Energy, Power, and Electricity Fundamentals

Power describes how quickly electrical energy is transferred. Energy describes the amount transferred over a time interval. A watt (W) is a unit of power; a watt-hour (Wh) is a unit of energy. The kilo prefix means 1,000 and mega means 1,000,000.

For a constant load, energy = power × time. A 2 kW machine running for 3 hours uses 6 kWh. Convert minutes to hours before multiplying kW by time. For changing loads, calculate each interval and add the energy totals.

Average power is total energy divided by the duration. It does not describe every peak. A nameplate rating describes equipment under specified conditions, not its exact annual consumption. Comparing energy requires consistent time intervals and measurement boundaries.

Practice example (illustrative): a server uses 0.6 kW for 4 hours and 0.2 kW for 6 hours. Its total is 3.6 kWh. At an assumed energy-only price of $0.20/kWh, the cost is $0.72. Actual tariffs may include other charges.

An efficient device can use less energy per task while total energy rises if the number of tasks grows. Always ask what was measured, over which interval, and whether the claim concerns power, total energy, or energy per task. These practice explanations and numerical examples are original AERIGRID teaching material.