The Italian Electric Transmission Grid has sensitively different characteristics among the various geographical areas of the country. The Northern Italy High-Voltage (HV) Grid – at 380 kV and 220 kV – is considerably meshed, especially in the areas to taller industrial concentration. The meshing of the Grid at 380 kV is partial in Central Italy, except for the zone of the Adriatic coast into the Marche, Abruzzo and Molise regions. In this area Grid at 220 kV is little present. The Grid at 380 kV in Southern Italy has many zones with low meshing, especially in Puglia and Calabria. The Grid of Sardinia region is asynchronous in comparison to the Grid of Italian peninsula. In fact, the power supply of the Island is being made through a DC connection at 200 kV, a DC connection at 500 kV and relative systems of converters. The Grid at 380 kV is composed of only one power line connecting the north and the south of the Island and energy transmission is almost entirely guaranteed by the Grid at 220 kV. Finally, the Grid of Sicily region is synchronous with the Grid of Italian peninsula, one AC 400 kV power line connection. In this Island the Grid at 380 kV is meagrely present and electric energy transmission is almost entirely guaranteed by the Grid at 220 kV.
Italian Transmission Grid at 380 kV and Sicilian Transmission Grid
At national level, a lot of countries are investing in the exploitation of electric energy from renewable sources, with particular interest in the most mature technologies, i.e. wind and solar (photovoltaic) power. Currently, in Sicily region there are 1.560,5 MW of wind power plants and 787,3 MW of solar power plants. The possible onset of problems of stability in the Power System due to the variability of the renewable sources, however, sets some limits to the penetration of the medium and small plants into the distribution grid. In this context, the conjunction of the systems of electric accumulation with the renewable source generators would temporarily allow us to separate production and consumption of electric energy favouring a greater penetration of such systems of generation that have production curves not easily forecast and often not coinciding with the load curves. The most common method of accumulating energy is to use the hydroelectric power plant. When there is an excess of production of electric energy, because the thermoelectric plants can’t be turned off without affecting the regulations in the primary electric system, water is pumped from a basin downstream to one upstream with the purpose of recovering the energy produced by the renewable source plants. For example, Saturday 5 November 2011 the wind energy production in Sicily has supplied the 48% of the requirement (load) and reached a peak of 965 MW. Sunday 6 November 2011 the wind energy production has supplied the 33% of the requirement (load) and reached a peak of 1007 MW. This was possible through the optimal use of the following hydroelectric plants:
- hydroelectric plant of Anapo: it produces 500 MW when generating energy and uses 580 MW when pumping. It is equipped with 4 groups of reversible turbines/pumps of 125 MW each in production and of 145 MW each in pumping. The distance between upstream and downstream is about 312 m. It is powered by the upstream basin of the Anapo, which has a maximum capacity of regulation to 405,30 m above-sea-level, with a volume of 5,6 million of m3;
- hydroelectric plant of Guadalami: situated in the upper course of the river Belice between the reservoir of Piana degli Albanesi, from which it is powered, and the basin of Guadalami, obtained from the course of the river. The plant, constisting of two ternary groups (turbine – pump) to horizontal axis and a binary group (turbine) also to horizontal axis. Its power is equal to 80 MW.
Coverage of the requirement (load) in Sicily on 5/6 November 2011
Considering the 24 hours period from Monday November 21st (15:00 pm) to Tuesday November 22nd 2011 (14:59 pm), instead, the average percentage of coverage of supply through wind generation was 50% with a peak the 77%:
Coverage of the requirement (load) in Sicily through wind energy for 24 hours
Finally, Sunday 8 April 2012 the wind energy production in Sicily has supplied the 60.9% of the load and has reached a peak of 1.234 MW. Monday 9 April 2012 the wind energy production in Sicily has supplied the 62,8% of the load and has reached a peak of 1.291 MW. The wind energy production was limited up to 250 MW due to the failure to install adequate electrical storage systems in Sicily.
Coverage of the load in Sicily on 8/9 April 2012
A further expansion of renewable energy sources in Sicily is expected in the next three years, due to the forecasted 2.200 MW and 1.000 MW of installed wind and solar power plants respectively. An obstacle to this development is constituted, over that from the possible interference of the technology with the landscape and architectural patrimony of numerous areas, also from the criticism situation of the net of Italian transmission, still only some endowed with systems of energetic accumulation, whose growth must increase together with to that of the renewable sources.
