Entry · Water
ENA: Natural inflow energy
How much energy would the water reaching the reservoirs allow to be produced?
Acronyms: ONS, National Electric System Operator.
In one sentence
Energy that can be produced from the natural flows into the reservoirs, calculated by the ONS with the productivities of the plants at 65% of the useful volumes.
Real example
On Sep 28, 2026, the gross ENA of the South was 242.8% of the MLTNature of the data: Observed; over 30 days (sum of ENA over sum of MLT), 253.4%Nature of the data: Calculated.
No Check this number record of its own in this example: the number comes from the panel's published database, which carries the source and the reference date.
Observed: Value published directly by the official or primary source. Calculated: Deterministic transformation made by Scrutiniums, with a published formula.
Why it matters
How it is measured
Gross ENA: product of the natural flows by the productivities of the plants at 65% of the useful volumes. Published by day in energy (columns ending in _mwmed; the ONS data dictionary describes the unit as MWmonth) and as a percentage of the long-term average (MLT).
Unit: energy (MWmonth, according to the ONS dictionary) or percentage of the MLT
Not to be confused with
EAR is the energy associated with the water already stored in the reservoirs; ENA is the energy that the arriving natural flows would allow to be produced. An ENA above the MLT does not say, by itself, how much is stored.
ENA is the value for the period; the MLT is the reference with which the ONS publishes it as a percentage. The dataset does not report the reference period of the MLT; that is why, in the panels, "above usual" comes from the historical distribution, not from the MLT.
What cannot be concluded
- The dataset does not report the reference period of the MLT.
Related entries
In the learning paths
Official source
ONSOpen data portal, dataset “ENA Diário por Subsistema” (description and data dictionary)
Literal excerpt from the document
Portuguese only“A Energia Natural Afluente (ENA) Bruta representa a energia produzível pela usina e é calculada pelo produto das vazões naturais aos reservatórios com as produtividades a 65% dos volumes úteis. A ENA Armazenável considera as vazões naturais descontadas das vazões vertidas nos reservatórios. [...] os dados podem servir de insumo para estudos energéticos e projeção do custo marginal de operação.”
Documents accessed and text checked on Sep 28, 2026.