Hydrogen Filling Stations: Tapping Into Gas
Author: Michael Vogel
Hydrogen filling stations are still rare. This is set to change in the foreseeable future. DEKRA is supporting this change with its own expertise.
The automotive industry is focusing heavily on the development of battery-electric drives worldwide. Meanwhile, it is still unclear what role fuel cells will play in passenger cars and commercial vehicles. One thing is certain: Such vehicles are already on the road today and there are usage profiles that are well suited to fuel cell drives – for example in buses in local public transport, waste collection vehicles, forklift trucks, or long-distance freight transport. In fuel cells, hydrogen reacts with the oxygen in the air. The energy released by this chemical reaction is converted into electricity. Ergo, a fuel cell vehicle does not require petrol, diesel, or electricity, but hydrogen. And it must be able to refuel somewhere.
Today, this often happens at filling stations located on company premises. But there are also filling stations in public spaces: According to figures from the H2.live portal, 165 filling stations are in operation in Europe and a further 41 are currently being built. DEKRA recently became one of only three testing organizations able to test and certify such refueling facilities. “The transition to the hydrogen economy is only just beginning,” says Dr. Christoph Flink, Vice President Hydrogen Economy Program Management at DEKRA. “We’re supporting it by offering the right safety concepts at the right time.” Traditional filling stations for petrol and diesel are also subject to such testing and certification requirements. Naturally, there are differences for hydrogen filling stations because hydrogen is a different type of energy source.
Research projects on refueling with liquid hydrogen
One kilogram of hydrogen can produce three times as much energy as one kilogram of diesel or gasoline. The problem is that the energy content of hydrogen per volume is very low because, as a gas, it has a low density at ambient temperature. To avoid having unrealistically large – and uneconomical – tanks in vehicles and at filling stations, hydrogen gas is stored in compressed form in pressurized containers. However, there are also research projects, for example by Daimler Truck and Linde, which aim to refuel with liquefied hydrogen. DEKRA is also gaining first experiences with liquid hydrogen refueling processes in a research consortium led by energy supplier Engie.
The vehicle tank of today’s fuel cell cars holds five to seven kilograms of hydrogen at a pressure of 700 bar. The car’s range is comparable to that of a diesel or gasoline engine. In comparison, fuel cell commercial vehicles consume considerably more and have a much higher total weight. The weight and volume of their hydrogen tanks are therefore less critical than for passenger cars. For this reason, but above all for historical reasons, the hydrogen in the tanks of commercial vehicles is only pressurized to 350 bar. It is possible that 700 bar tanks will prevail in all types of vehicles in the long term.
Refueling only takes a few minutes
When refueling, the dispenser must transfer the hydrogen into the vehicle tank. Externally, the handling is similar to the familiar nozzles of combustion engines, but that’s where the similarities end. The hydrogen nozzle is locked into the filler neck either manually or automatically. The dispenser and vehicle communicate with each other via an infrared interface. To determine the current fill level of the tank, the fuel dispenser first sends a short pressure surge of hydrogen. Soon afterwards, the actual refueling begins, which can also be recognized by the fact that the hose stretches under pressure. During filling, the short-term pressure differences can be up to 100 bar. The entire process only takes a few minutes. Exactly how long and how many vehicles can refuel one after the other without major interruptions depends heavily on the design of the refueling system.
“DEKRA tests and certifies the function of hydrogen filling systems for conformity with the ISO 19880-1 and DIN EN 17127 standards,” explains Flink. “We also test and certify the hydrogen quality, which must be very high for use in fuel cells.” Another standard, DIN EN 17124, specifically defines not only the hydrogen purity, which must be at least 99.97 percent, but also the maximum proportions of various impurities. DEKRA works on the tests together with the Center for Solar Energy and Hydrogen Research Baden-Württemberg (ZSW) in Ulm and the Center for Fuel Cell Technology (ZBT) in Duisburg. These partners carry out the respective measurements.
Hydrogen is transported to the filling stations by truck
At the hydrogen filling station, the gaseous hydrogen supply is only stored at pressures of 50 to 450 bar – the specific value depends on the safety regulations applicable in the respective country. Therefore, compressors must first generate the working pressure that is necessary for refueling.
At the moment, hydrogen is mostly transported to European filling stations by truck. That’s because a hydrogen distribution network, to which a filling station could generally be connected, so far only exists in exceptional cases. For example near chemical parks, because hydrogen also plays an important role for the production of basic materials in the industrial sector. However, with the increasing spread of hydrogen as an energy source, the situation regarding the distribution network could change, providing that there is enough hydrogen produced with renewable energies.
With regard to long-distance transport, the EU Commission has set the target of having a hydrogen filling station at least every 200 kilometers for trucks on trans-European routes by the next decade. The German government’s National Hydrogen Strategy also has an extensive expansion of the filling station network in mind.