The learning-curve concept is considered to be an important tool for predicting the future costs of renewable-energy technology systems. This paper sets out the underlying rationale for learning-curve theory and the potential for its application to renewable technologies, such as photovoltaic-module and wind-power generator technologies. An indication of the data requirements for carrying out learning-curve projections is given together with an assessment of the requirements necessary, for an analysis to be undertaken of the application of learning curves to other renewable-energy technologies. The paper includes a cost comparison and a figure-of-merit criterion applicable to photovoltaic-module and wind-power-turbine technologies.