holatarolo.hu shows measured data from Hungary's grid-scale batteries. This page explains where the data comes from, what is measured and what we calculate, and what the words mean. Wherever something is not our own calculation, the source is given next to it.
The batteries' charging and discharging is measured data (MAVIR), but it is not live: the page shows the latest complete day. Whatever we calculate from prices and measured data — the revenue, the ratios — is labelled as a calculated value. There is no measured data on home batteries.
Where does the data come from?
These are our sources, and for each one we say what we take from it.
- Storage: MAVIR chart 22361 (“Energiatárolók”, energy storage). MAVIR, the Hungarian transmission system operator, publishes the measured discharge and charge of grid-scale batteries every quarter-hour, along with their observable installed capacity. The data goes back to 1 July 2025 (on its publication: villanylap, 18 August 2026, in Hungarian). The daily figures come from MAVIR's daily average power: the average (MW) × the hours in the day = the day's energy (MWh); on the days the clocks change, the day has 23 or 25 hours. MAVIR may revise days it has already published, so a day's figures — and with them the records — can change slightly.
- Solar power, consumption and nuclear: MAVIR chart 20002. Solar power is the sum of three parts of the chart: utility-scale plants, rooftop systems (HMKE, household plants of up to 50 kW) and businesses' panels for their own use (SCTE). Consumption is MAVIR's “Teljes terhelés” (total load) series, nuclear the “Nukleáris erőművek” (nuclear power plants) series. We only use completed days from this chart.
- The exchange price (HUPX day-ahead): energy-charts.info. The Hungarian day-ahead price from energy-charts.info (Fraunhofer ISE), i.e. the HUPX DAM price, in euros per MWh; the price comes from Bundesnetzagentur | SMARD.de, CC BY 4.0. It has been quarter-hourly since 1 October 2025. The same price is also published on the HUPX website; we take it from energy-charts' openly licensed data series.
- Projects, tenders, rules. We collect these by hand from press reports, company announcements and legislation; every item comes with its source: on the map in Where are they? and in the timeline of The boom. The data file can also be read raw: tarolok.json.
- Households. A household uses 2,082 kWh of electricity a year (KSH, the Hungarian Central Statistical Office, 2024; the same constant as on holanap.hu and holadelej.hu): this is what the “What is that in real terms?” comparisons are based on.
Your browser does not call MAVIR or energy-charts itself: our own server fetches the data and caches it so as not to put a load on them — the quarter-hourly storage data for one hour, the background data (consumption and solar power) and the daily storage data for six hours, the price for a quarter of an hour, and the year of prices (for the revenue calculation) for six hours. If a source is not responding, the last good data stays in place. The page refreshes every half hour.
Home batteries are not included: there is no measured data on them (see the frequently asked questions).
Why isn't today shown?
MAVIR does not publish the storage data in real time: a day's data usually appears the next morning (observed on 30 September 2026: the 29th came in between 9:00 and 11:00). Until then, the day's rows are empty. This is a single observation; if the delay turns out to be different at other times, we will correct this page.
That is why the page shows the latest complete day: the one for which every quarter-hour has charge and discharge data (a day has 96 quarter-hours, or 92 or 100 when the clocks change). We do not fill in or estimate a missing quarter-hour: it stays a gap, not a zero, and the daily total is only calculated for complete days. As a result, before about 11:00 the latest day is usually the day before yesterday, and after that, yesterday.
The dot in the header shows the delay. Green (“with the usual delay”) if the last measured quarter-hour ended no more than 72 hours ago; yellow (“MAVIR is publishing later than usual”) if it is older — the latest-day section then says so too. A red dot means that the page itself could not update its data.
The electricity price, by contrast, is live: today's price is available, and — after about 13:00 — tomorrow's too (energy-charts). So the page never claims that the batteries are charging or discharging right now: the measured data is always from the latest complete day.
What does capacity mean?
