Sustainability claims in the data centre sector range from genuinely engineered efficiency to loosely-substantiated marketing language, and it’s not always obvious from the outside which is which. The useful distinction is between facilities that have actually redesigned their cooling and power systems around renewable and low-impact technology, versus facilities that have simply bought renewable energy certificates to offset a conventional, inefficient design. Both reduce a carbon footprint on paper; only one actually reduces energy consumption and cost.
Why cooling is where sustainability is won or lost
Cooling is typically the single largest non-IT energy draw in a data centre — often the majority of the overhead captured in a facility’s PUE figure. Traditional mechanical chiller systems are energy-intensive by design: compressing and circulating refrigerant to remove heat is fundamentally power-hungry, regardless of how efficiently it’s operated. Reducing reliance on mechanical chilling, rather than just making mechanical chilling marginally more efficient, is where the largest sustainability and cost gains actually come from.
Rainwater cooling in practice
Rainwater harvesting for data centre cooling uses collected rainwater — rather than drawing continuously from the mains supply — to feed evaporative cooling systems. Evaporative cooling works by using the energy required for water to evaporate to remove heat from air passing through the system, which requires dramatically less electrical energy than mechanical refrigeration for an equivalent cooling effect, particularly in the UK’s temperate climate where ambient conditions support evaporative cooling for large parts of the year. Using harvested rainwater rather than mains water for this process also reduces mains water consumption, which matters both environmentally and, in some regions, for long-term water availability and cost.
The practical effect is a facility that relies on mechanical chilling only during the relatively small number of days per year when ambient conditions and evaporative cooling alone aren’t sufficient — rather than running mechanical chillers as the default, everyday cooling method.
Solar power’s real contribution
On-site solar generation offsets grid electricity draw directly rather than through a certificate purchased elsewhere — the energy generated on the roof or grounds of the facility is energy that doesn’t need to be drawn from the grid at that moment. In the UK, solar generation is naturally variable with season and weather, so it’s realistically a supplementary source alongside grid power and battery/UPS systems rather than a facility’s sole power source — but every kWh generated on-site is a kWh that doesn’t carry the grid’s average carbon intensity, and doesn’t carry a cost that fluctuates with wholesale energy markets.
The measurable outcome: PUE
The honest way to evaluate whether sustainability measures are actually working is a facility’s measured PUE — not its design PUE, not a marketing claim, but an independently verifiable, continuously measured figure. Our own Cambridgeshire facility combines rainwater-fed evaporative cooling with on-site solar generation to achieve a measured PUE of 1.07, well below the 1.5-1.6 industry average reported in the Uptime Institute’s annual global survey. That’s not a marketing figure — it’s the actual ratio of total facility energy to IT equipment energy, continuously measured.
Why this matters beyond environmental reporting
- Lower operating cost, passed through. A facility using significantly less electricity per unit of IT load has lower power costs to pass on, which shows up directly in colocation power pricing rather than staying purely as an environmental talking point.
- ESG and supply chain reporting. UK businesses are increasingly required by their own customers, investors or regulators to report on supply chain emissions (Scope 3), and infrastructure hosting is a component of that. A hosting provider that can supply real, measured PUE and generation data makes that reporting considerably easier to complete accurately.
- Resilience alongside sustainability. Reduced reliance on mechanical chilling and diversified power sourcing (grid plus solar) also adds a degree of operational resilience against grid instability or extreme weather, which is a genuine side benefit beyond the environmental case.
Questions to ask if sustainability claims matter to your procurement
- What is the facility’s measured (not design) annual PUE?
- What proportion of cooling relies on evaporative or free cooling versus mechanical chilling, and across what proportion of the year?
- Is renewable generation on-site, or purchased as certificates/offsets elsewhere?
- Can the provider supply data suitable for your own Scope 3 emissions reporting?
If sustainability data is something you need for your own ESG or procurement reporting, our team can provide our measured PUE, cooling and generation figures directly — real numbers, not a marketing average.
