The best hour by hour stack paid one megawatt €17,621 in October 2025, €7,557 at the low point, and €13,339 in September 2026

The ceiling, month by month

In each hour the megawatt is sold into FCR-N, which covers both directions, or once upward and once downward into the best of the other markets, whichever pays more, and only into a market in which Fingrid bought something that hour. The bar is the month’s sum. It fell from €17,621 in October 2025 to between €7,557 and €13,339 a month since the turn of the year, while Fingrid’s count of batteries went from 1,215 to 2,057 MW.

The grey bar is a part month. A market enters the stack only in an hour in which its price and its volume are both in Fingrid’s files and Fingrid bought something.

Each market on its own

One megawatt sold only into that market, every month, on one scale so the markets can be read against each other. The single figures must not be added: a megawatt cannot be in two markets at once, except one up and one down, which is what the pairs below count.

The markets are filling up

Fingrid buys a roughly steady volume of upward fast reserve each hour, FCR-N, FCR-D up and FFR together, while the batteries able to sell it keep arriving. The line is Fingrid’s installed battery total divided by that upward volume in the same hours: 5.5 megawatts of batteries for every megawatt bought in October 2026, from 4.0 in March 2026. Counting aFRR up and mFRR up as well, which are slower products that other plant also sells, the ratio is 2.6 in the same month.

The ratio as a table

Month	Installed, average MW	Upward reserve bought, average MW	Ratio	Ratio with aFRR and mFRR up
March 2026	1,253	312	4.0	1.8
April 2026	1,274	312	4.1	1.9
May 2026	1,336	357	3.7	1.8
June 2026	1,597	354	4.5	2.0
July 2026	1,614	364	4.4	1.7
August 2026	1,639	338	4.8	1.9
September 2026	1,982	360	5.5	2.6
October 2026 (part)	2,020	364	5.5	2.6

The last twelve months, as a table

Euros for one megawatt, by Finnish month, before any cost. Every month and market as a CSV · the ratio as a CSV.

How each figure is made

Each row of a Fingrid price file has a start, an end and a price in euros per megawatt per hour; the money for one megawatt in that row is the price times the row’s length in hours, put in the month in which it starts, in Finnish time. A row counts only if Fingrid bought some volume in that market in that hour: if it bought nothing, no battery was paid, whatever price is shown, and an hour with no row earns nothing. The pair figures add the up side and the down side, because a battery can hold one megawatt up and one down in the same hour. The ceiling takes, for every hour, the better of FCR-N or the best upward product plus the best downward one. A second calculation written separately checks every figure before it is published.

When Fingrid uses a reserve it pays for the energy too: €65.7m for upward mFRR energy in the twelve months to September 2026, and €19.6m for upward aFRR energy

Everything above is what Fingrid pays to have a reserve held ready. When it calls on one it also pays for the energy delivered, at a price it publishes every quarter hour alongside the volume it activated across the whole market. Fingrid does not publish what any battery delivered, so this money cannot be put on one megawatt and is shown here as the size of the pot: the price times the activated volume, summed over the month. A battery’s share depends on its bids and its availability. The largest pot is upward mFRR energy, the manual reserve Fingrid activates to balance the system, which paid the market €11.8m in January 2026 at a volume-weighted €228 per megawatt hour.

Upward mFRR energy, euros paid by Fingrid to the market each month: Fingrid’s quarter-hour marginal price (dataset 244) times the activated power it reports (375, the quarter hour’s maximum) times a quarter hour, so each month is at most this. The grey bar is a part month. Every market, up and down, is in the table below.

Downward energy runs the other way: a battery that charges on Fingrid’s instruction pays the downward price, and is paid when that price is below nought

Downward activation means Fingrid asks a provider to take energy off the system. A battery doing so charges, and pays the published downward price for the energy; when the price is negative it is paid to charge. Over the twelve months to September 2026 the downward mFRR energy pot was €6.0m and the downward aFRR pot €2.3m, both paid by providers to Fingrid where positive. A month below the line is one in which providers were paid, net, to take energy.

Downward mFRR energy: Fingrid’s downward marginal price (dataset 106) times the activated downward power (376) times a quarter hour, with the price’s sign. Fingrid gives downward volumes as negative numbers; they are taken by size.

The imbalance price: a median of €12 in September 2026, below nought in 31% of quarter hours

A battery that delivers more or less than its schedule is settled at the imbalance price, so this is the price of being wrong. It was highest in February 2026, a mean of €118 with 17% of quarter hours above €200, and it was negative most often in September 2025, 46% of quarter hours, when being long paid rather than cost. The band is the middle four fifths of each month’s quarter hours, the line the median and the dot the mean; the mean sits above the median because the highest quarter hours are far above the rest.

The imbalance price as a table

Month	Mean	10th percentile	Median	90th percentile	Below nought	Above €200
October 2026 (part)	€34	−€2.22	€7.62	€102	25%	3%
September 2026	€52	−€7.2	€12	€157	31%	5%
August 2026	€43	−€5.21	€17	€142	25%	1%
July 2026	€12	−€9.73	€2.99	€49	39%	0%
June 2026	€46	−€5.51	€26	€128	23%	2%
May 2026	€57	−€18	€30	€160	28%	5%
April 2026	€42	−€20	€13	€150	32%	2%
March 2026	€27	−€20	€10	€94	30%	1%
February 2026	€118	€5	€99	€250	6%	17%
January 2026	€115	€0	€97	€250	10%	15%
December 2025	€30	−€19	€13	€95	34%	1%
November 2025	€50	−€22	€20	€152	35%	5%
October 2025	€54	−€20	€8	€146	41%	5%
September 2025 (part)	€32	−€51	€3.99	€150	46%	5%

Fingrid, dataset 319, the imbalance price for single price, single position settlement, every quarter hour, euros per megawatt hour, by Finnish month.

The energy pots, as a table

Euros paid for energy each month across the whole market, and the volume-weighted average upward price. Every market and month as a CSV · the imbalance price as a CSV.

FCR-N energy is paid too (datasets 420 and 421), at the imbalance price or a floor, on the energy each provider’s reserve delivered; Fingrid publishes the price and not the volume, so no pot is summed for it. Source: Fingrid open data, CC BY 4.0, read 18 October 2026; the calculation is fi/tools/energy.py in the repository, checked against a second calculation in pandas.

What is left out

Energy trading on the day-ahead and intraday markets, which batteries of two hours and more depend on, because those prices are Nord Pool’s and may not be shown here. A battery’s share of the energy pots above, because what each battery delivers is not published. Fingrid’s yearly FCR contracts, bought at prices not in the open data. Availability, degradation, the optimiser’s share, grid charges and imbalance costs, none of which is taken off. Whether a one-hour battery can offer its whole megawatt to every product under Fingrid’s rules for limited energy reservoirs, which have not been read. So these are the most a megawatt could have been paid, and a real battery earns less.

Source: Fingrid Oyj open data, CC BY 4.0, datasets 317 and 316 (FCR-N price and volume), 318 and 315 (FCR-D up), 283 and 281 (FCR-D down), 277 and 276 (FFR), 52 and 1 (aFRR up), 51 and 2 (aFRR down), 329 and 327 (mFRR up), 330 and 328 (mFRR down), and 424 (installed battery capacity), read 18 October 2026. The figures are calculated by Vitreous from Fingrid’s prices and volumes; Fingrid has not checked them. The method is in the repository as fi/hand/revenue-method.md and the calculation as fi/tools/revenue.py.