How to Schedule CI at Low-Carbon Times

The same job emits less carbon when it runs while the grid is powered by more renewables.

Grid carbon intensity swings through the day as solar and wind rise and fall. For jobs that do not need to run now, a carbon signal (from services such as WattTime or Electricity Maps) lets you defer them to a cleaner window. This helps only for genuinely deferrable work.

Steps

• Identify jobs that are deferrable (nightly suites, batch reports, cache warming).
• Query a carbon-intensity API for the runner region and gate on a threshold.
• Schedule a wide cron window and let the job run only when intensity is low.

Gate on carbon intensity

on:
  schedule:
    - cron: '0 */2 * * *'   # check every 2 hours
jobs:
  batch:
    runs-on: ubuntu-latest
    steps:
      - name: Check grid carbon intensity
        run: |
          INTENSITY=$(curl -s "https://api.example-carbon.org/intensity?zone=$REGION" | jq '.value')
          if [ "$INTENSITY" -gt 250 ]; then
            echo "Grid is carbon-heavy ($INTENSITY), deferring."
            exit 0
          fi
          npm run batch:report

Tradeoffs

• Only defer non-urgent work; never delay a job a developer is waiting on.
• The carbon win is real but modest per job; it compounds across many deferrable runs.

Related guides