Energy Efficiency Vocabulary — PUE, Carbon Intensity & Scope Emissions
Learn green IT energy efficiency vocabulary: Power Usage Effectiveness (PUE), carbon intensity, renewable energy certificates (RECs), Scope 1/2/3 emissions in IT, and energy-proportional computing.
0 / 5 completed
1 / 5
What is Power Usage Effectiveness (PUE) and what does a PUE of 1.0 vs. 2.0 indicate?
PUE formula: Total Facility Power / IT Equipment Power. PUE 1.0 = theoretical perfect (impossible in practice). PUE 1.2 = highly efficient (hyperscaler data centres like Google, Microsoft). PUE 1.58 = global average (Uptime Institute). PUE 2.0+ = inefficient. PUE above 1 represents overhead: cooling, lighting, power distribution losses, UPS losses. Reducing PUE is the primary data centre efficiency metric. 'Our data centre achieved a PUE of 1.3 through hot/cold aisle containment and free-air cooling.'
2 / 5
What is 'carbon intensity' in the context of electricity consumption for IT systems?
Carbon intensity examples: Norway grid ~20 gCO2eq/kWh (hydro-dominated). UK grid ~200 gCO2eq/kWh (mixed, improving). Poland grid ~700 gCO2eq/kWh (coal-heavy). Carbon intensity also varies by time: UK grid is cleaner at midday (solar) and windier periods. Carbon-aware applications shift workloads to low-intensity times/regions: 'By scheduling batch jobs to run during low carbon intensity windows, we reduced our compute emissions by 23%.' Tools: Electricity Maps API, WattTime.
3 / 5
What is a Renewable Energy Certificate (REC) and how is it used by cloud providers in sustainability reporting?
REC criticism: a company in a coal-heavy grid can claim '100% renewable' by buying RECs from a distant wind farm — the physical electrons are still from coal. More credible: Power Purchase Agreements (PPAs) — long-term contracts to fund new renewable capacity. 'Matched' renewable energy: procuring RECs that match consumption by hour, location, and time (24/7 carbon-free energy). Google and Microsoft pursue 24/7 CFE. When evaluating cloud provider sustainability claims, distinguish between REC-based claims (easier, less impactful) and PPA/CFE claims (harder, more credible).
4 / 5
What are Scope 1, Scope 2, and Scope 3 emissions in the context of IT operations, as defined by the GHG Protocol?
IT Scope emissions examples: Scope 1: on-site diesel generators, company-owned vehicles. Scope 2: electricity used by servers and data centres (location-based or market-based). Scope 3 in IT (often 70-80% of total): hardware manufacturing (embodied carbon), employee commuting, business travel, use of sold software products by customers, upstream cloud services. Scope 3 is hardest to measure but often largest. 'Our Scope 2 emissions decreased 30% following our data centre renewable energy transition, but Scope 3 Category 11 (use of sold products) accounts for 68% of our total footprint.'
5 / 5
What is 'energy-proportional computing' and why is it important for green IT?
Energy-proportional computing challenge: traditional servers consume 50-70% of peak power even when idle. A server at 10% utilisation uses far more than 10% of maximum power. Solutions: (1) Workload consolidation — fewer, fuller servers vs. many idle ones. (2) Autoscaling — scale to zero when idle. (3) Serverless/FaaS — no idle compute. (4) Modern hardware (ARM chips, custom silicon) with better proportionality curves. Cloud efficiency advantage: hyperscalers run at 65%+ average utilisation vs. 15-20% for typical on-premise data centres. 'By migrating batch workloads to serverless, we eliminated idle compute that previously ran at 8% utilisation overnight.'