A former water mill, sited on the River Cosa at Travesio in northern Italy, has been renovated and converted into a micro-hydroelectric scheme using the Archimedes’ screw concept, saving some 500 tonnes of carbon dioxide emissions per year.

The control of the system and the interface between the generator and the power grid is a Unidrive SP AC drive from Control Techniques. 

The Margarita Water Mill, which dates from 1906, has been sympathetically restored by renewable energy specialists, Energy Renewable Source srl. The company set out to produce a low environmental impact generating plant in the mill by using the ancient Archimedes’ screw design to drive a generator.  Unlike Archimedes’ original design, which was used to raise water, in this case the screw is reversed so that water flowing downhill turns the screw.   The proven design has no impact on river life, even allowing fish to pass through safely.

The hydraulic study and design of the scheme were entrusted to engineer Ottorino Vendramelli of Energy Renewable Source, who has extensive experience in the management of hydroelectric sites, many with small heads of water, capable of generating on average between 10 and 300kW of generated power.  The company has developed a software package, which, when used in combination with Control Techniques Unidrive SP drives, is able to optimise the power generation cycle across a wide variation in water flow rates.

Says Mr Vendramelli, “using this hydroelectric system, we have produced a reliable local source of clean renewable energy, all year round, generating useful revenue as well as helping to save a sizeable amount of greenhouse gas from being released into the atmosphere.”

The micro-hydroelectric plant uses the potential energy of the current of the river to turn the Archimedes’ screw set in a race, typically at around 30 rpm.  Fish both small and large (half a metre or more) can migrate through the screw with no damage, providing no impediment to their migration patterns. The screw itself can be five to eight metres in length and is totally safe, unlike other systems involving river barrages and high speed turbines.

The generator is a squirrel-cage induction motor connected to the low speed screw by a high efficiency gearbox. The generator, connected to a Unidrive SP inverter in regenerative mode, produces electrical energy that can be consumed by the user or supplied to the grid, since it complies with the statutory regulations in terms of quality of waveform. The drive is fitted with an SM Application module that runs the special program developed by Energy Renewable Source.

This project was the result of close teamwork between Energy Renewable Source and Control Techniques; the outcome of a process in which research, skills and experience were shared to achieve the best possible engineering solution and a high efficiency, environmentally friendly generating system. This technology is ideal for the creation of small capacity sites, including abandoned industrial sites, producing much needed renewable power, benefitting the environment and leaving the existing countryside undisturbed.

Energy Renewable Source also undertakes the restoration of disused mill water-wheels and other hydroelectric machines.