How the Super Soaker Inventor Built the Most Efficient Heat Engine Ever

Hot car engines. Factory exhaust stacks. Even power plants … when fuel gets used, there’s heat leftover. And unless you want to fry an egg on the hood of your Mazda after zipping around the block, that extra heat is waste, gone, useless. But what if there was a way to channel it, literally?

There’s a new engine that transforms waste heat straight into electricity … even the low-grade stuff today’s best systems can’t touch. It has no moving parts. None. And it could be on track to become as efficient as is physically possible.

But maybe the craziest thing about it? It was dreamed up by the same nuclear engineer who invented the Super Soaker. His name is Dr. Lonnie Johnson. The engine is called the Johnson Thermo-Electrochemical Converter, or JTEC.

And while the JTEC is still in commercial development, it’s an exciting enough project that I wanted to put it through its paces. Is this the engine that turns waste heat into something useful? And will the JTEC make an even bigger splash than the Super Soaker?

Imagine being told you’re hot your whole existence, but when it comes time to make use of that hotness, suddenly you’re just not the right kind of hot. It’s tragic really. But that’s the state of waste heat today. There’s an incredible amount out there. But most isn’t usable.

Take industry, it uses about a third of all the energy on the planet.¹ And it wastes a huge chunk of that as heat. Up to half, just drifting away.² We’re talking exhaust fumes, heat from cement kilns and steel mills, commercial bakeries, refrigeration, and data centers.³

Most of this extra heat isn’t even that hot! It’s low temperature heat between 100-200°C, or ~200-400°F.⁴ That’s hot enough to make a very dangerous cup of coffee, but not quite hot enough to turn an industrial steam turbine.

Technologies do exist to generate electricity from low-grade heat like this,⁵⁶ but the existing tech is expensive and not very efficient. That’s why you don’t see it everywhere.^789101112

It’s not just industrial heat that’s not hot enough. A lot of geothermal sources aren’t hot enough to efficiently generate electricity, either.¹³⁵ The JTEC offers a potential pathway to make use of all this excess, to make running on fumes an asset rather than a liability. Right now, it’s promising enough that even energy companies are taking note.¹⁴

Our major investor is an oil and gas company that came to us looking for technology because they could convert the low temperature heat of abandoned oil wells into power. Just about 20% of the abandoned oil wells in the country could supply all the US power needs.

There’s a lot of wasted potential energy out there. So back to our question. Is this finally the engine that turns waste heat into something other than waste? To answer that, we need to know two things. How does the JTEC actually work? And how efficient can it really be?

The JTEC works differently than traditional engines. A lot differently.¹⁵

First, it doesn’t burn fuel to create heat. It uses ready-made heat sources like industrial waste or geothermal. That means no emissions.

That heat isn’t turned into motion, the way nuclear, coal, and even traditional geothermal power plants boil water into steam to spin a turbine to generate electricity. That middle step is cut out.

Instead, the JTEC converts heat directly into electricity with … no moving parts. None. That means less mechanical friction, less wear and tear, and potentially fewer maintenance headaches.¹⁵

The JTEC heat engine cycles hydrogen gas between a heat source … and a cooler heat sink that can be room temperature.

As the hydrogen moves between hot and cold, it isn’t consumed like a fuel. It’s split into protons and electrons … and then put back together into hydrogen gas… again and again. Dr. Johnson’s team explained to me how this wild process works, but we’ll get to that in a second.

From Super Soaker to Heat Engines

First, I want to introduce the NASA engineer responsible for the JTEC. He’s kind of a genius.^{16 17}

Dr. Lonnie Johnson was an inventor decades before he came up with the Super Soaker. In high school, he built a robot named Linex. This was all the way back in 1968, and so it was powered by compressed air and controlled by jukebox switches.¹⁸ For memory, it had a reel-to-reel tape recorder. Look at this thing, it’s awesome!¹⁹

Back in the 60s, no one had robots back then. But I was watching robots on TV and nobody told me that those had people inside. So what the hell? I just had to try to build one.

Dr. Johnson trained as a mechanical and nuclear engineer, taking jobs at Oak Ridge National Laboratory in Tennessee and the Air Force Weapons Laboratory. And that was before working on the Galileo and Cassini missions at NASA’s Jet Propulsion Laboratory in California.²⁰¹⁷²¹

But that wasn’t enough to occupy his mind, and so, he’d go home and tinker. He was working on a new kind of refrigeration system using water instead of ozone-destroying CFCs when he saw how fast and far a nozzle he’d machined could shoot water across the bathroom.²²

I thought, you know, this is a lot of fun … What if I could make a toy gun that could hold a lot of water at high pressure and a little powerful stream coming out of it. So that was the genesis of the idea for the Super Soaker.

