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Note - I have tagged this as because, apart from feasibility, I'm hoping for some actual numbers that will tell me the capabilities of such vehicles.


Background

On a planet far away there are constant thunderstorms over the plains of Groth.

Until the advent of science and technology, the locals kept well away from the area, despite what would have provided excellent trading routes. This was because the chances of you and your pack-animals surviving were minimal.

Now however planet-wide electrical technology has reached the level of early 20th century Earth. Gasoline-powered vehicles have not been invented.

Someone has the idea that the Grothlanders would be the ideal people to test out the newly invented electrical motors because they live all around the perimeter of the Plains. There is a continual although not exactly continuous supply of electricity from lightning.

How the vehicles work

They are 4-wheeler carts steered from the front and powered by an electric motor driving the rear axle.

They have an aerial sticking out of the top to catch the frequent lightning strikes. The driver and passengers are protected by a Faraday-type cage to avoid being killed. They have padded helmets to muffle the constant deafening noise.

Question

Given a lightning strike every few minutes, would such a vehicle be feasible? It has to travel up to 100 miles across the Plains of Groth on any particular journey.

In particular, is it feasible to catch, store and use lightning in this way and would the weight of all the necessary equipment to make this work be excessive?

Assuming that the idea is feasible at all: Given the energy of a typical Earth lightning bolt, how often on average would a minimal-sized vehicle have to be struck in order to keep going pretty much continuously at, say, 30mph (approx 50kph)?


Assumptions

Please ask for further necessary details before answering.

  • A minimal-sized vehicle has condensers to store the electricity, an electric motor, is capable of driving hundreds of miles whilst being struck by lightning, carries a human-sized driver and one passenger, and a Faraday cage to protect them. The plains are more-or-less flat with firm but wet going. Some suspension is necessary but there is no rough terrain. Ball-bearings are available.

  • There are future plans for some kind of railway network. But but this is still years away. For now, all they have are self-contained 4-wheeler motor carts. Most of these are home-built apart from the electrical motors that they have to purchase.

  • The lightning storms are equivalent to those on Earth but go on day and night through some climate anomaly not disclosed here. If you venture onto the Plains you can expect to be struck pretty regularly. Exactly how often is part of my question.

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  • $\begingroup$ The hard-science tag was added while I was writing my question. Let me know if you want harder numbers than I gave you. $\endgroup$
    – JBH
    Sep 26, 2020 at 23:29
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    $\begingroup$ You need a flux capacitor. $\endgroup$
    – Peter Shor
    Sep 27, 2020 at 0:01
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    $\begingroup$ Did I say question? I meant answer. $\endgroup$
    – JBH
    Sep 27, 2020 at 0:56
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    $\begingroup$ It seems more practical to have fuel stations scattered about that collect the lightning. It seems like too much energy to power a car safely, especially with energy dissipation. A static station could deal with that, a home made vehicle might not. $\endgroup$
    – Muz
    Sep 28, 2020 at 7:13
  • $\begingroup$ Is it necessary to use an electric motor for propulsion? The problem with lightning is its power is hard to capture. But you could use it to heat up water and create steam (water is available from the rain), and you could run a steam engine. Or heat up one side of a Stirling engine (and cool the other side with the rain). $\endgroup$
    – Nyos
    Sep 29, 2020 at 17:58

7 Answers 7

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So the maths works
A lightning bolt contains ~5 gigajoules of energy, or as Wikipedia helpfully tells us 38 gallons of gasoline. So if you could get a lightning bolt to hit you, and could store all the energy at 100% efficiency, that's enough to drive a 2019 Acura 1000 miles. (Exactly 1000 - it's rated as 3.8 gal / 100 miles).

Even if you lose 90% of the energy, that's still 100 miles per strike. Even if your go-cart things guzzle fuel at 7.6 gal / 100 miles, that's still miles per strike.

But the lightning doesn't

The trouble is getting the lightning to strike you. Because of this, the exact design wont work.

Lightning travels in steps of about 60m - looking for the path of least resistance greedily like water flowing down hill. (This is why lightning can strike a tree a few hundred meters away from a tall building.)

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You attract all lightning to you over distance d based on this equation (from XKCD's "what if").

$$ d = \sqrt{ - h ( h - 120)} $$

If your car has a 3m rod sticking up - it will cast a lightning shadow 18.7m wide - so anything going to hit the surrounding 19m will come for your lightning rod.

10m? 33m radius. Once you hit 60m, the shadow is at its peak. A lightweight 4-wheeler cart with a 60m tower is going to fall over over on the slightest slope.

So what will?

However; Some 60m towers, spaced about 100m apart with lightning rods powering a nearby electric train network. That's starting to become possible.

