  Conventional energy production based on fossil fuels causes emissions which
contribute to global warming. Accurate energy system models are required for a
cost-optimal transition to a zero-emission energy system, an endeavor that
requires an accurate modeling of cost reductions due to technological learning
effects. In this review, we summarize common methodologies for modeling
technological learning and associated cost reductions. The focus is on learning
effects in hydrogen production technologies due to their importance in a
low-carbon energy system, as well as the application of endogenous learning in
energy system models. Finally, we present an overview of the learning rates of
relevant low-carbon technologies required to model future energy systems.
