What is a key characteristic of a renewable energy source?

A key characteristic of a renewable energy source is that it cannot be depleted. Renewable energy sources, such as solar, wind, hydro, and geothermal, are continuously replenished by natural processes. This means that as long as the sun shines, the wind blows, and water cycles, these sources can provide energy without the risk of running out.

While it may be true that some renewable sources like solar and wind are abundant and more accessible at certain times, they are not "always available" due to fluctuations in conditions. Additionally, while renewable energy can be more cost-effective over time, it is not always the cheapest option upfront, as the initial investment for renewable energy technologies can be higher than fossil fuels. Finally, renewable energy sources typically have some level of environmental impact, even if it is less than traditional fossil fuels. Thus, the aspect of being unable to be depleted distinctly emphasizes sustainability, making it the most defining feature of renewable energy sources.