Flick.

With the flip of a switch, a light turns on. 

But where does the electricity come from?

In one small German town called Geretsried, it will soon come from deep underground. Locals hope to power their homes with geothermal energy.

Right now, geothermal energy makes up less than one percent of the energy used in the world. (Imagine 100 houses. Of all those houses, not even one uses geothermal energy.) 

Geothermal energy works like this:

We walk and build on the Earth’s surface. It’s called the crust. Far below our feet is the Earth’s mantle. The mantle is made of extremely hot rock and magma. Between the mantle and the surface, Earth hides pockets of water flowing over hot rocks. That water becomes extremely hot too. (More than 300 degrees Fahrenheit!) 

People drill deep down. They bring that hot water to the surface. Hot steam rises. It is used to turn turbines at geothermal power plants. Those turbines produce usable energy. 

About 15 years ago, a drilling company couldn’t find enough hot water close to the surface near Geretsried. 

Too bad. It seemed then that using geothermal energy wouldn’t work. “We gave up. We had big hopes,” says Mayor Michael Müller.

But times have changed. People found a new way to get geothermal energy. They inject cooled water down into the dry, hot rock. That water gets hot. People harness the heat energy with the turbines. 

A company called Eavor drills two wells about 2.5 miles deep. The wells connect to create a loop. Water flows through it, getting hot and trapping energy. 

That hot water and steam will be used to make electricity. The very hot steam will travel through pipes. It will warm and heat water for about 36,000 homes. 

Why? Tapping into Earth’s natural heat may turn out to be a wise way to steward resources.