If you are reading this, I want your insight on specs for fuel cell power pods for drones. We see an opportunity to shift from consulting work to manufacturing a product that really matters (team background: autonomous vehicles, manufacturing, AI, software). Let's start with why:
American drones need more power.
There is a big technology gap between << 1 kWh/kg lithium batteries for small drones and >> $100k turbines for big drones.
The RU/UA war highlights the problem:
- Camera recordings frequently show LOW BATTERY alarms: these drones are being pushed to their operational limits
- The spiderweb of fiberoptic cables covering the battlefield is a stop-gap control solution for comms-denied environments. We will replace fiberoptics with onboard AI, but AI is power hungry.
- Medium sized drones (V-BAT, Bayraktar, Shahed) resort to reciprocating engines, which are loud, shaky, heavy, and less reliable than turbines. Additionally, they deliver power in the wrong form: we want electrical power for compute and nimble electric motors rather than torque, gearboxes, and driveshafts.
Off the battlefield, small commercial drones, like Zipline's Platform 2 VTOL drone, have tiny service ranges of ~10 miles!
If autonomous systems are reshaping warfare and commerce, and if power sources are a key limiting factor on autonomous system performance, America must lead the world in solving drone power.
Mature technologies can't get us there.
- Internal combustion engines: we've had a century or so to perfect these. They are still loud, hot, unreliable, and shaky. Advanced drone systems in the year 2035 will not be flying lawnmowers, but in some cases this is really the best we can do today.
- Lithium batteries: we might reach 1 kWh/kg with solid state batteries, but further breakthroughs are speculative. Despite poor energy density, rechargeable lithium batteries are convenient and cost-effective, making them the best solution for small drones today. Their high gravimetric power density (~5 kW/kg burst) makes them useful for hybrid power sources.
- Turbines: energy dense JP-8 fuel (12 kWh/kg) and high power density (~5 kW/kg) are hard to beat. They will remain the best solution for very large drones, but they are too inefficient for small vehicles under ~10 kW (tip clearance, combustor residence time, surface-to-volume ratio, and reynolds number effects all improve as turbines get bigger).
Fuel cells can.
The solution to all of these problems was supposed to be the proton exchange membrane (PEM) fuel cell (other fuel cell technologies are basically too heavy).
- hydrogen has a spectacular energy density of 33 kWh/kg
- proton exchange membrane (PEM) fuel cells are quiet, cool, clean, reliable, and deliver ~2 kW/kg as electricity.
So where are the drone fuel cells? Americans have tried, with programs like Puma, 2007 and Ion Tiger, 2009. But fuel cells have never been adopted widely or traveled down the manufacturing cost curve because hydrogen gas is a terrible fuel despite its gravimetric energy density:
- compressed hydrogen tanks are heavy (5% gravimetric efficiency) and bulky (1.4 kWh/L system). The volume required is comparable to lithium ion batteries and far lower than JP-8's volumetric density, 10 kWh/L.
- liquid hydrogen and cryo-compressed hydrogen logistics are too complex--keeping anything very cold is hard--and even then tanks are still heavy (7% gravimetric efficiency) and bulky (1.5 kWh/L system).
Can we power fuel cells with more complex molecules? Yes: solid oxide fuel cells based on yttria-stabilized zirconia can run directly on hydrocarbons, but they are heavy (1 kW/kg) and require slow preheating to reach operating temperature, making them less suitable for drones.
Can we break larger molecules into hydrogen? Yes: reforming light hydrocarbons into H2 and CO2 is feasible in situ, but reforming JP-8 is probably not (the military has tried for decades but desulfurization, coking, and steam process complexity are real problems). Additionally, the carbon monoxide reforming byproduct poisons many fuel cells.
Proposal
We think we see a way to thread this needle and create the world's best power source for < 25kg drones in the form of standardized energy pods, achieving:
- high gravimetric and volumetric energy and power density
- clean, quiet, reliable electric power
- simple supply chain for chemically bound hydrogen
- simple onboard conversion
- established fuel cell technology
So we're doing some very early, small-scale tests to see if this can really work, targeting usable prototypes in 2026. No promises yet, but no scientific breakthroughs required either.
Help us define the spec!
To standardize, we want to build a single energy pod form factor. Rather than expensive integrations for every platform, we can drive costs down with a standard solution:
- one hexagonal pod form factor under or above the drone (like drop tanks)
- one mounting system (swap pods like batteries, possibly with drone-specific adapter plate)
- one drone-to-pod communication protocol
Could this form factor work for your drone missions? If so, what parameters would actually move the performance envelope for you?
- Voltage: 24, 48, 72, 96 V?
- Max pod mass (kg) and dimensions
- Min energy (kWh/kg) and power (kW/kg) density
- Max pod cost ($/ea.)
- Preferred electrical connection standard
- Preferred communication protocol (UAVCAN/TSN/?)
If you have thoughts, I'd love to hear them: chris@ckwalker.com / 509.999.0449 / google meet. Thank you!