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You might see in this short, 2-minute video that billionaire Manoj Bhargava talks about creating cables from graphene to conduct heat from the underground sections of the earth to the surface.

But as per the properties of graphene, it is only a good conductor if the number of layers is one or very few. Once you start stacking it up, it is just normal graphite and it's conductivity gets reduced.

What's proposed in the video is a cable made from graphene. My question is how is it possible to make a graphene rope without stacking up graphene layers (and thus ending up with graphite) or without converting it into nanotubes?

I would also like to know why stacking up graphene reduces it's conductivity? Why don't the layers behave independent of each other?

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    $\begingroup$ I guess the solution is to isolate the layers from each other. $\endgroup$
    – ratchet freak
    Commented Mar 2, 2016 at 15:33
  • $\begingroup$ @ratchetfreak so something like insulating each layer? $\endgroup$
    – rahulgarg12342
    Commented Mar 3, 2016 at 5:58

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I'm sure the methods they are using and advertising in their video are extensively protected by patents that can be searched here: "Graphene Production" patent search

Remember that it is just a promotional video, and what they say is not necessarily true.
At 1:11, "...100 times better conductor than copper..." Not likely:
2500 W⋅m−1⋅K−1 Graphene/ 385 W⋅m−1⋅K−1 = only 6.5 times better it turns out.
At 1:24 "...and the middle is completely cool." I find it quite unlikely that even an exotic material like graphene can conduct heat without becoming that temperature ;-)

This phys.org article explains that the crystals must be aligned. "When two crystals are neatly lined up, heat transfer occurs just as predicted by theory. But if the two crystals have mis-aligned edges, the heat transfer is 10 times less."

In the past I have cut ice with low grade pyrolytic carbon that I originally procured for a diamagnetic demonstration. The very high conductivity is quickly evident and it works just like it does in this youtube video.
enter image description here

On the graphene wiki article: "Early measurements of the thermal conductivity of suspended graphene reported an exceptionally large thermal conductivity of approximately 5300 W⋅m−1⋅K−1,[129] compared with the thermal conductivity of pyrolytic graphite of approximately 2000 W⋅m−1⋅K−1 at room temperature.[130] However, later studies have questioned whether this ultrahigh value had been overestimated, and have instead measured a wide range of thermal conductivities between 1500 – 2500 W⋅m−1⋅K−1 for suspended single layer graphene."

As far as economic feasibility; there would have to be some major reductions in price and increases in conductivity to make it more economically advantageous than current geothermal fluid heat transfer systems; let alone other forms of power production.

Other references:
MIT, Technique for mass-producing graphene
MIT, Continuous rolls of graphene
PopularMechanics, Mass producing graphene

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  • $\begingroup$ Thank you for the answer. Yes of course some stuff in the video is untrue and just for marketing purposes. Regarding economic feasibility however, do you mean the initial investment or the maintenance costs involved? Don't you think their solution would be better compared to Solar Energy where solar panels have a high initial capital requirement? And less efficiency? Geothermal, if tapped is an enormous energy source. What do you think? $\endgroup$
    – rahulgarg12342
    Commented Mar 9, 2016 at 17:42
  • $\begingroup$ The capital cost of drilling to those depths alone is far more than the cost of equivalent solar power. Granted, it would be 24 hours a day, but the heat you pipe up still has to be converted to electrical energy via a thermodynamic cycle which is likely less efficient than the solar panels. If this graphene cable does become a viable technology the first place you will see it is in automobile cooling systems where small footprint and reliability are paramount. After it is successful there, it may possibly be a viable option in geothermal. $\endgroup$
    – ericnutsch
    Commented Mar 10, 2016 at 2:52

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