Geothermal is one of alternative energy for the future. This energy is derived from Earth’s heat. It’s clean and sustainable. The Earth’s core consists of very hot material. It will be sent to upper part. Those heat would be trapped and save by rocks beneath of the Earth’s crust. The part of earth’s crust which is rich of water content will be evaporated because of heat flow from the Earth’s core. Next, that steam will be processed and filtered for activating the electric turbine which result geothermal energy. Geothermal energy is made up on varies of deep. Nowadays, geothermal has been used in some countries around the world including Indonesia. In Indonesia, only 4 percent resources that has been explored from the entire geothermal capacity in this country. For some reason, geothermal is better and friendlier energy than oil. It can be extracted without burning fossil fuel, such as coal and oil. So, it doesn’t make any greenhouse effect. But, we still have to remember how to act wisely in every exploration step. If all of us drill with the wrong procedure, it will release hydrogen sulfide, a gas that smells like rotten eggs. Furthermore, doing the wrong procedure will cost us the environment. For you information, this awesome energy can only be explored in specific place which associate with volcanism activity.
Figure 1. Map of Geothermal Potency
Here are the description about Indonesia as the “geothermal-country” : Indonesia is a nation where 4 tectonic plates exist, which are Pacific Plate, Indian Plate, Eurasian Plate and the most recent plate is the Australian Plate that collided with Eurasian Plate at the eastern part of Nusa Tenggara Timur up to Papua Island. Therefore, appearing islands like now that called as Island Arc (Java, Sulawesi, Maluku, NTB and NTT) and Continental Arc (Sumatra). Both Island Arc and Continental Arc are formed as results from partial melting process, caused by a subduction between Indian Plate and Eurasian Plate. The subduction formed a series of volcano throughout Indonesian islands. This series is called The Ring of Fire. This explains why the content of magma below of Indonesia (especially in subduction zones) is abundant. It is caused by partial melting process which fills the magma chambers. The effect of existing magma chambers will give heat radiation to rocks that surrounds it through a path that is caused by geology structures (fault or joint). By viewing at the figure and Indonesia tectonic setting, we can conclude that Indonesia has the biggest potency for Geothermal Energy in the world, approximately 29GW.
One of the characteristics of geothermal existence is the occurrence of hot springs. Below are some well-known hot springs in Indonesia:
Pancuran Tujuh is located at Baturaden, Banyumas Regency, Central Java. People call it Pancuran Tujuh because there are seven water holes where the water is discharged. The temperature of Pancuran Tujuh is about 60˚ C and has neutral pH. In Geochemistry, water in Pancuran Tujuh is made from the mixture of bicarbonate sulfate and chloride. In this hot spring, we also can find Travertine. Travertine was made from precipitation Ca2+ Rich bicarbonate water that usually well-formed in an area that has geothermal potency. Baturaden geothermal reservoir consists of pyroclastic and andesite rocks, with 1-1,25 km thickness. The Na-K-Ca and Mg correction geothermometer delivers a 200˚ C – 210˚ C reservoir temperature that comes from Slamet Mountain (Utama, etc. 2012).
Dieng Plateau Area
Dieng Plateau is located about 26 km in the north of Wonosobo City. In this area, there are many geothermal manifestations in the form of hot springs, such as, Bitingan, Sileri, Siglagah, Pulosari, Kaliputih, and Sikidang Hot Spring. The temperatures of those hot springs ranges from 43˚C up to 61˚C and pH of 6 – 7. The geochemistry of hot water is bicarbonate, sulfate, chloride, and sulfate mixture derived from the condensation process of steam. Reservoir temperature ranged between 225˚C and 300˚C. In this area, Geothermal reservoirs that are recommended for further exploration or exploitation are a reservoir feeding Sileri and Sikidang hot water.
Cisolok – Cisukarame
Cisolok – Cisukarame is located at Sukabumi Regency, West Java. Temperatures of hot springs in Cisolok vary from 71˚C until 100˚C whereas hot spring in Cisukarame is about of 46˚C and pH of about 7.7. Geochemistry of hot water in Cisolok – Cisukarame is dominated by chloride and immature waters. Calculation of Na-K-Ca temperature geothermometer indicates reservoir 160˚C until 200˚C (Utama, etc. 2012). In Cisukarame, there are no surface alteration that can be found around the hot tub, except a mixture of colloidal silica and organic material found in the surface water of the hot pool. Cisolok – Cisukarame geothermal system is predicted as deep outflow from Mount Halimun.
Parangwedang is located at Bantul and Gunung Kidul Regency, Daerah Istimewa Yogyakarta. In this location, we can find two hot springs as geothermal manifestation. People usually call it Parangwedang 1 and Parangwedang 2. The temperature of Parangwedang 1 is 43°C and pH 7.5-7.7. The water has a salty taste, odorless and accumulated in pools of hot water. In the other hand, the hot water at Parangwedang 2 comes from wells, dugouts at a depth of 6 meters. The temperature is 50° C and pH 7.49. The water also has a salty taste, colorless, and odorless. The hot springs of Parangwedang 1 and 2 are controlled by Parangkusumo fault structure towards Northwest-Southeast. In this location was also found an altered zone that characterized by the presence of chlorite and serisit. There is also a volcanic rock or magma intrusion which is a remnant of the subduction zone in South of Java, which is estimated to be the source of heat from geothermal in this location. Geothermal system of this area is also possibly an outflow zone from Merapi Mountain.
Created by :
Hagi Ridho Raras
Mohamad Irza Fandi Pradana
Fransisca Ayuni Catur Wahyuandari
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- Utama. Dwinanto. Situmorang. Hikmi. Irshamukhti. 2012. Greenfield Geothermal System in Java, Indonesia. Proceeding, 1st ITB Geothermal Workshop 2012. Bandung : Institut Teknologi Bandung.