Where could you store the energy from a tornado?

Question

Assuming a very large device was constructed which could harvest up to 20% of the mechanical energy of a tornado. It is a mobile platform of some sort, and one or several of these are ready to deploy in a prone region such as America's tornado alley.

Assume the simplest scheme: the device turns the force of the tornado into rotational work, by deploying some construction of large vanes, kites, or other deflecting surface capable of withstanding the forces. On placing itself in the center of the cyclone, it is able to draw off 20% of the rotational energy and store it before the cyclone wanders away. The construction is unknown at this point. It is designed to handle the most common EF-2 cyclones, and can shut down and secure itself against larger ones. For calculation purposes, it can complete the harvest by maintaining itself within the center of the cyclone for two minutes, then the funnel wanders off with 75% of its original energy (the process leaves 5% lost as deformed metal, heat, deafening acoustic energy, and eroded metal).

While the energy capture device itself may currently be beyond our technology, the question simply concerns a storage mechanism that can recover as much of this huge rotational work as possible, while being accessible to a mobile platform (the unpredictability of tornadoes make it impossible to pre-stage your energy batteries, or the device, within some large construction). As such, the hard science tag only assumes the input of a known quantity of energy at a known rate from an unknown location or time.

What would be the most efficient means to store captured tornado energy given the high rate of delivery, and inability to predict the location?

My worlds are largely wind-powered so this answer can serve several applications generally.

Answer 1

Flywheels

Handwaving the many reasons why storing a tornado in a bottle (metaphorically) would not work, and would be an impractical way to gather energy, if you were going to try, based only on the parameters you’ve provided, I’d recommend flywheels.

• Are already a rotational form of energy storage
• Are heavy but can be portable
• Can charge very rapidly / under high impulse

Once the portable flywheel rig is set up and the tornado has passed, you can transfer the power to longer term storage e.g batteries at your leisure.

Answer 2

Gravity

Use windmills to capture the storm, then pumps to lift something like water from a low place to a high place, as in pump-storage hydroelectric dams.

It is a better way to store normal wind than tornados, but tornados tend to come with high winds.

Answer 3

A general alternative is "weight lifting", you use the energy you harvest to lift many tons of weight to a higher altitude; and then the controlled lowering of this weight, which can start and stop as needed, generates electricity.

A practical implementation is already in use: Excess solar power is used to pump water from a "low" reservoir to a "high" reservoir during the day, and during the night, controlled draining of the high reservoir into the low reservoir, through turbines, generates electricity at night. These are lake-sized reservoirs, obviously, often replenished by rain. In the high reservoir, this is a bit of free energy.

The reservoirs can be built, by digging for the low one, and using the material to build the high one. Or think of something like the Hoover Dam; which operates on nearly the same principle, except we aren't pumping to fill it; a river running downhill fills it for us.

This is a way to turn intermittent energy into energy on demand; although there is about a 15%-20% loss in the energy due to unavoidable inefficiencies in pumping. (That's why they use solar power directly if they can, to avoid that loss, but they are designed to over-generate by a significant factor so they can pump and cover the night needs.)

Answer 4

You have a big problem.

First, we need to know how much energy will need to be stored. According to the NIH, the typical EF2 tornado has 88 TJ worth of energy, so 20% means storing 17.6 TJ.

How much is that? Well, converting 17.6 TJ to TNT equivalent (4.184 GJ per tonne TNT) gives 4.206 KT of TNT roughly 30% of the atomic bomb dropped on Hiroshima. Energy storage systems are often expressed in terms of kWh. 17.6 TJ is 4.89 GWh

So, ignoring the other costs just for the moment, what is the cost of grid-scale storage for 17.6 TJ. According to the National Renewable Energy Laboratory in 2021, and using the low-end of the range for storage costs.

Lithium Ion    352 USD/kWh
Lead Acid      380 USD/kWh
Sodium-sulfur  599 USD/kWh
Pumped Water   150 USD/kWh
Compressed Air  97 USD/kWh
Flywheel      4320 USD/kWh
Thermal         20 USD/kWh

Pumped Water hydro storage is clearly not portable. Thermal and compressed air also also very unlikely to be portable - knocking out the 3 cheapest methods. So, what it the cost for lithium ion storage - 5.89E9 * 352 / 1000 = 2.07E9, or over 2 billion dollars.

