Geothermal power

What happens on a calm, cloudy day when there's no sunlight to absorb, or wind to capture? There's another renewable energy source, one that's far below our feet. It comes from the center of Earth, its core. The Earth's core is around 6000 degrees Celsius. This immense heat conducts towards Earth's crust, heating up masses of rock.

When water seeps into the ground and comes into contact with this rock, the water heats up tremendously. These pockets of heat are called geothermal reservoirs. Iceland rests on a delicate part of Earth's crust where two tectonic plates meet. A lot of heat bursts out of the ground in the form of steam vents and volcanoes. The country harvests this heat directly.

Water pipes are built into the ground, passing through the heat source. The pipes carry heat from the reservoir to houses and buildings. Iceland is a very cold country so the geothermal reservoirs are perfect for producing cheap, accessible heat for the population. Almost 90% of Iceland's people get heating from geothermal heating systems. Steam vents have lots of kinetic energy.

Build a power plant over the steam vents and the steam powers a turbine. After spinning the turbine, the steam is cooled down, changing into liquid water. The water is pumped back into the ground where it is heated by the hot rock and the cycle continues, ​free renewable energy. ​Geothermal energy is not affected by weather like wind or solar power, making it the most reliable renewable energy source. Steam power plants are also cheaper to build than other types of power plants. Iceland gets 30% of its electricity from geothermal sources.

There are other countries that are lucky to have thin crusts too. Kenya, El Salvador, and the Philippines get over 15% of their total electricity from geothermal sources. There are some places where the crust is thicker, so geothermal reservoirs are not easily accessible. In this case, people have to dig far down to reach the reservoir. Using geothermal heating is also not as simple, the reservoirs are deep underground so the heat has to travel further.

By the time it reaches buildings, it's not very hot any more. ​There is an electronic device that extracts heat from outside and pumps it inside, it's called a heat pump. Water pipes pass through the underground heat source and sends heat to the heat pump. In the heat pump, the warm water heats another fluid. The fluid changes from liquid to gas, the gas is then compressed causing the temperature to rise. This heat is sent into the house where it heats floors, radiators, and water tanks.

Heat pumps only use a little electricity to extract heat from existing sources. It still uses less power than generating heat directly from electricity. If the weather gets hotter you can reverse the way a heat pumps works. The heat from inside is pumped outside cooling the air inside. Heat pumps provide both heating and cooling. ​Geothermal reservoirs are a great source of energy, both for heating and generating electricity.

The only down side is that they are naturally occurring so you first have to find one before you can harvest its energy, but even if the wind dies down or clouds cover the sun, geothermal reservoirs keep pumping out the Earth's energy.