Why is the value sometimes a few mHz off 50?

Even tiny imbalances move frequency: a 100 MW shortage in CESA shifts it about 5 mHz. FCR / aFRR continuously correct, so the value stays in a tight band around 50 Hz under normal conditions.

Why is this Estonia-only when CESA shares one frequency?

CESA is synchronous, so any one PMU in the area gives a representative number. We publish the Estonian PMU value (sourced from Elering); Portugal would publish a virtually identical curve.

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Estonia grid frequency

Name: Estonia grid frequency
Creator: Volton
License: https://creativecommons.org/licenses/by/4.0/

Real-time AC frequency on the Estonian grid, which has been part of the Continental European Synchronous Area since 9 February 2025. The whole CESA shares one frequency in real time — Estonia and Portugal see the same number. Sourced from Elering, downsampled to 5-min mean and refreshed hourly.

Concepts

CESA (Continental European Synchronous Area)System imbalance / FRCE FCR (Frequency Containment Reserve)

Methodology

AC frequency is the heartbeat of the grid: nominal 50 Hz means generation exactly matches consumption. When generation exceeds consumption, frequency rises; shortage pushes it down. FCR responds within 30 s to keep the system inside ±200 mHz; aFRR brings it back to 50.000.

Sample rate here is downsampled to 5-min averages so the page is light to load. Volton samples at higher resolution internally for trading; the public feed is the 5-min mean.

FAQ

Why is the value sometimes a few mHz off 50?: Even tiny imbalances move frequency: a 100 MW shortage in CESA shifts it about 5 mHz. FCR / aFRR continuously correct, so the value stays in a tight band around 50 Hz under normal conditions.
Why is this Estonia-only when CESA shares one frequency?: CESA is synchronous, so any one PMU in the area gives a representative number. We publish the Estonian PMU value (sourced from Elering); Portugal would publish a virtually identical curve.

Get this data

JSON download and stable URL pattern available on the developer API page.

↓ JSON API docs →https://public-data.volton.energy/v1/grid-frequency/latest.json

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