Off-grid Base Camp Solar Power

 800 watts of panels, 5.4 kWH of battery*, satellite internet, all I could need for work-from-woods

This was a constant tinkering project, but it always basically worked all summer.

Parts!

• a pair of 440 watt panels. I got them at AltEStore, and I saved on shipping because their warehouse happens to be 30 minutes drive away so I picked them up. The market is constantly shifting and the best deal is different every month.
• Victron Energy MPPT charge controller from altestore
• Two "24V" 100Ah LiFePO4 batteries
• A 2000 Watt Giandel inverter (no link because I didn't like it, see below)
• Starlink internet
• Battery disconnect switch
• DC circuit breaker from altestore
• 6 AWG screw terminal lugs
• 6 AWG red+black wire
• MC4 Solar Panel cables
• distribution strip (one red, one black)
• Steel jobsite box
• wire shelves for inside jobsite box
• a few 2x4 to make the frame
• M8 screws and nuts to attach panel to frame
• 12A buck converter (batteries to 5V bus)
• screw terminal distribution block (used this for 5V bus)
• Raspberry Pi 4, USB SSD, USB 3 Hub
• Raspberry Pi Breadboard Hat
• USB GPS receiver
• AcuRite weather station (dislike, see below)
• USB security camera

Core Power

The panels were a good deal when I got them, about $0.50 per watt, but it looks like the market is more like $0.70 per watt now, but it could be different next month.

Matching panels and charge controller isn't hard but it does require some picky details and matching up all the numbers. The panels have a "nominal" voltage that you can pretty much ignore. Look for the "Open Circuit Voltage (Voc)" and the "Short Circuit Current (Isc)", those should be the maximums it will do. Right now I'm looking at a panel that is "20V" with a Voc of 40.5V and Isc of 10.5A. That's similar to what I got and after connecting my two panels in series I have often seen 80V out of them and occasional peaks to 100V. And that's why I got a charge controller rated for 100V and 30A.

Next read the manual on the charge controller and see how much power it can output and read the manuals on some batteries and see how much power they can take in. The batteries I got can charge at a peak input of 100A or 50A sustained. (50A * 24V) = 1200W. Since the panels only put out around 800W and there's a little loss in the charge controller, we're good here.

On the output side the inverter claims it can output 2000W sustained or 4000W peak. That's more than one battery can handle but if I put two in parallel they can support 2400W sustained or double that peak. All is well again.

I don't like the Giandel inverter. Its manual says it can accept up to 32V in but it has been regularly shutting down if it gets over 28V. I was able to tweak the settings on the Victron charge controller to decrease its peak output. The inverter also doesn't automatically restart after shutdown. No good for unattended usage. On either over-volt or under-volt someone needs to be there to push the button to turn it back on. The longest uptime I've seen on my system was about 3 days before the inverter went down.

For next year I have a Victron Energy inverter. I am increasingly impressed by Victron parts. Most of their parts have a hacker friendly 5V TTL 19200 8N1 serial port with well documented protocols. I was able to attach their USB adapter to my Raspberry Pi and install an open source python VE.Direct library and it Just Worked and I immediately saw the data I wanted from the charge controller. Worked for the inverter too.

Raspberry Pi Server

Skipping the inverter, I got a 12A buck converter to go direct from batteries to 5V. This powers the Raspberry Pi, the USB Hub, and the weather station console. I wired a Raspberry Pi Breadboard Hat with a couple screw terminals soldered to the 5V and GND pins on the GPIO header and the Pi works just fine with power coming in that way.

I was able to use gpsd to get readings from a USB GPS receiver and update the system time with that. No more clock drift! Also since I have internet I could just use NTP to get the time, but GPS is better ;-)

In addition to the weather station I attached a waterproof, IR illuminated, USB security camera so that I could have live action shots from the woods. A little scripting set that up to upload a picture once every hour.

Weather Station

I found open source code for getting data from an AcuRite weather station, and saw that they come with a USB cable to connect to a host, so I thought I was good to go. Nope! I read the source in more detail and it included comments that the AcuRite is a bad choice for unattended operation. On power-up it is always in the wrong mode to send data to the USB host, and it needs manual button presses to configure it. Every time. So, hopefully, my system is a huge Uninterruptible Power Supply because of the big batteries, but I'll be looking to replace this part once I'm over the grumpiness of buying the wrong one.

Design Lesson

This was a big upgrade from the previous 50W weather station. Generally it worked better.

Put switches everywhere. The panel disconnect and battery disconnect switches are essential. As pictured above there isn't a switch on the 5V board but I'm adding one at the 24V input so that I can shut off that whole subsystem and disconnect it if I need to. (Or just reboot the Raspberry Pi.) I have a power strip coming off the inverter with a separate switch on every outlet (I plan on using that to turn on and off various chargers and things separately to make sure they don't have any idle wasted power).

Mount things to a board. It doesn't have to be good, doing this will be better than not.

Shut Down for Winter

Unfortunately, LiFePO4 batteries don't like the cold, and can be damaged by charging while cold. The shutdown trip for this system was 2022 October 11. This system is much heavier so it shouldn't blow away this winter, my biggest worry is if it will structurally stand up to the snow load.

Next year I'll add small second inverter just for running the Starlink internet. That one can stay on all the time and the big inverter can be just on when we're there running things.