On this page, “capacity” is the observable installed capacity as seen by MAVIR, in megawatts (MW): the power that the batteries visible to MAVIR can feed into the grid together. On MAVIR's measured chart it was 877 MW in September 2026 (MAVIR, 22361). According to MAVIR's table of installed generating capacity, grid-scale batteries totalled 983.5 MW on 31 August 2026 (MAVIR's installed capacity data, in Hungarian); the two figures do not match, and we use the chart's, because that is the one the measured charge and discharge belong to.
Storage capacity (megawatt-hours, MWh) is a different quantity: it tells you how much energy a battery can hold. On 18 August 2026 MAVIR wrote of “more than 700 MW and 1,400 MWh” (villanylap); the ratio of the two is roughly two hours, and the revenue calculation (see the next section) follows that. We do not estimate the state of charge: the MWh capacity is not known precisely enough for that.
How do we calculate what a battery would earn?
This is a calculation, not a measurement: the revenue from one daily cycle of an imaginary battery at the exchange price.
- The battery is 1 MW / 2 MWh: it fills up in two hours and empties in two hours.
- It runs one cycle a day: it charges for 8 consecutive quarter-hours (2 hours) and discharges during a later, non-overlapping block of 8 quarter-hours. We check every such pair among the day's 96 quarter-hours and pick the one that earns the most — usually the cheapest two hours and a later, expensive two hours.
- It does not return everything it took in: the return ratio is 0.86, the ratio of measured discharge to charge across Hungary's batteries since spring 2026 (0.85–0.87 month by month; calculated from MAVIR's daily data). So 2 MWh charged becomes 1.72 MWh discharged.
- The revenue is the difference between the discharge price and the charging price (prices in €/MWh):
revenue (€) = 1.72 MWh × average discharge price − 2 MWh × average charging price
An example with made-up prices: if the average charging price is 20 €/MWh and the discharge price 200 €/MWh, one cycle earns 1.72 × 200 − 2 × 20 = €304.
The page calculates for tomorrow once prices for all 96 of its quarter-hours are in (after about 13:00), and otherwise for today; below that, the same with the prices of the last 30 days: the daily average, the best and the worst day.
One year. The same for every day of the last 365, from a single energy-charts query. The chart shows each month's average daily revenue (€/MW/day), with the observable capacity alongside; a month with fewer than 7 days (at the edge of the window) is left out, and one with fewer than 20 is drawn faintly and labelled with its number of days. The annual figure per megawatt is the daily average over the last 365 days × 365.
The gap between the best and the weakest month is mainly seasonal: when there is plenty of solar power at midday, midday electricity is cheap and the spread to the evening price is wide; in winter there is little solar power and the spread is narrow. Whether the growing number of batteries is narrowing the spread cannot be told from one year of data — that would take comparing the same season in two different years — so the page makes no such claim.
What is not included: reserve-market revenue (FCR, aFRR — see the glossary) and costs. Real revenue will differ; the calculation is indicative, not investment advice.
The records
- Most discharged and most charged in one day (MWh): from MAVIR's daily data, over the whole period since 1 July 2025; in a tie, the earlier day counts.
- Peak discharge and peak charging (MW): quarter-hourly power; the earlier peak and the newer ones come from different places, see below.
- Largest evening share (%): of the complete days among the last 35, the one on which discharge between 17:00 and 21:00 covered the largest share of consumption.
- Highest capacity (MW): the highest observable capacity seen in the daily data, and the first day it was reached.
The earlier value of the quarter-hourly power peak is recorded in the site's data file (tarolok.json) up to 28 September 2026; newer peaks are looked for in the measured data of the last 35 days, so the data file has to be updated by hand from time to time.
If the latest measured day broke the daily discharge or charge record, or the discharge or charging power record, the latest-day section shows a “New record” notice. A record here always means relative to the data MAVIR has measured since it started in July 2025. MAVIR may revise days it has already published: a day's figures — and with them the records — can change slightly.
How much do they matter?
The question: what share of the grid's evening consumption do the batteries supply, and how much energy do they charge compared with midday solar power? We calculate three ratios, for the latest complete measured day and for each of the past days:
- Of the evening peak: between 17:00 and 21:00 (17:00–20:59), discharge as a percentage of consumption.
