TSO (Transmission System Operator)
A Transmission System Operator runs the high-voltage backbone of an electricity grid — typically 110 kV and above — and is responsible for keeping it in second-by-second balance. In Estonia, Elering is the TSO; it operates cross-border interconnections, runs the balancing market and certifies BRPs and BSPs.
A Transmission System Operator (TSO) sits at the top of the European grid hierarchy. It does not sell electricity, does not own generation in most jurisdictions, and is structurally separated from retail supply. What it does instead is run the physical infrastructure that every other market participant depends on: the high-voltage backbone, the cross-border interconnections, and the second-by-second balancing of supply and demand on its control area.
Three core functions
First, operate the transmission grid — typically everything 110 kV and above in Estonia, including the Estlink HVDC links to Finland and the synchronous interconnections to Latvia. Second, keep system frequency at 50 Hz in real time by procuring and activating balancing services (FCR, aFRR, mFRR). Third, settle imbalances financially: every Balance Responsible Party (BRP) submits day-ahead schedules to the TSO and pays for any deviation between schedule and physical reality.
Estonia: Elering
The Estonian TSO is Elering, a state-owned (100% Republic of Estonia) joint-stock company. Elering certifies BSPs and BRPs, runs the Estonian leg of the Baltic balancing-capacity procurement (jointly with AST and Litgrid), and operates the imbalance-settlement clearinghouse via Datahub. The Baltic states disconnected from the Russian IPS/UPS grid on 8 February 2025 and synchronised with the Continental European grid on 9 February 2025.
Why TSOs are regulated monopolies
Every EU Member State has one TSO per control area, regulated under the Third Energy Package and unbundled from generation and supply. The economic logic: building a parallel transmission grid is uneconomic, so the natural-monopoly infrastructure is operated by a regulated entity with cost-plus tariffs set by the regulator. In Estonia, those tariffs are approved by Konkurentsiamet (the Competition Authority).
Usein kysyttyä
- What is a Transmission System Operator (TSO)?
- A TSO operates the high-voltage transmission backbone of an electricity grid — typically 110 kV and above — and is legally responsible for keeping it in second-by-second balance. The role is defined in EU Directive 2019/944 Article 2(35) and includes operating cross-border interconnections, maintaining grid frequency at 50 Hz, procuring balancing reserves and certifying market participants.
- Who is the TSO in Estonia?
- Elering is the Estonian TSO. It operates the 110 kV+ transmission grid, the EstLink interconnections to Finland and the cross-border lines to Latvia and Lithuania, runs the Baltic balancing market jointly with AST (Latvia) and Litgrid (Lithuania), and certifies BRPs and BSPs. Since the 9 February 2025 synchronisation, Elering operates as part of the Continental European LFC block.
- What's the difference between a TSO and a DSO?
- TSO operates high-voltage transmission (110 kV and above in Estonia); DSO operates lower-voltage distribution (0.4 kV to 35 kV). The TSO is one entity per area; multiple DSOs typically exist within that area. In Estonia, Elektrilevi (owned by Eesti Energia) serves ~87% of customers across ~95% of the country; Elering is the sole TSO.
- How does the TSO make money?
- Through a regulated transmission tariff applied to grid users (BRPs and DSOs), approved annually by Konkurentsiamet. The TSO is legally required to be financially neutral on balancing operations (EBGL Article 44) — the neutrality component on imbalance prices recovers any residual cost so the TSO neither profits nor loses on the balancing function itself.