The IN4climate.NRW Glossary explains all the key terms related to the climate-neutral industrial sector and the innovative technologies of the future. The glossary is constantly being expanded and updated. If you notice there is a term missing, then please feel free to contact us.


An intermediate product in the manufacture of plastics such as nylon or polyurethanes. Its production is associated with the emission of nitrous oxide, or laughing gas, which is harmful to the climate.

Alkaline electrolysis is a process of electrolysis using an alkaline (i.e. basic) solution as the electrolyte between the electrodes. In the case of alkaline water electrolysis for producing hydrogen, a solution of potassium or sodium hydroxide is generally used as the electrolyte. In order to avoid mixing the product gases, the electrode chambers are separated by a gas-proof membrane, a diaphragm, which allows the passage of hydroxide ions. Alkaline electrolysis is the most established process for water electrolysis and is characterised in particular by the high purity of the product gases.

A frequently-used chemical process for separating carbon dioxide, hydrogen sulphide and other acid gases from gas mixtures with the help of amines dissolved in water. The separated, pure CO2 can subsequently be utilised or stored.

Under normal conditions, ammonia is a colourless, water-soluble, toxic gas with a pungent smell, which serves as a base for a variety of products, such as fertilisers and medicines. Ammonia is produced from nitrogen and hydrogen in the Haber–Bosch process. Currently, this hydrogen is usually produced from natural gas by the steam reforming method, which releases CO2 emissions. The high demand for ammonia means that the Haber–Bosch process accounts for about two per cent of the global consumption of fossil energy sources. The hydrogen required can be gradually replaced by renewable hydrogen generated by electrolysers in order to continue this process on a sustainable basis and with no impact on the climate. Due to the good availability of nitrogen (air) and ammonia’s higher energy density compared with hydrogen, its use as an energy carrier is also under consideration.

Life on Earth would not be possible without the natural greenhouse effect – however human activity has caused sustained damage to this system, so that we now talk about man-made global warming. The main cause of the increase in greenhouse gas concentrations in the atmosphere due to human activity is burning fossil fuels such as coal, oil and natural gas.

This term refers to a technical process by means of which chemical products such as fuels, chemicals or carbon and oxygen are produced using sunlight, carbon dioxide and water.

Climatic effects are complex and regionally dynamic, so an enhanced greenhouse effect may lead to an increase in temperature, but may also cause a cooling process in some areas. For this reason, it is necessary to refer to an average global temperature to measure climate change.


Abbreviation for the term bio-energy with CCS, the combination of burning biomass and then capturing and storing the CO2 that is produced. With this technology, CO2 can be removed from the atmosphere as it is incorporated into biomass via photosynthesis beforehand.

Also known as vegetable charcoal, purely vegetable source materials are produced when charred using pyrolysis. The biochar that is extracted no longer rots like the original biomass and can therefore serve to capture CO2 for the long term.

In the energy sector, this term refers to organic matter of biogenic rather than fossil origin that can be used to produce energy, such as wood or biogas.

Term used for the carbon captured in the oceans and coastal ecosystems. Much of this is found in the form of biomass and sediments in mangrove forests, salt marshes and sea grass beds.


The most advanced form of carbonate looping, by means of which CO2 can be separated from flue gases even at high temperatures. Quick lime (CaO) is brought into contact with the flue gases at a temperature of 650°C, whereby it reacts with the CO2 contained in the gases and forms calcium carbonate (CaCO3). The calcium carbonate formed in this way is separated out and calcinated at 850-950°C, thus expelling CO2 which can be stored in high concentrations for subsequent use.

Catalytic cracking refers to a chemical process in which organic substances are heated with the addition of a catalyst. The process of catalytic cracking is used to break down various fractions of crude oil with higher boiling points.

Describes the maximum remaining amount of CO2-eq that can still be released into the atmosphere by mankind if we are to have a realistic chance of meeting the two-degree target. Emissions from burning fossil fuels must be drastically reduced and processes must be made more efficient in order to remain within the carbon budget. In addition, it may be necessary to remove CO2 or other greenhouse gases from the atmosphere in order to compensate for unavoidable emissions from agriculture and industry.

The system of chemical transformations of carbon compounds in the global systems of stone, water, atmosphere and biomass and the exchange of these compounds between these systems. Knowledge of this cycle, including its sub-processes, makes it possible, amongst other things, to evaluate human intervention in the climate and its implications for global warming, and to react in an appropriate way.

