Solar power: 7 days off grid using only a 13 Watt solar panel


Last Friday morning, we arrived at Camp Xray (our summer cottage) for a week’s worth of off grid living. It’s not like we havn’t done it before. This time, as an experiment, we wanted to carry along our comms gear (Local & HF), mobile phones for emergencies, and a tablet for pictures, blogging, or capturing video . As there is no grid power at Camp Xray, we needed to sort out how we’d power our devices. Sounds simple I know! It was many things but it wasn’t simple! also decided that this would be a great opportunity to test my /P power plan for voice and digital comms. If you’ve been following along, you’d already know that I switched over to Sanyo 2700 mah NiMH batteries for all my gear. I made a video about that earlier this month. I’m happy with this move, but this trip has shown me that I need to expand the concept further.  The devices we took along were:

    • Intek MT-5050 PMR radio for local voice
    • Motorola Talkabout PMR radio for local voice
    • FT-817ND for news and HF comms
    • VX-8R & CCW Digi Tracker for APRS Digi
    • Wouxun KG-819 with Mobilinkd BT TNC so my wife could track me when I was in the kayak
    • Samsung Galaxy Tab 10.1 for blogging, capturing video, images, and checking stats and servers while away from HQ
    • 2x Samsung smart phones

Solar Power System:

  • Topray Solar 13 w solar briefcase
  • 7A Topray Solar charge controller
  • 12v 7A SLAB

Most of the comms gear can use the NiMH batteries. The other radios have DC input allowing them to charge directly off of our charge controller. The tablet and smartphones benefit from a step down converter, dropping the voltage to the required 5v over USB.

Day 1

I setup the 13 Watt panel on the front of our cabin in a fixed position. The setup was a 13w solar briefcase, a 7Ah SLAB, 7A charge controller with outputs for load and battery charge. During this time of year, usable sun hits the cabin from the east from 8-11, the front of the cabin gets southern sun from 11-17. Then from the west for 2-3 hours during the evening. We do get sun from the north (midnight sun), but it was too much of a hassle to move the panel behind the cabin during evening hours. Hanging the panel in a fixed position would have been great if the earth didn’t move. Having only this single panel, I would need to track the sun, in order to maximize charge to my storage battery. Of course, initially I didn’t do that. This was stupid mistake number 1. I thought the indirect light from the sun would be enough. It wasn’t! Stupid mistake number 2 was not pre-charging the storage battery before we arrived, and thinking the panel could charge it up on its own, while also running high power devices. Perhaps in a perfect universe, where there are no thunderstorms or overcast. This was not a perfect universe, and I was a serious noob! From a technical perspective, this day was a failure. The technology was perfect, but they way I used it caused these problems.

Day 2

Thunder and lightening. Did I mention thunder and lightning? With heavy clouds and the storm’s, I had very little useable sun on this day. Not accounting for the possibility of storm’s, and thinking I could just plug in and recharge at will, my tablet was already in need of a charge. That killed digital HF comms for this day. The lesson here is to get up-to-date weather forecasts, so one can plan out energy usage and conservation for the next day or two. The second lesson is carry more reserve capacity for these kind of days. By the end of day two, we had voice comms and news. Most other devices were dead, and our storage battery was not charging because of the storm clouds. Thankfully, I did bring additional reserve capacity, in the form of x20, fully charged, Sanyo 2700 mah AA batteries. That made x2 12 volt 2.7A batteries. These got us through to day 3, when the sky gave us some relief.

We ended day 2 having to decide which was more important, voice comms, or the tablet. We chose voice comms, and a mobile phone.

Day 3

By day three there was a break in the weather. Being a little more clever, we added mounting points for the panel corresponding to the suns position in the sky, at a given time of day. This kept the panel in full sunlight from early morning until well past dinner time. Doing this got the storage battery full in 5 hours. After that we could start charging the other devices, and our solar powered adventure actually started to become fun and exciting.

We started with the tablet, but quickly ran into a minor problem. The morning brought us clear skies, but the afternoon brought clouds and thunder. The tablet needs a stable power source, 5v @ 1A. The clouds moving in front of the sun made charging impossible for the tablet. Ultimately, this prevented us from recharging any device which required more than 500ma during charging, but only on that day. That included the Vanson NiMH charger!