4 towers holding the corners of a large 100x100m mesh of thick wire will capture all lightning coming for the region under the mesh.

Also possible is lightning mixed with some technology to convert the power to liquid or gas fuel. Eg electrolysis to create a hydrogen fuel, and pumps to compress it. You lose a bit of power in the conversions but JBHs hypothetical maths can be a reality with a big factory cranking out compressed hydrogen.

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    $\begingroup$ +1! I like the idea of a stationary lightning rod that's powering electric rail. Especially if you expand the idea to inductive power where there's no rails, just power lines in the roads and cars that tap that power. Clever! $\endgroup$
    – JBH
    Sep 27, 2020 at 6:16
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    $\begingroup$ Not sure about this, but what about balloons for lightning rods? Is it absolutely implausible to have a say 50m cable with a ballon at the top that can take and conduct lightning strikes? Would you need handwavium for the cable or the material of the ballon? $\endgroup$
    – LordHieros
    Sep 27, 2020 at 18:16
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    $\begingroup$ @L.Dutch I'm referencing existing mathematics. Is it really best that's duplicated rather than referenced? If you want redundant calculations say so and I'll do it in the morning. $\endgroup$
    – Ash
    Sep 27, 2020 at 18:25
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    $\begingroup$ The mix of US customary and SI units makes my head spin… ! $\endgroup$
    – breversa
    Sep 28, 2020 at 8:27
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    $\begingroup$ I think the problem might be in that lightning follows the path of least resistance. If you storing the energy or doing work with the energy there is going to be resistance. If it's too difficult for the lightning to go through your apparatus, it will find another way to the ground. $\endgroup$ Sep 29, 2020 at 15:43
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I don't think it would work in practice...

While lightning has more than enough energy, you'd have problems harnessing it. Problem is enormous power (high voltage and current), ie. lots of energy which is delivered in very very short period of time.

And to transmit/store that high power, you need big conductors (to carry high current), with extremely low resistance (think ideally: superconductors). Otherwise, you'd have big power losses in small space, which amounts to extreme heating, which amounts to metal becoming vapor in very small fraction of a seconds, ie. explosion (not chunky enough conductors would be blowing like overloaded fuses)

What might work for mobile units is using lightning indirectly, by being isolated enough so lightning never strikes vehicle, and using other effects to harness its energy, perhaps like:

  • induction which is usually responsible for frying your electronics when lightning strikes. eg. any moving current (like lightning) creates changing EM field, and any voltage is induced in any conductor in changing EM field. Longer the conductor, higher the voltage. That's how modern wireless phone charging works (although phone wireless charging uses much lower voltages and MUCH more rapid changing)

  • making use of step voltages - ground potential is NOT the same on different radiuses from center point of lightning strike. Bigger the distance (and more perpendicular to the point of origin of lightning strike), higher the voltage difference.

Those two indirect methods generate MUCH less power than direct lightning strike, so they bring needed electrical devices into realm of possibility for car-like vehicle. However, unless the ground close to you gets hit by lightning VERY often, energy harvested would probably be too low to use such car (unless you park it for days in such stormy area to charge before using it).

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It won't work, but it's cool to think about

The good news: Oh, yeah, you could operate a car on lightning strikes. Lightning can deliver 10 GW of electricity. Now, that article downplays the power of lightning by telling you that when you extrapolate the power to KWh, it isn't much (and, in terms of running a whole city, it ain't). But that's still 10 GW to work with (you don't divide the power into the length of the lightning strike or the claim would be 50 MW).

So, 10 GW. That's a honking lot of power. From this source we learn that to drive 400 miles an "average" car (and that's one wild guess. Cars are all over the map, so you should treat this as a ball park figure) will burn 560 KWh. And... 10 GW / 60 / 60 kinda = 2,775 KWh or almost 5X the energy needed to run the car for 400 miles. So, you can easily run for 800 miles (10 hours of driving at 80 MPH) with the A/C on, every light you can hook up, and your stereo running loud enough to be heard in Iceland.

EDIT: Curiously, no matter how poorly I did the math, it appears I was basically right, anyway. From this source we learn that "A single bolt of lightning carries a relatively large amount of energy (approximately 5 gigajoules or about the energy stored in 38 gallons of gasoline)." Average passenger car gets 30 mpg so one bolt is worth 1,140 miles - well beyond a single day's supply.

But that's not the problem

The problem is how to attract the lightning. Electricity follows the path of least resistance to the lowest electrical potential — which will almost never be the car (and it's not just the high-insulation vulcanized rubber tires). Even if you paved the roads with silver (great conductor) and used gold instead of rubber for the tires (great conductor), the best you're going to get is an average electrical potential equal to the ground within about a 3 meter radius of you. If you're cresting a hill, you have a great chance of being struck. If you're at the lowest point around you... not so much.

