Glossary of terms


Chemical energy carriers

A chemical energy carrier is a substance that stores energy in the form of chemical bonds (e. g. hydrogen, methane, ammonia, ...). With its help, electrical energy can be stored in large quantities and over long periods of time. Chemical energy carriers can be produced synthetically


When we talk about CO2 emissions in our missions and in this context about CO2 balance or CO2 neutrality, we refer to the sum of all greenhouse gases, in particular methane (CH4) in addition to CO2.

"Dunkelflaute" (darkness and no wind)

This is as German term referring to a situation when neither the wind blows nor the sun shines. Then neither wind turbines nor solar cells generate electricity. The phenomenon occurs particularly frequently during wintertime.

Energy density

The term refers to the distribution of energy over a given quantity. The most common are volumetric energy density (energy per volume of space) and gravimetric energy density (energy per mass).


The term for us includes the possibility of retrofitting, i. e. that new engines from 2025 onwards are either directly H2-ready or can be converted for hydrogen operation in the future.


Life cycle analysis (LCA) or life cycle assessment is the systematic analysis of the effects of products or services on the environment. The procedure is specified in DIN EN ISO 14040/14044 and covers the entire life cycle from production and use to recycling and/or disposal.

Methane slip

Here we look at the uncontrolled escape of methane (CH4) from the engine into the atmosphere and refer to this as methane slip. There are quite a number of other sources of methane escaping into the atmosphere. For example, it escapes from biogas plants and during the extraction and transportation of natural gas and crude oil. Methane has a very strong greenhouse gas effect in the atmosphere.


Power-to-X, also PtX or P2X, means: Electricity ("power") is converted into a synthetic substance X. The electrical energy is stored in the form of chemical bonds. X can be, for example, hydrogen, gaseous or liquid hydrocarbons, ammonia or methanol. With the help of power-to-X, it becomes possible to easily store and transport the electrical energy and supply both industry and consumers. Mechanical engineering is the central supplier for the key technologies, both for power (e. g. wind energy) and for X (process technology) and for applications, e. g. in mobile machinery or marine engines.

Harmful emissions

By this we mean the substances carbon monoxide (CO), nitrogen oxides (NOx), hydrocarbons (HC), and particulates produced during the combustion process in the engine. Greenhouse gases such as CO2 and methane (CH4) are not included.

Open-minded approach to technology

Often, a specific goal can be achieved in different ways. In principle, this also applies to technological goals. We advocate defining the goal and leaving the search for the best way to get there to the competition of technologies.


Hydrogen (H2) is a colorless gas. It is differentiated with colors according to the way it is formed.

Green hydrogen is produced by electrolysis of water with electricity from renewable sources. The production of green hydrogen is CO2-free.

Blue hydrogen is gray hydrogen in which the CO2 produced is captured and stored (carbon capture and storage, CCS). It is considered CO2-neutral.

Turquoise hydrogen is produced by means of methane pyrolysis, i.e. the thermal splitting of methane. Solid carbon is produced as a byproduct. The process is considered CO2-neutral if the high-temperature reactor is fed from renewable energy sources and the carbon is permanently captured.

Yellow hydrogen, like green hydrogen, is produced by electrolysis of water using electricity. However, the electricity here comes from nuclear power plants, which is why yellow hydrogen is usually not considered sustainable.

Grey hydrogen is produced from fossil fuels, usually natural gas, which is converted to hydrogen and CO2 under heat (steam reforming). The CO2 released during production escapes into the atmosphere.