Carbon dioxide (CO2) is a component of the global carbon cycle and, as an integral part of the atmosphere, is a key greenhouse gas. As a result of human activity, particularly burning fossil fuels, the concentration of CO2 in the atmosphere has increased from about 280 ppm (parts per million) to about 410 ppm since the start of the industrial revolution. Current climate change and the rise in the average global temperature can be ascribed to this increase to a large extent.

This refers to a group of technologies which aim to remove CO2 from the atmosphere. This includes, for example, BECCS, biochar, enhanced weathering and direct air capture in combination with the storage of the CO2.

The term carbon leakage refers to a situation that can occur when, as a consequence of the costs associated with climate-protection policies, companies move their production to other countries with less stringent restrictions on emissions. This results in the loss of local jobs and the associated economic activity while the high levels of greenhouse gas emissions remain unchanged. To prevent carbon leakage, policy frameworks must be organised in such a way that the climate can be protected while also maintaining companies’ economic viability.

Refers to an eco-system or geological reservoir that absorbs and stores carbon dioxide temporarily or permanently. The term should not be confused with that of a carbon reservoir.  While a carbon reservoir is strictly speaking static, i.e. it can absorb a specific amount of CO2, carbon sinks provide dynamic storage facilities. Their storage capacity can grow (e.g. newly planted forests) or shrink. Industrial processes can also be carbon sinks, if they use CO2 as a raw material to produce carbon-based products.

Carbon Capture and Storage (CCS) refers to a group of technologies by means of which carbon dioxide is removed from  waste gases, for example in cement production, and is stored for the long term in compressed form in underground reservoirs. Pyrolysis of biomass and its subsequent storage also removes CO2 from the natural carbon cycle and can be defined as CCS.

Carbon Capture and Utilization (CCU) refers to the capture of carbon dioxide, particularly from combustion gases, and its subsequent use as raw material in chemical or biological processes, or directly, e.g. in greenhouses. The use of the carbon dioxide is thereby extended to achieve a full circular economy.

Co-electrolysis is a form of electrolysis in which several substances are converted simultaneously using electricity. One much-discussed example is the co-electrolysis of water and CO2,which produces syngas (a mixture of hydrogen and carbon monoxide). By using electricity generated from renewables, an important building block for the chemical industry can be obtained while reducing the consumption of fossil resources and making use of excess CO2 at the same time.

Climate sensitivity is a measure of the degree to which the globally averaged surface air temperature on Earth responds to changes in carbon dioxide concentrations. It refers to the temperature change that the Earth would experience in the event of a doubling of the atmosphere’s CO2 concentration and is indicated in degrees Celsius. The calculations assume that the climate is in a state of equilibrium before and after the change, i.e. an initial state and an end state are examined, with no account taken of the gradual warming between the reference points. If, on the other hand, the change in the climate is considered up to a certain point in time, this is termed “effective climate sensitivity”.

This term refers to depolymerisation by means of chemical degradation, e.g. in the form of hydrolysis.

By means of chemical recycling, plastic waste that was not previously recycled can be broken down into its original components and thus transformed into new chemical feedstock.

Chemolysisis the breakdown (lysis) of a compound using chemical agents. In the literature, the term is often used synonymously with solvolysis.

An electrolytic process for producing the key basic chemicals chlorine, sodium hydroxide and hydrogen from an aqueous sodium chloride solution. To avoid mixing the products, the electrode chambers are separated. The most relevant processes for this separation are the diaphragm, amalgam and membrane processes. Chlor-alkali electrolysis is one of the most important processes in chemical industry. For this process alone, around 2.5 % of the German net electricity generation is required.

A circular economy is also a system aimed at eliminating waste and emissions and at using resources and energy in the most efficient way possible. In a circular system, products are designed and produced in ways that minimise the use of resources and ensure that the products are durable and easy to repair; and at the end of their life cycle, they are not disposed of as waste, but rather reused in the best way possible as secondary raw materials according to the principle of cascading use.

A climate model is a computer model used to produce calculations and projections regarding the climate for a certain period of time. The model is usually based on a meteorological model, such as that used for the weather forecast. This model is expanded, however, for climate modelling. In general, ocean, snow and ice models for the cryosphere and a vegetation model for the biosphere are linked to the model.

