REXH₂®: The Type-Approved Marine Fuel Cell System

Until now mainly used as a raw material for chemistry and petroleum refining, hydrogen is more and more identified as an energy vector of the future because of its storage capacities and the fact that its use does not emit any CO₂. It is presented today as a possible substitute for hydrocarbons, and an effective means of facilitating the integration of renewable energies. While more than 95% of the 75 million tonnes of hydrogen produced per year worldwide are derived from fossil fuels, new technologies for producing carbon-free hydrogen continue to mature. The production of hydrogen from biomass or by electrolysis is supported by the emergence of new demand for “green hydrogen”.

In industrial applications, the use of carbon-free hydrogen is expected to occur in processes traditionally using fossil hydrogen, such as ammonia production and petroleum refining, but also in new processes as a substitute for other fossil materials. Projects to experiment with new ways of integrating carbon-free hydrogen or upgrading fatal hydrogen into production chains have multiplied in recent years, and the 2019 climate energy law sets a target of 20 to 40% of low-carbon and renewable hydrogen by 2030.

In transport, hydrogen vehicles represent a suitable alternative to meet the challenges of sustainable mobility. They only release water, have a range equivalent to a combustion vehicle and recharge quickly. In addition to the multiplication of the number of hydrogen car models, the year 2019 has been marked by the acceleration of the dynamics of the hydrogen railway with the multiplication of orders for the train developed by Alstom, and by the growing interest of local communities for the deployment of hydrogen bus lines.

As part of an increasingly renewable future electricity mix, the hydrogen energy vector makes it possible to compensate for the intermittence of renewable energies by storing, in gaseous form, the excess electricity produced during periods of high production and low consumption (Power to Gas). The energy storage made possible by hydrogen also makes it relevant to extend the perspectives of self-consumption to the scale of a house, a building or a village.

While batteries provide immediate short-term energy, hydrogen acts as a long-term range extender. The example of the Energy Observer vessel illustrates the huge advantage of hydrogen compared to batteries in real life. While the battery park weighs 1400kg for 112 kWh, the hydrogen storage and the fuel cell weigh a total of 1700kg for 1000 kWh. Comparing energy per kilogram, 1kWh therefore weighs 12.5kg when stored in batteries, and only 1.7kg when stored as hydrogen. In other words, this means that for equal weight, hydrogen storage contains 7.35 times more energy than battery storage, which is a considerable asset for mobility, whether maritime, land, or even air. For more details, see also the application example developed on board the Hynova 40, and the article on fuel cell – battery hybridization to be found HERE.

In terms of “contained” energy: 1 kg of H2 = 11 Nm3 = 13.6L of liquid H2 = 23.3L of H2 at 700 bars and contains 33 kWh of energy produced by 52 kWh of electricity (in industrial practice, the yield is 63% by electrolysis before compression or liquefaction). One liter of liquid H2 weighs 73.5 g and contains 2.4 kWh so 4 liters of liquid H2 = 9.6 kWh. A liter of H2 at 700b weighs 43g and contains 1.4 kWh so 7 liters of H2 at 700b = 9.8 kWh. We deduce in terms of energy (approximately): 1 liter gasoline = 9 kWh = 3000L of H2 (at Patm) = 7L H2 / 700b = 4L of liquid H2 / -253 ° C.

Currently, 95% of the hydrogen produced in France is of fossil origin, as is nearly 99% of that produced in the rest of the world. This hydrogen is most often obtained from the process of steam reforming methane, the main component of natural gas. Each kg of hydrogen produced this way emits 12 kg of CO₂, and its cost price varies from 1 to 2.5 € per kg. Almost 45% of world production comes from this technique.

About 25% of hydrogen production comes from “co-production” of refined products from hydrocarbons, which is then called “fatal” hydrogen. Its production cost is variable since in this instance it is a “waste” from the production of other chemical elements, and therefore its carbon footprint is too.

A third method uses coal, burnt at very high temperature (1200 to 1500 ° C) to separate the hydrogen – which should be called dihydrogen H2 – from CO₂, in the form of gas. This production, about 30% of the total, makes it possible to obtain hydrogen whose cost price per kg varies between 1.5€ and 3€ per kg, but releases 19 kg of CO₂ per kg of hydrogen.

These are industrial models that make “gray” hydrogen. “Green” hydrogen, which only contributes less than 1% of world production (around 5% in France), comes from the use of low-carbon or renewable energies (solar, wind, etc.). The electrolysis of water, which allows a zero carbon footprint, represented only 0.1% of global hydrogen production in 2019, due to a relatively prohibitive cost compared to other production methods, one kg of hydrogen costing between 3€ and 12€ for its production alone (excluding the cost of transport, distribution, etc.).

To allow the large-scale deployment of “green hydrogen”, electrolysis from a renewable energy source is one of the future undertakings , and it is clearly one of the strategies traced through the 2020 recovery plan, to make France and Europe champions of “green” hydrogen production.

A fuel cell is made of metal, graphite, electrodes, and its process is effectively chemical. The REXH2® system designed by EODev is based on Toyota fuel cell technology. The Toyota fuel cell system has already proven its benefits for many years in the Mirai, but more recently also in other applications such as buses and trucks. Its use for maritime transport is once again one more step towards the development of the hydrogen society.