The characterisation of the performance of energy systems in terms of efficiency and environmental impact is crucial for the validation of the static and dynamic models that we develop and for the quantification of the related uncertainties. At BRITE, we work on both pilot-scale and full-scale measurements of the performances of windmills and heat & power production units, at small, medium and large scales. We combine conventional and advanced measurement techniques and we collaborate with industrial partners to ensure that our data-driven models are in line with reality, and ready for robust optimisation.