Explained · power, water, myths
How big is a data centre, really?
Megawatts, terawatt-hours and litres are hard to picture. Start with five ideas that make every number on this site readable, then see the scale in homes, chips and swimming pools, with every number sourced, and the common rumours checked.
Five ideas behind every number
Each takes a minute and ends with Ireland's real figures. Pick any, or follow them in order.
A data centre is one part of a shared power system.
Follow electricity from where it's made to the servers. Each stage can set its own limit, so each answers a different question. Pick a stage.
Gas plants, wind and solar farms, and imports through the interconnectors put electricity into the system. Together they have to meet demand at every moment. How Ireland makes its electricity →
Measured · CSO In 2025, data centres used 7.7 TWh of the 33.0 TWh of electricity metered in Ireland: 23.2%. That is the site end of the chain. National supply totals can't say which power station or cable fed a particular site.
Figure: Ireland's electricity as one system, from source to use →
Used, contracted, possible
The overview's three headline numbers measure different things: electricity already used, grid capacity held, and demand that might come.
MW is a rate; TWh is an amount
The headline 23.2% is a share of electricity used across 2025, not a share of grid capacity.
The CSO recorded 7,662 GWh (7.7 TWh rounded) of metered data-centre electricity in 2025, or 23.2% of Ireland’s metered total. Dividing the unrounded annual use by 8,760 hours gives an equivalent average draw of about 875 MW. A real site’s power varies by hour; the average is a way to picture an annual total.
EstimateAverage MW and total metered TWh are derived from the CSO data.
Sources: CSO MEC02, 7 Jul 2026
Used, contracted and possible are different
Only the first figure is electricity already used. The others describe a connection allowance and potential future demand.
The CSO measured 7.7 TWh of data-centre electricity in 2025. EirGrid reports 2,400 MVA of connected or contracted capacity for data centres and some other new-technology loads; think of this as the size of a doorway, not how much passed through it during the year. The 5.8 GW figure comes from system operators’ market sounding cited by the CRU; it is possible new demand, not capacity approved or built. MVA and MW are different power measures, so these three numbers are intentionally not drawn on one scale.
Sources: CSO MEC02, 7 Jul 2026 · EirGrid AIRAA 2026–2035, Dec 2025 · CRU2025236, 12 Dec 2025
How much power is that?
Data centres used 7.7 TWh in 2025. Drag the slider to see what a site's megawatts mean in homes, chips and pools. Each comparison rests on its own assumptions, shown under it.Illustration · comparisons
A data centre drawing 135 MW, around the clock
These are illustrations, not a description of any real site. Real data centres run a mix of storage, cloud services, video and AI, with spare capacity. GPU count assumes every watt goes to AI servers. Sources: CRU Factsheet: Domestic Electricity and Gas Bills in Ireland (CRU20125), 2020 · NVIDIA DGX H100 User Guide, 2023-20 · Google Cloud blog, 'Measuring the environmental impact of AI inference' (+ technical paper), 2025-08 · Epoch AI (Josh You), 'How much energy does ChatGPT use?', 2025-02 · IEA commentary (George Kamiya), 'The carbon footprint of streaming video: fact-checking the headlines', 2020-12 · water from EPA annual reports.
Inside a data centre
Megawatts, MVA, MW thermal and PUE are measured at different points in the same building. Here is where.
Anatomy of a data centre, and where each number is measured
Power flows grid → substation → batteries → servers → heat. Each headline number is taken at a different point, which is why megawatts, MVA, MW thermal and PUE can't be compared directly.
Electricity arrives from the transmission grid, passes through an on-site substation whose contracted maximum import (in MVA) is the "capacity" in grid debates, then through batteries that bridge outages, to the servers in the data halls. The CSO's 7,662 GWh for 2025 is energy metered at the grid connection. PUE compares total power with power reaching the servers: the industry average is 1.54, meaning 54% extra for cooling and losses. Backup generators are rated by fuel input (MW thermal), roughly two to three times their electrical output, and need an EPA licence above 50 MW thermal; water is metered at the mains connection.
Sources: CSO MEC02, 7 Jul 2026 · EirGrid AIRAA 2026–2035 and Constrained Area Overview, Dec 2025 / May 2026 · Uptime Institute Global Data Center Survey 2025, Jul 2025 · Google Data Centers - Efficiency, 2026 · Our epa_generation pipeline (EPA LEAP AERs), 3 Oct 2026 · EPA LEAP licences and annual environmental reports, 3 Oct 2026
Electricity is not energy
The "a quarter of Ireland's energy" line mixes up the two. Electricity is only about a fifth of all the energy Ireland uses; oil for transport and heating is much bigger.
Electricity is not energy
Data centres used 21.2% of Ireland's final electricity use in 2024 (SEAI basis) but only about 4.9% of all the energy the country used, because electricity is just 22.9% of final energy.
