Energy

Clean energy?

Geothermal energy is usually considered clean energy. Its production in theory doesn’t produce dusts or toxic substances that could be dispersed in the atmosphere and there is no toxic waste to dispose of: the only subproduct of the energy process are the white plumes of the clouds of vapour that are released by the cooling towers. However, unfortunately, things are not so simple and “clean” in nature. The waters that flow underground are rarely freshwater: in the majority of cases they are highly concentrated saline solutions, which often contain highly toxic and polluting substances. Vapour is generally associated to other gases, like H2S and CO2, while the waters often contain heavy metals or arsenic. This characteristic, among other things, prevents a direct use of the geothermal waters: because of the chemical characteristics combined with the high temperatures, these waters are very aggressive and rapidly erode the pipes and machinery which they touch, so it is necessary to use special materials. These types of waters obviously cannot enter in direct contact with agricultural grounds and products, animals or food and their use must necessarily be indirect. From the environmental point of view, the quality of geothermal fluids is such that the discarded gases and fluids must necessarily be treated before they can be readmitted in the atmosphere or in the circuit of superficial waters. The best solution is to condense and separate the polluting gases before freeing the vapour and readmitting the liquids in the subsoil.
Moreover, the big cooling towers of a geothermal plant usually have a significant environmental impact from the aestethic point of view, even though, of course, this type of “pollution” is definitely preferable to that of a fossil fuel thermoelectric plant! However, natural expressions linked to the presence of geothermal fields, such as the emergence of thermal waters and phenomena lilke geysers, often make these areas particularly valuable from an environmental and landscape point of view; moreover, often in these areas there are prestigious thermal baths, of historical and economic value, therefore even the aestethic impact of the plants can represent a serious problem. The vapour turbines also produce a significant acoustic pollution, even if this problem can be easily solved through specific isolation systems. From these short considerations we can conclude by saying that geothermal energy is “clean” if some fundamental rules are followed!
Energy forever?
The Earth’s energy is, compared to the scale of human life, apparently inexhaustible, however even the use of geothermal fields has to be accurately controlled and managed. Geothermal fields tend to progressively cool down, which diminishes their productivity: the constant input of cold waters can noticeably increase this natural process. In the same way, the excessive withdrawal of fluids from the subsoil can trigger subsidence phenomena (as happened, for example, in Wairakei), which are very dangerous in densely populated areas. To remedy to this phenomenon the fluids have to be put in the subsoil: in this way, not only the nearby areas are protected, but the life of the geothermal system is prolonged, thus minimising its utilisation problems. It is clear though that this resource is also delicate and needs to be managed with care and knowledge in order to maintain a good level of productivity without harming the surrounding environment.