From water to electric current

Sentences without a label are documented facts; the others are marked "probable" or "uncertain".

For centuries the water of the Orco and its tributaries reaches the machines through canals and mill races and turns wooden wheels. In the nineteenth century the Cuorgnè Cotton Mill (Manifattura) sends it onto four turbines; then it turns it into electric current, with its own power stations. From 1921 Turin builds its plants in the upper valley; in 1967 the Manifattura's power stations pass to Enel. This page follows energy along this path and explains the physics needed to read it.

Water in the canals

The oldest mention in the Canavese of a plant driven by a water wheel, according to Cima, is the mill of the Valperga family below the Tellario rock, at Pont, cited in 1212. In 1487 the men of Oglianico obtain from the lord of Valperga the right to draw a mill race from the Orco to irrigate and to drive the wheels of a mill. In the mid-eighteenth century Rezia di Mombello writes that the Orco, although it does some damage, is useful for fishing, “for the use of the various forges and buildings” and for irrigation. In those years the mills of the province of Ivrea all have a wheel with a horizontal axle, fed from above in the mountains and more often from below in the plain.

A river is not enough to get energy: you need a head, that is, a difference in height between where the water enters and where it leaves. The canal takes the water from the river higher up and carries it, with a gentle slope, to the machine; there it lets it fall. The canal of the Cuorgnè Cotton Mill, begun in February 1873, serves exactly this purpose: a head of water of about ten metres. The water is taken from the Orco with a dam of dry stones and turf, about 1.4 km from the works, and carried into the bed of an abandoned branch of the river. A small lake forms between the river and the intake: the intake building stays sheltered from floods and the water leaves sand and gravel there.

The dams on the river were temporary, of dry rubble with grassy turf and moss, made on purpose to be swept away by floods: the laws of the time normally forbade permanent dams on mountain rivers. In 1923-24 they are replaced by a masonry dam. The intake has three openings divided by masonry piers, and a grating of iron bars stops leaves and wood. The canal is 836 m long, in masonry, 6 m wide and 2 high. The sluice gates are oak boards raised with rods, toothed wheels and a worm screw turned by a crank. A worm screw, in general, makes it possible to raise with little force a board pressed by the water with great force; moreover it does not turn back on its own.

Michele Chiesa, at the Industrial Inquiry of 1872, says that in Italy water costs almost as much as coal does to the English, because of the repairs to the canals. Bertotti writes that at Cuorgnè the water of the Orco is “soft and excellent for industrial use, with a hardness of two degrees”, as an analysis of 1900 confirms.

Sources: Cima 2025a, p. 41; Cima 2025b, pp. 40, 43, 151; Cima 1987, pp. 43, 65; Abà et al. 1995, pp. 26, 27, 28, 37, 313, 316, 317, 318, 319, 321, 341

The wheels

In the forges of the Orco the wheel drives the shaft of the tilt hammers. In the seventeenth century the “donkey-head” tilt hammer spreads, in batteries of two or three heads, driven by wheels with heavy stone hubs that act as a flywheel. A flywheel, in general, is a rotating mass that stores energy: it makes the motion more regular when the cams lift the hammers and let them fall. At the Castellaro forge the water on the wheels (and so the rhythm of the blows) was regulated by a sluice at the bottom of the chute, worked by the hammerman.

The wheels were not all the same. In the Canavet forge at Canischio the grindstone turns on an undershot paddle wheel, called “per di sotto” or “a schiaffo”, which is fast: Cima estimates about 200 revolutions a minute. The wheel of the hammers, on the other hand, is overshot, “per di sopra”, metal, recently rebuilt perhaps in place of a wooden bucket wheel; a slide valve regulates the water and gives the hammers different speeds. In an overshot wheel, in general, the water fills the buckets at the top and the wheel turns mainly through the weight of the descending water: it is slow and makes good use of small heads. In an undershot wheel the flowing water pushes the blades at the bottom: the wheel is faster but less efficient.

The wheels also drive the factories. In the silk mill of Agliè, built in 1736 on the Canale di Caluso, the water wheels in the basement drove the silk throwing mills. Around 1840 the Manifattura of Annecy and Pont has 22,000 spindles and 410 power looms, all driven by water wheels. In 1870 the water power available at Pont is about 700 horsepower, with three steam engines for periods of low water. In the nineteenth century the ceramics factories of Castellamonte drive their mills with wheels on the Roggia dei mulini and on the Canale di Caluso. At the Fornace Pagliero, from 1845, a single wheel drives the mills, an extruder and a goods lift through gears, pulleys and belts.

Sources: Cima 2025a, pp. 45, 105; Cima 2024, pp. 193, 204; Cima 2025b, pp. 157, 158, 226; Cima 1981, pp. 172, 173, sheet I05/15CA; Bussi 2026, p. 59; Giorda 1992, pp. 1, 4; Porro and Romanoni 2001, pp. 1, 2

The Manifattura's turbines

The Cuorgnè Cotton Mill was built between 1872 and 1874 to a design by Adolf Mauke, for a company with Italian-Swiss capital that chose the site for the textile industry already present and for the power of the Orco's water. The Cuorgnè museum writes that the works was “inaugurated in 1882”: the date does not square with 1872-1874. According to the museum the Manifattura was born on the “generous availability of energy” of the heads of water that in earlier centuries had already driven the machines of copper metallurgy at Cuorgnè. On 8 September 1875 the Manifattura buys the forges, the mill race and the water rights of Campore, to exploit “the two heads of water existing at the site”. According to Cima the “old mill” cited in 1470 stood where the upper power station of the Manifattura is today probable.

The building had a basement for the transmission shafts and four floors of machines probable. The four Girard turbines stand beneath the works in two groups of two, with an average head of 10.50 m, and together give 700-800 horsepower. A fifth, small turbine drives the workshop and the fire pump when needed. Against low water there is a steam engine, on granite blocks set in concrete. Its power is given in two ways: “4 boilers of 400 hp” and, at full load during low water, “from 600 to 700 hp” uncertain. In 1880-81 the Tavoletto mill, on the old Signorelli forges, is driven by the old canal of the foundry with a vertical-axis turbine of 200 horsepower.

What changes with the turbine, in general. The wheel turns slowly and is large, in the open; the turbine is smaller, enclosed, turns much faster and makes better use of the same water. The power that water can give depends on two quantities: the flow rate, that is, how much water passes in one second, and the head. The formula is P = ρ·g·Q·h, where ρ is the density of water, g the acceleration due to gravity, Q the flow rate and h the head; a real machine yields only part of it. One metric horsepower is 735.5 watts: 700-800 horsepower is between about 515 and 590 kilowatts.

Sources: ERIH, information sheet; Cima 2025b, pp. 40, 227; Abà et al. 1995, pp. 22, 27, 28, 39, 311, 319, 336, 337, 340; Museo Archeologico del Canavese 2016, p. 3

Electric current in the factory

The Manifattura soon switches to electricity. In 1873 it had set up a “lighting gas” plant for its own use, dismantled only in 1928; Cuorgnè would never have gas lighting. In 1885 an auxiliary turbine produces electricity, in 1889 the first real small power station is born at Tavoletto and in 1896 a diesel engine with a dynamo. From 1897 to 1915 the Manifattura buys energy from the Società Alta Italia. Public electric lighting reaches Cuorgnè with an agreement of December 1895 for 70 lamps: the service is tested on 16 June 1897 and switched on on the 27th, with Siemens & Halske equipment.

In general, a generator turns the rotation of the turbine into electric current: a coil turning in a magnetic field, or a magnetic field turning inside a coil. Current can be carried far away by wires. That is why the power station no longer has to stand beneath the factory.

The Sparone power station, of 1919, is the first one detached from the mills, more than 10 km away. It takes the water of the rio Ribordone with a small dam at the hamlet of Crosa and a canal of 4,300 m to the Bose basin; from there a penstock descends for 800 m onto a Pelton turbine. In 1936, because of disputes with the owners of a forge and with other users downstream, the Manifattura has to build a compensation reservoir of 5,000 cubic metres. A compensation reservoir, in general, collects water when the power station discharges more of it and releases it when it discharges less, so that those downstream receive a more regular flow.

In 1917 and 1924 the two “works” power stations are built on the two pairs of turbines. The Campore Basso power station, at Goriti, is built in 1924 on the old canal of the Signorelli forge; in 1923-24 the temporary dams of the main canal become a masonry dam. The Valle power station uses the discharge of the works power station; the Campore Alto one takes the Orco at Doblazio with two iron sluice gates 23 m long and has two Kaplan turbines. The dates of these last two vary in the book on the Manifattura: Valle is from 1928 or in operation from 1930, Campore Alto from 1948 or in operation from 1949 uncertain.

