Imagine an internal combustion engine with no moving parts—no pistons, crankshafts, or valves—just a pure, solid-state combustion engine. This may sound like science fiction, but two companies believe they can make it a reality. One of these pioneers is LightCell Energy[1], a company that could revolutionize our understanding of hydrogen and other fuels and even play a pivotal role in making electric flight a reality.
In this blog post, we will explore the groundbreaking technology behind LightCell Energy’s innovative engine, delve into its implications, and examine whether this concept is too good to be true.
Meet Danielle Fong: The visionary behind the solid-state combustion engine
Danielle Fong is no ordinary entrepreneur. She was a high school dropout who eventually attended Princeton to study nuclear fusion.
In 2022, she founded LightCell Energy, a company dedicated to developing an engine that converts fuels into light, and light into electricity—all with no moving parts.
LightCell Energy’s Bold Claims
LightCell Energy claims their engine can achieve electricity generation efficiencies between 70% to 80%. Additionally, the engine boasts a power density of over 5 kW/kg and an energy density close to 10,000 Wh/kg[1]. These numbers are astounding, but to truly understand their significance, we must put them into context.
Understanding the technology: The solid-state internal combustion engine
At first glance, LightCell Energy’s engine might seem like a new type of fuel cell, but it’s actually an internal combustion engine that operates through a combustion process—just without the moving parts.
This is what makes it a solid-state internal combustion engine, a concept that has the potential to revolutionize power generation.
Thermophotovoltaics: The core of LightCell’s Engine
The LightCell engine operates using a process known as thermophotovoltaics (TPV). Here’s how it works:
- Thermo: The engine burns fuel to generate heat.
- Photo: This heat is then converted into light.
- Voltaic: Finally, a photovoltaic (PV) cell converts this light into electricity.
This process is clever, but it also raises questions about efficiency, as multiple energy conversions typically lead to energy losses. However, LightCell Energy’s design incorporates ingenious engineering solutions that could minimize these losses and make the technology viable.
Potential applications of LightCell’s Engine
Imagine a portable generator the size of a milk jug that can output 10 kW of power. This silent, vibration-free engine could power robots, drones, electric vehicles, and even electric airplanes. The compactness and efficiency of this technology open up a world of possibilities, but there are challenges to overcome.
The origin of the idea: From Sim City to Steel Mills
Danielle Fong’s journey toward creating LightCell Energy began with a childhood obsession with energy, sparked by playing Sim City. However, the turning point came during a field trip to a steel mill. Observing the intense heat radiated as infrared light from the mill’s operations, Danielle realized the potential for harnessing such energy. This, combined with inspiration from a Fourth of July fireworks display, led her to explore intense, single-color light sources, ultimately leading to the creation of LightCell Energy[2].
Why combustion? The case for fuel-based power generation
In a world rapidly moving away from fossil fuels and toward renewables, it’s surprising that a leading inventor like Danielle would choose to develop an internal combustion engine. But there’s a lot of logic behind her reasoning.
Energy density: The power of fuels
One of the key reasons for using combustion in the LightCell engine is energy density. Fuels have incredibly high energy densities, ranging from 10 to 15 kWh/kg, which is at least 20 times higher than lithium-ion batteries. This means that the LightCell engine can be much lighter and more compact than current battery technologies.
Power density: Rapid energy release
Combustion processes are known for their rapid energy release, which contributes to high power density. In the LightCell engine, fuel and air are continuously fed into the combustion chamber, allowing for fast burning and high power output. The lack of moving parts further enhances this efficiency by eliminating friction and momentum limitations, typical in traditional internal combustion engines.
It’s like harnessing the power of a rocket engine in a small generator.
The engineering marvel: Converting heat to electricity
The key to this technology is converting heat into electricity, and this works in two steps. First, heat is converted into light. They found a clever way to turn all the heat so quickly released during the combustion process into light very efficiently using the sodium in table salt.
- Hot sodium emits very bright, nearly monochromatic light.
- Danielle’s design can produce 3,000 suns of yellow light near the surface.
- That’s 3,000 times the amount of light per square foot that the sun shines down on Earth.
The second step in the process is to convert the 3,000 suns of yellow light into electricity. We need to harness that power. Not even the best PV cells are very efficient. Under optimal conditions, the best lab-grade solar PV cell, which is III-V four-junction cell, works at 47.6% efficiency[3]. Compare that, for example, to a Li-ion battery’s round trip efficiency of 95% or more.
