Producing energy from lighting bolts

Question

An average bolt of negative lightning carries a current of 30 to 50 kiloamperes, transfers a charge of 5 coulombs, and dissipates 500 megajoules of energy (120 kg TNT equivalent, or enough to light a 100-watt light bulb for approximately 2 months). However, an average bolt of positive lightning (from the top of a thunderstorm) may carry a current of 300 to 500 kiloamperes, transfer a charge of up to 300 coulombs, have a potential difference up to 1 gigavolt (a billion volts), and may dissipate 300 GJ of energy (72 tons TNT, or enough energy to light a 100-watt light bulb for up to 95 years).

All that energy is being send to the ground instead of used. Why are there no ecologically-wise energy producing centrals that collect lighting (in lighting-oft regions)? Is it really that hard to collect the energy from lightings?

The problem is that "you don't know where and when the lighting will strike"? I think if McDonold's resturants on their own become energy collectors, a lighting bolts will occasionally strike on the right place.

Answer 1

All that energy is being send to the ground instead of used.

No it's not. This classic misconception is probably the origin of all these "harness the lightning" ideas.

Actually, the voltage across the ground is insignificant compared to the lightning itself. Instead, imagine that the lightning is a tungsten filament, or lightning is like the resistor connected between two HV terminals. With a hot tungsten filament ...would we say that all the energy is being sent into the wires and therefore wasted? No, it's being sent into the hot filament, not into the connecting wires. (Current is not an energy flow. That's the key concept. The path for current is in a closed circle, while the path for energy-flow is one-way: into the lightning plasma itself.)

During a lightning strike, how does the energy flow? Cloud-ground lightning is just a spark between two large "capacitor plates." The energy starts out as strong vertical e-field between the cloud-base and the Earth; between the two plates. During the lightning bolt, energy in the air below the cloud is flowing inwards towards the lightning. The energy-flow looks like a shrinking cylinder, with the lightning at its core. Energy in the wide-spread e-field ends up as energy in the tiny region of hot plasma (and then becomes emitted light and sound, and some hot air.)

If you see a lightning bolt, that means the energy is already wasted in powering the bolt. The current in the ground may be enormous, but the wattage there is miniscule.

In other words, if we want to harness lightning, we have to get rid of the lightning bolt, and replace it with some sort of energy-absorber which is connected to some sort of energy storage device. No huge flash, no noise, no miles of "bulb-filament made from plasma."

Instead, look at all that silent invisible e-field energy starting out between the cloud and ground: the two enormous capacitor plates. We want the field-energy to flow into a small point-like absorber on the ground. NOT flow into a miles-long vertical plasma-filament. So, to solve the problem, just tell everyone how to design a fairly tiny machine to efficiently suck the energy out of a capacitor where the plates are two miles wide and a half-mile apart.

Here's an 'easy' solution: build a tower that's a couple miles tall, and mount a metal sphere on top that's roughly the size of a thunderstorm. Then, when it passes through a moving storm, a major portion of the storm's electrical energy cam be collected but without wasting it as a mile-tall streamer of incandescent plasma.

Answer 2

wbeaty has answered the main question.

From your comments to your original post:

... but the hydroelectric power stations and other kinds of power providers must have means to store a lot of energy.

Yes, but it is stored before its convertion to electricity. Hydro stations store masses of water with high potential energy due to the head between the water surface and the turbines. Oil, gas and coal generators store the energy in the form of chemical energy in the fuel. The energy is released on demand.

Electrical energy storage is limited and expensive. In the case of hydro, pumped storage systems are used and these work by running the turbines in reverse to pump the water back up the hill - generally to the upper lake in a two-lake system. In the case of battery the electricity is used to reverse the chemical reaction in the cells and store energy as chemical energy again.

Wind generation is another example of this. Many windfarms can be under-utilised at night because the demand is lower. Energy storage solutions include pumped storage and, more recently, large batteries - Tesla recently supplied a large one for Australia.

None of these systems could be reversed to store all the energy of a lightning discharge in the time of the discharge (< 1 s).

As wbeaty points out, most of the energy will be dissipated in the lightning arc and not in the ground.