FROM UNITS TO DECISIONS
Energy Units Lab.
Work in pairs. Predict, calculate, then explain your units to your partner.
A rate or an amount?
TAKE IT INTO THE LECTURE
Check the unit. Then check the service.
Two projects can have the same power rating but produce different amounts of energy. Even equal annual energy does not mean electricity is available at the same hours.
TRY A DIFFERENT NUMBER
Power × time = energy
Assume constant power. Change one input and predict what will double.
7.2 MJ = 7,200,000 J
2 kWh × $0.05/kWh = $0.10
Illustrative energy charge only. Delivery charges, fixed fees and taxes are excluded; all dollar conversions keep the same currency.
Instructor notes & debrief
Suggested placement: after slide 3, before introducing cost metrics. Return to the battery and annual-output questions alongside slides 36–37.
Run it in pairs: 2 minutes on the unit reference, 8–10 minutes for the challenges, 2–3 minutes to compare explanations. Swap who calculates and who explains halfway through. No names or responses are collected; progress lasts only while this page remains open.
Ask before calculating: “Should the number get bigger or smaller?” Ask students to write the conversion factor so the unwanted units cancel.
Debrief: Why does converting MWh to kWh make the energy number larger but the price per unit smaller? What is missing from “this plant produces 300 MW”? Why can’t a battery’s MW rating tell us how long it will run?
Bridge to RiverCity next week: at 35% capacity factor, 300 MW produces 919.8 GWh/year. At 85%, the same rating produces 2,233.8 GWh/year. Equal nameplate capacity is not equal annual output, and annual output alone does not establish reliable service.
Exit ticket: explain $50/MWh = $0.05/kWh in one sentence and name the additional information needed to turn MW into MWh.