This refers to the percentage of expected yearly energy curtailment, relative to the yearly total generated or consumed energy. E.g. a “5% flexibility level” photovoltaic generation unit that could generate 100GWh of energy on an annual base will only be able to inject on average 95GWh each year into the Elia grid. At certain critical moments it will be required to reduce the production level of this photovoltaic generation unit due to grid constraints.