Processes and products are climate neutral if they do not have any impact on climate change – i.e. they do not involve greenhouse gas emissions. In order to limit anthropogenic climate change to an acceptable level, negative emissions may also be necessary (climate positive measures). Climate neutrality is often used synonymously with greenhouse gas neutrality.

Is a power plant combining the principles of a gas turbine power plant and a steam power plant. A gas turbine serves as the heat source for downstream steam generation which then powers a steam turbine. This combined mode of operation achieves a higher level of efficiency than a gas turbine operating on an open cycle or a conventionally-fired steam power plant.  Combined-cycle power plants are amongst the most efficient conventional power plants with an electrical efficiency level of up to 63%.

Simultaneous generation of mechanical energy that is usually transformed immediately into electric power and heat, which can be used for heating purposes (district or local heating) or for production processes (process heat) using a common thermodynamic process, usually in a power plant. 

Unit of measurement used to describe the climate impact of greenhouse gases calculated as the amount of CO2 having an equivalent impact. Through this conversion to CO2 equivalents (CO2-eq), various emissions can be more accurately compared in terms of their impact on the climate. Methane (CH4), for example, has a 28 times greater climate impact than CO2, so 1 kg of methane equates to 28 kg of CO2-eq. In the case of nitrous oxide (N2O) the figure is 265 of CO2-eq.

Power plants and industrial processes that emit large quantities of CO2 in high concentrations. These point sources are particularly suitable for using CCU/CCS systems, since the CO2 that is produced can be separated and used/stored directly with relatively little effort.


Describes the simultaneous occurrence of darkness and lack of wind. These weather conditions typically occur in winter and lead to limited energy production from solar plants and wind turbines at a time of year when demand for electricity is also high. In order to avoid blackouts in a network that is completely supplied by renewable resources, it is necessary to develop the following components: new independent storage solutions, load flexibilisation and a mix of technologies for power production.

Refers to the transformation of the industrial economy, particularly the energy sector, in order to reduce its carbon intensity. The aim is to only incorporate carbon into products but not to use it as an energy source. For example, only about 20% of the oil currently produced is used for products, while the rest is simply burned to generate electricity and heat and as fuel. 

DSM is a concept for managing the energy loads of large-scale consumers on the power grid which will enable industrial companies, in particular, to move their demand for electricity to off-peak hours, as guided by the grid operators, and to spontaneously switch on plants at times when there is a drop in demand. In consultation with the grid operator, they can agree on financial compensation for adopting this approach and thereby tap into an additional source of income.

This term refers to the process of breaking a polymer down into its monomers or oligomers, i.e. short chain polymer units.

Emissions that do not originate from a localised source, but are scattered over a wide area and are therefore difficult to control.

Refers to a group of technologies that can be used to remove CO2 directly from the atmosphere, without depending on CO2 point sources such as those in industrial environments.  In this way, not only are CO2 emissions avoided, but CO2 concentrations in the atmosphere are actively reduced. Technologies that have currently been developed for this are reversible absorption processes such as amine scrubbing or membrane processes, where CO2 is separated from the remaining components in the air.  Due to the low concentration of CO2 in the air, these processes are laborious and therefore relatively expensive at present.

In a direct methanol fuel cell (DMFC), methanol is oxidised into CO2 and water in a controlled reaction with hydrogen thereby generating electricity. Since the process is virtually silent and handling the liquid fuel (a mixture of methanol and water) is relatively easy compared to hydrogen, this type of power generation is mainly used for camping, military equipment or remote monitoring stations.

In this procedure used in cement production, the raw material, limestone, is indirectly heated and burned. The pure CO2 that is released in the process is captured and can subsequently be transported and utilised. Since the CO2 no longer needs to be separated from a mixture of waste gases, less energy is required for this process compared to other carbon separation processes.

Downcycling refers to the recycling of waste. In this case, however, the recovered material is used for a lower-value application and is subsequently of poorer quality than the original material. Building rubble, for instance, is frequently used as filling material in road construction.



Describes the efficiency level of a technical facility or device as a non-dimensional ratio or percentage, usually the ratio of the useful energy to the input energy.  The efficiency level is an important value to assess processes and storage technologies, particularly against the background of the energy transition and efficient energy use.