The top bar is all final energy used in Ireland in 2024 (144 TWh), most of it oil for transport and heating. The solid slice next to the red is electricity (22.9%), which the second bar stretches to full width. Data centres (red) used 7.0 TWh in 2024 according to the CSO; against the SEAI's electricity total that is 21.2%, while the CSO's own share of metered electricity is 21.9%. "A fifth of Ireland's energy" claims mix up the two bars; the electricity share is the right measure for the grid, the energy share for climate and energy security.
EstimateData-centre share of final energy = CSO data-centre use ÷ SEAI total final consumption, same year; the two bodies count slightly differently.
Sources: SEAI, Energy in Ireland 2025 report, Table 5.1, Dec 2025 · SEAI, Energy in Ireland 2025, Table 5.1, Dec 2025 · CSO MEC02, 7 Jul 2026
SEAI, Energy in Ireland 2025 report, Table 5.1, 2025-12 · CSO, Metered Electricity Consumption 2025 - Key Findings, 2026-07
How much water?
Less than you've heard nationally, more than you'd think at two sites, and very seasonal.
Litres per MWh of electricity, 2025
Equinix Blanchardstown (evaporative cooling) uses ~2,450 L per MWh; most Amazon sites 1–26 L.
The 2026 summer, million litres a day
Use rose with the hot summer from May, before the hosepipe bans (Dublin mid-July, national 24 July). About 0.6–0.9% of Dublin's supply at the peak.
EPA annual environmental reports (public-supply water) · Uisce Éireann via Dáil answers and The Journal · Maynooth MUSSI Working Paper 31 · as of 2026-10-03
How a data centre "brings its own power"
Since December 2025 a new data centre has two separate obligations: one physical, one on paper.
Firm power it can switch on
80% matched by new Irish renewables
Mostly Scotland
Dublin can't take it
CRU2025236 (Dec 2025) · EirGrid Constrained Area Overview (May 2026) · Gas Networks Ireland Winter Outlook 2025/26 and Network Development Plan · see the Power and Policy tabs for the evidence.
Rumours, checked
What people say about Irish data centres, and the verdict. Each opens its full check, with the numbers and sources.
- misleading"Data centres use a fifth (or a quarter) of Ireland's energy." →They use 23% of metered electricity (CSO, 2025), but electricity is only ~23% of all the energy Ireland uses; oil for transport and heat is over half.
- misleading"Data centres will cause blackouts." →There have been no supply-shortage blackouts; EirGrid issued amber 'system alerts' (1 in 2017, 0, 0, 3, 6, then 8 in 2022), which are warnings, not power cuts.
- misleading"They run on 100% renewable energy." →A data centre draws the same grid power as everyone else: 48% of Irish generation was gas in 2025 (about 40% of demand, with imports making up the rest); renewable claims rest on contracts (PPAs, certificates) that match annual totals on paper.
- false (nationally); partly true locally in summer"Data centres use as much water as a city / caused the hosepipe ban." →Measured public-supply use was ~1 billion litres in 2025, about 0.17% of the 1.7 billion litres Uisce Éireann treats every day - roughly 400 Olympic pools a year, or the daily use of ~20,000 people.
- false"Every AI prompt uses a bottle of water." →The source paper said a 500 mL bottle per 10-50 responses for GPT-3 in 2023, counting water used at power stations too; its own Ireland row is ~70 responses per bottle, with only 0.08 mL per response used on site.
- misleading"Data centres support 876,000 Irish jobs." →KPMG's 876,000 counts jobs in sectors it calls 'dependent' on digital infrastructure - about a third of all employment - not jobs created by data centres.
- false"Data centres pay no tax." →They pay commercial rates (our estimate ~EUR 73m a year from the valuation list) and KPMG puts employment-related tax at ~EUR 280m in 2024.
- partly true (size uncertain)"Data centres are making my electricity bill higher." →Probably yes through wholesale prices, by an amount that depends on the model.
- mostly true"They're all in Dublin." →44 of the 55 operating campuses in our directory are in the four Dublin council areas, and Dublin sites account for ~81% of the grid draw reported to the EPA.
- misleading"Ireland has stopped building data centres." →New grid connections have nearly stopped (one new contract in ~3.5 years after Nov 2021), but data-centre electricity still grew 10% in 2025 as existing sites fill ~1.0-1.4 GW of capacity contracted before the rules changed.
- false (for diesel); the gas story is real"Their diesel generators run all the time." →Backup diesel fleets ran the equivalent of ~1-6 full-load hours a year in EPA reports, against 72-200 permitted, and on-site fuel was 0.3% of reporting sites' energy in 2025.
- unknown"Irish data centres are mostly running AI." →No Irish body publishes what the computing in Irish data centres is for, and operators report energy to a confidential EU database.