- Of midday solar power: between 11:00 and 15:00, charge as a percentage of solar power.
- Of the whole day: discharged energy as a percentage of daily consumption.
Consumption and solar power come from MAVIR chart 20002 (see the first section); the hours are Budapest time. If data is missing for a quarter-hour, the ratio cannot be calculated and is left blank — we do not count it as zero.
It would be tempting to draw, next to consumption, what it would look like without the batteries. But MAVIR's “Teljes terhelés” (total load) series does not say whether it counts charging as consumption. If it does, a “without storage” curve would be double counting; if it does not, it would have to be calculated differently. We cannot tell which, so we draw no such curve — we show ratios that make sense either way.
Nor does the midday ratio claim that the batteries are charging with solar power: the measurement does not say where the energy comes from. It only shows how much energy they charged relative to the amount of solar power.
Glossary
- Discharge
- When a battery delivers energy to the grid (discharging). MAVIR publishes it as non-negative power (MW).
- Charge
- When a battery takes energy from the grid (charging). MAVIR publishes it with a negative sign; the page shows it as a positive number. Charge and discharge can both be non-zero in the same quarter-hour, because not every battery is doing the same thing; so we show the two separately and do not calculate a net figure for the headline numbers.
- MW and MWh
- A megawatt (MW) is power: the rate at which a battery delivers or takes in energy at any one moment. A megawatt-hour (MWh) is energy: how much it can store, or how much it has delivered. 1 MW for one hour is 1 MWh; 1,000 MWh = 1 GWh. Greenvolt's battery at Buj, for example, is 99.8 MW / 288.6 MWh: at full power it could deliver for about three hours (ess-news).
- Observable capacity
- The combined installed capacity (MW) of the grid-scale batteries visible to MAVIR — not the energy they can store. In detail: What does capacity mean?
- Return ratio
- Discharged energy divided by charged energy. Over longer periods it is below one, partly because of the batteries' losses: for Hungary's batteries it ranged between 0.76 and 0.87 month by month from July 2025 to September 2026, and has been 0.85–0.87 since spring 2026 (calculated from MAVIR's daily data). On a single day it can be above one, because the batteries can also release energy charged the day before.
- Cycle
- One charge and one discharge together. In the revenue calculation there is one cycle a day: two hours of charging, two hours of discharging.
- Heat map
- The chart in which each row is a day and each column a quarter-hour. The colour is the net power (discharge − charge): violet where the batteries gave out more than they took in, gold where they charged more; blank space is missing data.
- Day-ahead price, HUPX DAM
- The price of electricity on the exchange — in Hungary, on the HUPX day-ahead market (DAM), set on the day before delivery; tomorrow's price is known after about 13:00. We give it in euros per megawatt-hour (€/MWh); it has been quarter-hourly since 1 October 2025. It is not what households pay (Hungarian household tariffs are fixed): the exchange price shows when the grid has a surplus and when it is short. Source: energy-charts (Bundesnetzagentur | SMARD.de).
- Negative price
- When the exchange price drops below zero: anyone buying electricity then gets paid for it. It happens when there is more electricity than the grid can take — in Hungary, typically in the sunny midday hours (in April 2026 the average price between 11:00 and 15:00 was −1.1 €/MWh). In 2025 there were 281 hours with negative prices, in 2026 up to 28 September 223.5 hours; the lowest price was −500 €/MWh (26 April 2026, 13:15). Calculated from energy-charts data. For the last 30 days, the “Charging at noon” section shows how many quarter-hours had negative prices, how much the batteries charged during them, and what percentage of the 30 days' charging that was.
- aFRR
- Automatic frequency restoration reserve: MAVIR buys capacity that the provider automatically ramps up or down on MAVIR's signal to bring the grid frequency back to normal. Batteries are fast, so besides the price spread the reserve market is their other source of revenue. aFRR accreditation is a condition both for the transmission fee discount (Decree 10/2024 of MEKH, the Hungarian energy regulator, § 42) and for the RRF grant (the call for proposals; both in Hungarian).
