However, the intellectually coherent manner to proceed towards this internalisation would have been to tax the externality itself, i.e. to impose taxes on GHG emissions and the use of imported fuels, rather than to impose certain technologies on the market. Guaranteeing long-term revenues to VREs only, whether through feed-in tariffs or other instruments, is thus at the origin of the technical and pecuniary externalities that are created by the variability of wind and solar PV. This reduces the profitability of alternative means of electricity production, which nevertheless remain indispensable to ensure the security of supply and thus will require additional revenues through capacity mechanisms.