Merge pull request 'estimated footprint' (#53) from earl-warren/documentation:wip-co2 into main

Reviewed-on: https://code.forgejo.org/infrastructure/documentation/pulls/53
Reviewed-by: fnetX <fnetx@noreply.code.forgejo.org>

README.md

@@ -33,6 +33,26 @@ It is possible to help cover the costs of the hardware running at Hetzner by [ad
 
 Please reach out to the [devops team](https://codeberg.org/forgejo/governance/src/branch/main/TEAMS.md#devops) to get the information.
 
+### Estimated carbon footprint
+
+[Power consumption declared by Hetzner](https://www.hetzner.com/dedicated-rootserver/matrix-ex/) December 2024:
+
+* ex44 - idle 25W - max 118W
+* ex101 - idle 32W - max 116W
+
+[The CO₂ emissions factor in the German electricity mix](https://www.statista.com/statistics/1386327/co2-emissions-factor-electricity-mix-germany/) was 380 grams per kilowatt hour, based on initial estimates for 2023.
+
+* ex101 - idle 75% - max 25%
+  - 32W * 24h * 365d * 0.75 = 210kWh
+  - 116W * 24h * 365d * 0.25 = 254kWh
+  - Total = 464kWh => 139Kg CO2
+* ex44 - idle 90% - max 10%
+  - 25W * 24h * 365d * 0.90 = 197kWh
+  - 118W * 24h * 365 * 0.10 = 103kWh
+  - Total = 300kWh => 114Kg CO2
+
+Grand total for 1 ex100 + 3 ex44 => 1 * 139Kg + 3 * 114Kg => 481Kg rounded to 500Kg CO2 per year.
+
 ### hetzner01
 
 [EX101](https://www.hetzner.com/dedicated-rootserver/ex101) Hetzner hardware dedicated to LXC containers with [Forgejo runners](runner-lxc).