Dr. Johnson put together his first prototype from an empty soda bottle and PVC pipe with nylon tubing and homemade valves.²¹¹⁷ These water guns used a pump action to compress air to drive a powerful stream, and they changed the game.²³ The neighbor kid’s Super Soaker blew away the dinky little water pistol I had back then.

Over a billion dollars of Super Soakers have sold since the 90s.²⁴ And Dr. Johnson’s share of that money? He’s used it to advance other inventions like the JTEC.²² It’s maybe the most clever crowdfunding campaign of all time.

The JTEC has been in development a long time. Dr. Johnson thought up the idea in 2003,²⁵ long before some of the materials it uses even existed.²⁶ And it wasn’t until 2020 that he brought together a team of engineers at JTEC Energy in Atlanta, Georgia, to make it happen.²⁶ The question now is whether the JTEC is ready for lift off. But we have to get to the question, how does it even work?

So what’s the secret for making electricity with no moving parts?²⁷¹⁵

Electricity is essentially electrons flowing through a circuit. The JTEC gets those electrons from hydrogen gas. Unlike in combustion processes, hydrogen isn’t a fuel, which is to say, it isn’t used up. Hydrogen loans electrons to the circuit … where they provide electrical current … and then hydrogen takes them back.

The genius of the JTEC is forcing hydrogen gas to loan the electrons … temporarily. And the part of the JTEC that makes that happen? A proton-exchange membrane.²⁸

A membrane is like airport security. It sets the rules for how to get through. At JTEC airport, hydrogen gas (H₂) has to put its electrons (2e⁻) through the baggage scanner and pass through the metal detector (the membrane) separately as two protons (2H⁺).²⁹

And that conveyor belt? That’s the electric circuit. That’s the electrons making their own journey. That’s … electricity.

On the other side of that metal detector, protons pick the electrons back up and become hydrogen gas (H₂) again.

So, you’ve got a membrane that splits hydrogen, lends the electrons to an electrical circuit and then brings everyone back together again.

If this is airport security, where is hydrogen flying? Someplace cooler, because all that waste heat is driving hydrogen through the membrane.

With enough heat, gases expand, and that puts pressure against the membrane. Think of a plastic bottle with soda left in a hot car. It’s rock hard when you return to it, since heat drives up the pressure of gases.

The only way to relieve that pressure is for the hydrogen to pass through the membrane to the low pressure zone on the other side. Like 100 pounds-per-square-inch dropping to just 0.01 pounds-per-square-inch.

The pressure is off. These hydrogen atoms are on vacation, moving towards that cooler zone.

Trouble is … they still have to get to work next Monday. To fly home, they’ve got to pass through another security checkpoint, another membrane.

And that, as we all know from dragging ourselves home from vacation, is a lot of work. These hydrogens have to move from their cooler, low pressure vacation, back to the high pressure work environment, and back to the heat.

The good news is: the vacation pays off. The energy gained from going on vacation is more than the energy needed to go back to work. Our hydrogen returns from its trip relaxed, ready to get to work, and with a couple stories for the water cooler. Or in JTEC terms, the voltage produced on the hot side is more than enough to drive the reverse reaction on the cold side, with plenty leftover as free electricity.¹⁵

Of course, the bigger lesson, as we head into summer, is we all need some vacation, even if it’s just cooling off at the pool. That’s Matt Ferrell’s fifth law of thermodynamics.

The JTEC isn’t impressive just because it has no moving parts, or because it splits hydrogen and puts it back together again. It’s of what it could mean for efficiency.¹⁵

And efficiency is the whole ballgame. If waste heat is going to stop being waste, the JTEC has to convert it better than anything we already have. So how does it stack up?

On paper, the JTEC could convert heat into electricity with less wasted energy than the traditional route of burning fuel, boiling water into steam, and spinning turbines to generate electricity.³⁰³¹

Instead of pistons and turbines, I use electrochemistry to do the compression-expansion process. And instead of steam, I’m using hydrogen.

In 2020, a laboratory version of the JTEC reached 17.1% thermal efficiency with a heat source at 200°C, or about 400°F.³² For these operating temperatures, that’s nearly half of Carnot.

