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July 2013 Issue

Electrolysis for Efficient Offshore Wind Energy Storage
Dr. Graham Cooley

There has always been a mismatch between energy supply and demand. Conventionally, supply met demand by turning thermal power plants off and on, but as we integrate more intermittent renewables into the energy mix, supply becomes increasingly governed by, for example, the strength of the wind.

It is difficult for electricity grid operators to accept wind power at times of low electricity demand. Unfortunately, even at today’s low level of renewable energy generation in the U.K. (less than 10 percent capacity), we frequently experience curtailment events, where renewable power is not utilized. This usually incurs a penalty—payment to a wind farm operator not to generate. Without a steep change in energy storage availability, there is little chance of reaching the ambitious renewable targets of the U.K., which stipulate that 15 percent of the country’s energy demand be met with renewable sources by 2020.

Electrolysis could have a significant role to play in enabling more renewable energy to be accepted by the electricity grid. At times of excess electricity supply, electrolyzers can convert electricity into hydrogen at high efficiency by splitting water into hydrogen and oxygen gases. The hydrogen can be exported from the electricity sector to the transportation or gas sectors, potentially seeding an infrastructure of clean fuel for hydrogen vehicles or enabling bulk energy storage in the natural gas grid.

At times of high electricity demand, the electrolysis systems can be turned off, thereby relieving pressure on the network. Control over multiple electrolyzer plants can be exercised by electricity grid operators or utility companies remotely.

Power-to-gas is an energy conversion and storage process that involves electrolysis, allowing electricity to be held in reserve in the megawatt range. Existing network infrastructures could be utilized by linking power and natural gas grids, allowing the storage of significant amounts of power in the gas grid and the provision of CO2-neutral fuels in the form of the resulting gas derived from renewable energy.

The generated hydrogen can be stored temporarily or sold to the gas network when importers pay a premium. When electricity demand suddenly rises, power-to-gas would improve fuel security.

The process involves renewable power and water being consumed by an electrolyzer, which splits the water into hydrogen and oxygen. The hydrogen is then stored or transferred immediately to the existing natural gas network or a local industrial heat process, while the oxygen is vented. There is also the option to synthesize methane using a CO2 stream, or methanation.

A PEM (polymer electrolyte membrane) electrolyzer can respond to a change in electrical input in less than 1 second and is thus best suited to absorbing fluctuations in supply. The electrolyzer does not consume energy when it is not required, and takes minimum time and energy to start generating hydrogen, thus making it a very efficient means of supply-demand matching.

Power-to-gas systems are suitable for hybridization with other forms of energy storage technology. For example, battery storage may be discharged to the electrolyzer during periods of low wind.

Power-to-gas would have a significant impact on the renewable energy market, with benefits such as encouraging wind and solar farm proliferation, which would spur job creation. It would help suppliers offset transient wholesale price rises and could lead to lower electricity and domestic gas prices. Environmental benefits include reduced CO2 and sulfur-oxide emissions.

An example of this technology is ITM Power’s (Sheffield, England) electrolyzers, which use a modular design: a 1-megawatt system comprising up to 16 electrolyzer stacks. In response to varying load requirements, each stack can be turned up and down dynamically, either independently or coordinated. This provides tremendous flexibility for system operation and maintenance. Integration with an overarching energy management system enables real-time decisions to be made as to optimal operational mode and overall efficiency.

Each stack has a conversion efficiency exceeding 75 percent at full load, higher at part load. Owing to the higher operating pressure of the stacks, there is no need for a compressor for gas grid injection. This eliminates the energy consumption associated with an external compressor and significantly reduces system maintenance.

The power industry can deploy and control the operation of these units to valley fill local electrical-load profiles, ensuring that wind farms never need to be shut down. Unlike other forms of energy storage, there is no need to reconvert the stored energy to power or to control the timing and duration of power transfer.

The electrolyzer can operate at any time, absorb various power levels up to 1 megawatt and cycle several times per day if required. It can provide up to 24 megawatt-hours of storage daily. The generated hydrogen would be directed to the natural gas grid to reduce the carbon footprint of gas turbines, boilers and other gas-fired heating equipment.

ITM Power’s technology is currently being deployed in a number of projects. Its first refueling station is situated at the energy technology building at the University of Nottingham. ITM is currently building two refueling stations on the Isle of Wight and has also sold a power-to-gas energy storage unit to the Thüga Group (Munich, Germany). The first deployment of a refueling station in the U.S. is set to take place very soon.

Graham Cooley joined ITM Power as CEO in 2009. Before that, he was business development manager at National Power plc and spent 11 years in the power industry developing energy storage and generation technologies. His previous positions also include CEO of Sensortec Ltd., founding CEO of Metalysis Ltd., a spin out from Cambridge University, and founding CEO of Antenova Ltd.


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