Which characteristic defines renewable energy sources?

The defining characteristic of renewable energy sources is that they can be used continuously without depletion. This includes sources such as solar, wind, hydro, and geothermal energy, which are replenished naturally and sustainably over time. Unlike fossil fuels, which are finite and take millions of years to form, renewable energy sources are inherently sustainable since they harness natural processes that are continuously available. For instance, sunlight is consistently available during the day, and wind can be harnessed as long as atmospheric conditions allow.

The other characteristics listed do not accurately reflect renewable energy sources. They are not limited and non-replenishable; rather, they are infinite in scope within human time scales. They also do not rely on fossil fuels, which are actually the opposite of renewable, being depleting resources, and while some renewable energy systems might require human intervention for implementation, the energy itself is primarily derived from natural processes rather than activities that manipulate the environment in a harmful way. Therefore, the attribute of being continuously usable without being depleted distinctly characterizes renewable energy sources.