Real World Solar Charging

I've said in the past that my camp trailer is a huge part of my emergency plans, and that still holds true. Part of using my trailer as a bug out vehicle is being prepared to be as off-grid as possible, and that means learning to live on limited resources.

This winter, my parents gifted me a set of RV solar panels that they have no real use for as virtually all of their RV time is spent in parks with full hookups. Most of mine is as well, but there are places that I enjoy camping that do not have utilities at each site. In these places, you're constrained to what you can haul and what you can generate, and these constraints mean I have 58 gallons of water and whatever amperage my batteries are charged to when I leave home. When I reach the ends of that, I need to either be headed home or have a way to resupply.

Today we'll look at recharging those batteries. Without an electrical outlet to plug into, my charging options are pretty limited:

1. I can hook my truck electrical system to the trailer, similar to jump starting, but that's very inefficient and doesn't provide a good charge to RV batteries. 
2. I can hook a generator to my trailer and create 120v power, which works very well with regards to convenience and utility, but it is quite loud, which the neighbors don't appreciate. Generators are also fairly heavy, require regular maintenance, and take up quite a bit of space. 
3. Use a small solar array.

We've discussed solar power before in various use cases, but not this particular one. RV solar arrays are easily portable, collapsing into a footprint that fits easily into storage compartments. They're commonly available with up to a 400 watt output, with the majority of them being in the 100-200 watt range. They're not big enough to effectively power home systems, but they provide far more power than the small cell phone type solar chargers.

The panel I have is a single-pane 40 watt panel with a 7 amp charge controller. This means that I could add a second panel on the same charge controller without any other parts. 40 watts isn't enough to power everything in my trailer, especially not for an extended period, but what it can do is buy me a fair bit more time in the wilderness, especially if I'm careful how much power I use. Also, I don't expect to get full rated output on a solar panel. Weather conditions can reduce output, as overcast skies reduce the amount of sunlight the panel receives. Higher latitudes also cut into your output, as the sunlight is more indirect. How much real-world loss that amounts to has yet to be seen, but once I hook up the panel to my trailer I'll put a meter on it to test. Fortunately, RV style panels are highly mobile, and can be aimed into the sunlight throughout the day to maximize output.

Once I have actual power generation numbers, I can compare them to my battery storage capacity and consumption numbers to determine exactly how far I can stretch my power budget. If I were buying panels, I'd run the calculations beforehand and buy panels sized to my needs, but since these panels were free, the math gets run backwards to see how far they'll take me.

Lokidude