How much of the NEC applies to portable solar arrays?

[rebelrider.mike]

Hi all.
I'm planning an interactive solar/battery installation, and I plan to have a large permanent solar array and a smaller portable one with its own MPPT and battery that I'd like to connect to the house battery while I'm not using it elsewhere. I'm reading through the NEC, and I'm not seeing any language specifically for portable solar arrays. Here's a diagram of what I have in mind:


The portable system would be in a camping trailer which I think counts as an RV according to the NEC. For now I'm thinking of it as an Article 690 thing. But any insights would be appreciated. I've been reading the NEC 2020 code, but Washington is going to adopt the 2023 cycle in a couple months. I haven't got hold of their amended version yet. This book is not an easy read, LOL.

 

[sunshine_eggo]

551 is RV electrical, and I was surprised to read that autotransformers are forbidden. I did not see any reference to solar.

Electrical Code - AM Solar | Solar Panels for RVs | RV Solar

amsolar.com

indicates there is no specific codes for installing solar on RVs.

I don't think complete complying with 690 is possible, but using it as guidance is likely sensible.

 

[rebelrider.mike]

I heard about autotransformers. The issue with them is when a park has too much demand for electricity, the park electrical system has a brownout (undervoltage). People use autotransformers to bring the voltage back up to normal as it enters their RV. But in doing so, it causes even more strain on the park electrical system, which is already experiencing problems. If many people do this, it leads to a very unsafe situation. I've never experienced this. I've only heard other peoples' stories.

Anyway, thanks for the article. My biggest concern is making sure that plugging my trailer's solar into the house battery will not pose any risks. Since it has its own MPPT and battery, I'm thinking of it like a portable solar generator. But I haven't found any NEC rules about how to plug such a device into a house battery.

The good news is that I don't have to appease the fire insurance company or the local utility. So I don't need an inspection for the trailer. But I still want to do it all up safe. As far as I've heard, there are no surprises in this area of the 2023. But then I haven't read it myself yet.

 

[Hedges]

Buck-boost autotransformer would do that. But so would SMPS like LED bulbs and electronic appliances. And motors. Only heating elements and incandescent lamps would reduce draw at reduced voltage.

Maybe the concern with autotransformers is grounding and shock hazards.
They can work if connected correctly, but they could instead make neutral offset from ground. Used as voltage converters between US and UK/Europe.

Your diagram seems to show only DC connection between trailer and fixed equipment.
Mismatched battery voltages at time of connection can be an issue, and other than that that no charging occurs until a charger on the other side decides to. Maybe you want to plug in an AC powered charger.

 

[rebelrider.mike]

I totally forgot to mention: The trailer is 24V and the house battery is 48V so I'd use a boost converter with current limiting to match the voltage.