Though this is a stretch, it becomes much less feasible when you consider have much time you have to charge your storage system. Attempting to charge that much lithium ion storage in 2 minutes would result in a very large fire. Other storage systems would have similar problems. You need to store energy at the rate of 146.7 GW - 6.5 times that output of the Three Gorges Dam.

Regardless of you storage system, you need to be able to store the power at the rate of 146.7 GW - this will never be true in a portable device that you must guide into the storm path. An F2 system has a remarkable amount of energy.

I would say the nobody is ever going to capture that tornado

Answer 5

You want to harvest static electricity and temporarily store it in super-capacitors.

These can be charged very quickly and will hold their charge for a few days (depending on the capacitor design). It would essentially look like one of those mega trucks. You wheel it in front of the tornado path, charge your capacitors, then drive it off to some central location to offload the energy.

This would be similar to a Van de Graaff generator (https://en.wikipedia.org/wiki/Van_de_Graaff_generator) but the mechanical element is already provided by the tornado.

As the air particles drag though your apparatus, an enormous amount of static will be created which you can then store in super capacitors (https://en.wikipedia.org/wiki/Supercapacitor).

Capacitors are very elastic as well so you can do this over and over with minimal degradation. As a bonus, it should be possible to design a static generator with no moving parts, which will last much longer (you know, if your energy collecting truck doesn't get hit by a shed)

Edit: As noted by @Goodies, the specific energy of capacitors is low in comparison to other storage mediums. The wikipedia page has the higher end at about 100 Wh/kg. Supposing we want to store 1 GWh (for simplicity) we would need 10 million kgs of capacitors.

Considering that the worlds largest truck (https://en.wikipedia.org/wiki/BelAZ_75710) can load a meager 450000 kg, you would need about 20-25 of these bad boys working together to harvest the tornado.

Answer 6

Ignoring like others, the issue that your device isn't ever exposed to more than a small proportion of its highly movable and unpredictable rotational energy, I reason this way for my answer......

@GaryWalker outlines the extreme high rate of charging or storage implied. @Amadeus explains his lifting a large mass against gravity in theory works but in practice wouldn't be much help.

Solution - large volumes of stored/possibly somewhat pressurised air

Building on those, I'd suggest your device converts rotational energy into a pump, and pressurises an immense air container made of some elastomer. Here's why:

• Lifting an object stores energy but is limited by the mass involved, you want a lot of mass for it. Pressuring air also stores energy very nicely but you don't need to carry round a 100,000 ton block of concrete or steel (or whatever mass it is) for the purpose. Its far more scalable.
• Its also much better suited to this situation. Air can be pressurised by fans at very high rates, if the fan is adequately powered to rotate fast - just think of a jet airplane's turbofan engine. Now power an array of them with vertical intakes, by rotation from a tornado. (The engines can be stripped right down as you need a gearing element and something the tornado will rotate to turn it, and they never leave ground level so they can move easier or form from individual carriers that pack together and move cohesively or something to track the storm)
• Airbags can accept ultra fast pressurisation easily if well designed and large. They'd need restraining or the storm would catch them, that's easy enough, exercise for the OP. The elastomer design ensures that they have a tendency to deflate, makes extracting energy easier, although really all that's needed is to roll them up and use the emerging air jet.
• Simple and fairly foolproof.

It's important to note the purpose of pressurisation in this solution.

We are using pressure to quickly store huge volumes of air very very fast, while the storm rages, not to store it at ultra high pressures or liquefy it. (Those are options, of course, for variant answers).

Air can take immense pressurisation, and we need that for rapid storage. But really you only need a big airbag, because even without high pressure storage, as you roll it back up, you'll create a powerful air jet to reuse, purely because of volume of stored air, even if not especially pressurised.

(Think of the blast of air from an airbed as you sit on it to get the air out when you pack it away)

So the pressure is much more about ability to capture ultra-high air volumes at an ultra-high rate, which may be at some pressure (but doesn't really need to be), than about storing it at high pressure. So the bags don't have to be able to resist huge pressures, except at the point of intake.

Other physical side effects

Also note you'll have thermal effects. Compressing and decompressing does that. We can handwave those, but really, the only high pressure process here is compression, and we design the intake fan system to dispel thermal effects. they'll get hot, and the incoming air will be a bit warm I guess, but not super hot. The outgoing air is released at a much slower rate, so that's much less an issue.

You could have condensation effects too, but that's veering more to hard science/realism, and if they're ignored in a story nobody will notice.