But hope is not lost for good science fiction!

Because what you could do is operate your car on negative voltage compared to "ground." And in a car, that's "chassis ground" or the voltage of the chassis metal. (Said another way, to keep passengers safe, the chassis of the car is used as the 0V reference.) Normally a car operates at +6VDC, +12VDC, or +24VDC (depending on what kind of vehicle it is).

Yours operates at -480VDC. And that honker can haul the mail! The benefit? You can put the -480VDC charging terminal on the top of the vehicle where it will (science fiction) draw all the lightning bolts you can handle!

And when your car is charged, a +24VDC plate covers the connector so that the lightning is pushed away from it. And we'll ignore what happens when two plates with a potential difference of 504VDC do. It's called a capacitor. Just ignore it. Science fiction. :-)

But is it safe?

It's your world. Declare it to be safe. Those folks grew up on it so lightning management would be a fundamental technology. The operator's cabin would be electrically isolated (very well insulated) from the rest of the car. There'd be some way of discharging electrical "overburden" (me, I want an arc lamp that rivals The Luxor Hotel).

And keep in mind, you'd need to only be struck once a day at the most to keep this car rolling. You can't run a city on lightning — but a car? Not hard at all.

Big ol' trucks might need to be hit multiple times a day.

A motorcycle might need to be hit once in your lifetime. Your lifetime, not the motorcycle's. Your people probably abandoned motorcycles a long time ago. The 2 Km search radius for the rider was too much work for the Search & Rescue team.

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    $\begingroup$ You are confusing GW and GWh. 10GW/60/60 is 2,775 kW/h which is the wrong unit and doesn't mean anything. You need to find the number of joules and divide that by an hour. $\endgroup$
    – user253751
    Sep 27, 2020 at 10:24
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    $\begingroup$ "Lightning can deliver 10 GW of electricity." Surely you mean 1.21 giggawatts. Surely. :-) $\endgroup$ Sep 27, 2020 at 10:52
  • $\begingroup$ 3 meters? That seems way too low when the car has a giant metal rod sticking into the air. It might still be too low to expect to get hit in an Earth thunderstorm, but increasing the frequency of strikes (quite) a bit might make it more realistic. $\endgroup$
    – NotThatGuy
    Sep 27, 2020 at 11:23
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    $\begingroup$ 10GW * 5/1000s = 50MJ. 50MJ/110.25kWh = 0.126. That means, you need about 8 lightning strikes to cover 40miles. $\endgroup$ Sep 27, 2020 at 11:56
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    $\begingroup$ The most powerful laser in the world is 2 petawatts, which is about three hundred times the total global electricity generating capacity. But we can’t power everything using it (and we can power it), because it only runs at that power for a trillionth of a second. Lightning is the same — very high power for a very short time — and so its power is meaningless in this context. You need to be talking about the energy. $\endgroup$
    – Mike Scott
    Sep 27, 2020 at 20:09
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Yes, it is possible to make such a machine. A lightning strike would bring about one billion (1,000,000,000) joules of energy. Aviation fuel contains 43 million joules per kilogram. Hence we have the equivalent of 23 kg of fuel from the single strike, 6 gallons. BMW i3 Giga can drive 846 miles, 1361 km on that! Even a small aircraft like Cessna 172 only requires about 10 gallons for a whole hour. So under any bearable efficiency of the lightning collector, a vehicle getting a strike per minute could not only ride, but even fly, even if heavy and inefficient. Or, probably, a strike per half an hour should be enough.

Some sources estimate the energy of the single strike to be about 20 times less (and there are different types of lightnings). This would still work even for the mentioned Cessna aircraft if we count on a strike per minute.

It is however technically challenging to extract all power from the lightning. Some kind of advanced supercapacitor is required that could take lots of energy very quickly and be charged to a very high voltage. Then no less advanced voltage converter needs to convert the energy into something that a normal electric engine could use. So probably not with the steampunk technology and not with 100 % efficiency. But if really a strike per minute, it seems that there is a huge efficiency margin for building something that just moves over ground.

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    $\begingroup$ Where do you take this number from? (This)[energy-cast.com/41-lightning.html] only mentions 50MJ. Factor of 20 less. $\endgroup$ Sep 27, 2020 at 16:09
  • $\begingroup$ All numbers are provided with the sources that are referenced in this answer, links under the numbers. Other sources may give different numbers, there are multiple types of lightnings after all. However even if we have just 1 kg of fuel rather than 23, this is still more than enough to run a car for a one minute. $\endgroup$
    – eigenvalue
    Sep 28, 2020 at 11:09
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This is likely to be far more 'practical' if the lightning strike were to generate steam, and not be stored as a pile of electrons.

