# How could we possibly harness the energy from the Earth's negative charge?

I've been reading the Feynman lectures, and in this lecture about lightning, he describes how the Earth is negatively charged, and how there is thus an electric field of about $100\ \tfrac{\text{V}}{\text{m}}$ near the surface of the earth.

To me, it seems like $100\ \tfrac{\text{V}}{\text{m}}$ could provide a lot of energy, a lot of small appliances run on $9\ \text{V}$ batteries, and the power point provides $240\ \text{V}$, which would be the potential difference between $2.4\ \text{m}$ of air, not all that much. There are probably problems in attempting to harness the electric field around the earth, but if I were to design a simple machine to harness the energy, how would I do so?

• Don't confuse electromotive potential with energy or power. The issue here is that we need to consider the resistivity of air, which let's say is $~1.3e16$ $\Omega / m$ which comes out to roughly $7.7e{-15}$ $A$ or $7.7\,femto-amps$ and $7.7e{-13}\,Watts$ of power available per vertical meter. (although we could also consider horizontal areas too) That's not much available power, even if you could somehow "pull it out of thin air". Your best bet might be to try to charge a very very wide and tall capacitor, but I'm not sure what the details would be. Certainly an entertaining question! – Falimond Oct 16 '15 at 6:08
• @Falimond is the conductivity of air really the problem at hand? I could simply just have a structure made from copper that would acquire a great potential across its ends with no air present, and with coppers low resistance pull a lot of power if the resistance of air were really the main problem – Joshua Lin Oct 16 '15 at 6:11
• I believe there's some effect of shielding due to the high resistivity of air that you need to consider. Briefly scanning the lecture, it sounds like this effect is largely, if not completely, due to ionic charging at the different strata in the atmosphere. When you're standing 2m tall, you're displacing the ions that would have taken up the volume where your body stands, and there's no potential difference from your head to your toes. – Falimond Oct 16 '15 at 6:29
• Consider people and things being struck by lightning. This only happens when there's dielectric breakdown, and oh boy does current flow in that situation! Again, I think there's something critical here having to do with shielding. Hopefully someone else can chime in. – Falimond Oct 16 '15 at 6:31
• It sounds like something Nicola Tesla tried to do in the early 20th Century but failed [en.wikipedia.org/wiki/Nikola_Tesla]. – Fred Oct 16 '15 at 12:16