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Wind power and hydrogen: complementary energy sources for sustainable energy supply – Part 2


Alexandra Huss – AKOMBE, Cologne, Germany

The North Rhine-Westphalia region in Germany recently began daily operation of its first wind power electrolysis plant, which independently and reliably supplies the h2herten application centre with renewable energy. Part 2 of this article describes the Energy Complementary System at the core of the plant, and its several components.

This article is taken from the April 2013 issue of the Fuel Cells Bulletin newsletter – check out the sample Digital Edition.

North Rhine-Westphalia’s first wind power electrolysis plant is part of the h2herten application centre, Germany’s first municipal technology centre based on hydrogen and fuel cell technology. The wind power electrolysis plant takes the centre far beyond its original focus on hydrogen and fuel cell technology, developing an energy supply concept that sets the standard for the sustainable and decentrally organised energy supply of the future.

Plant layout

The wind turbine, which is located in the immediate vicinity of the h2herten application centre on the Hoppenbruch mining waste heap, is not directly connected to the application centre. The connection is made virtually via a so-called wind turbine simulator, which feeds the wind power into the supply system in real time.

Should the energy produced by the wind turbine be greater than the centre’s requirements, the excess current is either stored directly in the integral lithium-ion battery bank or – once the batteries are full – converted into hydrogen by the alkaline electrolyser. The hydrogen produced is brought up to the necessary pressure in a compressor and then stored in pressurised containers.

Conversely, if too little wind energy is available, the stored energy is instead converted back from the battery and the hydrogen. The main role of the battery in this process is as a buffer for the conditioning (voltage and frequency regulation) of the wind energy, while the hydrogen serves mainly as a backup to be converted back into electrical energy in the event of a prolonged calm or to cover a brief peak load via the PEM fuel cell system. In this way h2herten’s energy needs can be covered at all times using regenerative energy, independently of the national grid.

The hydrogen generated in the plant will also be used to supply a planned hydrogen fueling station. And the heat generated in all of these processes can be reused for energy purposes, considerably increasing the plant’s efficiency.

Core of the plant – the Energy Complementary System

The main purpose of the project was to develop and integrate the Energy Complementary System (ECS).

This can be divided into three functional levels:

  1. Energy conversion: Alternating current (AC) converted into direct current (DC) using rectifiers, and into hydrogen using the electrolyser.
  2. Energy storage: Short-term storage of direct current in batteries, and medium- and long-term storage of hydrogen in pressurised containers.
  3. Reconversion: Battery DC converted into AC and hydrogen by inverters, either using fuel cells and inverters or also into AC using a hydrogen internal combustion engine (HICE) and generators.

Key components of the ECS

The core components of the Energy Complementary System are the alkaline electrolyser for producing hydrogen, the PEM fuel cell system for generating electric power, the ionic compressor for pressurising the hydrogen, and the two energy stores – the lithium-ion battery bank and the hydrogen tank.

When the plant was built, care was taken to ensure that the components selected were available on the market and that their durability, robustness, and reliability had already been tried and tested in other projects and applications. New components were developed only where there were no comparable products on the market, which was the case with the power electronics in particular (supplied by Gustav Klein GmbH).

Electrolyser

An industrial electrolyser (supplied by Hydrogenics), with its robust, reliable and highly efficient operation, is used. The alkaline electrolyser, which was actually designed for constant operation, is used dynamically in the ECS due to the fluctuating wind energy and resulting short-term load requirements. When operated at full power, the electrolyser can generate up to 30 Nm3 of hydrogen per hour, with an outlet pressure of 10 bar (145 psi) and high quality (performance).

Fuel cells

A PEM fuel cell system (also supplied by Hydrogenics) is used for reconversion into electrical energy, as this is the most suitable option for the dynamic requirements of the energy supply system when compared to other types of fuel cell. The fuel cell system delivers a peak output of 50 kW.

In order to ensure that the reconversion process can be carried out while running the fuel cells at an optimum operating level, and gathering experience with other systems, a combustion-driven hydrogen generator is planned for use in reconversion alongside the fuel cells. However, this will not be integrated into the system until a later date.

Compressor

To make it possible to store the hydrogen gas generated by the electrolyser in the hydrogen tank in the required quantities, it has to be compressed to 50 bar (725 psi). This is carried out using a so-called Ionic Compressor, supplied by Linde. Instead of the fixed (metal) piston, as in a conventional compressor, the hydrogen is compressed using an ionic liquid in this system. The advantages of this type of compressor are a higher level of efficiency, higher compression performance, and lower maintenance requirements. The compressor has a capacity of 30 Nm3 per hour, with inlet pressure of 5–10 bar and output pressure of 50 bar.

Battery storage

Modern lithium-ion batteries with a capacity of 30 kWh (supplied by Saft) are used for the short-term electricity storage facilities. The batteries serve first and foremost as a buffer, to condition and stabilise the electricity network. They have a peak output of 50 kW.

Hydrogen storage

The hydrogen tank (supplied by Vako GmbH) provides medium- to long-term energy storage. The hydrogen generated in the electrolyser and to be used for reconversion into energy is stored in a tank 22 m high, which has been built next to the application centre. It has a capacity of 115 Nm3 with accumulator pressure of 50 bar. This gives around 5300 Nm3 or 470 kg (1036 lb) of H2.

Efficiency and availability

In simulated operations, the efficiency of the plant overall lies between 58% and 70%, depending on to what extent the heat lost through the various conversion processes (and which is not currently utilised) is included. Assessments of the plant’s actual operations will be required in order to make any binding statement on the actual degree of efficiency.

An availability value of at least 90% is targeted. Technical downtime and maintenance have already been built into this figure. In any case, it will not be possible to know what the effects of the plant’s dynamic operations will be on the individual components until day-to-day operations begin.

Acknowledgments

This project is funded by:

The White Paper on which these articles are based was written by Alexandra Huss of AKOMBE Technologie- & Marktkommunikation (Cologne, Germany), and published in March 2013 by Anwenderzentrum h2herten GmbH.

In Part 1: The development of the h2herten application centre.

In Part 3: Differences from other model projects in the field of wind power electrolysis.

Technical contacts:

Peter Brautmeier and Dieter Kwapis at the h2herten application centre

Prof. Dr.-Ing. Karl H. Klug at the Westphalia Energy Institute

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Energy efficiency  •  Energy infrastructure  •  Energy storage including Fuel cells  •  Green building  •  Wind power

 

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