Measuring Electricity: MW, GW and Energy
How can a power number tell two different stories?
How it works
Power (how fast energy is used) can rise or fall. A watt measures that rate. One kilowatt equals 1,000 watts. One megawatt, or MW, equals 1,000 kilowatts. One gigawatt, or GW, equals 1,000 MW.
Energy is the amount used over time, like a whole day. A kilowatt-hour means one kilowatt used for one hour. MWh means megawatt-hour (a megawatt of power used for one hour). Multiply steady power by running time to find energy.
Headlines may show planned limits, working supplies or computers alone. Cooling and other equipment also need power. Check what each number covers.
Home demand changes during the day. Air conditioning raises demand. Comparing homes and data centers needs a time period and clear baseline.
Picture the scale
EIA gives a familiar example: a 40-watt light bulb running for five hours uses 200 watt-hours. The 40 watts describe how fast energy flows. The 200 watt-hours describe the total used. Keeping a light on longer fills a larger energy total, like water filling a bucket.
Why should I care?
Your family pays for electricity used over time. A long gaming session uses more energy than a short one at the same power.
Words to know
- Power
- A rate of energy use; like how fast water leaves a tap.
- Energy
- The amount used over time, like a whole day; power multiplied by time.
Check yourself
1. A 1 kW device runs steadily for two hours. How much energy is used?
- 2 kW
- Half a kWh
- 2 kWh
Show answer and why
C. 2 kWh. Multiply the rate by two hours.
2. Which unit measures a power rate?
- MW
- kWh
- MWh
Show answer and why
A. MW. MW is power; units with hours measure energy.
3. Why ask whether a figure covers the whole building?
- Only computers use electricity
- Cooling adds power use beyond computers
- Every planned MW figure describes operating equipment
Show answer and why
B. Cooling adds power use beyond computers. The boundary determines what is included.