Power-to-X: From green energy to green fuels

In a time of growing concern over climate change and the urgent need to transition to cleaner and more sustainable energy sources, the concept of Power-to-X (P2X) has emerged as a promising solution. This brief introduction presents the principles and challenges of Power-to-X, exploring the diverse range of energy carriers it can produce and its implications for the global energy landscape.

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Published: Jun 14, 2023 at 1:24 PM

Power-to-X (P2X) can be easily explained as the process to create an energy carrier from renewable energy. This requires access to surplus renewable energy. The conversion process from renewable energy to energy carrier is defined by the desired end-product. The simplest process is electrolysis, splitting water into hydrogen and oxygen. The hydrogen (H2) can be used directly or further processed into ammonia (NH3), methane (CH4) or syngas (a mix of hydrogen and carbon monoxide in various ratios). 

Ammonia requires the addition of Nitrogen (N2) to create NH3. The typical process to create ammonia is through the Haber-Bosch process. This is a process which requires additional energy. Both hydrogen and ammonia can be used in combustion or fuel cells and have no CO2-emissions in use.

Methane, and other syngas-based fuels such as Methanol (CH3OH) are carbon-based energy carriers, often referred to as E-methanol or E-Methane in this context. To create carbon-based E-fuels carbon dioxide (CO2) needs to be captured and combined with the produced hydrogen. The process of methanol and methane synthesis require additional use of renewable energy. The syngas-based products can be further processed to kerosene, diesel, petrols, waxes and other chemicals. Due to the CO2 capture, the energy carrier is regarded as carbon neutral, but it does however emit CO2 in use.

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Two of the biggest challenges related to P2X is access to surplus renewable energy and its comparatively low roundtrip efficiency compared to direct power usage. Most electrolysers used for generating hydrogen are around 60-70% efficient using lower heating value. That means that 30% of the energy is lost in this process to convert electricity and water into hydrogen. When creating other hydrogen-based fuels, such as ammonia and methanol, the energy loss is even higher due to increased required power. In comparison, direct charging of batteries is 95% effective. When looking at the process of going from energy carrier and back to power (X-to-Power), the efficiency is even lower . Fuel cells, used to generate electricity from H2, generally have an efficiency of 50%, resulting in a total loss of 65-70%.   

There are many possibilities related to Power-to-X, and E-fuels can be an important part of the decarbonization of hard to abate sectors. However, it requires a thorough assessment of the energy situation to avoid energy shortage and waste. Direct electrification or use of less energy intensive fuels should always be evaluated first.