“Green” is an easy word to put on a hosting provider’s page and a hard one to verify. Two providers can say exactly the same thing: the first runs its servers on electricity from a gas plant and buys certificates that cover its annual consumption on paper; the second buys its power on a long contract with a wind farm and cools its halls with outside air for most of the year. Both are “green” in the advert, and the gap between their actual emissions is large. This article turns the word into numbers and questions: data centre efficiency, where the electricity comes from and how it’s bought, hardware and cooling efficiency, then what you control as a site owner, and how to check any provider.
01PUE: how much a data centre spends beyond its servers’ needs
(PUE) is the ratio of all the electricity a data centre draws to the share that reaches the IT equipment alone. A value of 1.0 means every watt goes to the servers; 2.0 means that for every watt the servers use, another goes to cooling, power conversion and lighting. These are approximate values that vary with climate, size and age:
| Type of data centre | Approximate PUE | What reaches the servers out of every 100 W |
|---|---|---|
| Modern hyperscale sites with outside-air or liquid cooling | 1.1 to 1.2 | About 83 to 91 W |
| Industry average in Uptime Institute surveys | About 1.5 to 1.6 | About 63 to 67 W |
| Old or small server rooms | 2.0 or more | 50 W or less |
But PUE doesn’t tell the whole story. It doesn’t measure the source of the electricity: a site at PUE 1.2 on coal power emits far more than one at 1.5 on wind. It doesn’t measure the efficiency of the servers themselves: an idle server improves the ratio and gets nothing done. And it doesn’t measure water: evaporative cooling lowers PUE and consumes water, which is why WUE, litres of water per kilowatt-hour, is used alongside it. Ask the provider for a measured annual PUE, not a design figure recorded on a winter’s day.
02Where the power comes from: generation, contract, certificate, offset
When a provider says it runs on renewable energy, it means one or more of these methods, and they are not equal:
| Method | How it works | Real effect |
|---|---|---|
| On-site generation | Solar panels or turbines at the data centre itself | Direct, but usually covers a small share of the site’s needs |
| Power purchase contract | A long-term [[ppa|power purchase agreement]] with a renewable plant, often built because of the contract | The strongest: it adds new clean capacity to the grid |
| Certificates of origin | [[eac|Energy attribute certificates]] bought to cover consumption on paper, such as GOs in Europe and RECs in the US | Varies: often cheap, and they don’t change the electricity you actually draw |
| Carbon offsetting | [[offset|Carbon offsetting]]: funding projects that cut emissions elsewhere, such as tree planting | Doesn’t change the source of the electricity at all; its quality depends on the project |
The key distinction is between matching and offsetting. Matching means covering every kilowatt-hour you consume with a renewable kilowatt-hour set against it: annually through certificates, or hour by hour in the newer and harder approach known as 24/7 carbon-free energy (24/7 CFE). Offsetting accepts the emissions as they are, then pays to reduce emissions somewhere else. A provider matching hour by hour through purchase contracts is better for the environment than one offsetting the emissions of a coal plant, even if both carry the same label.
03Hardware and cooling
- Performance per watt: Each new generation of server processors does more work for the same energy. A modern server with dozens of cores replaces several older servers and uses less than they did combined, so a hardware refresh is an energy decision too, not only a performance one.
- Consolidation through virtualization: An idle server draws a large share of its peak power, approaching half depending on the machine. Virtualization packs dozens of virtual servers onto one machine running at a higher load, so fewer machines burn electricity while doing nothing.
- Cooling: Cooling is the biggest overhead beyond the servers. What cuts it most: separating hot aisles from cold ones, raising server inlet temperature within ASHRAE’s recommended range (18 to 27 °C), using outside air in cold climates, and liquid cooling for high-density racks.
- Hardware lifetime: Part of the footprint is spent before a server runs for a single day, in manufacturing and shipping. Moving machines to lighter duties before they retire, then recycling them, spreads that cost over more years.
04What you control as a site owner
Every byte your site sends is carried by networks, processed by servers and rendered by devices. A lighter page is faster, cheaper to host and less energy-hungry all at once, so there’s no conflict here between performance and sustainability:
- Page weight: The median mobile page has passed 2 MB in recent years according to the HTTP Archive, most of it images and JavaScript. Give every page a budget, such as 1 MB, and watch it with every change.
- Image formats: WebP is usually about 25 to 35% smaller than JPEG at the same quality, and AVIF is often around half the size. And serve each image at the width it’s actually displayed at, not at camera resolution.
- Caching: A page built once and served from cache thousands of times saves CPU and database work on every visit. Turn on server-side page caching, and long Cache-Control headers for static files.
- Content delivery network: A CDN serves files from a point close to the visitor, shortening the distance data travels and taking requests off your server.
- Code and plugins: Every unused WordPress plugin adds files and queries that may load on every visit. Remove what you don’t need, defer external scripts, and block abusive crawlers that load your server for no benefit.
These commands convert your images to both formats on Ubuntu 24.04 or Debian 13 and later, then check that the server compresses files and asks for them to be cached:
sudo apt install -y webp libavif-bin# WebP at quality 80: a good balance for most imagescwebp -q 80 hero.jpg -o hero.webp# AVIF at quality 60; higher means a sharper image and a bigger fileavifenc -q 60 hero.jpg hero.avif# Compare the three sizesls -lh hero.jpg hero.webp hero.avif# Does the server compress files, and how long does it ask the browser to keep them?curl -sI -H "Accept-Encoding: br, gzip" https://bahr-tartus.com/style.css | grep -iE "content-encoding|cache-control"
05How to check a provider
The is a nonprofit that keeps an open database of hosting providers that have shown evidence that they avoid, reduce or offset the emissions of the electricity they use, and a provider renews its evidence at least once a year to stay verified. You can check any site with the Green Web Check tool on its website, or from the terminal through its API:
# Is the server hosting this domain run by a provider listed in the database?curl -s https://api.thegreenwebfoundation.org/api/v3/greencheck/bahr-tartus.com
But a listing is where the question starts, not where it ends. Open the published evidence the directory links to the provider, and look in it for answers to these questions:
- 01What is the measured annual PUE of each data centre?
- 02How is the electricity bought: on-site generation, purchase contracts, certificates, or offsets?
- 03Is the matching annual or hour by hour?
- 04Does the claim cover every data centre, or only some?
- 05Who audited the figures, and when were they last published?
By the same method, this is what Illevante publishes on its sustainability page: five operating data centres on renewable power from sun and wind, a sixth in Syria coming soon on hybrid power, and low-consumption servers with virtualization. Illevante is listed as a verified provider in the Green Web Foundation’s directory with seven services, from shared hosting and VPS servers to storage, and the evidence is published on the sustainability page, which the directory links to its record. Read it with the five questions above, as you would any other provider’s.
06Practical recommendation
Start with what you fully own: measure the weight of your most visited pages, convert their images to WebP or AVIF, remove the plugins you don’t use, and turn on caching. These steps cut your site’s consumption and speed it up in a single day, whoever your provider is. Then look your provider up in the Green Web Foundation’s directory, and ask it the five questions.
The direction is clear: as data centre consumption grows with AI workloads, the standards are moving from “an annual renewable percentage” to hour-by-hour matching and published PUE and WUE figures for each site. A provider that publishes its numbers today is easier to choose tomorrow.
