Stationary Systems for Seasonal Energy Storage

During the 1990s, many RFC systems for the storage of regeneratively produced electricity were tested at different locations. One of the first systems was tested in California and consisted of an alkaline bipolar electrolyzer operated at 790 kPa. 

The oxygen that was produced during electrolysis was not used in the system. A PEFC was used for the reconversion of the hydrogen into water. The system was constructed in June 1991 and went into full-time automatic operation in August 1993, and was subsequently operated for more than 3900 h [94]. 

Lead acid batteries were used for short-time energy storage. For the seasonal storage, the electrical energy is converted in an alkaline electrolyzer with 30% KOH solution operated at 80 °C and a pressure of700 kPa. After electrolysis, the hydrogen thus produced is compressed to a pressure of 15 MPa and oxygen is compressed 

Initially, an AFC with a maximum power of 6.5 kW was used in the system. However, owing to problems with automatic operation, the complex design and losses of the liquid electrolyte, a 5 kW PEMFC stack was later integrated into the system [19, 96]. 

Another regenerative system was also tested in Neunburg vorm Wald, Germany [20]. Similar components were tested in this project, but the focus was on the supply of hydrogen for different applications and not on the seasonal storage of energy. 

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