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News | 23.6.2014
Focus on the hydrogen storage process chain

Focus on the hydrogen storage process chain

The researchers assessed the alkali electrolysis unit (illustrated) as less profitable than PEM electrolysis in the long term.
© DLR Stuttgart

In the PlanDelyKaD project, scientists studied the option of storing surplus electricity as hydrogen and converting it back for use. They considered the entire process chain from generation to storage and use. The research focused on hydrogen electrolysis and gas storage in salt caverns. The study completed in May 2014 reveals the method’s potential on the market.

Surplus electricity generated by wind turbines or photovoltaic systems could be stored as chemical energy using power-to-gas. By 2050, the surplus electricity will rise to roughly 50 to 60 terawatt hours per annum. Surplus electricity is generated in particular when strong winds or periods of high pressure persist for several days. Water electrolysers are the key technology to generate hydrogen at a scale relevant to the energy sector. Due to its highly dynamic operating characteristics, and combined with storage facilities, hydrogen electrolysis can provide secondary and minute balancing energy in the electricity grid. The PlanDelyKaD project assessed the prospects for the method on the market. The German Aerospace Centre (DLR) coordinated the project. Other contributors included the Fraunhofer Institute for Solar Energy Systems ISE, Ludwig-Bölkow-Systemtechnik GmbH and KBB Underground Technologies GmbH.

The study evaluated the technological risks in implementing these systems. To do so, the researchers examined two scenarios with currently available technology and assuming a continuation of the technological development to 2030. A 5 megawatt facility was designed based on the state of the art, both with alkali and PEM technology, while for 2030 a facility with a capacity of 100 megawatts was designed, also using both technologies. The investment (CAPEX) and the operating (OPEX) expenditures calculated were the basis for the further technical and economical simulations in this study.

Using salt caverns for hydrogen storage

A wide range of aspects play a part in choosing the location for future hydrogen storage facilities. The availability of suitable geological formations is essential. Other criteria include the distance from wind and solar power generating systems, and to future consumption centres. In the end, the goal is to find the best compromise. The study identified possible locations for hydrogen storage caverns from a geological and geotechnical point of view. As earlier studies focused more on the North German coast, this project intentionally concentrated on regions further south.

Based on the assessments, the researchers proposed specific locations for hydrogen storage facilities. Future hydrogen storage facilities can be implemented as a supplement to existing natural gas storage facilities, as the geotechnical requirements for hydrogen caverns are largely identical to those for natural gas caverns. For this reason, the scientists listed existing storage cavern projects for natural gas and liquid hydrocarbons. German federal states are showing increasing interest.

Hydrogen can be used economically in the transport sector

There are four main markets for hydrogen:

  • As a chemical base material in industrial applications,
  • In the transport sector,
  • Feeding into the natural gas network and
  • Conversion back into electricity as a classic electricity storage medium.

The researchers examined the economic prospects of these markets from the point of view of a prototypical wind and hydrogen plant operator. Depending on the application, volatility of the electricity prices and electrolysis capital costs, the specific hydrogen costs ranged between three and seven euros per kilogram of hydrogen. This level of revenue can only be earned in the transport sector.

With high electricity costs and low investment costs, optimal operation of the electrolysis plant occurs at a low capacity utilisation of 2,500 to 3,800 full-load hours per annum. A system of this kind could be used for load management of fluctuating renewable energy. The profitability of the system could be increased in two ways: The first is to remunerate load management, for example via corresponding market mechanisms. The other is lower prices for surplus electricity.

The profitability can also be increased by selling the oxygen produced and using the resulting heat. The oxygen can either be used directly for end consumers or for a more efficient, decentralised conversion back into electricity. The waste heat can also contribute to energy-efficient temperature maintenance in the process. Both the electrolysis plant and the fuel cell system for conversion back into electricity require a heat supply in standby mode.

Prospects of hydrogen usage

The industry is currently virtually the only consumer and producer of hydrogen, at over 20 billion Nm³ of hydrogen per annum in Germany. However, in future, use as heating fuel,  storage medium and motor fuel will increase significantly. By 2050 the industrial hydrogen demand is forecast to reduce to roughly 15 billion Nm³. By contrast, the consumption as a fuel in fuel cell and gas vehicles is to increase to approx. 22 billion Nm³. Power plants with gas turbines, gas and steam turbines or fuel cells will require approx. 7 billion Nm³ of hydrogen. Ammonia and methanol manufacturers as well as refineries are the main industrial users. In particular the decrease in use of the fossil fuel crude oil will reduce the demand for hydrogen in this sector from its current level of approx. 9 billion Nm³ to 1.4 billion Nm³ in 2050.

Balancing energy in the electricity grid

Researchers expect the secondary balancing energy demand of the electricity grid to increase only slightly from the current 2,100 MW to approx. 2,300 MW by 2050. However, the balancing energy demand in the minute sector will almost double to just under 5,000 MW. Conversion back into electricity with fuel cells or combined cycle power plants provides positive balancing energy, whereby the latter can only do so in the minute sector. The provision costs are decreasing, with a simultaneous increase in the working prices. The price development depends in particular on the legal framework conditions in breaking down the tender quantities into tranches and the forecast errors with a higher percentage of renewable energy in the electricity grid. Compared with the status quo, the demand peaks in the minute sector will almost double as early as 2030.

Hydrogen in the natural gas network

Feeding hydrogen into the natural gas network eliminates the need to lay additional pipelines throughout Germany. Technically, it can be transported and distributed through the natural gas pipeline network. The influence of hydrogen concentrations of up to 20% volume can be managed technically. With a total quantity of natural gas transported of approx. 93 billion Nm³ in 2012, up to 19 billion Nm³ of hydrogen could be transported in future – this is equivalent to approx. 40% of the hydrogen quantity required in 2050 – and approx. 74 billion Nm³ of natural gas. However, the scientists see a need for research into consumers, i.e. gas turbines, compressors, combustion engines and steam boilers. There are no studies on addition of higher hydrogen levels to natural gas.

Supported by: The Federal Government on the basis of a decision by the German Bundestag

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