A hydrogen pump looks reassuringly like a petrol pump. A nozzle, a hose, a screen, a price. Almost nothing behind it is comparable. The gas is compressed to hundreds of times atmospheric pressure, chilled to forty degrees below zero before it reaches your car, and delivered under a protocol in which the dispenser and the vehicle negotiate with each other throughout. Understanding why turns hydrogen from an intimidating novelty into something predictable, and explains why "there is a station there" tells you even less than it does with diesel.
Why the fuel has to be cold
Compress a gas quickly and it heats up. Filling a car's tank from empty to full in a few minutes is a very fast compression, and the heat generated would take a composite tank past its safe operating temperature.
The industry's answer is to remove the heat before it appears: pre-cool the hydrogen at the dispenser. The refuelling standard, SAE J2601, defines temperature categories for exactly this: T40 at −40 °C, T30 at −30 °C and T20 at −20 °C, with T40 the coldest and best-performing.
It also defines two pressure classes: H35 at 35 MPa and H70 at 70 MPa, the latter being the 700 bar most passenger cars use.
The headline performance figure follows from all of this: under reference conditions, J2601 targets a fill time of three minutes to a state of charge of 95–100%. But that target assumes a T40-rated dispenser. Warmer fuel delivery or high ambient temperature stretches the fill out. The standard is explicit that the dispenser's cooling capability drives performance.
The practical consequence: two hydrogen stations advertising the same three-minute fill can behave completely differently on a hot afternoon, depending on their pre-cooling rating and how recently the previous car left. This is not a fault. It is the physics the standard is written around, and it is invisible from any map.
The car and the pump hold a conversation
The second departure from petrol is that filling is not a one-way transfer.
J2601 supports fuelling with or without communications. Where communication is used (alongside the companion standard SAE J2799) the vehicle reports its tank temperature and pressure, and the dispenser manages the fill dynamically against that feedback, which is how the optimal state-of-charge targets are reached.
Without communication, the dispenser is working blind and must fall back on conservative assumptions. The fill still happens; it is slower and typically ends at a lower state of charge.
Which means a hydrogen fill can be technically successful and still leave you with meaningfully less range than the same car got yesterday at a different site, without anything being broken, and without the screen telling you why.
What the law is building
Hydrogen infrastructure is not being left to develop on its own. The Alternative Fuels Infrastructure Regulation, Regulation (EU) 2023/1804, sets concrete obligations.
By 2030, hydrogen refuelling stations must appear at a maximum spacing of 200 km along the TEN-T core network. Each must have a minimum capacity of one tonne per day and provide at least one 700 bar dispenser.
The unit in that requirement is worth pausing on, because it has no equivalent in petrol retail. A conventional forecourt is described by how many pumps it has; nobody publishes its daily throughput, because the underground tank holds far more than a day of demand. A hydrogen station is specified by tonnes per day, and one tonne is not a large number when a passenger car takes roughly five kilograms.
Why capacity is the thing that will strand you
This is the part that genuinely differs from every other fuel, and it deserves to be stated plainly.
Hydrogen stations are supplied either by delivered trailers or by on-site production, and their buffer storage is modest relative to demand. A station can be open, undamaged, correctly listed on every map, and simply unable to fill you because it is between deliveries or because its compressors are recovering after several consecutive fills.
Back-to-back fills also drain the pre-cooling capacity. Arriving third in a queue can mean a slower fill and a lower final state of charge than arriving first, at the identical station on the identical day.
With petrol, "the station exists" is close to "you can buy fuel". With hydrogen, those two statements come apart routinely, and there is no widely published feed that closes the gap.
What to do if you drive one
- Plan around stations, not range. The network is sparse enough that the constraint is where the stations are, not how far the car goes. Treat a route as a chain of specific sites with specific alternatives.
- Always know your fallback. Not the nearest second option in principle: the one you can still reach after finding the first one unable to serve you.
- Expect variability and do not read it as failure. Ambient heat, pre-cooling rating, queue position and whether your car is communicating with the dispenser all move the outcome. A shorter fill is usually physics, not a fault.
- Check the pressure class matches. H70 and H35 are different; a 700 bar car at a 350 bar dispenser gets a fraction of a tank.
- Ring ahead where it matters. For a sparse network with capacity limits, a phone call remains the single most reliable check before committing to a long leg. That is an unsatisfying answer and it is the true one.
The honest limits of what a map can tell you
We would like to show hydrogen availability properly, and it is worth being exact about why nobody can yet.
Geographic data records that a site dispenses hydrogen. The fuel tagging scheme has entries for it. What no static database anywhere contains is the state that actually decides your journey: how much is in the buffer this afternoon, whether the compressors are keeping up, whether the pre-cooling is at temperature, and whether the two cars ahead of you have just taken the capacity you needed.
For petrol, a map that knows locations is most of a useful answer. For hydrogen it is a small fraction of one. The remaining part exists only as something a person observed: someone who filled there today, and said whether it worked.
That is the same principle this whole site runs on, and hydrogen is simply the case where it stops being a preference and becomes the only thing that works. A location is a fact about geography. Whether you can fill is a fact about this afternoon, and where nobody has looked, the honest display is an empty space rather than a green dot.