Impact assessment of policy instruments is an important element of the policy development process. It represents a systematic attempt to shed light on the possible effects of policy proposals. This paper assesses the impact of two representative policy instruments, namely energy-related Demonstration and Deployment (D&D) programmes and a carbon-equivalent (C-eq) tax, on attainability indicators in the areas of climate change and security of energy supply, two important dimensions of sustainable development. Specifically, we pay attention to the effectiveness of these policy instruments in stimulating technological change that could lead to a more secure and climate-benign global energy system in the long-term future. Although the numerical results presented here are specific to our particular analysis and highly dependent on the characteristics and limitations of our modelling tools, we offer this analysis as a contribution towards the development of more comprehensive methodologies for the assessment of impacts of policy instruments in the context of the quest towards a sustainable global energy system.