Abstract If geothermal resources are utilized excessively for electricity production, the reservoir can be temporarily (almost) depleted. Regeneration of an overutilized resource can take a long time. This paper presents a System Dynamics model for geothermal power plant expansion considering the dynamics of geothermal resources on a system’s level. The model consists of three main modules: resource dynamics, plant construction, and geothermal economics. Thereby, it captures the following dynamics: The geothermal field stock decreases due to utilization for electricity production and increases through natural recharging. Changes in geothermal stock, and thus in well production capacity, lead to additional well requirements to maintain electricity production levels. This influences the unit cost of electricity. To show the effect of geothermal resource dynamics on a national system’s level the model is applied to Iceland’s geothermal resources. Four main scenarios are simulated and compared based on the level of resource utilization, assuming high and low demand growth (i.e. 2% and 4.4%), and whether geothermal resource dynamics are incorporated or not. Sensitivity analysis is performed with respect to well capital cost and natural recharging rates for geothermal fields. The findings indicate that geothermal resource dynamics significantly increase costs because of the well drilling activities that are required to maintain production.