But they found a clever solution to that problem. LightCell uses a special direct band-gap semiconductor material that almost exactly matches the wavelength of the sodium’s monochromatic light. That means that it’s fine-tuned to absorb precisely the color of light that hot sodium emits.
This material is what NASA uses as a top layer of the most efficient multi-junction space solar cells. The material can be 10,000X thinner and lighter (50 microns) than a normal PV cell. They say it’s flexible, has very low resistance, and allows a very high current density.
Semiconductor materials: The key to high efficiency
The success of LightCell’s engine hinges on using a direct band-gap semiconductor material that closely matches the wavelength of sodium’s light. This material is crucial for achieving high conversion efficiencies. Although the exact material remains a trade secret, we can make an educated guess.
The key is tuning the semiconductor’s bandgap to the light’s energy which is 2.1 eV. So, we’re looking for a direct band-gap semiconductor that is used in space PV cells and with a band gap very near 2.1 eV.
Several options fit the bill:
- Germanium cells are a popular choice for space applications, and so are several of its alloys. It’s used in high-efficiency multijunction solar cells in very thin sheets[4].
- Germanium carbide has a tunable band gap of 2.11 eV, almost exactly the energy of the light sodium emits[5].
- Galium Arsenide (GaAs) is another direct bandgap semiconductor typically used in space solar panels, but its band gap is more than a bit off at 1.42 eV. However, I found an article that says it can be fine-tuned by adding aluminum. An alloy with 54% of Galium atoms replaced with aluminum would have a direct band gap of exactly 2.1 eV[6].
But why does a matching direct band-gap semiconductor matter so much? It turns out, it’s the key to the crazy efficiency numbers LightCell is stating. To understand that, we have to look at how PV cells work.
Brief overview of photovoltaic cells
For a PV cell to generate electricity, it needs to excite one of its electrons in the valence band, where it’s tied to the nucleus, to the conduction band where it’s free to move around and generate electricity. That requires a very specific amount of energy called the band gap.
Think of it like taking the entrance to a fast-moving freeway full of cars.
Electrons on the valence band are like you waiting at the stop sign trying to enter the freeway. To get into the freeway you need a strong push to speed up and match the speed of the incoming traffic, or you’ll crash.
In a PV cell, light is what gives the electrons the push to reach the conduction band. For a photon to excite an electron across the band gap and generate electricity, the photon’s energy must be equal to or greater than the band gap energy.
- If it’s lower, you just won’t get any electricity.
- But if it’s higher, the excess energy is usually lost as heat, reducing efficiency.
So, it’s best if the cell’s bandgap exactly matches the light’s wavelength or energy because it minimizes energy losses during absorption. LightCell claims it can reach PV efficiencies as high as 90% using a sodium lamp and band-gap-matched PV cells. With their current setup, they also claim they’ve tested fuel-to-electricity efficiencies as high as 60% but think they can achieve up to 80%.
The challenges: Material considerations and efficiency questions
There’s a lot we don’t know about this technology, but it brings several interesting questions about the cell’s construction. First, if combustion is happening inside a glass tube, why doesn’t everything melt?
Combustion chamber materials
The combustion happens in an inner tube surrounded by a vacuum and an outer tube before the PV cells. That inner tube is made of quartz for experimentation because it’s cheap and easy to work with.
Long-term, the company is thinking of using sapphire which can take higher temperatures. However, sapphire is also much more expensive and can thermally expand and break. Polycrystalline alumina is the ideal material but it’s hard to get in bulk.
The sodium chloride cycle
The next question is what happens to the salt? Where does it go in? Is it encapsulated, or is it fed with the combustion mixture?
That’s hard to tell from the schematics alone and they’re not saying. When heated, the salt melts, then evaporates, and then decomposes into sodium vapor and chlorine gas. The hot sodium vapor is what emits the yellow light. But after it cools down, sodium and chlorine recombine to form table salt again.
The question here is where exactly does the sodium chloride go?
There are only two possibilities for me:
- It’s all contained inside a sealed glass cylinder surrounding the hot flame.
- Or it’s fed in with the fuel.
The first case is unlikely because it would just take too long for the heat from the flame to reach the sodium chloride, so you would lose a lot of heat. The second case makes more sense because you maximize contact with the flame. But, you would lose the salt to the exhaust!
Danielle does mention that you may have to “replenish” your sodium chloride supply every now and then, which suggests that the sodium chloride is recuperated somehow but a small portion still makes it out through the exhaust.