Process by which substances are broken down into their component parts using an electric current. The main electrolysis processes serve to produce hydrogen, aluminium, chlorine and sodium hydroxide. In particular, water electrolysis to produce hydrogen using electricity from renewable energy sources is a key component of moving towards a climate-neutral society.

Instrument of environmental policy aimed at reducing pollutant emissions at the lowest possible economic cost. The quantity-based system is adjusted to the initial problem (carbon budget). Allocation takes place at market level. In the European Union, the Emissions Trading System (ETS) was introduced into legislation in 2005. The EU ETS currently covers power production and a few industrial sectors such as steel and cement manufacture.

Energy balance indicates the overall cost of the production, operation and further utilisation (disposal or recycling) of products. In this respect, it is not only the energy consumed in production that is taken into consideration, but also the energy needed for manufacturing and waste management as well as the resources required.

Describes the ratio of product, resource or energy output to energy input. The term energy efficiency is therefore understood to mean the rational use of energy. By means of optimised processes, the quantitative and qualitative losses that arise specifically in the conversion, transport and storage of energy are minimised to achieve a prescribed energy use with reduced primary or final energy consumption.

Means maintaining an appropriate, stable and predictable energy supply.  The transition from the controllable use of fossil fuels to volatile renewable energy sources, such as wind power and photovoltaics, poses new challenges for the energy market, which must be met with a mix of technologies for producing and storing energy and for load flexibility.

Against the backdrop of the energy transition, these systems serve to store energy that is available, but not currently needed, for use at a later stage. This energy is often converted into another form of energy, such as electrical into chemical energy (battery or P2X), which can then be converted back into the required form for subsequent use when needed.

Enhanced weathering describes a method of removing CO2 from the atmosphere whereby pulverised rock is spread over large areas and absorbs CO2 in the course of weathering; as a result, a new mineral is formed. Due to the larger surface area of the pulverised rock, the weathering process is significantly accelerated.


The energy that is supplied to final consumers and is available for energy services after deducting transmission and conversion losses. Final energy is particularly relevant when discussing various energy sources in the context of the energy transition, since significant losses can sometimes occur in the conversion of electricity.

Fischer–Tropsch synthesis is a process in which syngas – a mixture of carbon monoxide and hydrogen – is converted into liquid, long-chain hydrocarbons. These hydrocarbons are used as synthetic fuels, engine oils and as raw materials in the chemical industry. In conventional processes, syngas is obtained from fossil raw materials by gasification; alternatively, it can also be produced from CO2 through conversion with hydrogen or by means of co-electrolysis with water, providing the basis for carbon-neutral synthetic fuels.

Fuels containing carbon, which have formed as a result of processes that take millions of years and are therefore not renewable in the human time frame. When they are burned, CO2 that had been captured for millions of years is released into the atmosphere.

In a fuel cell, the energy produced by the chemical reaction between a continually supplied fuel and an oxidation agent is converted into electrical energy. In everyday use, the term fuel cell is often synonymous with hydrogen-oxygen fuel cells. Apart from hydrogen, however, many other fuels can be used, in particular methanol, butane or natural gas.  A fuel cell does not store energy but rather converts it. The energy is fed into the fuel in a chemically bound form.


The German Electricity and Gas Supply Act (Energiewirtschaftsgesetz – EnWG) first came into force in 1935 and was last revised in 2005. It contains fundamental provisions on the law governing grid-based energy. The purpose of the EnWG is to ensure that the general public is supplied with electricity and gas in an as safe, reasonably priced, consumer-friendly, efficient and environmentally responsible manner as possible, while also enabling effective and undistorted competition.

The German law for developing renewable energy sources (in short: the Renewable Energy Act, EEG 2017) regulates the preferential feed-in of electricity from renewable sources into the power grid and guarantees renewable energy producers fixed feed-in tariffs. Since the EEG amendment of 2016/2017, the law has largely shifted to the tendering system, under which the prescribed deployment corridors are to be achieved as cost effectively as possible.  The quantitative limitation of the expansion of renewable energy in the context of the Renewable Energy Act is the subject of controversial debate.

Global warming due to greenhouse gases in the atmosphere. Energy in the form of short-wave radiation reaches the Earth through the sun’s rays.  Longwave radiation, on the other hand, which is emitted as thermal radiation from the Earth’s surface and the warm air, cannot pass through the atmosphere unhindered and is partially reflected back by greenhouse gases, resulting in an accumulation of heat.

