Power-to-X (also P2X and P2Y) are electricity conversion, energy storage, and reconversion pathways from surplus renewable energy.^[1][2] Power-to-X conversion technologies allow for the decoupling of power from the electricity sector for use in other sectors (such as transport or chemicals), possibly using power that has been provided by additional investments in generation.^[1] The term is widely used in Germany and may have originated there.

The X in the terminology can refer to one of the following: power-to-ammonia, power-to-chemicals, power-to-fuel,^[3] power-to-gas (power-to-hydrogen, power-to-methane) power-to-liquid (synthetic fuel), power to food,^[4] power-to-heat. Electric vehicle charging, space heating and cooling, and water heating can be shifted in time to match generation, forms of demand response that can be called power-to-mobility and power-to-heat.

Collectively power-to-X schemes which use surplus power fall under the heading of flexibility measures and are particularly useful in energy systems with high shares of renewable generation and/or with strong decarbonization targets.^[1][2] A large number of pathways and technologies are encompassed by the term. In 2016 the German government funded a €30 million first-phase research project into power-to-X options.^[5]

Surplus electric power can be converted to gas fuel energy for storage and reconversion.^[6][7][8][9] Direct current electrolysis of water (efficiency 80–85% at best) can be used to produce hydrogen which can, in turn, be converted to methane (CH₄) via methanation.^[6][10] Another possibility is converting the hydrogen, along with CO₂ to methanol.^[11] Both these fuels can be stored and used to produce electricity again, hours to months later.

The purpose of power-to-heat systems is to utilize excess electricity generated by renewable energy sources which would otherwise be wasted. Depending on the context, the power-to-heat can either be stored as heat, or delivered as heat to meet a need.^[14]

Power-to-mobility refers to the charging of battery electric vehicles (BEV). Given the expected uptake of EVs, dedicated dispatch will be required. As vehicles are idle for most of the time, shifting the charging time can offer considerable flexibility: the charging window is a relatively long 8–12 hours, whereas the charging duration is around 90 minutes.^[2] The EV batteries can also be discharged to the grid to make them work as electricity storage devices, but this causes additional wear to the battery.^[2]

According to the German concept of sector coupling interconnecting all the energy-using sectors will require the digitalisation and automation of numerous processes to synchronise supply and demand.^[19]

A 2023 study examined to role that power‑to‑X could play in a highly‑renewable future energy system for Japan. The P2X technologies considered include water electrolysis, methanation, Fischer–Tropsch synthesis, and Haber–Bosch synthesis and the study used linear programming to determine least‑cost system structure and operation. Results indicate that these various P2X technologies can effectively shift electricity loads and reduce curtailment by 80% or more.^[20]

• Grid energy storage
• Flywheel