The turbines chosen say something about the water, in general. The Pelton receives fast jets of water on a wheel of buckets: it is suited to high heads with little water, like a penstock coming down from the mountain. The Kaplan is a propeller with adjustable blades: it is suited to low heads with a lot of water, like a valley-floor river.

The four power stations on the Orco lie within just 6 km and the water passes from one to the next: the same water is used several times, because the power station exploits the head and does not consume the water. The installed power is 12,997 kVA, with an average power of 7,700 kW. kVA measure the apparent power of electrical machines, kW the power that actually becomes work; the average is lower also because the water is not always there. The Orco, already exploited upstream by AEM, changes its flow over the hours of the day and the Manifattura has to regulate its power stations according to the time. In the Gallenca valley too, several mills and forges become small power stations in the twentieth century: the Crosetto mill supplies electricity to San Colombano, Canischio and Prascorsano until the end of the Fifties.

Sources: Abà et al. 1995, pp. 123, 124, 128, 311, 341, 342, 344, 345; ERIH, information sheet; Cima 1981, p. 166, sheets 13CA and 18CA

Turin goes up the valley

By royal decrees of 1921 and 1925 the Municipality and the Province of Turin, then the Azienda Elettrica Municipale, obtain the concession of the water of the Orco and its tributaries for four plants: Serrù-Mua, Ceresole Reale-Rosone, Telessio-Rosone and Rosone-Bardonetto. A Turin magazine of the Twenties or Thirties describes the building site of the dams as a “new life” for the valley and explains that the “golden water” will be turned into energy probable. The Ceresole reservoir is completed in 1925; the Lake Serrù dam in 1952. A high-altitude reservoir, in general, stores the water of the melting snow and releases it in the months when the river carries little. The Ceresole reservoir, moreover, holds back and dampens the flood waves of the Orco.

The inspection of 1953 finds in the Rosone-Bardonetto plant a head of 126.70 m and an average flow of 6,646 litres per second since 1951. The AEM publication gives for the Bardonetto power station a head of 128 m and for the one at Pont, on the right bank of the Orco, a head of 111 m. After 1952 AEM calls Rosone its “capital” in the Orco Valley: around the power station, which will reach 140,000 kW, a village of houses for the employees grows up next to the old houses threatened by the landslide. The hamlets of Rosone and Bertodasco, on a slope that is slowly sliding, were included in 1956 among the settlements to be relocated.

Other factories too take their current from the mountains. The two works of the Manifattura of Rivarolo and San Giorgio receive their motive power from two power stations in the Valle Soana probable. Which ones they were and when they were built is not known uncertain.

Sources: Regione Piemonte 2025, pp. 1, 2; Rivista municipale torinese, pp. 93, 224; Troisi 1997, pp. 33, 34; AEM, p. 18

From the Manifattura to Enel

The Manifattura reached about 1,300 employees probable. In 1953 the balance sheet calls the sale of energy to third parties a “safe source of income”; for the authors of the book on the Manifattura, from the post-war years energy weighs in the accounts perhaps more than textiles. With nationalisation, from 1 January 1967, the Sparone, Campore Alto and Campore Basso power stations pass to Enel, which pays 629 million lire in 1974. The Manifattura closes in 1991 and the Municipality buys it to restore it; today it houses CESMA with the archaeological museum and the art museum probable. The reasons for the closure are not given in the sources read uncertain.

Sources: ERIH, information sheet; Abà et al. 1995, pp. 123, 341, 347

For the class

Three power comparisons with the figures on this page. First: with P = ρ·g·Q·h calculate the theoretical power of the Rosone-Bardonetto plant (head 126.70 m, average flow 6,646 litres per second) and compare it with the Manifattura's turbines (700-800 horsepower). Second: the Rosone power station will reach 140,000 kW; how many times the power of the Manifattura's turbines is that? Third: the Manifattura's four power stations on the Orco have 12,997 kVA installed and an average power of 7,700 kW. Discuss why the average power of a hydroelectric plant is lower than the installed power and what the fact that AEM, upstream, changes the flow of the Orco over the hours of the day has to do with it.

Sources: Regione Piemonte 2025, p. 2; Abà et al. 1995, pp. 27, 28, 345; AEM, p. 18