Prof. em. Dr. Hanno Schaumburg, Hamburg University of Technology, Germany
In the framework of the more than 20 year-long cooperation between Turkmen and European Union partners with coordination from Germany in 2011 a 5 kWpeak solar station was set up in the Turkmen State Institute of Transport and Communications with a 35 kWh battery backup. Since that time practical applications have demonstrated that for a professional use under unfavorable weather conditions like in winter even such a large and expensive battery backup is by far not sufficient for the continuous operation of an autonomous solar station where typically an amount of 200 kWh backup is necessary. State-of-the-art experience shows that presently the only commercially acceptable alternative is an energy backup using compressed hydrogen gas. The equipment required for this technology – electrolysis of water with hydrogen tank storage and electricity production using fuel cells – due to new improvements in membrane technologies and mass production has reached a price range for a cost-effective use in commercial autonomous systems, where generally moderately higher electricity costs are acceptable. This creates one of the first industrially attractive segments of the coming “green (using only renewable energy)” hydrogen technology, which will be indispensable for a climate-neutral energy use (with largely reduced greenhouse gas emission) mandatory for the near future.
In view of the ample sunshine and considerable wind strength in many regions the climate conditions in Turkmenistan are well suited for the application of autonomous energy systems based on renewable sources and green hydrogen storage – that are essential for the necessary energy supply in desert and steppe areas with no or little access to the public grid.
Presently in Europe strategies are developed to employ green hydrogen as a zero green house-gas emission fuel for the energy production in general: For this option – due to a lack of mere land space – the renewable energy production in Europe will not be sufficient, with the consequence that an import from abroad of green hydrogen – transported through natural gas pipelines – is mandatory, possibly also from Turkmenistan.
- Greenhouse gas effect
It is a well-known fact that the presently ongoing dramatic climate-change is largely due to a layer of greenhouse gases in the upper atmosphere that deviates the sun shine reflected from the surface of the earth back to the surface – thus increasing the earth temperature (fig. 1):
- Average earth temperature without green house gas layer: ca. -18 C
- Average earth temperature with natural green house gas layer: ca. +15 C
- Average earth temperature with man-made (anthropogenic) green house layer: larger up to much than 15 C.
Fig. 1: Greenhouse Gas Effect1)
In Table 1 for the year 2017 the concentration of green house gases is given together with their typical properties.
Table 1: Concentration of relevant green house gases together with typical properties 1)
It turns out that the most relevant greenhouse gas is carbon dioxide CO2, followed by methane CH4 in a much lower concentration, but a green house potential that is a factor of 21 higher than that of CO2.
- The hydrogen alternative
The Paris Climate Protection Agreement from 2015 demands a rapid reduction of energy-related CO2 emission down to zero until 2035, largely eliminating conventional energy sources like coal, oil, and natural gas. Presently the most important alternatives are hydrogen and nuclear power energy. In Germany due to the unpredictable damage caused by serious emergencies (Tchernobyl, Fukushima, and many others) in connection with the unresolved problem of the nuclear waste disposal the use nuclear power is forbidden, leaving mainly hydrogen as an alternative.
The advantages of hydrogen as an energy carrier are evident:
- It produces CO2-free energy à”environmentally clean” à decarbonization,
- “Green” hydrogen can be readily produced in large-scale (fig. 2) by all forms of renewable energy, preferably using solar and wind energy in unexploited areas like deserts, steppes and the open sea,
- It can be used for long-term storage,
- It can be transported by pipelines.
- It is non-toxic
On the other hand, potential problems are:
- It is highly inflammable and explosive,
- It can diffuse through solid materials like many metals and alloys
- It is highly volatile, can cause leakage problems
- It favors embrittlement of high strength steel, titanium,…
- It can increase material failures by enhancing crack propagation
- It has a negative Joule-Thomson coefficient: heating with gas expansion
All these deficiencies can be taken care of, but require specific care.
Fig. 2: Large scale green energy production in the North sea (Germany) 2)
Hydrogen energy directly and indirectly can be used for most applications
- Power generation in connection with fuel cells in cars, trucks, ships, trains, airplanes
- Direct combustion of synthetic hydrogen fuel for heating, combustion motors, gas turbines
- Direct reduction of materials in the chemical industry, for steel production, and other application
- Many other applications in science and engineering…
Typical physical properties are in comparison with other fuels3)
Energy density in kWh/kg
- Hydrogen: 33,3 kWh/kg = 120 MJ/kg
- Hydrogen storage in Perhydro-N-Ethylcarbazole: 1,9
- Natural gas: 13,9 (9 – 14)
- Benzine: 11,1–11,6 (40,1–41,8 MJ/kg)
- Diesel: 11,8–11,9 (42,8–43.1 MJ/kg)[
- Methanole: 6,2
- LOHC (N-Ethylcarbazol): 1,93
- Li-Ion-Battery: 0,2 (ca., depending on type)
Energy density in kWh/liter
- Hydrogen gas (normal pressure): 0,003
- Hydrogen gas (20 MPa / 200 bar): 0,53
- Hydrogen gas (MPa / 700 bar): 1,855 (h) ´
- Hydrogen storage in Perhydro-N-Ethylcarbazole: 2,0
- hydrogen (liquid, −253 °C): 2,36
- natural gas (20 MPa): 2,58
- Benzine: 8,2–8,6
- Diesel: 9,7
- LOHC (N-Ethylcarbazol): 1,89
- Li-Ion-Battery: 0,25–0,675
- Hydrogen production
Typical hydrogen production technologies include
- Electrolysis of water
- High temperature steam reforming of natural gas, methane, oil and coal
- Photochemical processes using water
- Photobiological processes using water and biomass.
