Geothermal energy in the lake basin

Our area has very favourable characteristics for the exploitation of geothermal energy of medium and high ‘enthalpy’: the geothermal fluid available is found at modest depths (from 1 km onwards) and has high temperatures. This is the reason why there are many requests for authorisation, both for research into this resource and for its cultivation. (See list)

Two plants in the project phase

The most advanced projects in the process of administration are those on the Alfina Plateau, one at Castel Giorgio and another at Torre Alfina, so-called ‘closed cycle’ pilot plants (a type never before built in our area), and that of the ‘Nuova Latera’, a conventional ‘flash’ type plant, the same used in the power stations of Mount Amiata.

What is geothermal energy?

Geothermal energy is the thermal energy contained in the centre of the Earth. The term is also used for a plant engineering technique by which heat is extracted from the subsoil in order to use it for domestic heating or to produce electricity.

What does this plant engineering technique consist of?

It varies according to the type of heat source.
The technique for low enthalpy extracts heat from the subsoil at a shallow depth near the environment to be heated.
Medium enthalpy plants extract geothermal fluid at a maximum temperature of 150°C through wells 1,000 metres or more in depth; those for high enthalpy extract fluids at temperatures above 150°C.
The distinction is only administrative: authorisations for the medium enthalpy plants are of regional competence, while those of high enthalpy are of state competence.

What are medium and high enthalpy power plants?

The geothermal fluid at high temperature is extracted from the subsoil through production wells connected to a power station. In this, the fluid gives up its energy. The cooled fluid is re-injected into the same source formation by re-injection wells. These are located a few kilometres away from the production wells to avoid extracting cooled fluid from those.

On what hypotheses are they based?

This geothermal technique presupposes two essential hypotheses:

• that the re-injected fluid flows horizontally in the subsoil to return to the production area, re-heating itself along the way;
• that the geothermal fluid does not rise in the subsoil to the surface aquifers, contaminating them.

In our area both hypotheses are scientifically contested because the ground in the subsoil is strongly fractured and has a high number of vertical faults that obstruct the horizontal flow and facilitate the ascent towards the surface aquifers.

What risks are involved in our area?

If the fluid from the re-injection zone can’t return to the production zone, there is a permanent transfer from one area to another, creating pressure and thermal imbalances. Other imbalances are created in the fluid extraction area (underpressure) and in the re-injection area (overpressure). All these imbalances over time increase the seismic risk.

Another aspect of the fractured subsoil structure is the possible vertical communication between the geothermal and the surface aquifer that contains drinking water. In the re-injection zone the pressure is necessarily higher than the natural one, so it can cause the geothermal fluid to rise up along the faults towards the surface aquifer. The geothermal fluid contains carcinogens, including arsenic, and there is a risk of contaminating the aquifer that feeds the drinkable water network.

On the other hand, in the production area the reverse situation occurs: the underpressure in the geothermal reservoir draws fluid from the drinking water aquifer, depleting it.
Both of these effects are real and have been observed in the Mount Amiata area.

Given that it is impossible to demonstrate a priori the absence of these serious risks, one should apply the principle of precaution.

What are the characteristics of the new plant planned for Latera?

The New Latera power plant is of the ‘flash’ type. These are old-style systems called ‘1st generation’, the commonest all over the world. All of the Amiata power stations are of this kind. Their characteristic is that decompression of the extracted fluid is very rapid (‘flash’), transforming it into high pressure steam. This drives turbines that generate electricity through generators. After use, the ‘condensable’ portion of the cooled vapour is condensed in the liquid phase and fed into the re-injection wells.

The ‘incondensable’ part of the vapour is almost entirely released into the atmosphere; only a part of the hydrogen sulphide, ammonia and mercury is retained in special filters. In particular, a large quantity of carbon dioxide (CO2), of water subtracted from the geothermal reservoir (which creates an additional imbalance in the geothermal reservoir), of malodorous and toxic gases and of other dangerous pollutants are released.

The consequence is a widespread pollution of the area and of the population with a significant increase in mortality, as observed for the Mount Amiata plants.

Another consequence is that, because in our zone the concentration of carbon dioxide contained in the geothermal fluid is very high, the quantity of this gas introduced into the atmosphere far exceeds that which would be emitted from a modern gas plant producing an equal amount of electricity. Geothermal energy in our areas is neither renewable nor sustainable, and the provision of incentives is unjustified because emissions do not reduce the greenhouse effect, rather they increase it.

And the ‘pilot’ plant at Castel Giorgio?

These are systems that pass the geothermal fluid through an exchanger, which transfers heat to an independent fluid that drives a turbine. The cooled geothermal fluid is re-injected entirely into the subsoil: no gas is released into the atmosphere – a closed cycle system.
However, all the negative aspects which disturb the structure of the subsoil remain, even increased for the same amount of electricity produced, due to the greater movement of fluid due to minor performance.
It is important to note that the president of ENEL Green Power, referring to the experience of ENEL in our area with experimental plants of this type, considers these plants unrealisable and dangerous, precisely because of the high level of incondensable gas in geothermal fluid.

In conclusion?

There is no question of geothermal yes or no, but where yes and no. In our area geothermal energy of medium and high enthalpy is not sustainable and is opposed by the mayors and by the population, because it is in contrast to the vocation of the territory; because it pollutes the drinking network aquifer with arsenic; because ‘flash’ systems release greenhouse gases and other harmful substances into the atmosphere; because it increases the seismic risk and because it endangers the hot water resources of the thermal springs.

What can we do?

Inform ourselves and others; join one of the committees of the area.

Comitato Farnese – Ambiente, Salute e Territorio
Tel. 3494065766
https://www.facebook.com/comitatofarnese
comitatofarnese@gmail.com

Comitato Latera
comitatolatera@gmail.com

Maremmattiva
https://www.facebook.com/maremmattiva/
maremmattiva@gmail.com

Comitato Castro – Ambiente Salute e Territorio (Ischia di Castro)
https://www.facebook.com/comitatocastro/
comitatocastro@gmail.com

Comitato Difesa Ambiente e Territorio di Canino
https://www.facebook.com/comitato.territorio.canino/
comitato.territorio.canino@gmail.com