The advantages of LightCell’s technology
If everything they claim is true, LightCell’s technology brings significant benefits:
- High Efficiency: Potential to achieve up to 80% efficiency.
- Compactness: Much smaller and lighter than traditional engines or batteries.
- No Moving Parts: Reduced wear and tear, leading to a longer lifespan.
- Quiet Operation: No significant noise or vibrations.
- Versatility: Can be used in a variety of applications, from drones to electric airplanes.
It also has a long lifespan. In a high-pressure sodium lamp, which is the closest example, the tube is made of translucent polycrystalline alumina to withstand high temperatures and the aggressive hot sodium. Typical lamp lifetimes can reach 10,000–20,000 hours or longer.
So, what if we put this generator in a car and use it every day? How long would the lamp last?
We spend on average 30 minutes to 1 hour on our daily commute[7]. We can round that off to about 300 hours per year. That would mean that we’d have to replace the sodium lamps, the main power source of our light engine, roughly once every 33 to 66 years, as long as you don’t crash and brake it!
Not bad considering the average lifespan of an ICE car is around 14.8 years, and for an EV is 22.2. So this sloid-state engine has the potential to outlive the car itself.
Comparing LightCell Energy and Mesodyne: Two approaches to solid-state engines
LightCell Energy isn’t the only player thinking of using combustion as a power source to make electricity with a solid-state device. Another company called Mesodyne is also working on the problem.
Mesodyne’s LightCell
Mesodyne, another company in the solid-state engine space, has developed a similar thermophotovoltaic system[8] but with some key differences. Mesodyne’s system integrates the combustion chamber, nanophotonic emitter, and PV cell into a small chip, making it extremely compact. However, its efficiency is significantly lower, at around 13%, compared to LightCell Energy’s claims of 60% to 80%.
LightCell vs. Fuel Cells
Another key technology is fuel cells. Fuel cells are currently the most efficient way to convert chemical energy into electricity, with efficiencies ranging from 40% to 85% in cogeneration schemes[9].
Despite this, fuel cells face challenges such as catalyst degradation, sensitivity to impurities, and scaling issues, and their power output doesn’t come close to direct combustion. LightCell’s engine addresses these problems by offering higher power density and robustness.
The silver lining: Potential applications in aviation
One of the most promising applications for LightCell’s solid-state engine is in aviation. The combination of high energy density and power density makes it an ideal solution for electric flight, where energy storage is a significant challenge.
By providing a more efficient way to convert fuel into usable energy, LightCell’s engine could pave the way for the next generation of electric aircraft.
The sustainability question: Can solid-state engines be green?
While LightCell’s technology is impressive, its sustainability depends on the fuels used. For this technology to be truly green, it must rely on carbon-neutral or sustainable fuels, such as hydrogen produced through renewable energy. However, current methods for producing hydrogen and other synthetic fuels are not yet efficient enough to make this a completely sustainable solution.
A revolutionary idea or a pipe dream?
LightCell Energy’s solid-state internal combustion engine is a revolutionary idea with the potential to change the way we generate and use energy. However, it is still in its early stages, with many challenges to overcome. The company has yet to produce a working prototype, and its efficiency claims remain unverified.
While the technology holds promise, it is essential to approach it with cautious optimism. Only time will tell whether LightCell Energy’s engine will become a game-changer in the energy industry or fade into obscurity.
As we continue to explore new ways to generate and use energy, innovations like LightCell Energy’s engine remind us of the endless possibilities in this field. Whether or not this particular technology succeeds, the pursuit of more efficient, compact, and versatile energy solutions will undoubtedly lead to breakthroughs that could shape the future of power generation and transportation.
Stay tuned as we keep a close eye on LightCell Energy and other emerging technologies that could redefine our energy landscape.
Sources
[1] https://lightcellenergy.com/
[2] https://youtu.be/1U_KbgF-sAc
[3] https://en.wikipedia.org/wiki/Solar-cell_efficiency
[4] https://www.umicore.com/en/newsroom/from-earth-to-space/
[5] https://www.sciencedirect.com/science/article/abs/pii/S0368204820300372
[6] https://www.batop.de/information/Eg_AlGaAs.html
[7] https://www.statista.com/statistics/1427497/workers-average-daily-commute-length-united-states/
[8] https://mesodyne.com/#technology[9] https://www.energy.gov/eere/fuelcells/articles/fuel-cells-fact-sheet