Mostly used is water electrolysis (pict. 3).
Pict. 3: Photo electrolysis of water
- Principle 1)
- Industrial eletrolyzer 3)
- Fuel cells
The conversion of gaseous hydrogen to electricity is implemented by fuel cells (fig. 4a): An oxygen partial pressure gradient causes the diffusion of oxygen ions, thus creating an electric potential difference (fig. 4b). Fig. 4c shows different types of fuell cells operating at different temperatures. Presently the most importen fuel cell seems to be the Polymer electrolyte Fuel Cell (PEFC).
Fig. 4: Fuel cell
- Principle 9)
- Band diagrams 5)
- Fuel cell technologies for various temperature ranges 9)
- Autonomous (stand-alone) electricity stations based on green energy and hydrogen storage
A very perspective new technical development are autonomous (stand-alone) electricity stations based on green energy and hydrogen storage6) (figs. 5 and 6): It can be shown in practice that in case of low regenerative energy levels (like at night and in winter) a full battery backup in most cases is not sufficient and economic compared to hydrogen storage6, although a small Li-Ion battery can be beneficial taking care of overload conditions.
Fig. 5: autonomous (stand-alone) electricity stations based on green energy and hydrogen storage 7) 8)
Fig. 6 shows the performance of stand-alone microgrid (SAM) system under the climatic conditions of Australia 6).
Pict. 7: stand-alone microgrid (SAM) system with hydrogen storage components´operation in
- December (Australia) 6)
- June (Australia) 6)
- Hydrogen storage tanks and pipelines
High pressure Hydrogen storage tanks are usually made from carbon fiber, composites, and specialized steel10-14). Special care has to be taken to avoid
- Hydrogen loss by diffusion
- Hydrogen embrittlement
Often inner coatings are used. Polymer pipelines are uncritical.
In Germany hydrogen pipelines are used for a long time 14-18)
- hydrogen -pipeline Rhein-Ruhr (from 1938 (!),Air Liquide, 240 km)
- hydrogen -pipeline Rodleben-Bitterfeld-Leuna-Zeitz (Linde AG, 90 km)
- H2HoWi project: conversion of existing natural gas pipelines to
- hydrogen transport/storage
The present situation for natural gas pipelines is:
- certified: 10% hydrogen in natural gas,
- extension to >20% possible
- in R&D: Extension to 100% hydrogen
In pipelines with a mixture of hydrogen and natural membrane technologies for the hydrogen separation.
- Green hydrogen for a world-wide decarbonized energy supply
Although green hydrogen technology seems to be most important to meet the ambitious requirements of the Paris Treaty within the foreseeable future, a solution for a massive production of green hydrogen for a world-wide consumption so far is not in sight. The bottleneck is the huge amount of renewable energy necessary for a green hydrogen economy. In Europe there is simply not enough space to produce this energy, neither by sunshine, wind, biomass, or others. Plans to produce green hydrogen in the Sahara desert and transport it to Europe have been developed but seem to be on hold. Probably the network of existing pipelines will play a crucial role in solving this task which makes future green hydrogen technology also an interesting topic for Turkmenistan.
1)V. Quaschning „Regenerative Energiesysteme“, 2019 Carl Hanser Verlag München
2)Internet pages of the RWE and Vattenfall companies in Germany.
5) H. Schaumburg, Sensoren, B. G. Teubner-Verlag Stuttgart, 1992, p.438
6)F. Dawood, GM Shafiullah, M. Anda in Sustainability 2020, 12, 2047; doi:10.3390/ su 12052047
Prof. em. Dr. Hanno Schaumburg can be contacted at Hamburg University of Technology, Lohkampstr. 100, D-22523 Hamburg, Germany – Tel. +49-40-5708600 (Hamburg), +49-4641-8457 (Brarupholz 8), Mobile: +49 (0) 172 201 4036, email: firstname.lastname@example.org
/// nCa, 14 April 2021