Tracing an energy system means naming what goes in, what changes along the way and what comes out, including the energy that is not useful. In an exam you may be asked to label a diagram, calculate efficiency or explain where losses happen.
This lesson builds on explaining a food-supply constraint and belongs to food, water and energy systems. Use the food-web and energy-flow explorer to practise reading arrows, and the statistics and distribution explorer for the arithmetic.
How do you trace a system, step by step?
- Identify the source (input): fuel, sunlight, wind or flowing water.
- List the stages: conversion, transmission, use.
- Mark the losses: at most stages some energy leaves as waste heat.
- Name the useful output: electricity delivered or heat used.
- Check the balance: input = useful output + losses.
Worked example
The numbers are invented for practice. A gas-fired power station takes in 500 units of energy per second in fuel. It produces 200 units of electricity.
Station efficiency. 200 ÷ 500 = 0.4, so efficiency is 40%. Waste heat is 500 − 200 = 300 units.
Transmission. Cables lose 8% of the electricity on the way to towns. Loss = 200 × 0.08 = 16 units. Delivered = 200 − 16 = 184 units.
Overall. 184 ÷ 500 = 0.368, so only 36.8% of the fuel energy reaches users as electricity.
Check. The losses are 300 + 16 = 316, and 184 + 316 = 500, so the system balances.
Written answer. Fuel energy is the input. In the station, most is lost as heat, and a further share is lost in the cables, so users receive a little over a third of the original energy. Reducing losses in the station would raise this figure most.
What mistake does this lesson prevent?
Mistaken answer: “The station uses up 316 units of energy.”
Energy is not destroyed. The 316 units become waste heat in the station and the cables, spread into surroundings. Say “lost as heat” or “not useful”, and check that the numbers still add to the input.
Another slip is to calculate efficiency using the loss rather than the useful output. If you divide 300 by 500 you get 60%, which is the waste share, not efficiency.
Check yourself
1. A plant takes in 800 units and delivers 280 units of electricity. Efficiency?
Show answer
280 ÷ 800 = 0.35, so 35%. Losses are 520 units.
2. A solar farm receives 1,000 units of sunlight energy and produces 180 units of electricity. Efficiency and losses?
Show answer
180 ÷ 1,000 = 18%. Energy not converted to electricity is 820 units.
3. A 50 MW supply runs for 4 hours. How much energy is delivered?
Show answer
50 × 4 = 200 MWh.
Where does this lead next?
Next, compare management approaches descriptively, such as supply-side and demand-side responses. You can check your arithmetic in the mixed practice set.
Efficiency questions improve quickly with someone checking your units. That is part of online one-to-one Geography tuition.