The lesson here?

  • A MPPT charge controller
  • Higher capacity (and fully charged) storage battery
  • We need a portable battery charger which draws less power (like 4 batteries at a time instead of 8) otherwise we need more watts (more panels)

On the other hand, the FT-817 is quite tolerant regarding the quality of the DC voltage coming in. Thanks to that, we were able to get on 6 meters during the storm. The band was open from southeast Europe to Scandinavia and I made several QRP QSO’s into Czech replublic and Switzerland using 5 watts, the standard FT-817 antenna, and internal batteries augmented by our solar generator. The 817 was plugged into the “load” port on the charge controller. This allowed us to enjoy the band for the rest of the evening. Day 3 was an incredible learning experience but we still had a ways to go, if we were to catch up from the blunders of day one and two.

Day 4

Rock and roll!  Reading the weather forecast for day 4 the previous night, we knew what to expect. We positioned the panel to the east the night before, and by the time we woke up, we had a perfect power station. The storage battery was full, and with clear skies and hot weather, I almost thought I was back in the pit. With no clouds in the sky, the tablet charged in a few hours. Ironically, our charge controller complained of too much power coming in, so we added more devices to charge. All devices were up and running by early evening, but not without a fight. We had a constant struggle to find balance between keeping the storage battery charged, and having enough amps to run or charge the devices. Nevertheless, we managed to upload a video about the 13w solar briefcase to YouTube.

Regarding the charge controller, we ran into a strange problem that I had no experience with. The charge controller was not able to route abundant power past the battery to the load circuit! It seemed as if the charge controller wanted to keep on charging the battery although it was full. In full sun, it was often the case that removing the battery from the charge controller and  working with the panel and controller respectively, gave better results than with the battery in the circuit.

This was very annoying! It prevented us from taking full advantage of clear days with high sun and no clouds, until we found the work around. I’ll need to do the research and find the best charge controller I can find which is more intelligent, and not too heavy. I’m hoping 8DigitPDX or perhaps GC can give some advice on this point, as he was able to deploy his solar powered simplex repeater remotely with few outages if any.

We had so much energy generation today, that once again, I thought we should have a way to store it. More storage capacity! But when does more capacity, start to interfere with /P mobility? The answer, “it doesn’t have to”. On day 4 I realized “storage capacity ” and “portable power” are two different things. Operating from a  base camp, I realized that I can have a higher capacity storage battery at camp, happily collecting power for me to use when I need it. Then carry carry with me into the field, portable power packs which I use when I am away from the cabin. The solar power station can continue to collect energy, while I take my power packs out to the back-country for field comms. On the other hand, for day excursions, perhaps the portable power packs augmented by a a solar panel (to increase comms run-time) would be another way to go. Certainly what I take from day four, is there is no simple “best way” to do this, because environmnetal conditions are never “under control”. What we can control, is the amount of reserved capacity we carry with us, and that’s it! Based on what I’ve learned on day 4, what I need is power packs for portability, and storage capacity for base camp. Having tried to do both, meant I had neither doing any good at all.

Day 5

Today was splendid! Energy production was in abundance, so I was able to watch the latest episodes of Jack Bauer in London, and Falling Skies Off Grid 🙂 Having learned the hard way about the limitations of my energy production and storage, adaptation and improvisation have come pretty quick. Conservation is key to such a low power system. So its critical to understand how much operating time one has with a particular device, and the amount of time and energy required to recharge it. Still, this was an excellent day with lots of sun. We just put our gear charging, while we enjoyed going back and fourth between the wood sauna and the lake. Unfortunately for this article, today was pretty boring as everything worked as it should.

Best case charge times:

    • SGT 10.1 (+/- 3 hours)
    • SGT S+ (1 hour)
    • FT-817 (+/- 5 hours internally, 4 hours externally)
    • 8x 2700mah AA batteries in the Vanson charger (+/- 4 hours)

 Day 6 and 7

Like day 5, we had an abundance of energy generation until early evening when clouds were intermittent. Gear was all charged and I could get some pictures and video of Camp Xray from the lake. I took the kayak out and snapped a few! I was also able to upload the latest draft of this blog, check website and youtube stats.

