mFRR (Manual Frequency Restoration Reserve)

mFRR is the manually activated frequency restoration reserve. The TSO's control-room operator picks individual bids from a merit-order list and dispatches them by phone or via API. mFRR releases aFRR back to its working range and takes over for sustained imbalances that aFRR cannot handle alone. Full delivery is required within 12.5 minutes of activation.

Activation pattern

mFRR is the slowest and least automated of the three operating reserves but also the most flexible product to bid into. Bids come in two flavours: scheduled (committed for a specific block of trading periods) and direct activation (available on call but not pre-committed). Estonian BSPs typically bid into both. Activation prices in Estonia are dominated by sustained system imbalances after wind forecast errors and large generator outages.

Why it matters most for Estonian batteries

mFRR capacity revenue is currently the single largest revenue line for grid-scale BESS in Estonia. The market is shallow enough that a 5–10 MW battery materially moves marginal price; 1–2C duration is the sweet spot, since mFRR activations rarely run longer than two hours. Stacking — bidding the same MW into mFRR capacity and aFRR/FCR simultaneously and re-allocating where dispatched — is what separates a 12% project IRR from 22%.

MARI and the EU integration roadmap

MARI (Manually Activated Reserves Initiative) is the European platform that does for mFRR what PICASSO does for aFRR — pool activation across all Continental TSOs into a single merit order. (TERRE is a separate platform, for Replacement Reserves.) The three Baltic TSOs (Elering, AST, Litgrid) connected to MARI on 10 October 2024, joining the German TSOs and ČEPS who went live in 2022. Estonian mFRR activations now flow through MARI's pan-European merit order, expanding the pool of bids available to Elering's control room beyond the Baltic-only market.