Carnot is the maximum theoretical efficiency for a heat engine turning heat into electricity.³³³⁴ For comparison, the most popular low-temp-heat-to-electricity technology achieves around 12-13% efficiency at these temperatures, which is around one third of the Carnot ceiling.¹²¹¹

Johnson’s goal for the JTEC is to reach about two-thirds of Carnot, and he says his team now has test data indicating that’s achievable.³⁵¹⁹

Not only is the JTEC an efficient heat engine; it’s a heat engine that can be run backwards or forwards. And when the JTEC runs in reverse, it cools. It uses electricity and becomes a refrigeration system.¹⁵

Dr. Johnson says,

Reversibility clearly has a direct relationship with efficiency.

We talk a lot on the channel about another really efficient and reversible system: batteries.

Batteries reversibly charge and discharge. That’s why we refer to their ‘round-trip efficiency:’ how much of the energy you put in while charging that can be pulled back out during discharging. To improve round-trip efficiency, you lower the internal resistance of the battery using electrode materials that allow charge to move back and forth easily. You want as little lost as possible.

Efficiency is a materials issue for the reversible JTEC, just like with batteries. But instead of electrodes, the pinch point is the JTEC’s membrane.

The primary loss component or issue with it is the conductivity of the membranes because that’s the internal impedance.

The membrane’s responsible for a lot. It’s got to hold hydrogen gas back, but allow protons to easily pass through with little heat or side reactions. If it does that with low enough loss, then the system runs efficiently either way: forward to make electricity, or backwards to provide cooling.

So having good conductivity membranes, having thin membranes is a way to also improve that … and of course keeping them hydrated.

The ability to run in both directions is pretty cool. But what I want to know is whether we need to cool our expectations for the JTEC in the near term. Because it won’t matter if this heat engine works technically, if it can’t compete economically. Tech is cool, but price is king.

What we are looking at now actually [are] lower cost membranes … Even with the Super Soaker it was, you know, get the price right so everybody could afford to buy one.

When working with high-temperature heat around 500-600°C, the JTEC works with a ceramic membrane.³⁶ With low-temperature heat, like for waste heat or geothermal, the JTEC uses a thin, flexible membrane sandwiched between support layers.³⁶ These membranes have to be strong enough to hold back pressurized hydrogen gas … the higher pressure, the better.³²³⁵ That’s a lot of pressure for a little membrane!

Still, Dr. Johnson is optimistic about the JTEC’s cost per MWh of electricity.

In about five years we’ll be competitive with other systems … Ten years from now our projection is that we’ll be the lowest cost energy system in the world.

There is a scaleup challenge … waste heat isn’t always easy to gather and shoot towards a membrane. There are a lot of barriers to collecting that 20-50% of industrial energy lost as heat. Sometimes the heat is from batch processes, so you’re not getting a round-the-clock source to power the JTEC. Other times, waste steam has chemicals that need to be filtered out, so the system gets more complex. And just capturing heat off the surfaces of industrial equipment isn’t necessarily an easy challenge to overcome. Do you know how to collect heat radiating from an abandoned oil well? I sure don’t. ³⁷

Right now, the company is targeting 250 kW units, a size that competes with generators.²¹¹⁹ Their first commercial unit is being built right now for a “major Southeast utility company.”²⁴

Our initial markets will be waste heat from existing engines … particularly turbines and things like that, gas turbines.

That makes sense. Many natural gas power plants already send their hot exhaust through a second heat engine designed to generate electricity at a slightly lower temperature.³⁸ With a device like the JTEC, another cycle working with cooler leftover heat could squeeze a bit more electricity out of the same initial fuel.

So back to where we started. Is this finally the engine that turns waste heat into something valuable?

Here’s my take. The physics is real. The efficiency claims hold up in the lab. The question is whether the membranes can be made cheaply enough at scale. If Johnson hits his cost targets in five years, this is the most important heat engine since the steam turbine. It might just be the ticket to salvaging industrial waste heat and even capturing geothermal energy from abandoned oil wells.

Johnson has been working to commercialize the JTEC for almost a quarter century. But where he could just mill a nozzle and some valves in his workshop to demonstrate the Super Soaker, the technology needed for the JTEC has required significantly more effort. He’s had to persevere.

I often ask myself, would I have started this if I had known all the obstacles and challenges? Probably because, you know, I would have been bored otherwise.