A perpetually powered wireless outpost

For [Justin], the topic of remotely powering electronics in the field comes up often. So often in fact he decided to put up a tutorial for powering electronics from solar power and batteries, as well as sending and retrieving data with the help of a cellular connection.

The electronics [Justin] chose for his remote wireless project include an AT&T 3G connection to the Internet provided by a Beaglebone, BeagleTouch display, and BeagleJuice battery pack. Of course an Arduino had to make it into this project, so a few light sensors were wired into a few Arduino Unos and connected to the Beaglebone.

After finding a few deep cycle boat batteries, [Justin] wired up a pair of solar panels that put out about 200 mA in full sun. This equates to about 2700 mAh a day, about 300 mAh more than his Beaglebone/Arduino/3G connection/WiFi setup needs per day.

As for what [Justin] can do with his wireless outpost, it makes setting up remote sensors for agriculture a breeze, and could easily be used to automagically send pictures from a game camera straight to a web page. Pretty neat, and very useful if you need to wire up sensors in the field to the Internet.

Edit: Yes, [Caleb] jumped the gun on publishing this post. He’s in the corner now, thinking about what he did.

24 thoughts on “A perpetually powered wireless outpost

  1. He stating it as mAD instead of mAH, which isn’t a standard unit of measure but given that he has a periodic input (sunlight) operating on a 24 hour period, it kind of makes sense. Give him a break.

  2. Solar powered is lovely and all that, but what’s he going to do when it stops being long summer days?

    What about when instead of 13.5 hours of high sun, he’s getting 6 hours of poor quality sunshine?

    needs to either add more solar panels, (so that he can get the power generation higher) or needs to ramp up the storage, so that there is a good enough bank of power to see him through the fall, winter and spring.

      1. Depends on your jurisdiction. In Missouri, yes. There is no direct physical link to the hardware. You have big coils in a shack underneath the high tension lines running across your property, and they don’t connect to anything except your breaker box? Nothing illegal about that. Without a physical connection, it gets real hard to show intent to steal power. They can always route around your property, if they like, but their government mandated “right-of-way” across your property doesn’t negate your right of ownership.

  3. If a PV panel outputs 200 mA in full sunlight then it will produce perhaps 6 x 200 mA = 1200 maH/day in mid summer and perhaps 2 x 200 mA = 400 mAh in winter. Actual figures will vary with location and weather variability.

    The output is FAR lower than daylight hours x peak_mA_output because much of the daylight during a day is at levels far below full sunlight. An excellent resource which lists a range of solar and wind parameters for many hundred of locations worldwide can be found at http://www.gaisma.com . A good way to access the relevant page is to web search for: gaisma city_name. eg gaisma houston produces http://www.gaisma.com/en/location/houston-texas.html
    All the charts are useful, but the 5th chart down contains the line
    Insolation, kWh/m²/day 2.51 3.13 4.13 5.17 5.52 5.74 5.98 5.61 4.94 3.99 2.84 2.34
    These are the effective sunshine hours per day for Houston, averaged by month. So 2.51 hours/day in January, 3.13 hours/day in February etc.
    So, under 3 hours/day for the 3 winter months and over 5 hours per day for 5 months from April to August. BUT far less than the 13,5 hours o f daylight.
    Note that the Gaisma page also give daylight hours, sunset and sunrise times, compass angle to sun throughout day, angle above horizon throughout day and much more.
    A “rule of thumb” for a solar powered system using an efficient battery and PV panel well matched to battery – or using MPPT is
    continuous_mAh_OUT_of_battery = (Panel_mA x SSH / 30)
    Where SSH = sunshine hours per day equivalent full sunshine (as per Gaisma table).
    The factor of 30 takes into account there being 24 hours in a day plus an allowance for panel to battery matching and battery storage inefficiency. In MOST cases this factor is too low and a figure more like 50 should be used in many systems. This is because PV panels are rated not only at full sunshine “insolation” BUT also only make full power when their voltage is at optimum level. When Vbattery is not Voptimum the panel makes less than full power. In the equation above I used Panel_mA and not Panel_power and in fact this gives a slightly better feel for how things really work. But, too much detail for here.
    Google: Russell McMahon BOGO
    for my experience in such matters.
    Russell – apptechnz@gmail.com

    1. MPPT (maximum power point tracking) is a means of getting maximum energy from a PV panel by matching the panel to the load – it acts like an electronic gearbox.

      With PV panel prices being far lower than in recent years, whether MPPT makes sense or not is an economic decision. In a well designed system MPPT can provide an additional 30% more energy at best, but gains will usually be lower or much lower.

      If a 10 Watt panel was used for this router and if all up costs of panels was say $5/Watt.mp then panel cost = $5 x 10 = $50. To provide an additional 30% more panel will cost an extra $15. If MPPT cannot be added for $15 and if there is room to mount extra panels it makes sense to just use more panels in place of MPPT. The figure of $5 / Wmp is well above the commercial all up cost for large installations but is unrealistically low for a 10 Watt one off system. A 10 Watt panel on ebay costs about $60 so lets say all up cost installed is $200. Any additional 30% would notionally cost an extra $60 (but in fact it will be far less than that as a 15 Watt panels costs hardly more than 1 10 Watt and mounting is essentially identical. ) If we do allow $60 for the extra 30% an MPPT controller would need to cost under $60 to make sense. While the component parts could cost far less than that, the cheapest MPPT controllers on ebay cost about $50 – These can handle far more than 10 atts but in this application are marginal at best $ wise. The extra 30% in panel area will equal MPPT very worst case and will produce 30% MORE than MPPT in best conditions. Other system sizes will produce different results – and MPPT will still make sense for very large systems. But probably not in this case unless integrated in a purpose built controller at low cost.

      1. Russell, thank you very much for the gaisma.com link!! I’ve been scouring the internet for months for a resource as comprehensive as that!!!

        I’ve been building a low-cost solar power system for our family farm and a handy chart like that is just what I wanted to see.

        Also, as far as MPPT goes– it doesn’t make economic sense and is actually MORE inefficient to include MPPT on many kinds of small installations because of the increased cost-sensitivity of these applications and their low power usage. For example, consider the solar powered pocket calculators.

        All that adding MPPT would mean for these units is a higher cost.

    2. Certainly, you’re going to post an informative link or hack-a-day article demonstrating an open source, extensible, and effective MPPT project right Rockets4Kids????

      Thanks in advance for the way that you’re really helping to further the maker community and not just trolling other people’s projects on the internet like so many useless whiners!!!

  4. from experience, I could not keep ahead of the power requirements to keep the batteries _warm_ during the winter, even with MPPT and massive overpanellage.

    Solar is great for temperate climes and places where you can keep the batteries heated.

  5. While it’s a power source that should operate well for some time it’s certainly not a perpetual power source. While as another mentioned it while itdepends on jurisdiction, even”government mandated “right-of-way”” may have restrictions what the land owner can do on the right of way. Pasturing live live stock or farming may e permitted, but there may be things that are legally prohibited. Often people get interesting notions about right of ways that may not be so. Before taking on an entity that may have deeper pockets than yourself, best to get the best advice available before investing a hundred dollars to save a penny. Having said that I never have considered using a distribution lines magnetic field to induce current in another circuit theft, but my opinion doesn’t count.

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