FREE SAMPLE · TOPIC 1

Energy, power and electrical quantities

Read a power profile, calculate energy and explain what the numbers mean for a commercial decision.

Allow about 15–20 minutes. No energy background or account required. This sample covers MW and MWh, not the entire electrical-quantities topic.

Power is a rate. Energy is an amount.

MW · power

How quickly electricity is being delivered or used. A 90 MW reading describes a rate; it does not tell you the duration.

MWh · energy

The quantity delivered or used over time. Running at 90 MW for one hour delivers 90 MWh; for one-third of an hour, it delivers 30 MWh.

Energy (MWh) = average power (MW) × time (hours)

Use the average power over the stated period. One brief peak is not enough to calculate total energy. One MW is 1,000 kW, and one MWh is 1,000 kWh. MWh means megawatt-hours, not megawatts per hour.

Units reference: EIA: Measuring electricity. This source explains physical units, not Australian market rules.

One site, three readings

A fictional industrial site records average power at its grid connection for three consecutive ten-minute periods. We want its energy use, its average demand and an illustrative energy cost.

Equal widths represent equal durations. The area of each block—not its height alone—represents energy. Original synthetic data.

Calculate each interval before adding the energy
Period	Average power	Energy calculation
00–10 min	30 MW	30 × 10 ÷ 60 = 5 MWh
10–20 min	60 MW	60 × 10 ÷ 60 = 10 MWh
20–30 min	90 MW	90 × 10 ÷ 60 = 15 MWh

Total energy: 30 MWh. Add 5 + 10 + 15. Do not add the MW readings and label the result MWh.
Average power: 60 MW. Divide 30 MWh by 0.5 hours. The highest interval-average power is 90 MW; shorter peaks are unknown.
Energy-only cost: A$2,400. Assume a flat A$80/MWh across all three periods: 30 × 80. This excludes network charges, demand charges, taxes and other adjustments.

Ten-minute periods make the arithmetic easy to see. This is not a NEM dispatch or settlement reconstruction, a quoted tariff or a full customer bill.

Now make a decision

An operations manager proposes spreading the same consumption evenly: 60 MW for all 30 minutes. Before reading on, calculate the new total energy and highest interval-average demand.

Compare your reasoning

The new profile uses 60 × 0.5 = 30 MWh, with highest interval-average demand of 60 MW rather than 90 MW. At the same flat A$80/MWh, its energy-only cost remains A$2,400.

Lower peak demand does not automatically mean a lower bill or a smaller permitted connection. Ask for the demand-charge measurement window, time-varying prices, contract terms, operational constraints and higher-resolution meter data before recommending the change.

Change the assumptions

Energy = average power × minutes ÷ 60

Average power (MW)Duration (minutes)

30 MWh

Use interval-average power, not a peak reading. This model assumes the stated average applies throughout the duration.

Your one-minute briefing

“The original profile uses 30 MWh and averages 60 MW. Its highest ten-minute average is 90 MW. Smoothing the profile could reduce that peak without reducing energy; the financial benefit still depends on tariffs and operating constraints.”

These distinctions lead into wholesale pricing, customer procurement, battery duration and large-load connections. A good analyst keeps the physical calculation separate from the commercial conclusion.