Are infrared active gases such as water vapour, carbon dioxide (CO2) ozone (O3), nitrous oxide (N2O) and methane (CH4) that contribute to the greenhouse effect. They absorb and reflect part of the longwave infrared radiation emitted by the ground, which would otherwise escape into space, and therefore cause an accumulation of heat in the atmosphere.

A process can be described as greenhouse gas neutral if it causes no greenhouse gas emissions, meaning that it has no impact on the climate. The term can be extended to whole sectors or companies. Greenhouse gas neutrality is often used synonymously with climate neutrality.

Whereas ozone (O3) serves a protective function in what is known as the ozone layer in the stratosphere because it absorbs some of the sun’s harmful UV radiation, when it is at ground level it harms living organisms. It can irritate the respiratory tract and damage the leaves of plants, thereby reducing growth and crop yields. Ground-level ozone occurs mainly in summer (“summer smog”), when it is formed from substances such as nitrogen oxides or hydrocarbons (e.g. from vehicle exhaust fumes) that react with the intense sunlight.


Storage devices for thermal energy. Heat energy storages can be constructed in different sizes ranging from small decentralised systems to large centralised storage facilities. Alongside the storage of thermal energy, the key aim of heat energy storages is to decouple the production and consumption of heat in terms of time.

A device that absorbs thermal energy by technical means from a reservoir at a low temperature (e.g. the air or the soil) and transfers it – along with the operating power – as useful heat to a system requiring heating at a higher temperature. This operating principle is the reverse of the combined heat and power process.

High-pressure electrolysis is an electrolysis process carried out under high pressure. Usually electrolysis is carried out at ambient pressure or at a moderately increased pressure. Particularly in the case of water electrolysis, increased process pressure of up to 200 bar is beneficial as it eliminates the need to subsequently compress the hydrogen produced, which can be expensive.  Due to the solid electrolyte, PEM electrolysis is better suited to high-pressure electrolysis than alkaline electrolysis.

In the Haber-Bosch process, ammonia is produced from nitrogen and hydrogen. Currently, this hydrogen is produced from natural gas by the steam reforming method, which emits CO2. The high demand for ammonia means that the Haber-Bosch process accounts for about 2 per cent of the global consumption of fossil energy sources. The hydrogen required can be gradually replaced by renewable hydrogen generated by electrolysers in order to continue this process on a sustainable basis and with no impact on the climate.

High-temperature electrolysis is a process for water electrolysis that features a high process temperature of up to 900°C (compared to the usual temperature of < 80°C). The water is therefore added as steam. As a result of the high temperature, the reaction kinetics of the electrolysis improve so electricity consumption falls. High-temperature electrolysers are usually made with sold oxide electrolyser cells (SOEC) that are permeable to O2-  or H+ ions. The high operating temperature can be provided by waste heat from other processes, for example.

Hydrocracking refers to a modern, highly efficient process for cracking crude oil, in which heavy hydrocarbons are broken down to form saturated light distillates under high pressure and at a relatively low temperature, using hydrogen and a solid catalyst.

Is considered the fuel of the future, since it does not cause any harmful emissions, particularly carbon dioxide, when it is produced by water electrolysis using renewable energy such as wind or solar power. Currently (2019), hydrogen is still made almost exclusively from fossil-based primary energy sources, mainly by means of natural gas reforming. Using hydrogen produced in this way does therefore generate CO2 emissions.

In a hydrogen fuel cell, generally referred to simply as a fuel cell, hydrogen and oxygen are allowed to react in a controlled way to form water, whereby energy is released.  Since the overall reaction in the fuel cell corresponds to a combustion reaction, this application is called “cold combustion”. The reaction taking place here is the reverse of hydrogen electrolysis, where water is separated into hydrogen and oxygen using electricity.


The IPCC is short for Intergovernmental Panel on Climate Change. The main task of the panel is to gather fundamental scientific knowledge and current global research on the impacts of climate change and it risks, as well as on mitigation and adaptation strategies, and to evaluate this information from a scientific point of view. 


Laughing gas (nitrous oxide, N2O) is one of the oxides of nitrogen and has a greenhouse effect that is 265 times stronger than that of CO2. Alongside natural sources of nitrous oxide, in particular, man-made sources of the gas include combustion processes and intensive agriculture.

