Conception of a new 4-quadrant hydrogen compressed air energy storage power plant with an integrated electrolyzer

A hydrogen compressed air energy storage power plant with an integrated electrolyzer is ideal for large-scale, long-term energy storage because of the emission-free operation and the possibility to offer multiple ancillary services on the German energy market. This paper defines analyzes such a storage concept and conducts an extensive comparison with four additional storage concepts based on various criteria. The results show that the combination of storing compressed air and hydrogen offers a higher efficiency than storing only hydrogen and lower specific investment costs than storing only compressed air. This result is confirmed with analysis of the optimal sizing of each power plant component for simultaneous participation on multiple energy markets with a linear optimization dispatch mode. The hydrogen compressed air energy storage (HCAES) power plant can utilize more revenue possibilities than a hydrogen energy storage because of the higher round-trip efficiency and the combination of the air compressor and the integrated electrolyzer during charging mode. The integration of the electrolyzer, however, offers a couple of challenges itself because of the highly flexible operation mode. A new concept for the controllable 24-pulse diode-thyristor rectifier of the electrolyzer is presented, that uses mostly common components while offering little to no grid harmonics and a long lifetime. The flexible integrated electrolyzer allows for the 4-quadrant operation of the storage power plant.