’t get them. I didn’t have this set laying around, though - I bought them used. Have you tried to get lead acid batteries lately? :stuck_out_tongue:

Oof that’s some money, but if they’re as solid as they say, a pair for 80" with the load capacity is pretty solid. However, I’d be a bit worried about dynamic loading, as in wind/rain loads on the panels. Unless you also do fold-out feet or angled to connect to the bottom edge of the trailer to provide support.

Some 1/2+" tube with some bolt-through connections to the bottom edge of the trailer angled to 18-24" from the edge could add a LOT of load support. In either direction.

Yeah, the problem isn’t supporting the panels. It’s supporting them in the wind. Even the current setup isn’t ideal in the wind, and the trailer remains stowed on windy days (which is perfectly fine - it’ll remain charged just fine with the panels horizontal).

The plan right now is to focus on designs that don’t require exotic setup/teardown - though we definitely want to expand out, eventually, into larger panel frames. I’d love a 6 or 9 panel trailer, we just have to figure out how to do it in a way that’s not going to come apart in the first good wind.

Typical usage of one of those slides would a couple hundred pounds of outdoor kitchen, and yeah, twist loads.

I’m still a fan of linear actuators over hydraulic lift cylinders for stability purposes, and you can get the ones meant for wheelchairs pretty cheap.

There are a few ideas still in the “We’ll play with these at some point” bucket regarding lifting, but I don’t think linear actuators are on the list - rather go with simpler, mechanical, easier to maintain and fix systems.

One of our “Ohhh, we totally need to do this!” ideas is a fully blacked out trailer. :wink:

Just for fun, and to prove the party trick, I hooked up a 240V EV charger to it. Charged the Volt just fine at 3.3kW, though the battery bank was sagging pretty hard under the load (no surprises, it’s an undersized bank). If I wanted to charge the Volt off that trailer regularly, which I might do, it would be better suited to 120V charging.

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What’s your thought for the panels with the wind? Is it the panels pulling off, or because the trailer is so relatively light, that the right direction/gust and it might tip the trailer over? And any ideas for what you might do to handle that sort of thing?

I’m not that worried about the panels, but we’re short a couple support struts right now, so it could wobble around enough to cause problems in the right wind. Once we’ve got it better supported, it shouldn’t really be a big deal, though I’ll still tuck them down in the wind.

If they’re stowed (flat) and latched down, there’s not enough wind area to matter.

For deployed, if the wind proves to be a trailer tipping problem, we could potentially add some additional camper style corner legs, but I don’t know if that’ll be an issue. The intended use is that the stuff is stowed flat for high winds, but also that we’ve built things stout enough that it’s unlikely to actually be a concern.

I just don’t want to destroy the prototype quite yet in testing, mostly.