A generic term for types of batteries based on lithium compounds in all three component parts of the electrochemical cell. Both the materials in the negative and positive electrodes and the electrolyte contain lithium ions. Lithium-ion batteries have a high charge density compared to other types of batteries, but usually require a protection circuit since they can be damaged if totally discharged or overcharged. 

Describes the ability to use electricity in a flexible way. The flexible use of power in energy-intensive processes is a key element of the energy transition; this approach can provide a buffer against fluctuations in electricity output from volatile renewable energy sources (sun, wind),  thus preventing an overload on the power grid and avoiding the need for additional energy storage systems.


Main component of natural gas and biogas. In the atmosphere, methane has a greenhouse effect that is 33 times stronger than that of CO2,making it the second most important greenhouse gas caused by man.

A chemical reaction whereby carbon monoxide or carbon dioxide is transformed into methane using hydrogen. The methane produced can be fed into the existing natural gas network, which extends the utilisation chain of the carbon component.

One of the most commonly produced organic chemicals, which serves as a starting point for manufacturing a range of chemical products. Methanol can be produced from CO2 and water, meaning that sustainable access to the chemical value chain is provided.

Methanol is commonly synthesised from syngas, a mixture of carbon monoxide and hydrogen. Alternatively, CO2 can serve as the carbon source in a slightly modified process in order to provide the chemical industry with this important basic chemical without the release of carbon dioxide. Since the chemical value chain is currently based on fossil resources, the syngas route has until now proven more efficient. In the transition to a climate-neutral industrial sector, however, an economically viable system based on CO2 is strongly anticipated.

A term meaning “reduction” or “limitation”, used in the field of climate research to describe efforts to reduce or prevent greenhouse gas emissions. It is used both for technical measures aimed at reducing emissions and for the creation of carbon sinks.

Hydrogen is assigned different colours according to the impact of its manufacture on the climate. The production of grey hydrogen, which is based on fossil fuels, causes CO2 emissions. Blue hydrogen is produced using the same process, but the CO2 emissions are sequestrated or removed and are therefore not released into the atmosphere. Green hydrogen is produced from renewable energy sources using electrolysis and therefore involves hardly any CO2 emissions.


Negative emissions refer to the targeted removal of greenhouse gases, particularly CO2, from the atmosphere,either by expanding ecosystems that absorb CO2 or through industrial processes. Industrial processes are based either on removing CO2 from the air (direct air capture, enhanced weathering), combined with capturing CO2 in products or storing it, or on using biomass in combination with a storage solution (biochar, BECCS).

Are technologies that aim to remove greenhouse gases from the atmosphere, for example, direct air capture, pyrolysis-CCS, BECCS and enhanced weathering.

In their 2018 report, the IPCC pointed out that greenhouse gas emissions need to be reduced to zero in order to stabilise global temperatures. Since there are areas where these emissions cannot be totally avoided, such as in agriculture or certain industrial sectors, these emissions must be compensated for in order to achieve net zero emissions.

The term Network Development Plan (also known as the Grid Development Plan) refers to two studies into the development of Germany’s electricity and gas network over the next ten years, submitted in accordance with the German Energy Industry Act (EnWG). The Network Development Plan for Electricity and the Network Development Plan for Gas are each prepared by Germany’s transmission system operators in the respective fields of electricity and gas. In the context of the transformation of the energy system, however, there is an increasing need to discuss the interconnection of the electricity and gas networks with a view to using hydrogen as an energy carrier.


A combustion process in which pure oxygen is fed in instead of air. This process has two main advantages: on the one hand, it avoids the formation of nitrogen oxides, which develop at high temperatures from oxygen and nitrogen (the main component of air). On the other hand, the exhaust fumes consist of almost pure CO2, which can be used without energy-intensive purification processes or can be stored.


Agreement made by the 197 parties to the UNFCCC aimed at climate protection to succeed the Kyoto Protocol. The agreement signed in 2015 specifies that human-caused global warming should be restricted to well below 2°C relative to pre-industrial levels.

Short for Proton Exchange Membrane or Polymer Electrolyte Membrane Electrolysis. A process for water electrolysis with a solid electrolyte that simultaneously serves to separate the electrode chambers and prevent the product gases from mixing. The solid electrolyte is permeable to H+ ions. PEM electrolysis is highly adjustable in terms of its operational performance and therefore particularly well suited to being operated using electricity from volatile renewable energy sources. Due to the durable solid electrolyte, the need for maintenance is low. PEM electrolysers are currently still operated in relatively low power ranges.

