A flexible power system responds quickly to changes in external conditions; therefore, if it is supposed to make a power system more flexible, it must react to excessive fluctuations in electricity generation and consumption. Electrolyzers must be flexible by themselves to be considered as a flexible source for power systems. An electrolyzer's flexibility can be characterized by load flexibility, cold start-up time, warm start-up time, the heating curve, the potential for part-load operation, and load variation during shutdown and start-up. The purpose of this chapter is to discuss electrolyzers and their potential as a source of flexibility in power systems. To achieve this, various types of electrolyzers are reviewed and compared from energy, economic, environmental, and technological perspectives. Next, the characteristics and potential of electrolyzers for flexible power systems under variable supply and demand will be discussed. On-grid hydrogen production will be discussed under dynamic conditions, and the impact of dynamic operation on the efficiency, safety, degradation rate, etc. The methanation as a P2G approach will be addressed briefly. The economics of electrolyzers and the policies concerning on-grid electrolyzers will be presented. The technical challenges of utilizing electrolyzers, along with the associated environmental considerations and case studies, will be addressed.
