How Power-to-X works

Copyright by the International PtX Hub. Inspired by nova Institute (2020): nova-paper #12 on Renewable Carbon 2020-09

Power-to-X - how does it work?

Power-to-X converts renewable electricity, from wind, solar, hydro, and geothermal power plants, into a wide variety of end products (X).

Renewable electricity can directly heat and cool buildings and power trains and cars (direct electrification). This is called decarbonisation: renewable electricity replaces oil and gas for heating, cooling, and powering battery-electric trains and cars and thus, the element carbon is no longer involved.

When molecules are necessary, Electrolysis splits water (H2O) into its components hydrogen (H2) and oxygen (O2). This water needs to be purified before it is fed to the electrolyser (water processing). For example, seawater must be desalinated for hydrogen production. Pure hydrogen can then serve as energy storage to compensate for intermittency of renewables in the electricity system (backup power) or be used as fuel for high processes temperatures, for example in the glass or cement industry, or as reduction agent, for example in the steel industry. Here, we are also talking about decarbonisation since the element carbon is directly substituted by hydrogen.

Swing Adsorption extracts nitrogen (N2) from the ambient air. Multiple processes to produce green ammonia exist, the most known is the Haber-Bosch synthesis. In all, hydrogen (H2) is combined with nitrogen (N2) and converted into ammonia (NH3). Ammonia is a key feedstock for the fertiliser industry, therefore crucial for food production and farming, for explosives in mining, but also in the chemical industry for cosmetics and pharma and as a fuel in maritime shipping. No carbon involved, meaning decarbonisation.

To produce sustainable synthetic hydrocarbons (CxHy), renewable carbon (C) is needed. The carbon can either stem from non-fossil, renewable sources, such as direct air capture (DAC) and biogenic residues or be recycled from unavoidable industrial point sources (Carbon Capture and Use from Industry, CCU), for example from cement plants. There are different processes to produce synthetic hydrocarbons, the most known is the Fischer-Tropsch synthesis. In the Fischer-Tropsch synthesis, carbon (C) is processed to form all kinds of hydrocarbons, or a kind of synthetic crude oil often called syn-crude. Further processed, the syn-crude can be turned into specific products, such as Jet-fuel for aircrafts (Power-to-Liquid Sustainable Aviation Fuel, PtL-SAF; Fischer-Tropsch Hydroprocessed Synthesised Paraffinic Kerosene, FT-SPK; Fischer-Tropsch Synthetic Paraffinic Kerosene with Aromatics, FT-SPK/A). Synthetic hydrocarbons in different forms can defossilise the chemical industry, cosmetics, and pharma production as well as maritime shipping and aviation.

As carbon is still necessary in this process, it is called defossilisation instead of decarbonisation. The crucial transformation is the switch from fossil to renewable carbon.