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Electrical Riddle No.53 - Harnessing energy in cloud/lightning
Can we collect charges in clouds before it discharges to objects in ground? Also is it possible to store energy discharged via a down conductor during a lightning strike in a capacitor?
Author : Sinnadurai Sripadmanaban - From: Srilanka
Thu, March 17th, 2011 - 13:05
The amount of lightning energy is not very huge; indeed in lightning phenomenon we face to moderate energy in very short time duty. Each cloud-to-ground lightning flash has energy approximately equal to 109 J.  This is approximately equal to the energy required to operate ten 40-W light bulbs continuously for 29 days. Even if it were possible to capture all flash's energy (the bulk of this energy is not delivered to the strike point since it is lost to heating the air and producing thunder, light, and radio waves), one would need to attract 12 flashes to the energy storage facility in order to operate these ten light bulbs for one year. The probability of lightning strike to a given point on ground is very low.  For example, a 1 m2 area in some area is struck by lightning on average, once in 105 years.  A grounded structure protruding above earth's surface is more likely to be struck by lightning.  A 60-m tower located in that place is expected to be struck by lightning once every other year.  Thus, one needs 24 such towers covering a large area of 1 km2 or so to operate ten 40-W light bulbs, which appears rather impractical. Thus the two main problems with the utilization of lightning energy can be formulated as follows:
- The power associated with a lightning flash is very high, but it is released in pulses of short duration (of the order of 10-4-10-5 s).  As a result, lightning energy, the integral of high power over a short period of time, is rather moderate, comparable to the energy consumption by a typical household (the integral of relatively low power over a long period of time).  This energy is equivalent to that released in the burning of 20 to 30 kg of oil.
- The capturing of lightning strikes would require the use of a large number of tall towers, which is rather impractical.
Additionally, as noted above, not all the lightning energy is delivered to the strike point.  Using a typical measured value of energy per unit resistance (action integral) for negative lightning of 105 A s2 and an assumed range of effective resistances at the strike point of 10 to 100 Ohm, we estimate a range of the lightning energy delivered to the strike point to be from 106 to 107 J, which is only 10-2-10-3 of the total energy.
Author : Barak - From: Israel
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