Italian heritage - profiling hydro in Italy20 April 2006
A profile of hydro power in Italy, from early increases in storage capacity to the current situation and requirements for the future
Italy is a long peninsula, solidly anchored to the middle of Europe and protruding in the Mediterranean almost to Africa. The country could be considered to be divided into three zones; the Northern part, with a continental climate, maximum rainfall, and river flows highly influenced by the snows and glaciers of the Alpine chain; the Southern part, including the two major islands of Sicily and Sardinia, with a semiarid climate, rainfall mainly concentrated in winter, and the river streams often dry in summer; and finally a Central zone with intermediate characteristics with local variations due to particular geography or microclimate.
Italy’s average annual rainfall amounts to 300km3, corresponding to about 1000mm of rain over an area of 300,000km2.
As already mentioned, the rainfall follows different patterns: summer rains and winter snow prevail in the North, while winter rains (and some snow) prevail in the South. A broad transition zone also exists with spring and autumn rains.
Generally speaking, the rainfall distribution is as follows:
• 40% in the Northern region.
• 22% in the Central region.
• 24% in the Southern region.
• 12% in the major islands.
Of the overall rainfall volume only one half, 150km3, represents the surface water (with runoff coefficients varying from 0.6km in the North to 0.2km in the South) but only 100km3 is potentially available for civil and industrial uses.
Taking into account that the overall national demand for water is about 50km3, one could say that Italian water resources are largely sufficient. But in reality, because of seasonal variations, the fact that water is more available when the demand is less and so on means that the surface water which could be exploited from the non-regulated river flows is only 15-16km3, corresponding to 16% of the potential resources and 30% of the nation’s demand.
In order to increase the amount of water that is readily exploitable, numerous artificial reservoirs have been built during the past century which, with a combined volume of about 10km3, have brought the available resource to 40km3.
The remaining portion of the demand (10km3) is now being satisfied by groundwater, which is subject to hydrological fluctuations, table depletion, climate changes and other unfavourable side effects.
Therefore, in order to assure a more reliable water supply, various studies carried out in recent years show the necessity for Italy to build in the medium term (within the next 10-20 years) additional storage capacity of an amount no less than 5km3.
The history of dams in Italy is summarised in Table 1. The highest average increase took place during 1950-1970 (when the capacity rose from 3 to 7km3), while from 1970 up to now (when capacity went from 7 to about 10km3), the increase was almost entirely due to the work done in the South. This has been possible thanks to the Cassa del Mezzogiorno institution, a special agency for interventions in the South that operated from 1953 to 1993.
We can add that out of a total capacity of 10km3, 5km3 is for hydroelectric use or mainly for hydroelectric use, while the other 5km3 is for non-hydroelectric use; that is for irrigation, drinking water and so on. This figure also includes the regulated volumes of the five major Alpine lakes (Maggiore, Como, Iseo, Idro, Garda), which amounts to about 1.2km3.
It is to be noted that of the 328 hydroelectric reservoirs, about 50 are also used for other purposes besides the production of electricity: 41 for irrigation and drinking water and nine for flood regulation.
Dam types range from early hand-placed masonry to modern rolled earth embankments. Concrete dams are sited in the propitious gorges, especially in the Northern Alpine chain.
In the last 50 years, technical progress has promoted the embankment dam with variegated solutions for the water barrier: embankment dams nowadays make up about 35% of Italy’s whole dam system. Not considering the Vajont arch dam (262m high), which is no longer in service, the maximum height of 174m is reached by the gravity Alpe Gera dam, in full service since 1960.
The maximum embankment volume of 12 x 106m3 is attained by Monte Cotugno, one of the largest earth dams in Europe, including a reservoir that has reached, to date, the maximum filling of about 500hm3. The Italian dam network is quite aged; almost 60% of the structures are more than half a century old.
Hydro power generation plants
Several studies have evaluated Italy’s technically exploitable generation capability to be around 65TWh/yr. Present power plants generate an average of 46TWh/yr; this corresponds to about 70% of this potential. In Table 2, the power plants are grouped by various types of owners and split between mini hydro and others. Figure 2 shows the historical trend of the hydro capacity installed from 1920 to 1990. The hydroelectric production (46TWh/yr) accounts for about 15% of the total electric consumption (approximately 300TWh/yr).
Pumped storage plants
At the end of the 1960s there was considerable growth in demand on the Italian grid, as a result of the high rate of industrialisation in the country. Consequently, Italy’s electric company ENEL undertook a major programme for the construction of thermal stations and at the same time, to respond in the best possible way to the power demand during peak hours, a parallel programme of building large pumped-storage plants. This programme has led to the installation of more than 7000MW of capacity. Table 3 shows the key parameters of the plants.
As far as the type of machinery is concerned, the oldest plants adopt ternary units (motor-generator, turbine and pump), while the more recent stations include reversible pump-turbine units of the single or multistage type, depending on the installation head.
The single stage reversible machines can be started both in the generation and pumping mode using their regulating guidevanes. The multiple stage machines are not equipped with guidevanes: they only work at full load both in the generation and pumping modes. As a consequence, in the generation mode the start-up is quite conventional and the spherical valve is used to throttle the flow. In the pumping mode the unit to be started is driven electrically (back-to-back) by another unit working in the generation mode.
As already mentioned, despite the considerable storage capacity already available in Italy, an additional capacity of 5km3 will be needed in the near future. This target could be achieved by:
• Exploiting the capacity still available in the reservoirs in operation.
• Accelerating filling reservoirs whose dams have been completed.
• Fostering the completion of the projects whose dams are under construction.
• Planning and implementing new projects.
Table 4 shows some data regarding dams already in operation, whose reservoirs are still subject to some limitations in their storage volume mainly because the commissioning procedures have not yet been completed. As can be seen, almost 1000hm3 will be available once the above mentioned limitations have been removed.
Table 5 shows the dams already completed whose reservoirs are ready to be filled once the adduction channels or the commissioning procedures have been completed or other problems have been solved. Their volume amounts to a total of around 300hm3.
Table 6 shows the dams presently under construction; some of them are almost completed and near to being put in service; for others, accounting for less than one third of the total volume, the construction works have been temporarily interrupted. Their volume amounts to a total of 387hm3. The storage capacity obtainable with the first three bullets (above) is about 1700hm3.
Many projects for new dams have been studied during recent decades, however most of them have been abandoned for various reasons. Table 7 shows some of them – at various stages of design definition – that are more likely to be implemented provided that the necessary financing can be found and other difficulties overcome. None of the bullets above should be taken for granted, again for economic and financial reasons and sometimes also because of environmental issues. Nevertheless, the efforts aimed at improving the response to water demand in the country should be continued.
While at present only one major power station is being put into operation (Pont Ventoux, 150MW), a further increase in capacity and generation capability has been promoted by the green certificates programme. Thanks to the relevant legislative provision introduced in 1999 a number of new small plants have been or are being put into service and several large plants have been or are being refurbished and repowered. 421 power stations have already been repowered and another 115 are planned to be in the near future. The total increase in generation capacity is 3.6TWh/yr, an 8% increase. Further increases are expected to be planned and implemented in the next decade.
Information supplied by the Italian National Committee on Large Dams (ITCOLD). For further information on dams and hydro power in Italy, visit ITCOLD’s website at www.itcold.itTablesTable 1 Table 2 Table 3 Table 4 Table 5 Table 6 Table 7