published on 22 December 2016 in energy
Geothermal stories: what can we do with the hot water?
Close your eyes and think of the word ‘geothermal’. What you see? In addition to hot springs, the spectacle of geysers and the production of electricity, what can we do with the hot water? Actually, despite little is said of it, there are already many uses of geothermal energy and many others have yet to be perfected: from the cultivation of roses in Kenya to wine making in Spain, from the production of cheese in Italy to drying timber in New Zealand .
The possibilities of geothermal energy: resources and technologies
To try to bring some order to the meanders of terrestrial heat, let us first of all try to classify the geothermal resource, which is normally divided into:
- vapour-dominated hydrothermal systems: if the geothermal fluids contain both water and steam, with the latter in much higher percentages;
- water-dominated hydrothermal systems: when water in the liquid state or a mixture of water and steam is present;
- hot dry rock systems: these are found in areas with high temperatures and low permeability;
- geo-pressurised sand: in a sedimentary context, where the fluids present in the pores are subjected to high pressures.
As Lindal already described in his diagram in 1973, the applications that can be introduced depend on the temperature of the geothermal fluids. If we consider the energy content, the resource can be divided into three main categories:
- high enthalpy (the fluids have a temperature exceeding 150-200°C)
- average enthalpy (the fluids have a temperature between 100°C and 200 °C)
- low enthalpy (the fluids have a temperature below 100°C)
Finally, from a technological point of view, geothermal energy can be divided into direct and indirect uses. In the first case, the terrestrial heat is used directly in the form of thermal energy, for example for aquaculture or air conditioning, while in the second case, it is converted into electricity and fed into the grid.
Now that we are ready, let us abandon the classifications and get to the heart of four geothermal stories.
In the heart of Tuscany, in the town of Monterotondo Marittino, a few kilometres from Larderello, the dairy tradition and geothermal tradition have combined their efforts at the San Martino farm, which produces its cheese with the milk from Massa sheep raised wild within a radius of 300 km, for a total of 50,000 tons of milk, 40,000 rounds of Pecorino and 20,000 of Ricotta.
Considering that the cheese production, maturing and storage processes require significant amounts of energy both to heat and to cool, the company decided to reduce its production costs by taking advantage of the presence of a nearby geothermal power plant. In the electricity generation process via the turbines driven by steam, geothermal plants have, as a by-product, a fair amount of residual heat that is often not used. And it is precisely this heat that the San Martino farm decided to use, thus reducing its energy consumption costs, costs which previously amounted to 10,000 euros (8-9% of the total cost of production).
To transport the steam from the geothermal power plant to the dairy, a 72 mm diameter, 500 metre long, insulated pipeline was built.
The farm is part of the “Taste Clean” Slow Food project, which aims to promote food production through the use of sustainable energy. This is a direct use of geothermal energy which is particularly important for Italy, where the food industry plays a fundamental role and where 30% of energy consumption regards medium-low temperature heat requirements.
The Unterhaching power plant
The town of Unterhaching, in Bavaria, near Munich, was the first town in Germany to use geothermal energy as a source of thermal energy, used for both district heating (since 2007) and for electricity generation (since 2009). The geothermal resource of this plant has temperatures of between 60 and 120 °C and provides approx. 37.5 MW (Megawatts) which should ensure the necessary energy for the 22,000 inhabitants of Unterhaching for some time to come.
Also this is a case of production of electricity from geothermal sources, with subsequent indirect downstream uses. This is a very advantageous approach that could be easily replicated in many regions of southern Italy which have similar geothermal characteristics.
Air conditioning with mines
The transition towards clean energy and the depletion of certain deposits means that Europe is dotted with old abandoned mines. This is the case of the city of Heerlen, in the Netherlands, where the last mine was closed in the 70s and where the European Union has supported the Minewater project. The initiative was established in 2005 with the idea to convert these sites and turn them into a clean energy source, capable of launching an alternative development model and new employment opportunities.
In these abandoned coal fields, water is drawn from various levels of the mines and used for air conditioning (heating/cooling). The tunnels also have another function: seasonal storage of heat in the ground.
This is again a case of direct use that could be widely applied in Italy, where, especially in Sicily and Calabria, there are now many abandoned mine tunnels.
The last short geothermal story that we propose is that of Bodegas Regalia in Ollauri (Spain). This is the first company in the world to use geothermal energy to produce wine. Here the geothermal plant is used – through heat pumps – in both the wine-making process, as well as for air-conditioning (in summer the geothermal fluid cools the buildings and in winter heats them).
A positive example internationally, Bodegas Regalia could also be an important source of inspiration for our South, a region that rightly can be considered as much a wine producer as having geothermal energy.
By Anna Pellizzone
Sources and insights: