Event Support | Portable Solar Power Strategy

Hello Operators

My wife and I were “discussing” a portable power strategy for an upcoming event and associated road trip. We knew technically speaking how to achieve our goals, but wanted to do it all on the down low.

The Subaru Outback will serve as our home away from home for ~5 days. The trip would be over paved roads, but in very remote areas. The Outback will serve as our office and kitchen when stopped. It would also need to provide portable power to the friends whose cross country adventure, we are supporting.

The team has batteries, gopros, camera drones, tablets, phones, … all needing top ups during our off-grid rendezvous. Naturally it’s possible to use the Outback itself to charge all that gear, but running the engine to do that, is a waste of the Outbacks resources. It also increases costs, running the engine unnecessarily. The diesel boxer engine is cheap to run, but it’s not free.

Our friends will use the 576wh solar generator I built in February 2019. I may need to add 2 more USB ports but otherwise, it’s looks ok. Their original idea was using a Goal Zero Yeti, but they quickly realized I had G’Zero interest in that idea. 😀

We’ll need a small inverter or DC DC boost converter for their editing laptop. That’s easy as cake since the solar generator was designed with that in mind. I already have an inverter, but would prefer using a boost converter. It’s the same boost converter we use to boost voltage from the DC output on the Outback, making the charge controller Happy on the solar generator.

We can charge or recharge the Solar Generator while on the road, using the rear DC port in the Outback (if needed). The Boost converter I’m using also has current limiting, so we can prevent charging the solar generator at too high a charge rate. Remember the charge rate or too high of a charge current, will reduce the life cycles of our cells. So we only fast charge, in an absolute emergency.

When we’re stopped, we will deploy the PowerFilm R28 panels on the roof of the Outback using the parallel cable. The R28 panels are completely waterproof, we can even call them submersible. So they can stay there doing their job, regardless of the weather. This is the strength of the rollable R-series from PowerFilm. This is also the main difference between the FM series and the R series. The FM series can definitely get wet, or rained on, but they were never designed to handle a sustained downpour. If I were deploying in a dry climate environment, I would definitely take the FM series. Deploying in a swamp, the R-series is definitely the way to go.

The R-Series will lay flat on the top of the Outback when deployed, without being very noticeable. My wife wanted to avoid using a permanent roof rack with rigid or semi-flexible panels on the Outback, choosing instead to deploy them as/when required. This would help prevent unnecessary attention to the Outback. Fair enough, although that Overland look is one I admire very much. Still, we’re all about being The Grey Man, and don’t want to bring any unnecessary attention to the equipment inside the Subaru.

On gray days we can augment the 28 watt panels, with the R21 from the hiking trailer, and/or 120 watt PowerFilm FM16-7200 from the solar-powered field station. We can either do that using the paralleling cables, or with the second solar input port on the solar generator.

Even while charging all of their devices simultaneously, there isn’t very much load on the solar generator. In this kind of scenario we have calculated about 11 amps continuous. Mostly we’re charging 5 volt USB devices, laptop, recharging camera drone batteries, and things like that. So in actuality, the solar generator is complete overkill for this project. Still, it’s better to have too much capacity, than too little.

Powering the solar generator and recharging from the Sun is almost completely free. Once we have the solar generator, and we have our solar panels, there’s nothing left buy throughout the cycle life of the system. Some people often wonder why we wouldn’t just use a small Honda generator for this task. I could consider using a gasoline generator for Rapid charging in an emergency, but using it to power or charge our gear isn’t efficient. You always have to refill the tank, which costs money. Since generators have no battery or storage capacity, they work much better as a backup, than a primary power source.

Others havd asked why not use the Outback itself. Absolutely nothing wrong with recharging from the vehicle itself while moving. In fact if we’re not able to recharge purely from solar power, we will top up the solar generator with the Subaru on the go.

We must also considering the gear we are charging is not in the vehicle with us. Since we are acting as a roving charging station for the team, it’s more efficient and robust to use the vehicle as a backup power source, with the solar generator in the primary power role for their gear.

Opportunity to learn

If we look at this as an opportunity to learn, we take our gear off grid, we take our solar panels off grid, and recharge from the Sun. Not only do we avoid needlessly running the engine, we gain valuable experience powering up devices in an unfamiliar scenario. I think far too often we are looking for some AC outlet to plug in our equipment. DC power isn’t complicated, it isn’t difficult, but it’s not for the lazy. If one is truly thinking about off grid portable power but mentioning a television or air conditioning in the same sentence, there’s something terribly wrong with the strategy.

We’re using this event as an opportunity to learn more about operating off grid. Building the solar generator was one step, understanding how efficient the solar panels are in varying conditions is another. Using our equipment to charge or recharge gear in various states of discharge, within a finite amount of time, is what we’re up against. These are all important aspects to learn from, if we are going to be successful with Off the Grid portable power. It doesn’t matter if we’re talking about grid down ham radio, preparedness, or managing portable power for a couple of guys cross country skiing across the country. We learn.

About the PowerFilm R28 and R21.

Some may be wondering why we would have chosen the R21 and R28 from PowerFilm solar.

The R21 was chosen because its primary purpose is providing power for the hiking trailer. This allows me to keep charging, even while I’m on the go, and on the trail. So we use it to augment other projects when it’s not on the hiking trailer or charging the fatbike battery.

The R28 panels were chosen simply because there was no budget for the 2x R60 panels straight away. Piecing together our solar power system using smaller panels, adding to the system one by one over time, is more expensive in the long run, but gives us more freedom to manage our budget while building the system. We also have the luxury of deploying only what we need since the system is broken apart into smaller solar panel sets. The solar generator was already designed with this strategy in mind, using fewer or more solar panels as they become available. This is why it has parallel solar inputs.

PowerFilm Solar

It’s also important to point out why we’re using PowerFilm Solar, solar panels. The bottom line is portability. They’re certainly other manufacturers out there like Lensun for example, but if you’re in a situation where maximum portability is a critical requirement, your research will undoubtedly lead you to PowerFilm Solar. PowerFilm Solar solar panels are the most portable solar panels available today. If you measure them in terms of cost per watt, it goes wrong. If you look at them in terms of portability, robustness, and expected lifetime, we begin to understand the value.


Amateur radio in the field provides a pretty stable and efficient platform for testing the solar generator, and the solar panels. Twice now I’ve taken the system to the field to test charging, and pulling loads from the solar generator. Gray days are always a challenge, but adding capacity isn’t very difficult when you have the convenience of a solar surplus. Determining how much power needs to come in to maintain autonomy in the Solar Generator, is calculated by amount of load placed on the system, and for how long. Naturally we would like to get the same amount or just a little bit more power coming in m, then the current draw on the system. That’s not always practical, but remember we can continue charging, even after the load has been removed. The key goal is achieving a +/-0 point, while the load is applied. It’s also okay if the system plays “catch up”, provided we have enough hours of sunlight during the day, to top up the system.


julian oh8stn

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