Year 9 Science · Unit 3 · Lesson 3
Challenge Worksheet
Learning Goals
Evaluate the claim
Someone claims...
"The efficiency of this rooftop solar panel is only 22%, it is a complete waste of money. Nearly 78% of the sunlight hitting it is wasted, so solar panels are basically useless. We would be better off just burning natural gas, which produces much more useful energy per dollar."
(a) What part of this claim is supported by science you have learned in this lesson?
(b) What is misleading or missing from this claim? Use energy conservation principles to explain what happens to the "wasted" 78% of sunlight, and why the comparison with gas may not be fair.
(c) What additional information or evidence would you need to properly evaluate whether a 22%-efficient solar panel is better value than a natural gas system? List at least TWO factors.
1. A natural gas heater uses 2,000 J of chemical energy and delivers 1,700 J of useful heat (efficiency 85%). An electric resistance heater uses 1,200 J of electrical energy and delivers 1,140 J of useful heat. Calculate the efficiency of the electric heater. Which device is more efficient, and why might this comparison still be misleading without knowing how the electricity was generated?
2. Construct a reasoned argument for why improving the efficiency of existing devices (like cars and appliances) might reduce Australia's total energy demand more quickly than building new power stations. Use the concept of waste energy in your argument.
Wrap Up
In one sentence, what was the main idea of this lesson?