What is Geothermal Energy?

The earth consists of three parts: the core, the mantle, and the crust. The heat, which is highly concentrated in the earth’s core, constantly flows out and transfers to a layer of rock called mantle. Because of high temperature and pressure, some rocks of the crust melt. This is called magma which is the most important source of geothermal heat. Since magma is less dense than nearby rocks, it rises towards the earth’s crust closer to the earth’s surface. As magma moves up, it transmits heat through the deeply circulating fluids moving within the fractured reservoir. When the superheated water or steam rises to the surface, it forms hot springs, geysers and fumaroles.

What elements compose a geothermal system?

A geothermal system can be likened to a covered pot filled with water. When heated the water boil and produced steam just like in a geothermal system.

Four elements compose a geothermal system, namely:

1. A heat source, which is the magma that comes close to the surface of the earth in volcanic areas.
2. A permeable underground reservoir rock, which can hold or store water.
3. A solid cap rock, which maintains pressure and does not allow the heat, water or steam to escape.
4. Water, which serves as the medium for carrying the heat.

Where does the steam come from?

Geothermal reservoirs consist mainly of rainwater or “meteoric water” that seeps slowly via cracks and faults. This water ultimately reaches depths of over 3 kilometers where it is heated by hot rocks. Hot geothermal fluids are tapped by wells at depth and flashed into steam at the surface or at the wellbore.

One way to recharge a geothermal reservoir is by reinjecting the spent geothermal fluids. If done properly, reinjection can help maintain reservoir volume and pressure. However, experience in several geothermal fields has shown that reinjecting cold brine too close to production wells can adversely affect steam production.

What signs indicates the presence of geothermal resources?

The presence of geothermal resources is indicated by volcanoes, hot spring, fumaroles and solfataras. The Philippine archipelago hosts several volcanic areas where geothermal resources occur. Geoscientists believe that a potential of about 4,339 MW (megawatts) can be tapped from these resources.

How long does a geothermal field lasts?

There is a finite volume of hot fluids available in any geothermal reservoir. Natural recharge is usually very slow and production wells begin to decline as soon as commercial operation starts. Therefore the “lifetime” of a particular field will depend on the development size (that is, extraction rate) and re-injection strategy.

Many fields have produced geothermal steam and generated power for over 30 years through drilling of new wells to replace declining ones.

The Larderello field in Italy was first developed in 1904 and is still generating about 547 MW of power today.

Locally, the Makban and Tiwi Geothermal Fields had been in commercial operation since 1979 or for more than 27 years.

How is geothermal energy converted into electricity?

Geothermal steam is extracted from the reservoir through steel pipes. A mixture of hot water and steam under its own pressure flows up to the pipe. Upon reaching the surface, the water and steam pass through a separator to separate the water and steam and through a scrubber to remove any impurities. The steam is directed to a power plant to spin the blades of a turbine while the condensed water is re-injected back to the reservoir. Attached to the turbine is a generator which produces the electricity.

The electric current is then transmitted to homes, offices, factories and other industrial users.

Can a geothermal operation cause a volcanic eruption?

Scientists agree that no man-made activity can cause a volcanic eruption. Scientific studies have shown that the drilling of wells or other geothermal operations have never caused any volcanic eruption. Geothermal drilling up to 3 km. depth is too shallow to affect a magma chamber, which typically occurs at a depth of about 15 km.

Where in the Philippines can we find producing geothermal fields?

The total geothermal power capacity of the Philippines is 1,977.69 megawatts.