HyTra System - Mobile Hydrogen Infrastructure


Prototype of the HyTra system, developed by the Fraunhofer IVI in Dresden
Prototype of the HyTra system, developed by the Fraunhofer IVI in Dresden

Hydrogen is seen as a possible energy carrier for the traffic of tomorrow. Its potential for a virtually pollution-free chemical conversion in fuel cells and conventional combustion engines, as well as its CO2 neutral production using renewable energies from the basis for a future-oriented and sustainable mobility concept. In order to achieve market penetration, a comprehensive hydrogen infrastructure needs to be established. That is why extensive resarch and demonstration projects regarding the creation of a hydrogen filling station grid are conducted in addition to the development activities undertaken by the automotive industry.  

A number of different hydrogen-powered vehicle fleets are already being tested in public transport scenarios. At the moment, however, Germany and Europe both lack the appropriate infrastructure. For test activities, a flexible and reliable supply is necessary even in regions without direct access to hydrogen filling stations. At the moment, this supply gap is closed by the gas providers, who ensure the refuelling of the vehicles by providing large gas bottles and tanks.

The HyTra system, a development of the Fraunhofer IVI, was designed as a novel, highly flexible alternative to stationary H2 production facilities.


Schematic of the HyTra concept
Schematic of the HyTra concept

HyTra stands for »Hydrogen Transform, Transfer & Transport«. The concept consists of a combination of hydrogen production, storage and supply via a trailer. With these features, the HyTra system is a mobile production unit and a filling station at the same time.  

With the help of a truck, the trailer can be transported to different locations and produces gaseous hydrogen directly on-site through the process of electrolysis that uses electricity and water. A compressor conveys the gas into an internal pressure tank and compresses it to the desired fuelling pressure. The actual refuelling is realized through an overflow process via a flexible high-pressure pipe with a standardized H2 filling nozzle. A comprehensive safety concept guarantees easy handling and safe operation. The trailer is moved only when empty, so that no hazardous goods are being transported. The fully automated operation of the HyTra system without any supervision by extra staff is possible. The only things needed at the supply location are a house connection to electricity and a sufficient supply of water.

This concept allows tailor-made infrastructure solutions for the test campaigns of various hydrogen-powered vehicles. The size and specifications of the internal components (electrolyzer, compressor and storage unit) can be individually adapted to the concrete filling scenario. In addition, the HyTra system is an option for providing hydrogen for events and test vehicle presentations on very short notice.


Filling of the AutoTram®
Filling of the AutoTram®

A first HyTra prototype was assembled at the Fraunhofer IVI for the location-independent supply of hydrogen to the fuel cell-powered AutoTram® test vehicle.The prototype provides gaseous hydrogen at 200 bar pressure. The ultra-clean hydrogen is stored in an internal pressure tank with a volume of 600 l. This means that a maximum of 8 kg hydrogen can be filled during one filling process.

The production and filling is realized in six steps:

1: De-ionization of tap water in a desalination system. Complete desalination is guaranteed by two desalination cartridges that are connected in series. Due to the limited maximum permitted temperature, the desalination system is located in an air-conditioned space.

2: Production of ultr-clean hydrogen in the hydrogen generator. A Hogen 40 Series 1 elektrolyzer manufactured by Proton Energy Systems is used as a generator. It applies the PEM method (Precise Electrochemical Machining) and has a production rate of one standard cubic meter per hour at a maximum pressure of 13 bar. The hydrogen produced has the quality label 5.0, which stands for a purity level of 99, 999 %. This purity level fulfils the typical requirements of automotive fuel cell systems. In order to avoid damages through low temperatures, the electrolyzer is located in a tempered room.

3: Storage of the hydrogen in the intermediate storage unit. In the storage unit, the hydrogen is temporarily stored dried. The storage unit is directly connected to the H2 generator. A non-return valve prevents the backflow of hydrogen into the generator.

4: Compression of the hydrogen and filling of the internal pressure tank. A compressor is used to compress the the hydrogen to a maximum of 200 bar and feed it into the internal pressure tank afterwards. The compressor will automatically take up its work at a pressure level on the low-pressure side between 1.0 and 4.5 bar. As soon as the maximum pressure on the high-pressure side is reached, it will switch itself off automatically. The gas outlet is secured against excess pressure using an integrated rupture disc. In case of a rupture (230 bar ± 5 %), the gas will not leak into the atmosphere but stay inside the compressor.

5: Storage of compressed hydrogen in the internal pressure tank. The tank consists of a rack of twelve 200 bar pressurized gas cylinders. Its total volume is 600 l. A safety valve secures the tank against excess pressures. In order to prevent the backflow of hydrogen into the compressor, the tank is equipped with a non-return valve.

6: Filling process. The filling of vehicles is realized without an intermediary compressor on the basis of the overflow principle. The standardized TK15 nozzle manufactured by WEH is used as a filling nozzle. A breakaway system prevents gas leakage in case of an accidental unwanted disconnection of the tank connection and the filling hose.


Internal pressure tank of the HyTra prototype
Internal pressure tank of the HyTra prototype

The implemented explosion protection system is based on avoiding the creation of a dangerous explosive atmosphere. To ensure this, the HyTra system is divided into different potentially explosive areas (zones). The electrolyzer is installed in a closed space. The creation of a dangerous explosive atmosphere is prevented by a ventilation system with redundant control that has an air exchange rate of 100 per hour. The intermediate sorage unit and the compressor are located in a naturally ventilated. As a general rule, no sources of ignition are placed in areas where a dangerous explosive atmosphere cannot be entirely ruled out.

Various sensors monitor important parameters such as the hydrogen concentration, system pressure, temperature and ventilation in different areas. The operating procedure prevents the system's operation in case of one or more parameters exceeding their limit values. Back-up batteries ensure the continued hydrogen monitoring even if the external power supply is interrupted. Each and any deviation from standard operation will be registered by detectors will lead to an immediate and safe shut-down of HyTra. At the same time, the system will send a short message to the operators via a GSM module.

The HyTra system was approved by the TÜV-Süd according to § 14 of the Industrial Safety Regulations. It is therefore a filling station in the terms of the Industrial Safety Regulations.

Technical Parameters:

  • Base vehicle: tandem-axle trailer
  • Voltage supply: 400 V / 3-ph / 63 A
  • Power consumption: 9 kW on average
  • Water connection: 1.0 - 4.5 bar; consumption 0.9 l/h
  • Maximum permitted weight: 2.8 t
  • Total length: 5.9 m (can be transported using a small van)