Final answer:
The book 'The Boy Who Harnessed the Wind' provides the example of solar cells converting sunlight into electricity as a way of harnessing energy from the sun, in accordance with the law of conservation of energy.
Step-by-step explanation:
In the book 'The Boy Who Harnessed the Wind', an example that illustrated how you can use the sun to produce energy is the use of solar cells. When sunlight impinges on a solar cell, it produces electricity. This electricity can then be used to power an electric motor, showcasing the transformation of solar energy into electrical energy, which can further be converted into mechanical energy.
Notably, this is an expression of the law of conservation of energy, which states that energy cannot be created or destroyed but can be changed from one form to another. Thus, in a solar cell, energy from the sun (solar energy) is conserved and transformed into a usable form for human activities, exemplifying the solar energy conversion process.