Techniques that play a role in the field of carbon capture, the process of trapping the CO2 produced in industrial processes. In contrast to pre-combustion, in this case the CO2 is separated after burning the fuel. Examples of post-combustion techniques include calcium looping and amine scrubbing.

Is an energy sector concept (and a type of technology) with which hydrogen is produced through water electrolysis using electricity. The power-to-gas concept also includes the potential downstream methanisation of CO2. The gas produced can serve as a resource in various sectors of industry, e.g. to power fuel cell vehicles, or as an energy storage solution with subsequent reconversion into electricity.

Refers to various technologies for storing or alternative use of electricity. Power-to-X technologies (also known as P2X and PtX) are particularly important at times when there is a (future) surplus supply from variable renewable energy sources such as solar power, wind power and hydropower, in order to make efficient use of these peaks in supply.

The abbreviation ppm refers to the concentration of something, like per cent or per mil, and stands for ‘parts per million’. Amongst other things, this unit of measurement is used to describe the concentration of greenhouse gases in the atmosphere. The concentration of CO2, for example, is around 410 ppm.

Techniques that play a role in the field of carbon capture, the process of trapping the CO2 produced in industrial processes. In the case of pre-combustion, the CO2 is captured before burning the fuel, for instance by converting natural gas mixed with steam into CO2 and hydrogen. The hydrogen that is produced in this way can subsequently be used as a source of energy.

A storage power plant that stores electrical energy in the form of potential energy (gravitational energy) in a reservoir.  Water is pumped up to the reservoir by electric pumps so that it can be reused later on to drive turbines to produce electricity. The benefit of the high efficiency rate of 75 – 80% is countered by the challenge of a considerable impact on the natural surroundings.

Is the thermal treatment of compounds containing carbon at temperatures of 350 to 900°C in an oxygen-deficient atmosphere. During this process, three carbon-based products emerge, which can then be stored in different ways to generate negative emissions: biochar (used to improve soil or for building up coal deposits), pyrolytic liquid (creosote), pyrolysis gas (can be transferred as CO2 to geological storage facilities after the incineration process).


The raw materials industry includes all industrial sectors that extract and supply raw materials (e.g. ores, rocks, crude oil, salt, wood) so they can be used in the manufacturing industry. Because resource extraction often requires a lot of energy, this area offers substantial potential for reducing greenhouse gases.

Increases in efficiency often reduce the costs of products or services. This can lead to a change in the way users behave: they consume more – the initial savings are partially offset.  This is called the rebound effect. Increases in efficiency are a key strategy to reduce the use of resources. The increase in energy efficiency, for example, is the central pillar of the energy transition, alongside the expansion of renewable energy.  In this context, environmental policy must take into account that rebound effects diminish the reduction in the use of resources. If it does not, the envisaged reduction in the use of resources will be lower than expected, and the environmental and resource targets will not be met.

The product of a recycling process, conditioned, secondary raw materials. E.g., recycled fibre in the paper industry.  

Acronym for Reducing Emissions from Deforestation and Forest Degradation. This refers to a financing mechanism of the UN Framework Convention on Climate Change, which pays compensation (mainly from industrialised nations) for renouncing the destruction or harmful exploitation of forests (mainly in developing countries).

See “Renewable Energy Directive”

A type of battery where the electrical energy is stored in chemical compounds that are dissolved in liquids within the system, circulate and can be stored in separate circuits.  Charging and discharging takes place in a central cell that determines the maximum power of the battery. The storage capacity, however, is determined solely by the size of the storage tanks used.

Part of the process of refining. Different processes, depending on the operational context, used to carry out the chemical transformation of hydrocarbon fractions that are mainly in liquid form (naphtha or pyrolysis oil).

Any type of energy that is replenished as a result of natural processes at a speed that is at least as fast as the consumption rate, for example sunlight, wind or biological resources.


A plausible, frequently simplified description of future events based on a range of assumptions including those on the interaction and the driving forces of a development.

