The geological subsurface offers large potential renewable energy storage sites through cavern or porous media storage systems. This work presents a methodology for assessing the size of the storage systems required, for modelling the storage operation and for predicting the induced effects and impacts on the environment by numerical simulations. The methodology is demonstrated for a hypothetical porous medium hydrogen storage and for geothermal heat storage. It is found that induced pressure effects may range over kilometers for gas storage, while temperature effects are limited to a few tens of meters for heat storage.