- FCR
- Frequency containment reserve: a fast reserve that MAVIR buys at auctions to keep the grid frequency stable. Its price fell as batteries moved in: the monthly volume-weighted price was 5,400–30,200 HUF/MW/h in 2024, and 2,400–11,000 in the first nine months of 2026 (MAVIR auction results, in Hungarian).
- RRF tender
- RRF-6.5.1-23: the 2024 tender for grid-scale batteries, funded by the EU's Recovery and Resilience Facility (RRF). 62 bn HUF, a target of 885 MWh, batteries with at least two hours of storage, a deadline of 30 June 2026; about 50 winners on 25 April 2024. The winners receive 135,000 HUF/kW in support (up to 30% of the cost) and a revenue top-up for ten years (up to 160 €/kW a year). Sources: Portfolio, the call for proposals (both in Hungarian).
Frequently asked questions
Why can't I see today?
Because MAVIR only publishes the storage data after the day is over, usually the next morning. So the page shows the latest complete day; the only live data is the electricity price. The details: Why isn't today shown?
Why did the batteries sometimes return more than they charged that day?
It does happen, for example on 28 September 2026: the batteries can also release energy left over from previous days, and the end of a calendar day is not the end of a battery's cycle (MAVIR, 22361). Over a whole month, though, they have always returned less than they charged: the return ratio has ranged between 0.76 and 0.87.
Where are the home batteries?
They are not included: there is no measured data on them — MAVIR's series for them shows 0.00 MW — and no official total of how many there are. Since 29 August 2026, every stationary battery above 2 kWh has to be registered, and existing ones by 30 June 2027 (Government Decree 131/2026, Greenergy); that will eventually provide data. Under the Home Energy Storage Programme, a state grant scheme, about 57,200 successful applicants are receiving support to install a battery of at least 10 kWh (Telex, HVG; all three in Hungarian); if they are all built, that comes to at least 572 MWh — this is our calculation (57,200 × 10 kWh), not measured data.
Do they charge with solar power?
The measurement does not tell us: MAVIR publishes how much they took from the grid, not where the energy came from. What is visible is that they charge at midday, when electricity on the exchange is cheap: in 2026 up to 28 September, the average price between 11:00 and 15:00 was 58 €/MWh, and between 18:00 and 21:00 207 €/MWh (calculated from energy-charts data). The ratio to solar power is therefore only a comparison of scale; it does not claim that the energy charged is solar power.
Why are there only so many projects on the map?
Because we can only map named projects: together they account for about a quarter of the observable capacity (the exact share is given in the Where are they? section). The rest are smaller batteries published without a name. We collect the projects by hand from press reports and company announcements, so the list is not complete; the marker sits on the town or village because the exact site is not always public.
How to cite
If you use a figure or a chart, you can use this text:
Source: holatarolo.hu, based on MAVIR data and the HUPX day-ahead price (energy-charts.info; Bundesnetzagentur | SMARD.de, CC BY 4.0)
We take MAVIR's data from the data export on MAVIR's website; the exchange price (HUPX DAM) comes from energy-charts.info (Bundesnetzagentur | SMARD.de, CC BY 4.0 — the licence asks for the source to be credited). The calculated values (the revenue, the ratios) are not published by MAVIR but calculated by us: cite them as calculated values, not as measurements.
What's changed
- — the first version of the site: the latest measured day, the batteries' rhythm, tomorrow's revenue, the boom, the project map, the real-scale comparison, home batteries.
- (later the same day) — records, how much the batteries matter, the heat map, the share of energy charged at negative prices, a year of revenue, and this methodology.
- — three languages: the whole site and this methodology are now also in English (holatarolo.hu/en) and German (holatarolo.hu/de), with a language switcher in the header. If the price source fails, the “How much would a battery earn?” section shows the latest day with complete prices, flagged as out of date, instead of an error.
We will also note here if the way something is calculated or a source changes.