The exploitation of the geothermal field of Nisyros.
A step towards industrialization

Nikos Nikolopoulos, PhD Mechanical Engineer
Andreas Sfakianakis, MSc Mechanical Engineer, Member of the Board of Nysirian Society ‘Gnomagoras’
Nikos Frantzis, Civil Engineer, Vice President of Nysirian Society ‘Gnomagoras’

With the issue of Geothermal Energy once again being under consideration, this article has been written to inform the Nisyrian society, of some of the adverse effects such an industrial establishment will bear upon the natural environment and the biodiversity of our island. The authors, in advance, ought to declare their favourable inclination towards the development and exploitation of all kinds of renewable sources of energy – including geothermal energy – in Greece. However, due to the fact that Nisyros poses a somewhat distinctive case, the incentive for our effort has been the need for preservation of the uniqueness of the beauty of our island.

Some historical facts
The research and appraisal of the geothermal potential of Greece began back in 1972. The agency that took up the project was the Institute of Geological and Mining Studies (IΓΜΕ). The systematic appraisal and analysis of the data collected in order to produce results started in 1977, as an outcome of the collaboration between the Greek Public Power Company (ΔΕΗ) and its Italian counterpart (ENEL).

Upon initiation, the research focused on the islands of Milos, Nisyros and Lesvos, as well as in the areas of Methena, Sperchios and Edipsos, i.e. areas whose hot natural springs were known since the antiquity. In due course, the islands of Kos, Santorini, Kimolos, the greater Strimonas area, Ksanthi and the island of Samothraki were added.

The geothermal field of Nisyros
The geological research on the island commenced in 1973, consisting of a total of nine research drillings in an average depth of 70m inside the area of the caldera. Initial results revealed a considerable thermal anomaly in the area, which was in the order of 20 times that of the average surface temperature. These readings lead to the conclusion that the geothermal potential of the area is of the order of 40-50MWe. Given the load of the Nisyros, which peaks at about 1.5MWe, such a potential would easily suffice for the power supply of neighbouring islands, such as Kos, Tilos, Kalymnos and Leros.

Deeper drillings (2000m) that followed later in order to investigate the quality of the field, revealed a high enthalpy field (i.e. which can be utilized for the production of electrical power) inside the caldera. The initial scenario for the exploitation of the field encompassed the establishment of two power plants capable of producing 5MWe, with the Greek Public Power Company (ΔΕΗ), being the sole contractor and eventual management company of the plants. In due course and following an environmental impact study, ΔΕΗ designated the south of the island as a favourable location for the erection of one 10MWe power plant.

Advantages and disadvantages of Geothermal Energy
Some of the most important advantages of the use of geothermal energy are listed below:

1. It constitutes a largely renewable source of energy, should all the necessary infrastructure is in place to allow for the replenishment of the reservoir with geothermal fluid.
2. It bears minimum impact to the environment, should all measures are taken to prevent accidental/unwanted gas release to the atmosphere and the geothermal brine is managed properly – the meaning of brine is analyzed in due course.
3. The cost of operation of a geothermal power plant can sometimes be less compared to that of other renewable means of production, for example wind turbine farms.
4. Geothermal power, apart from being utilized for the production of electric energy, can be used in agriculture, as well as in the climatic conditioning (heating, cooling) of households. Such use constitutes what is called Low Enthalpy utilization of geothermal power and finds the authors favourably inclined towards it, as in the case of Nisyros it poses minimum, if any, impact on the environment.
5. Processing of the geothermal brine can yield to the production of by-products with many practical uses.

Among the disadvantages of the use of geothermal energy are the following:

1. The relatively high cost of field research and constructing the infrastructure for production of electric power.
2. The lack of adequate construction experience of power plants utilizing geothermal fields of active volcanoes, which raises the risk of the investment, as well as the environmental risk.
3. The inevitable fact that during the early stages of construction, pollutants such as NH3 and H2S will be released into the atmosphere in large concentrations.
4. The problem of re-injecting the geothermal brine, together with the condensed steam, back into the reservoir. Alternative ways of disposal are very often sought and these frequently include disposal into the sea or nearby rivers.
5. The limited life span (about 15-25 years) of the production wells and the relevant machinery/equipment, taking into account that the pressure of geothermal fluids used for production is diminishing at a rate of 5%-10% annually.
6. In addition, geothermal fluids consist of a large number of pollutants, which tend to cause significant wear of various parts of the plant, raising maintenance costs. The most important pollutants are small particles, such as ammonium minerals and nitrides, which float inside the geothermal fluid, as well as diluted gases such as methane and sulfur.
7. The significant concentration of salts in the geothermal fluid accelerates the electrolytic corrosion of the plant machinery. It is widely accepted that the life span of the equipment of a geothermal plant is about 25 years, whereas those used in drilling (piping, pumps, etc.) have a life span of less than 10 years.
8. There is an inherent difficulty in predicting of the number of wells for production and their location in the field – so that they do not overlap each other. Note that the small area of the field in Nisyros (about 3km2) is in those terms extremely limited for the production of 50MWe, which is its full potential.
9. Depending on the underground geology, as well as the frequency and rate of re-injection of the fluid back into the reservoir, the likelihood of inducing earthquakes of small magnitude is increased.

The problem of disposal of Geothermal Brine

Geothermal energy cannot be regarded as ‘clean’ energy source - with the conventional significance of term - such as solar or wind. This is because a basic by-product of the productive process is the liquid phase geothermal brine (salt water with various impurities), which is produced in significant quantities. The chemical composition of geothermal brine depends on the specific local geological and hydrological underground conditions [l].

