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I am exploring some IoT applications I could work on. One of them is a sensor that does some periodical measurements of soil and saves it into inner memory or broadcasts over low-power radio channel.

I'd make the device as low in power consumption as possible, e.g. small size, low-voltage transmitter, long periods when the device runs measurement (say 2 times a day).

I know there are many factors that can impact it, but is there a chance that soil around the device could give it enough power to function or is it impossible to count on it as a source of energy in a real world project and I should abandon this idea and use batteries?

The idea comes from the article about "earth batteries", which creates a battery by burying two electrodes in the soil.

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    \$\begingroup\$ Uhm.. how did you figure you could get any power from the soil? Have you seen any other project even mentioning it? \$\endgroup\$
    – pipe
    Commented Mar 20, 2017 at 10:52
  • \$\begingroup\$ Solar cells might be an option? \$\endgroup\$
    – Andy aka
    Commented Mar 20, 2017 at 10:53
  • \$\begingroup\$ I am quite an amateur in this area, but I found some info about these things are theoretically possible. en.wikipedia.org/wiki/Earth_battery \$\endgroup\$
    – Sergei Basharov
    Commented Mar 20, 2017 at 10:54
  • \$\begingroup\$ @SergeiBasharov I added the link to the question, feel free to change the sentence. \$\endgroup\$
    – pipe
    Commented Mar 20, 2017 at 11:00
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    \$\begingroup\$ Without knowing any of the engineering, you can still use the basic argument that if it were possible to get meaningful power from dirt, it would be regularly done. \$\endgroup\$
    – Olin Lathrop
    Commented Mar 20, 2017 at 11:01

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This isn't going to work. Think about it. If dirt to power worked, it would be done regularly. There are some ways that soil can help to get some energy, but these will be difficult to extract or the amounts would not be useful for most purposes:

  1. Sufficiently wet soil can be the electrolyte of a battery. It wouldn't be a very good electrolyte, and the energy would come more from the plates that you'd insert into the soil than the soil itself. Therefore saying you're getting power from soil is a bit of a stretch.

  2. From thermal differences. You can use soil as a big temperature averager, especially if you go a few feet or more down. The instantaneous temperature difference between the ground and the air represent power that can in theory be extracted.

    Note that the Carnot efficiency is not your friend here. Carnot says that the maximum possible theoretical efficiency of a heat engine is Tdiff/Thot, when the temperatures are measured on some linear absolute scale, like Kelvin. For example, Lets say the soil is 68 °F and the air 90 °F. That's 293 °K to 305 °K, for a Carnot efficiency of only 4%. That means you have to have a large thermal connection to both the soil and the air to extract meaningful power levels.

I would look into solar cells. Perhaps these could keep a battery charged so that the device can run whenever it wants to, whether the sun is shining at that moment or not.

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  • \$\begingroup\$ I would say that its not only a stretch but totally wrong to say that you extract energy from the electrolyte. I like the idea though of the thermal differences, I never thought of it. With a heat pipe like arrangement deep into the earth there could be some useful energy flow. This reminds me somewhat of the (ammonia filled heatpipe like) cooling rods used to stabilize rail tracks in permafrost environments. \$\endgroup\$
    – PlasmaHH
    Commented Mar 20, 2017 at 11:30
  • \$\begingroup\$ @PlasmaHH: There are many types of batteries, including flow batteries, in which the energy is indeed stored in the electrolyte. Also, consider the ordinary lead-acid battery, in which the composition of the electrolyte changes drastically between charged (sulfuric acid) and discharged (essentially water). \$\endgroup\$
    – Dave Tweed
    Commented Mar 20, 2017 at 13:14
  • \$\begingroup\$ @DaveTweed: In none of these you seem to use soil as the electrolyte. \$\endgroup\$
    – PlasmaHH
    Commented Mar 20, 2017 at 13:16
  • \$\begingroup\$ @PlasmaHH: I'm sorry. I thought your first sentence was a more general statement about all batteries. \$\endgroup\$
    – Dave Tweed
    Commented Mar 20, 2017 at 13:20
  • \$\begingroup\$ @DaveTweed: nope, it was totally just for the paragraph about the soil battery, read it like an edit suggest of s/stretch/bollocks/ ;) \$\endgroup\$
    – PlasmaHH
    Commented Mar 20, 2017 at 13:22
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In principle, yes. The available power from such a battery is highly dependent on the design and install location, so I suggest that you research and experiment with earth batteries and determine how much power you can reliably achieve.

From that data you can determine a power budget and therefore the hardware and software requirements.

I imagine that any such battery will require regular inspection and maintenance, and that the performance will vary substantially with weather. Reliability and predictability are not going to be easy to achieve, I suspect.

I seriously, seriously, doubt that you'll be able to take this beyond "interesting demonstration of the idea" stage. It's not going to work as a product. Maybe an art installation or something.

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  • \$\begingroup\$ Such a battery is not extracting any power from the soil, it is using the soil as electrolyte, extracting power from the electrochemical decomposition of the electrodes. \$\endgroup\$
    – PlasmaHH
    Commented Mar 20, 2017 at 11:24
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    \$\begingroup\$ Yes, I think that's understood by everyone. Considering the electrode + soil system as a whole, you're still getting voltage and current, so I think "power" is a valid term to use. \$\endgroup\$
    – jfowkes
    Commented Mar 20, 2017 at 11:32
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Although it's possible to construct a battery to extract energy from the bare electrodes, this is unlikely to provide a viable long-term solution. The electrodes themselves are sacrificial (they store the energy as refined metal), and over time your battery internal resistance will rise as the waste products build up. You'll probably also need to use a super-cap (maybe only a small one) to maintain the voltage whilst the mcu is active.

A small solar cell and a small battery is probably a better combination. Keep the battery at the coldest part of the enclosure, particularly if you use LiPo technology.

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http://ieeexplore.ieee.org/document/4553917/ this link may help.It is always helpfull searching patents.

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    \$\begingroup\$ It's may be helpful if you have a subscription, but link-only answers are discouraged on Stack Exchange sites regardless because they become useless if the link dies. \$\endgroup\$
    – PeterJ
    Commented Aug 15, 2017 at 12:50
  • \$\begingroup\$ or googling about the idea :google.com.tr/… \$\endgroup\$
    – argu sagturk
    Commented Aug 15, 2017 at 12:53
  • \$\begingroup\$ oh i see, i was reading something else on a patent site, and entered "earth battery". in the search column, so the link came up :o) \$\endgroup\$
    – argu sagturk
    Commented Aug 15, 2017 at 12:57
  • \$\begingroup\$ In slideshare.net side look for "free-energy-from-the-ground", there is an interesting article about a patent. \$\endgroup\$
    – argu sagturk
    Commented Aug 15, 2017 at 14:17
  • \$\begingroup\$ also there is a book which might interest you, which you can find in google books, , \$\endgroup\$
    – argu sagturk
    Commented Aug 15, 2017 at 14:19

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