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Chapter 2. Solar Energy Powers the Water Cycle

Solar energy is an important part of the water cycle. The water cycle describes how water moves from the Earth, into the air, and back to the Earth’s surface. It is powered by heat from the sun. Without the sun, there would be no water cycle. The sun heats the water up and makes some of the water evaporate. When water evaporates it turns into a gas that goes up in the air. Eventually it gets so high that it can form clouds. When water is a gas it is called steam or water vapor. This water can condense back into water or even freeze into ice when it is high in the sky. It weighs so little that is able to float (for a while) because the sun is heating the Earth which continues to push air upward.

Water in clouds can eventually fall back to Earth as rain or snow. Water sticks to other water very easily. In clouds, tiny drops of water connect with other drops of water and get bigger and bigger. When they get too big, they will start to fall back to earth. If this water immediately runs into a river, lake or ocean, it is still in the water cycle. If this water is immediately absorbed by a plant’s roots, then it helps the plant make energy (more on that next chapter!). If that water falls in your mouth, it is delicious!

Think about the energy that this process takes! The sun is warming water on earth, which makes it move. As water drops get higher, they gain the potential energy to fall back to earth. When the drops get big enough, they fall back to earth. The energy from falling rain can move pebbles and dirt as water runs into streams. And, the energy stored in water can be used by plants to grow tall, make seeds, and sink roots deep into the earth. All this energy starts with the sun and is transformed over and over again. It’s a great example of how energy changes forms but never is destroyed!

Humans use water’s energy. Smart!

Humans have figured out that energy from the water cycle can be used to produce electricity. Hydropower is creating energy (such as electricity) from moving water. When water is released from a reservoir, which is a large lake that stores water, it enters a turbine. The turbine spins the water. The turbine is connected to a generator, so when the turbine spins the generator produces electricity. Hydropower uses energy to create work. That work is making electricity. Hydropower uses moving water, which we consider to be renewable (remember “renewable” from chapter 1?). Why is moving water renewed? Because the water cycle allows water to circulate across the earth all the time. The water cycle is an endless, recharging cycle, which makes hydropower a renewable energy source. 

The Environment & You

If you want to show some love to your planet, then try cutting down your shower time. According to USGS, old showers used up to 5 gallons of water per minute. Water-saving shower heads produce about 2 gallons per minute. Cutting back even a few minutes, can save many gallons of water. Which adds up over the years and decades you will be showering!

Topic for Another Day

Some readers start asking, where does the Sun get its energy? If you want to explore this idea, search for “Sun” and “fusion” to learn how the sun transforms energy from hydrogen into solar energy and helium.

Writing Topic

Do you agree solar energy powers the water cycle? Write a paragraph explaining your answer.