Zwei identische Büros. Jeweils fünfzig Personen. Gleiche Schreibtische, gleiche Beleuchtung, gleiche Stunden. Eine Flotte wurde zugekauft 2020, the other in 2026.
Run the numbers at the German business rate of €0.2058/kWh (Eurostat, H1 2026): the 2020 fleet burns about 41.7 kWh per machine per year, the 2026 fleet about 28–31. Over three years, that gap is €341 for fifty machines. Not a fortune. But it is the cheapest line item in the entire green office, because nobody has to change how they work to get it.
Here is the ranking, built from measured watts — not spec sheets.
The ranking: measured watts, annual kWh, annual cost
Usage model: 8 hours a day, 250 days a year (2,000 hours), 70% light use (email, browser, video calls) at measured idle draw, 30% at measured load. Price: €0.2058/kWh, the German business rate from Eurostat’s H1 2026 data.
| Rank | Machine | Idle (W) | Load (W) | kWh/yr | €/yr |
|---|---|---|---|---|---|
| 1 | ThinkPad X1 Carbon Gen 13 (Arrow Lake U) | 5.1 | 30.5 | 25.4 | 5.24 |
| 2 | Mac mini M4 (desktop) | 4.1 | 38.0 | 28.5 | 5.87 |
| 3 | MacBook Air 13 (M4) | 8.7 | 29.9 | 30.1 | 6.20 |
| 4 | MacBook Air 13 (M5) | 9.3 | 29.4 | 30.7 | 6.31 |
| 5 | ThinkPad X1 Carbon Gen 13 (Lunar Lake) | 9.0 | 35.0 | 33.6 | 6.91 |
| 6 | Dell Pro 13 Premium (Lunar Lake) | 13.3 | 25.8 | 34.0 | 7.01 |
| 7 | Framework Laptop 13 (Ryzen AI 5 340) | 5.0 | 46.7 | 35.0 | 7.21 |
| 8 | Dell Latitude 9410 (2020, 10th gen) | 17.0 | 29.8 | 41.7 | 8.58 |
Sources for the wattage: NotebookCheck reviews for the MacBook Air M4 and M5, both X1 Carbon Gen 13 variants, and the Dell Pro 13 Premium; Principled Technologies for the Dell Pro 13 Premium and Latitude 9410 (June 2026); independent measurements by Linus Sebastian’s team (Geerling) for the Mac mini M4 and Framework 13.
What the table actually says
Three things, in order of how much they matter.
1. The chip you pick matters less than the year you buy. The spread between the best and worst 2025–2026 machines is €2 per machine per year. The spread between a 2020 machine and a 2026 machine is €2.30. If your fleet is older than four years, the upgrade is the efficiency project — not the brand debate.
2. The same laptop, two different chips. The X1 Carbon Gen 13 ships with either Lunar Lake or Arrow Lake U. NotebookCheck measured the Arrow Lake variant at 5.1 W idle and 30.5 W average load; the Lunar Lake variant idles around 9 W and pulls 35 W under load. Same chassis, same price bracket, €1.70 per machine per year apart. When the vendor quotes you a “premium” configuration, ask which silicon is inside — the spec sheet will not volunteer it.
3. A desktop is the quiet winner for people who sit down. The Mac mini M4 idles at 4.1 W at the wall and peaks at 39.6 W (Geerling’s measurements). Against the MacBook Air M5 it saves €1.31 per machine over three years — €65 across fifty. Against the 2020 Latitude, it saves €8.13 per machine, €406 across fifty. For the 60–70% of your office that never leaves their desk, a €599 mini plus a used monitor beats a €1,099 laptop on both the energy line and the purchase line.
What you save
A 50-person office that swaps its 2020 laptops for the most efficient 2026 options saves €341 over three years on electricity alone — €6.82 per machine. Swap the stationary half of the fleet to Mac minis instead and the saving grows to €406. The purchase price of the hardware is a different conversation; the electricity is free money, and it is the only line item where the green choice and the cheap choice point the same direction.
Context for the skeptics: ENERGY STAR 8.0, the current US certification for office computers, requires certified systems to use roughly 30–40% less energy than standard models. Every machine in the top six of the table above would pass. Der 2020 Latitude would not.
Methodology
Wattage: measured values from NotebookCheck (idle min/avg/max and load avg/max), Principled Technologies (whole-setup idle and Teams-call draw, June 2026), and Geerling’s independent measurements (wall draw, idle and max stress). Where a source reports a range, the average is used. Annual energy: blended draw × 2,000 hours (8 h/day × 250 days). Price: €0.2058/kWh, German business rate, Eurostat H1 2026 (nrg_pc_205, 500–2,000 MWh band, excluding VAT and recoverable taxes). The EU business average is €0.18/kWh; scale the euro figures by 0.88 if your office sits at the average.
Sources
- NotebookCheck, MacBook Air 13 M5 review (power consumption): https://notebookcheck.net/Apple-MacBook-Air-13-M5-laptop-review.1242707.0.html
- NotebookCheck, MacBook Air 13 M4 review (power consumption): https://notebookcheck.net/Apple-MacBook-Air-13-M4-laptop-review.1002534.0.html
- NotebookCheck, ThinkPad X1 Carbon Gen 13 Aura Edition review (Lunar Lake): https://notebookcheck.net/Lenovo-ThinkPad-X1-Carbon-Gen-13-Aura-Edition-laptop-review-The-X1-Carbon-is-finally-back.924998.0.html
- NotebookCheck, ThinkPad X1 Carbon Gen 13 5G review (Arrow Lake U): https://notebookcheck.net/Trading-efficiency-for-optional-5G-and-Lunar-Lake-for-Arrow-Lake-Lenovo-ThinkPad-X1-Carbon-Gen-13-laptop-review.1144426.0.html
- Principled Technologies, Dell Pro 13 Premium vs Latitude 9410 power test, June 2026: https://www.principledtechnologies.com/
- Geerling, Mac mini M4 and Framework Laptop 13 power measurements: https://github.com/geerlingguy
- Phoronix, ThinkPad X1 Carbon Gen 13 Linux review (20 W average, 37 W peak over 33 h): https://phoronix.com/review/lenovo-thinkpad-x1-gen13-linux/14
- Apple Newsroom, MacBook Air with M5 (pricing, 3 Marsch 2026): https://www.apple.com/newsroom/2026/03/apple-introduces-the-new-macbook-air-with-m5/
- ENERGY STAR 8.0, computer specification: https://www.energystar.gov/products/computers
- Eurostat, electricity price statistics (nrg_pc_205), H1 2026: https://ec.europa.eu/eurostat/statistics-explained/index.php?title=Electricity_price_statistics
Next leak to fix
Computers are the small leak. The big one is what sits next to them: the monitors. A 27-inch panel idles at 15–25 W — more than the entire Mac mini — and most offices run them 12 hours a day, 5 days a week, including the hours nobody is in the building. Before you buy a single new computer, set the display power settings to sleep after 5 minutes and measure a week of meter data. The monitors will show up first, and they will be bigger than anything in this table.
Carla Lavigne is Green Ops Editor at mycompanyisgreen.org and the colleague who brings the calculator to the audit.
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