Power-to-X basically describes the storage of electricity in times of oversupply. Storage can be broken down by energy form, resulting in options for converting electricity into heat (power-to-heat), into gas (power-to-gas) or into a liquid (power-to-liquid). In most cases, the latter storage options are used, since the achievable energy densities in heat storage are significantly lower and reconversion of stored heat is technically complex and usually inefficient.
The now best-known use case in the field of power-to-X is probably the conversion of renewable, electrical energy into green hydrogen. In particular, when surplus renewable energy is used to produce hydrogen from it, it is emission-free and can be produced at low cost.
In Germany, wind turbines are regularly shut down or slowed down because electricity generation is significantly too high for current consumption. This unused energy is ideal for producing hydrogen, which can be used later or, in rare cases, converted back into electrical energy. The expiry of feed-in tariffs for wind turbines or solar parks is also a much-discussed topic at present. Here, too, it can be worthwhile to use the energy to generate hydrogen and thus achieve higher revenues than with the direct feed-in of unsubsidized electrical energy.
However, hydrogen is not necessarily needed at the place where it is produced. In addition, in integrated systems with simultaneous production and consumption of hydrogen, the quantities of production and consumption must be coordinated and in some cases buffered with storage tanks, which are currently still relatively expensive. However, since there is currently no hydrogen pipeline network, the hydrogen is transported from the point of production to the point of consumption via so-called "virtual pipelines". Trailer filling, i.e., filling truck trailers with hydrogen that can then be transported to the desired point of use, is used for this purpose.
Filling pressures vary quite widely, but are usually in the range of 200 bar to 700 bar. Thanks to the broad compressor portfolio of the NEUMAN & ESSER GROUP, with piston compressors, diaphragm compressors (MKZ) and hydraulically driven piston compressors (TKH), the most efficient and cost-effective solutions can be identified for each application. It is now possible to transport up to 1.5 tons of hydrogen in one truck. In contrast to the transport of liquid hydrogen, this is under pressure at ambient temperature and thus does not have to be evaporated (so-called boil off). This means that the gaseously stored hydrogen can be transported in the trailer over long distances without losses and store for any length of time.
In parallel, concepts for transporting hydrogen via pipelines are currently being developed in various approaches. The goal is often to build a cost-effective, Europe-wide hydrogen network analogous to the existing gas transmission network for natural gas. The latest studies show that it is even possible to use the existing natural gas networks for this purpose with only minimal modifications, including to the seals and the compressors. The seals must be able to prevent the diffusion of hydrogen into their material. The compressors should be replaced in large parts: Turbo compressors are usually used in gas networks, but they are not suitable for compressing hydrogen due to the low molecular weight of hydrogen. Here, for efficiency reasons, it makes sense to switch to piston compressors in the future - NEUMAN & ESSER GROUP is already in talks with many gas network operators in this context.
Since free gas pipelines are still available, especially in Germany, a pure hydrogen network or a network with a natural gas-hydrogen mixture could thus be established with relatively little effort. The pressures for transport in the gas networks are around 80 bar to 100 bar - this pressure range will probably also become established for the transport of hydrogen. Here, the piston compressors of the NEUMAN & ESSER GROUP can be used in particular. Furthermore, when using the gas networks, the existing storage possibilities for natural gas, especially salt caverns, the so-called Cavern Storage, can be used to store hydrogen in the long term. Initial model tests for storing hydrogen in salt caverns at around 200 bar are already underway. This would solve the biggest challenge of the energy transition in particular: the storage of green energy. While large-scale storage in batteries is not sustainable enough and actually not affordable, the potential sites for pumped storage power plants in Germany and Europe have now almost all been developed. Other storage options for electrical energy are still in experimental stages, or have never made it past this stage. However, by storing hydrogen in salt caverns, the energy demand of a longer period can now be stored and retrieved in case of a longer dark period.
Several options exist for recovering the energy from the hydrogen. Probably the best-known approach is to generate electricity from hydrogen by means of fuel cells. Here, approx. 60% of the energy stored in the hydrogen is converted into electricity, and the remaining 40% is available as waste heat. In addition, the hydrogen can also be burned, for example as an admixture in the natural gas network in "classic" gas heating systems. Most manufacturers now state that they are able to process up to 20% hydrogen admixture with their standard products. Furthermore, hydrogen can also be burned and basically be used like gasoline - even if this application is now more of a niche.
Hydrogen is also a starting material for the production of synthetic fuels (synfuels). This requires a carbon source in addition to the hydrogen. This is obtained, for example, by capturing CO2 from combustion or fermentation processes, the process of carbon capture and usage, and combining it with the hydrogen, e.g. by methanation. In this process, methane (CH4) can be produced using energy, which can be used in the same way as natural gas (by feeding it into the natural gas grid, as CNG or as LNG). If a "green" CO2 source is used, e.g. from biogas plants - climate-neutral natural gas can be produced via this route. These advanced fuels emit CO2 when they are burned, but only as much as was previously bound in them. This pathway can thus be used to decarbonize areas where direct electric application or the use of hydrogen is not economically viable - these include aviation or shipping.
During the production of crude oil or natural gas and the subsequent treatment of the produced medium, the gas treatment, various gases are separated. These so-called offgases are not needed for the subsequent product and must therefore be removed from the extracted crude oil or natural gas. However, these waste products can be made usable by desulfurization processes. For example, NEUMAN & ESSER compressors are used on offshore platforms to compress off-gases and make them usable as desulfurized gas.
For use in batteries and fuel cells, the raw materials e.g. green coke, synthetic or natural graphite and silicon must have special properties. Decisive factors in comminution and rounding are fine but steep particle size distributions, the highest possible tap density, maximum specific BET surfaces and particle shape as round as possible. To avoid losses of the raw material, NEUMAN & ESSER Process Technology developed a solution to separate the grinding process from the rounding process. The NEA|Sphere grinding and rounding units developed in-house are used for this purpose.