Saturday, December 22, 2018

DIY Portable Solar Generator update by Julian oh8stn

Hello Operators
Small update for the solar generator project.
All the Headway LiFePO4 cells have arrived. That makes 12x, 15ah 40152s LiFePO4 cells. This gives us a total of 45 amp hours or 576 Watt hours, through 12 cells in 4S3P configuration
It’s actually quite astonishing, to fit all 12 of these cells inside the ammo can, with room to spare for the electronics.
Each 15ah cell weighs in at ~466g. That’s about 5.5kg or 12.25 lbs. Not bad for more than half a kilowatt of off grid portable power. The 12 cell cluster isn’t going to make it up Everest, but it will certainly make it any place you or I might need it. My weight goal for this project is 8kg, including:
  • 500 watt hours of useable battery storage
  • 120 watt solar panel to top it up in the field
It’s definitely going to get down to the wire. Even if that goal is exceeded, I doubt there are any commercial options with the combination of capabilities and portability offered by this solar generator and solar panel team up.
I’m also reminded of something which requires some elaboration. When we’re talking about portable power for emergency communications or preparedness, we are often shown these large, heavy, truck or camper portable solar generators and battery boxes, which are far beyond reasonable from a portability perspective. If you study natural disasters along with the statements from disaster survivors, there’s a common thread amongst them. We often hear “they grabbed what they could carry, and got out”. I think we can learn from this.
Admittedly it’s nice to have large capacity battery storage and solar generators, but at some point the logistics of having such large systems, will reduce our responsiveness & our mobility. This is especially true if we’re traveling on foot, overland, … where space and carrying capacity are limited.
So rather than building larger, heavier, solar generator systems, for highly portable, “high-speed low-drag” Ops, we can also change the way we use the energy we can carry. For example, you see no inverters in this project. If we keep everything DC, we can reduce the losses from converting DC to AC then back to DC through a wall wart. That simply wouldn’t be an efficient use of our available energy.
This system represents the maximum capacity of batteries and solar power generation I can effectively carry in a man portable configuration, using the hiking cart, pulk sled or fat bike. It’s also about the right size when travelling/operating from our Subaru Outback.

What’s left?

There are still a few more Powerwerx components incoming. Surprisingly the costliest part of this project are the Powerwerx Panelpod through panel ports. With the high price of those PanelPods, I decided to reach out to Powerwerx in hopes of some sort of collaboration, to offset the cost of the Powerwerx products used in this build. Powerwerx wasn’t having any of it, so a Powerwerx/OH8STN collaboration is a No-Go! Definitely no hard feelings but, perhaps we’ll explore 3D printing the Powerwerx PanelPod products, or in projects where we’re not thinking about ARES interoperability, using XT60 connectors as a cost-effective alternative to Anderson Powerpoles.
Finally there’s different gauges of wire, some switches, and fuse breakers required for the powerpole DC outputs. Once those other components arrive, I’ll be able to mock-up the generator, then measure how much of each gauge of wire, needs to be ordered.
It looks like I’ll do the build during the first and second week of January, then publish it on YouTube by the end of January.
If you haven’t watched or shared the introduction video for the solar generator project, have a look at it here.

There’s also a blog post giving some background about the build. http://oh8stn.org/blog/2018/12/09/diy-solar-generator-576wh/
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