Renewable Energy

Suppose you have a one-year subscription to your favorite magazine. At the end of the year, you do not want to miss a single upcoming issue. Fortunately, most magazine publishers have very easy ways for you to renew your subscriptions and never miss a single issue. As long as you keep renewing the subscription, you will never stop receiving your favorite magazine. 

Energy sources are like your subscription—you definitely do not want them to run out. But, there is a major difference—only some energy sources can be renewed. If we can replenish our supply of energy after we use it, we never run out. One example is hydropower. Electricity from hydropower comes from running water. Since the water cycle always replenishes our water supplies through precipitation, we can always rely on hydropower. This is a renewable energy source.

In contrast, a non-renewable energy source eventually runs out. Like a magazine whose publisher decides to stop making the magazine—it cannot be renewed. Once we use up all our fossil fuels and uranium supplies, they are gone for good. We cannot replenish them.

Why are fossil fuels and uranium considered non-renewable?
 

These take nature millions and millions of years to make. They are definitely not renewable on human time scales.

Consider three important renewable energy sources: solar power, hydropower, and wind power? How are all three of these dependent on the Sun?

Solar power is derived from radiant energy from the Sun. Hydropower relies on water supplies in the water cycle, which is in turn driven by energy from the Sun. Likewise, the wind blows because of temperature and pressure differences caused by the Sun.