Ancillary services: how Energinet pays for grid balance

Ancillary services are the reserves Energinet — the Danish transmission system operator — buys to keep the power grid stable at 50 Hz. When production and consumption drift apart, reserves such as FCR-D, FCR, aFRR, mFRR and FFR pull the frequency back into place. Providers are paid for standing ready, and through an aggregator, ordinary households can take part and earn a share of that payment.

Why the grid needs reserves

Electricity cannot easily be stored in the grid itself: production and consumption must match at every moment. The grid frequency shows how well they match — 50 Hz means balance, and every deviation means someone must react fast. Why the frequency must stay at exactly 50 Hz is covered in our guide to grid balancing. Because no power plant or consumer reacts instantly on its own, Energinet buys reserves in advance: capacity that stands ready to respond automatically or on request.

The five reserve types, briefly

The reserves differ mainly in how fast they react and how long they run. From fastest to slowest:

FCR-D — the reserve NM1 delivers

FCR-D (Frequency Containment Reserve — Disturbances) is a Nordic reserve that reacts automatically when the frequency leaves its normal band — for example when a large power plant or an interconnector suddenly fails. Enrolled devices respond within seconds and hold the frequency until slower reserves take over. This is the service NM1 sells to Energinet on behalf of households, through daily auctions — one for every hour.

FCR — the everyday workhorse

FCR (Frequency Containment Reserve) handles the small, constant deviations of normal operation. It responds automatically within seconds and keeps the frequency close to 50 Hz minute by minute.

aFRR — automatic restoration

aFRR (automatic Frequency Restoration Reserve) activates within minutes, steered by a signal from the transmission system operator. Its job is to bring the frequency all the way back to 50 Hz and free up the containment reserves for the next event.

mFRR — the manual backstop

mFRR (manual Frequency Restoration Reserve) is activated on request when an imbalance lasts longer. It is the slowest of the reserves and relieves the faster, automatic ones so they are ready again.

FFR — the sprinter

FFR (Fast Frequency Reserve) is the fastest reserve, reacting in around a second. It supports the Nordic grid in situations with little inertia — for example when few large, rotating power plants are running and the frequency can move quickly.

How Energinet buys ancillary services

Energinet buys the reserves in auctions. For FCR-D, the auctions are daily — one for every hour of the following day. Providers bid the capacity they can guarantee, and those who win are paid for standing ready in those hours. Prices vary from hour to hour and from day to day with supply and demand.

Earnings depend on, among other things, market prices, Energinet's needs, regulation and your own consumption and equipment, and they can change over time. FCR-D prices are set in daily auctions. Historical earnings are no guarantee of future earnings.

How households take part

A single household is far too small to bid on its own — bids are measured in megawatts. The way in is aggregation: an aggregator pools many small devices into one virtual power plant (VPP) and bids their combined flexibility into the auctions.

That is what NM1 does. We aggregate household devices — electric heating elements and hot water tanks, heat pumps, and home batteries — and sell their flexibility as FCR-D to Energinet. Activations are short, typically seconds to minutes, and designed not to affect comfort or equipment. Earnings are shared with you — see calculate your earnings — and paid out quarterly as an ordinary bank transfer. NM1 has been live since June 2025 — and is one of the only aggregators running heating devices at scale.

See which devices can join and which brands we connect, or try the earnings calculator to find out what your home could earn.