Without all the stress of trying to manage the solar panel and storage, I had time to listen to 18 meters DX coming in from SoCal USA, with the FT-817. With my reserve packs charged, I knew I had a good 10 hours time to use the FT-817 before I would even have to think about a recharge. My wife used the Yaesu VX-5R to listen to local radio for almost the entire day. It was nice to be able to get her on board with the solar system. She likes to sun bath at the edge of the lake, but wont take the other more delicate radios. She likes VX-5R because it’s rugged, waterproof, has a great battery, and has great audio for such a small device. I like it because it’s also got a 12v charge port, low current drain, and generous lipo battery. Day seven was very much the same. We understood the limitations of our system, and by now were well practiced on using the system.

Final thoughts

From a comms perspective, the simple fact that I was able to make +2000 km QSO’s or listen to global DX under these conditions, brings more credibility to the /P & /PM comms concept. We are not always going to have big towers, high power, or the perfect conditions to operate from. With projects like this, we will have practical experience about what our gear is actually capable of, and under what conditions. From the words of one of my favorite YouTube channels, this kind of felt like Guerrilla Comms

Energy conservation

When you have modest energy storage capacity, the internal storage capacity of devices used off grid, becomes critical. Upgrading all the batteries in my devices to the Sanyo 2700 mah NiMH batteries before the trip, saved me from the unnecessary frustration of short runtimes. Any other devices which didn’t fit with the energy conservation needs of /P operations, were removed from my gear, and donated to other groups or club’s who could make better use of them. Those devices that remained had atleast two or more of the following properties:

  • 9-16v DC charge port
  • Internal Lipo battery with built-in DC charge port
  • Accepts AA Sanyo NiMH batteries
  • Low current consumption during stand-by or receive

Thoughts on storage capacity

Now that I have had this experience (and thoroughly enjoyed it), I realize that my storage capacity should be equal to or greater than double all of the current requirements of all my gear for an entire day of operation. This would save us the frustration of not getting devices charged for more than a day, while plagued with bad weather.

Of course we could augment the solar power station with a micro-gas/diesel generator, but lets leave that to winter ops in Scandinavia 🙂

Extending tablet life

Having received a full charge the previous day, the tablet life was extended by adjusting a few settings. Firstly, putting the tablet in “flight mode” when not in use, and turning off all wireless and mobile data not actively used. Next we reduce the screen brightness to the lowest acceptable level. We also try to limit use of the tablet to night time to reduce screen brightness even further. We also force close all the Google crap running in the background. This increases the operating time from hours to days. For the next trip, I’ll root this tablet, and remove all Google and Samsung bloatware. I’ll also remove any apps that require location services as they use cpu power to poll devices for network or GPS based location.

Charge controller

Although I appreciate Biltema sending us this panel and charge controller, I cant recommend that any of my viewers or readers use the Topray solar charge controller for off grid electronics. I would use it for keeping my motorbike battery topped up during off months, but not for serious off grid solar power where every bit of energy collected is critical to success. Instead I recommend people find a good MPPT charge controller.

12v Portable Power packs

Although my own portable power pack development was not ready to take along on this trip, the importance of portable power packs with 12v and 5v outputs is critical to any man-portable off grid adventure. I now understand why leading adventurers use Goal Zero power packs like the Sherpa 50 and Sherpa 100 power packs. Its not unreasonable to consider carrying two Sherpa 50 power packs and a 13 watt foldable panel in ones gear.

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One thought on “Solar power: 7 days off grid using only a 13 Watt solar panel”

  1. Quick update
    Thanks to 8digitpdx, Markus Kessler and GuerrillaComm for giving some very useful feedback

    I have decided to upgrade my charge controller to the Genasun GV-5.
    Benefits from this are
    – more efficient use of my panels
    – extremely low current draw
    – lower energy losses
    – panel profiling and output adjustment 15 times per second

    I will also try to double the watts to 25w minimum for solar comms expeditions (if sponsors agree) Its not that the 13 watt panel was a failure. In fact, its simply about having more amps when the sun and weather are not cooperating as planned.

    Guerrillacomm used this charge controller in his mountaintop simplex repeater project. This would be a positive upgrade to my current system. I may try to get one here for testing. Please check out his youtube channel

    More info coming
    is it time to look at the Sherpa 50 it 100 from goal zero?