Which of the following best describes a renewable energy resource?

• A. Solar and wind energy that are replenishable on human timescales.
• B. Oil and coal that are finite and deplete with use.
• C. Natural gas that is always cheap worldwide.
• D. Nuclear energy is not part of renewables.

Answer: (A)

Renewable energy resources are those that can be replenished naturally on human time scales, so we won’t run out if we use them wisely. Solar and wind energy fit this description because the sun continues to shine and the wind continues to blow, providing supply that naturally regenerates and is effectively inexhaustible for our lifetimes. This contrasts with fossil fuels like oil and coal, which form over millions of years and are finite, so their reserves can be depleted with use. Natural gas is also finite and not replenished on short time scales. Nuclear energy isn’t considered renewable because it relies on finite uranium and produces long-lived radioactive waste; its fuel isn’t replenished on human time scales. So solar and wind energy best describe a renewable resource.