How they work • Water • Energy • Cooling • Upgrades
Inside a modern data centre — thousands of servers running 24 hours a day
A data centre is a specialised building (or group of buildings) designed to house thousands of computers called servers. These servers run continuously, storing data, running websites and applications, processing information, and delivering digital services to people around the world.
A single large data centre can contain tens of thousands of servers and use as much electricity as a small town.
Data centres perform three main jobs:
When you take a photo on your phone and upload it to the cloud:
The same process happens with emails, WhatsApp messages, streaming, and conversations with AI tools. There is no invisible cloud — only physical buildings full of computers.
Data centres generate enormous amounts of heat. Cooling is one of their biggest operational challenges and costs.
| Cooling Type | How it Works | Water Use |
|---|---|---|
| Air Cooling | Cold air is blown through the servers using fans and air conditioning. | Low–Medium |
| Liquid Cooling (Direct-to-Chip) | Cooling plates sit on the hottest chips and carry heat away with liquid. | Medium |
| Immersion Cooling | Servers are submerged in a special non-conductive liquid. | Low |
| Free / Evaporative Cooling | Uses outside air or large cooling towers that evaporate water. | High |
Data centres are extremely energy-intensive. Here are the main ways they get power:
Most data centres draw power from the national electricity grid. In Ireland this is managed by EirGrid. The electricity mix usually includes natural gas, wind, solar and some imported power.
Large companies often sign long-term contracts called Power Purchase Agreements (PPAs) to buy renewable energy from wind or solar farms. This is what they usually mean when they say their data centres are “100% powered by renewables”. In practice, they rarely own the wind or solar farm itself. Instead, they buy the contractual output and the associated renewable certificates (called Guarantees of Origin in Europe).
The actual electricity flowing into the building at any given moment still comes from the shared national grid, which mixes wind, solar, gas and imported power. On a still night when the wind is not blowing, the building is mostly running on gas-fired power — even if the company holds enough certificates to balance its annual consumption on paper. “100% renewable” is usually an annual accounting match, not a moment-to-moment fact.
Not all PPAs are equal. At the honest end, a company funds a brand-new wind or solar farm that would not otherwise have been built — its money genuinely adds clean power to the grid. At the weak end, a company simply buys certificates detached from any new build, and nothing new gets built at all. The phrase alone does not tell you which.
Long-term PPAs also give large buyers a price advantage. Corporate PPA rates in Europe have typically been benchmarked well below the roughly 30–38 cents per kWh that Irish households pay (SEAI), letting large energy users secure power at a fraction of the household price. Exact Irish data-centre PPA rates are commercially confidential.
Some data centres generate part of their own electricity on site. This can include:
Almost all data centres have large banks of diesel generators. These run during power cuts or testing and can be a source of local air and noise pollution.
Since the Commission for Regulation of Utilities (CRU) published its Large Energy Users Connection Policy (Decision Paper CRU/2025236) on 12 December 2025, new data centres can no longer simply connect to the national grid and draw power. For connection applications above 10 MVA, they must now:
This is what “Bring Your Own Energy” (or “Bring Your Own Power”) has come to mean in practice.
So far, the dispatchable generation being installed is overwhelmingly natural gas:
Other operators have installed or proposed gas turbines and gas engines for the same reason. Some projects say they are “hydrogen-ready” or plan to use biomethane certificates, but the physical plant being built today runs primarily on natural gas.
In the short-to-medium term, yes. Every new gas engine or turbine adds fossil-fuel generation capacity. Even where operators buy biomethane certificates or plan for future hydrogen, the plant can — and often will — run on fossil gas, especially in its early years. This adds gas demand and power-sector emissions at the very time Ireland and the EU are trying to cut both, and it risks locking in fossil infrastructure for 15–25 years, in tension with Ireland’s Climate Action Plan and EU renewable-energy targets. The CRU’s policy is explicitly designed to avoid fully “islanded” fossil-powered data centres — yet in practice its dispatchable-capacity requirement is, for now, being met largely with gas.
Modern high-density servers (especially AI and GPU racks) generate extreme heat. Water is one of the most effective substances for absorbing and moving that heat away.
Cooling systems need very clean water. Untreated or low-quality water causes mineral scaling, corrosion, and biological growth that can damage expensive equipment. This is why many data centres prefer treated drinking water from the public supply.
It is important to distinguish between what leaves a data centre into the air and what leaves in liquid form.
As water evaporates in the cooling towers, the chemicals and minerals left behind become more concentrated. Operators periodically discharge some of this concentrated water. This is called blowdown and is usually the main liquid outfall from the site.
As computer chips become smaller and more powerful, the amount of heat and electricity used per rack increases dramatically. Older data centres designed for air cooling often cannot handle modern AI and high-performance computing racks.
With the growth of AI, upgrade cycles are expected to become faster in high-density areas. Liquid cooling is becoming standard in new builds and major retrofits. Immersion cooling is also growing in specialist facilities.
Data centres create significant pressure on Ireland’s electricity grid:
Data centres used about 22% of all electricity in Ireland in 2024 — up from 5% in 2015 — according to the Central Statistics Office. That is more electricity than every urban household in the state combined. On current trends, EirGrid projects this could rise to around 31% by 2034.
Because data centres run at a high, constant level 24 hours a day, they increase the number of hours when expensive gas-fired power stations set the wholesale electricity price. A May 2026 report by ecological economist Dr Seán Fearon — commissioned by Friends of the Earth Ireland and Beyond Fossil Fuels — modelled this effect using hourly data from 2015 to 2023. It estimated that data-centre demand added an average of about €360 to each Irish household’s electricity bills over that period, with a cumulative cost to households of roughly €715 million.
A note on this figure: it is a modelling estimate, not a measured amount — the author is explicit that it is an estimate — and the data-centre industry has disputed the findings, arguing that households are not subsidising data centres. We include it as a named, published estimate and flag the disagreement.
Rapid demand growth also requires major upgrades to the electricity network. In December 2025 the Commission for Regulation of Utilities (CRU) approved a network investment package of up to €18.9 billion for 2026–2030 (its Price Review Six), with a baseline of €13.8 billion. These costs are recovered through network charges on electricity bills. The CRU estimates this will add roughly €1 per month to a typical household bill at the baseline level, rising to about €1.75 per month if the full investment is delivered.
This page is part of The Ripple Rebellion’s citizen information work. It is intended to help people understand how data centres actually function so that public discussion can be better informed.