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    $\begingroup$ This is a very short answer. You should expand on it with more details and possibly sources and diagrams. $\endgroup$ Sep 27, 2020 at 17:21
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Let's approach it from the other direction.

Let's audit the tech available at the time.

Electric cars were abundant, readily available, and just worked. They were the vehicle of choice for society ladies who wished personal mobility. Gasoline engines required a "driver" who was as much a mechanic to keep the fidgety engines working - on Downton Abbey this was Tom Branson's original job.

Without any application for engine starting, lead-acid batteries become a poor choice, done only on the cheapest vehicles. So other tech, notably Edison's nickel-iron batteries, are a huge winner. (Nickel-iron batteries are long-lived and almost indestructible, but have high internal resistance, so do poorly with "engine cranking". Not an issue for electric cars, but it may be an issue here.)

However, I'm burying the lede.

The 600 pound gorilla of the early 20th century was electric railroads. This technology had exploded onto the scene, with streetcars replacing horse cars, but much more importantly, interurban electric railroads.

These are high-speed (for the time) trains that ran at 70-100 miles per hour. They ran as small as single cars (a bit longer than a streetcar), or fairly long trains. The electric power ran normally at 600 volts, but as high as 4000 volts DC or 12,000 volts AC.

This is dragging us to a conclusion: The right way to do this is ferry the automobiles on flatcars on the interurban railway.

Catching the lightning

The trolley wire will be a magnet for lightning strikes. You build this system with a huge amount of capacitance at megavolt levels - so you make the rail network as vast as possible, without circuit breaks.

Now, here is where we need to know the polarity of the lightning. If your lightning is consistently the same polarity, that will play nicely with a DC system. Otherwise some of your strikes will work against you, and those tend to be the more powerful strikes. Remember, we don't get diodes in this half of the century.

It won't work to have one track positive and the other track negative polarity. The lightning either wouldn't care or would be drawn to the more opposite.

AC is right out. First, half your strikes will be the wrong polarity (because of timing), and the net energy would be nil. Second, a vast system with a lot of capacitance will have a lot of problems both due to the capacitance and phase drift due to the vast distance.

Substations, in as many places as possible, will have some sort of unknown ultra-capacitor technology of some kind, including possibly a very tall stack of those lovely, indestructible Edison batteries.

Another option is to have a transmission line well above (vertically) the trolley wire. The transmission line would catch the lightning. This transmission would be the highest voltage DC that can be mustered given the tech of the age. It would have DC-DC conversions at substations. This was not easy in 1915, but not impossible.

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  • $\begingroup$ "AC is right out. First, half your strikes will be the wrong polarity (because of timing)," Three-phase AC might fix this problem. $\endgroup$
    – nick012000
    Sep 28, 2020 at 5:38
  • $\begingroup$ @nick012000 The problem is the lightning is probably going to go for the phase with the greatest voltage difference (highest attraction), so then it'll always strike the wrong phase. Same problem with having one track be + and the other -. $\endgroup$ Sep 28, 2020 at 7:03
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I would say no. Safety is probably the core issue.

Air around lightning is heated to 50,000 degrees F. Air is a terrible conductor but unless the devices used to store AND ground the lightning are superconductors, there's bound to be tremendous heat around it. Since it's possible to expect one every few minutes, catching two in a row within seconds might be too hazardous.

Shock waves from the thunder are enough to cause property damage and bruises. It's similar to that of an explosion or supersonic aircraft 'boom'.

Let's assume the heat and shock waves don't kill you. We're looking at 10 GW of electricity. Living within 50m of a 765 kV power line carries risk of cancer. Lightning is over 1000 times stronger than that, and at a much closer proximity. You'll likely get a lot of near fatal radiation over one drive.

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  • $\begingroup$ Downvote for citing "emfacademy"'s nonsense about power lines causing cancer. This has been repeatedly debunked. $\endgroup$
    – jdunlop
    May 11, 2021 at 22:14
  • $\begingroup$ @jdunlop The article you linked clearly states "Although the studies we have included do not show an association with MF, our results are broadly consistent with previous pooled analyses of MF and childhood leukaemia in that the elevated risk we found was limited to < 50 m of a 200 + kV lines, a distance at which MF are more likely to be elevated." There's a table: nature.com/articles/s41416-018-0097-7/tables/4 $\endgroup$
    – Muz
    May 17, 2021 at 3:06
  • $\begingroup$ The formula for an electric field is also k * Q / r², meaning that as r (radius) becomes slightly higher, the risk drops drastically. A field at 1m is 2500 times stronger than a field at 50m, and 10,000 times stronger than a field at 100m. And with 1000x the power, that field has another 1000x multiplier. $\endgroup$
    – Muz
    May 17, 2021 at 3:09

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