Solvolysis is a special type of chemical depolymerisation (the two terms are often employed synonymously in the literature), which is used in the case of polycondensates (e.g. polyester, polyamides), and particularly in the form of hydrolysis (the breakdown of a compound using water as the reactant). Various solvents can be used. Consequently, solvolysis can be further sub-divided into glycolysis, methanolysis, hydrolysis and aminolysis.

Is currently the most important industrial process for producing hydrogen from carbon-based energy sources and water. In this process, CO2 is always produced as a by-product, putting steam reforming at a disadvantage compared to water electrolysis using electricity from renewable energy sources. Natural gas is currently the most important raw material; in principle, many hydrocarbons are suitable as raw materials including light petrol, methanol, biogas or biomass. The efficiency rate (natural gas to hydrogen) is around 60 to 70%.

Conventional fuels such as petrol, diesel or kerosene are produced from crude oil and have a correspondingly negative impact on the climate. Synthetic fuels can have the same properties as conventional fuels, but can be produced from renewable resources, although this may require a comparatively large amount of energy.

In the chemical industry, this refers to a mixture of hydrogen and carbon monoxide, which can be used in a flexible way for the synthesis of a wide variety of compounds. Syngas is currently derived predominantly from fossil resources. In the future, however, it will also be possible to produce it sustainably from water (electrolysis) and CO2.


Synonym for chemical recycling.

Thermal depolymerisation refers to depolymerisation by applying energy at high temperatures. It is currently used for PMMA and to a limited extent for polystyrene. In this case it is a version of pyrolysis.

The Earth’s climate system is based on a series of essential building blocks, known as tipping elements, which could lose their decisive meteorological function as a result of the negative impacts of human activity. The loss of such a function is a tipping point in the climate system, which triggers a disproportionate global warming process. The Potsdam Institute for Climate Impact Research (PIK) has defined 16 such tipping points, including the melting of Arctic sea ice, the destabilisation of the Indian monsoon, the destruction of coral reefs and the transformation of the Amazon rainforest.

The Paris Agreement obliges the countries of the world to restrict the rise in the average global temperature to well below 2°C relative to pre-industrial levels and to make efforts to limit the temperature rise to 1.5°C in order to curb the negative impacts of climate change and avoid reaching potential tipping points.


Process-related CO2 emissions that cannot be avoided despite optimisation of the production process or the product.

Abbreviation for United Nations Framework Convention on Climate Change. The aim of this international treaty, which was adopted in 1992, is to stabilise greenhouse gas concentrations in the atmosphere at a level that will prevent dangerous anthropogenic interference with the climate system. Since 1995, the countries participating in the UNFCCC have met annually at so-called climate summits to discuss concrete steps towards achieving the agreed target. In 1997, the Kyoto Protocol was adopted by the UNFCCC; this is a supplementary protocol for implementing the Convention on Climate Change. In the Paris Agreement adopted in 2015, all countries are obliged to define and implement reduction targets for the first time, and to subject their progress to a monitoring system. Every five years the targets are to be compared to the state of scientific development and adapted in the light of this.









The term value chain describes the stages involved in production as an ordered sequence of activities. These activities create value, consume resources and are interconnected within processes. The concept was first put forward in 1985 by Michael E. Porter, an American expert in business management, in his book Competitive Advantage. In terms of sustainability, the challenges facing the industrial sector lie in the gradual conversion of individual processes in its value chains to a renewable energy and raw material basis, or even in the establishment of new value chains in a changing market.


In everyday use, a clear distinction is not often made between weather and climate, but it is essential for an understanding of the climate system. Weather is the constantly changing atmospheric state that we experience on a daily basis and which is only predictable over short periods. Climate, however, refers the average weather in a specific place over a longer period of time. Climate is therefore not directly measurable but rather a compilation of statistics obtained from a large number of measurements.

White certificates are systems used to oblige market players, mainly energy providers and grid operators, to achieve a specific savings target in a certain time period and to implement energy efficiency measures for consumers. The certificates verify the energy saving measures in terms of the quantity and time period. For energy savings implemented, the market player receives corresponding certificates, which it can either use to meet its own obligations or sell to other obligated market players. If an obligated energy provider or distributor has collected too few or no certificates, it is liable to be fined.

The colloquial term (in German) for the regular progress reports from the IPCC. Every five to seven years, the status of global research on the causes and impacts of climate change and the potential for mitigation and emission reduction are summarised in an editorial process involving designated specialists.


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