The usual way of geothermal brine disposal is by pressure re-injection into the reservoir via another drilling. This methodology not only minimizes environmental impact, but also enriches the underground geothermal field increasing its life span. What is not widely known is that this re-injection bears many technical problems due to the various metals’ deposition onto the surfaces both of pipes and pumping stations and the re-injection equipment in general.

It is worth noting that the geothermal brine’s disposal into the sea , will have as an effect the characterization of the wider area as an industrial zone, a direct consequence of which will be the forbiddance of public swimming, as well as all other exploitations and manifestations by the local residents [1].

Another point, which perhaps is not widely known is that both marine and coastal area of South Nisyros and the island of Stroggili, are part of the network NATURA with a site code GR4210007 belonging to category SCI (indicating Community Interest).

South Nisyros is a protected area and the exploitation of geothermal energy will transform this part of the island into an industrial zone. We wonder with whose authorization and under what terms?

Therefore, based on the aforementioned remarks it is deduced that the most likely long-term environmental impact from the disposal of inadequately treated geothermal brine into the sea can be linked with its bio toxicity. The major toxic pollutants of geothermal brine, which are found in significant concentrations, are ammonia (which is toxic for the fish), and arsenic (which has a cumulative long term adverse effect in crustaceans), as well as boron and manganese, which are found in geothermal brine at high concentrations [1].

Regarding the disposal of geothermal brine in the sea, the Greek legislation empowers the Local District for the institution of laws, which determine under what conditions (eg. Purifying/cleaning processes) toxic waste can be disposed into the aquatic environment of its territory and what are the maximum allowable values of the disposable toxic elements. In a question of ours regarding this matter, forwarded to the Environment Agency of the Prefecture of Dodecanese, we received the reply that no decision by the Prefect for this subject has been made and there is no consideration of doing so in the future.

The land-planning Decree for Renewable Sources of Energy (RES)

All new plans for the land-planning Decree for Renewable Sources of Energy, prepared by the present government, have been characterized by many environmental and non-environmental institutions as disastrous for the islands, promoting failed evolutionary models, comparable to the case of the anarchic touristic growth of southern Spain. Because of this, the Ministry Of Environmental Planning and Public Works retracted in many parts of the law.

With regard to the specific context referring to RES and particularly the exploitation of geothermal fields all over Greece, the Decree is characterized by the haste shown to extract favourable conditions for such facilities, omitting the individual characteristics of geothermal energy; thus revealing particular improvisation in the confrontation of environmental subjects. It equates geothermal energy with wind farms, referring to the same criteria for exclusion zones except one minor addition: it considers that a zone radius of 1500 metres around traditional communities or protected areas (forests, natural parks etc.) is sufficient to reduce any environmental impact. In other words, it tries to convince that pollution is contained within a distance of 1500 meters from its source [15]. The possibility of possible seismic stimulation is nowhere mentioned.

The Relationship of the Geothermal Energy with Seismicity

Scientifically proven link between the exploitation of geothermal fields with an increased seismicity does not exist in the recent literature. Furthermore, there are no applications comparable to the example of Nisyros, i.e exploitation of a small in size (3km 2) field over an active volcano in a particularly earthquake-prone area (Southeast Aegean). Let us not forget that over the last years we have lived quite a few times Nisyros seismic flares, either tectonic or volcanic (1996).

Experience in applications outside of Greece has shown that it is possible, with the assistance of the underground geological composition, the rate and pressure of re-injection of geothermal fluid into the reservoir to often cause earthquakes of a magnitude around to 3-4R. You may argue that the intensity of such an earthquake is small, but man-caused earthquakes usually occur in shallow depths and thus their impact is disproportional to their size, as they are characterized by large accelerations. This has happened repeatedly in wells in Northern California in the settlement named as «The Geysers» [10]. Such earthquakes are being felt within a distance of 3-5km. Note that the village of “Nikia” is 3km away from the proposed location of the facility in Agia Irini.


In this article, we made an effort to present the experience gained by the scientific community on the issue of Geothermal Energy, as well as to pose some considerations of technical and environmental nature, relevant to the exploitation of geothermal fields for the production of electrical power. Because of both the Nisyro’s unique case (small area of useable geothermal field and topography of the landscape) and lack of adequate experience of exploiting the field of an active volcano, our concern is even more intense than it would be in the case of more suitable sites for installing such a station (e.g. Lesvos).

In addition, the lack of necessary safeguards in case of improper operation of such stations and the absence of the necessary legal framework (maximum allowable concentrations of heavy metals in both air and sea), makes the case of Nisyros comparable to an experimental model on how to exploit the high-enthalpy geothermal energy, thus incorporating extremely high risks.

We therefore believe that the best solution is to use the naturally available low enthalpy geothermal energy in order to cover part of the energy needs of the local community of Nisyros (heating greenhouses, homes, etc.). The high risks of the installation of power plants and the associated consequences of ill management - which is not unusual in Greece - or any consequence of seismic excitation, will be very unpleasant for the local population and the recent’s years very intensive touristic growth. As far as the required energy generation is concerned, which will cover the necessary needs of the island, it would be much more appropriate and safer the use of truly renewable sources such as solar or the wind, which are readily available throughout the year in abundance and contribute positively to sustainability. But no one has ever seriously considered such a possibility.

The problem of exploitation of geothermal energy in Nisyros is primarily a matter of landscape and therefore insuperable. . A Geothermal power plant in Nisyros will create more problems than it supposedly will solve. Geothermal plants operate successfully around the world, but in well-organized states, over large geothermal fields and away from residential areas, with the possibility of direct intervention in the case of an accident.

Concluding we would say thatConcluding, we would say the local community should decide on the operation of such a system or not, taking into account the aforementioned parameters, since the same people will bear the consequences.

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