Yes, you can get energy from an “Earth Battery” No, it ain’t free

April 29th, 2010
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I received a question today from someone who asked me if I “believe in” earth batteries and whether an earth battery can actually produce energy.  Apparently they had read about it online or seen some of the Youtube videos out there.   They may have also read the Wikipedia article, which is totally wrong.

An earth battery is pretty simple in principle.   Two metal rods are driven into the ground, ideally in soil that is reasonably wet or at least moist and has a slightly acidic pH.   The rods are made of dissimilar material, for example iron and zinc or carbon and zinc or copper and iron.   If the rods are connected to a voltage meter, you will find that there is a small amount of electricity being produced.  The voltage is generally low and the potential amperage is low as well, but if the conditions are descent you can use this current to drive a small load such as an LED or a digital watch.

In theory you could produce a lot more voltage and electrical power if you simply added more and more rods and connected them together.   Just like any battery, when connected in series, multiple battery units will produce higher voltages.  When connected in parallel, the voltage will remain the same, but the potential maximum amperage will be increased.   Therefore, it would be possible to power your house with enough rods stuck in the ground.


However, here’s the big party killer:  The electricity is not limitless, it’s not free (although some websites that sell the supplies claim it is) and it’s not even really coming from the ground, but rather from the metal rods.   When the rods are placed in ground they undergo a simple chemical reaction – they begin to corrode.   If the ground is fairly dry and composed of inert material like sand, then they will corrode slowly, but if it’s moist and composed of more reactive organic matter, they will corrode faster.    As they corrode, they an electrical potential is produced.  Because the two rods are made of different materials, they corrode at different rates and produce dissimilar electrical potential.   When connected, voltage flows between the two.   This is why more corrosive soil conditions lead to more electricity being produced.

The soil is just incidental to the reaction.   In fact, soil is not a very efficient medium for producing the kind of reaction necessary to produce an electrical current.   If you wanted this same setup to produce more electricity and do so more efficiently, you could replace the soil with something zinc chloride, which is basically how a zinc-carbon battery works.   You could also replace it with an acid, which is how some other battery types work. These substances have better electrolytic properties.

Unfortunately, the effect is not going to last very long.   As the metal rods corrode, the electricity produced will be reduced.    This may be remedied (at least temporarily) by pulling the rods out of the ground and grinding off the layers of corrosion that build up on their outside.   This will at least bring the raw metal back in contact with the soil and allow it to corrode quickly again, but it’s only a temporary fix, as before long the metal will all be gone and all that will be left is some worthless oxide.

Really, what you’re doing is just powering your stuff on a disposable battery, a very crude, very inefficient battery.   You would not try to power your home on AA batteries because it would be astronomically expensive.   Doing so with one of these things would be the same deal, only even worse!

There is, however, a practical use for this principle.   In the environment, some metals (for example zinc) are more prone to oxidation than other metals (for example iron) and produce a greater electrical potential when they oxidize.  By connecting a piece of zinc to an iron structure in a corrosive environment, the zinc will corrode and in the process, produce electrons which give the iron a negative electrical potential.   This opposes the oxidation of the iron and acts to slow the rate at which it rusts.   It is known as galvanic or cathodic protection.


This entry was posted on Thursday, April 29th, 2010 at 9:57 pm and is filed under Bad Science, Good Science, media, Misc. You can follow any responses to this entry through the RSS 2.0 feed. You can leave a response, or trackback from your own site.
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155 Responses to “Yes, you can get energy from an “Earth Battery” No, it ain’t free”

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  1. 151
    6PTsocket Says:

    I may be a little off topic but I was looking at those cheap soil moisture meters and they appear to be just an earth battery. I took a piece of solid insulated electric wire (#14 I think) and shoved through a piece of polished (with 0000 steel wool) steel brake line so about an inch of bare copper stuck out. In sopping wet soil I got around 0.92 volts. In much drier soil I was down around 0.85. These cheap analog meters have a scale where the lowest 20% is marked dry and the Highest 20% is wet and in between is called moist. From my crude experiments it seems that once there is even a little moisture the “battery” goes almost to the full potential between the two metals being used. Is this the way earth batteries behave? My experiment seemed to be almost go, no go rather than linear as those cheap meters would have you believe. Some other moisture testers use two separate rods of identical metal and take a resistance reading to estimate moisture content of the soil. Is this more valid? Thanks for any info, guys.


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  2. 152
    DV82XL Says:

            6PTsocket said:

    Some other moisture testers use two separate rods of identical metal and take a resistance reading to estimate moisture content of the soil. Is this more valid? Thanks for any info, guys.

    Proper soil moisture testers work by measuring resistance rather than potential. Better ones use alternating current to avoid the electrodes becoming depolarized.


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  3. 153
    6PTsocket Says:

    Thanks, DV82XL. Since readings are taken at different depths, I would think that you would have to have a small amount of conductive material at the ends of your resistance probes. If the whole of the probes were conductive wouldn’t the resistance go down as the amount of parallel surface increases, as the probes are pushed deeper causing a shallow test to read dryer than a deeper one? Holding off on the AC for a moment, do you have any thoughts on probe material and spacing, otherwise I’ll have to find out the hard way. No point in reinventing the wheel. Thanks again


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  4. 154
    DV82XL Says:

            6PTsocket said:

    Since readings are taken at different depths, I would think that you would have to have a small amount of conductive material at the ends of your resistance probes.

    Of course the probe’s active area is fixed depending and on the design can be large or small. There is a wide variety depending on application, and made of several different materials. Given the low cost of some of the simpler ones aimed at the home gardener, I would be inclined to buy rather than go to the trouble of homebrew. Having said that, the probe should be made of a material that will not oxidize or form a nonconductive film, so I would start with stanless steel, rather than copper or aluminum.


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  5. 155
    6PTsocket Says:

    Thanks again DV82XL. Stainless is the way I’ll go if I don’t find something cheap. Everything is mail order today. The brick and mortar stores have nothing. I live in the suburbs but it might as well be the Yukon for the limited stuff you can get over the counter.


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