CAT Reservoir (Bagnall, 2015)

CAT itself is built upon an existing slate quarry. Higher up in the hills houses a reservoir which was used to power the quarry’s machinery.  To present day, that same reservoir is being used to power a larger hydro-electric turbine, providing an electrical supply to the site.

Hydro-electric power is generally produced by the force of gravity-fed water from a high source, spinning a turbine at a lower source (vertically), which in turn generates electricity. It is said that for a large system like this to work, the reservoir water level should be greater than 20m higher than that of the turbine, so that the force which gravity provides the water with is the greatest amount of kinetic energy to power the turbine (smaller turbines can be used at smaller vertical height, however will not produce a large amount of electricity).

CAT’s APPLICATION OF HYDRO-ELECTRICITY

Pipework from reservoir to turbine (Bagnall, 2015)

Referring specifically to CAT, the reservoir they own is 30m above site (calculated through water pressure on site; 1bar = 10m, site pressure of 3bar) where the water provides both electricity through the turbine and drinking water. The reservoir is ideally located, surrounded by slate hills which provide an easy surface run off for all the rainwater. There is also a backup pipe which fills the reservoir from a higher valley, This secondary valley is made up of a chalk soil, also causing an ease run off surface. Due to the 30m height difference, the water builds up a high kinetic energy to power the turbine.

Down on site, we were involved in an experiment with a small scale turbine running off of the reservoirs water. The exposed water wheel of the experiment allowed us to see how by changing the resistance of the electricity (variable resistor connected in series) altered the speed of the wheel; speed of the wheel slowed when more of an electricity demand was asked for. By calculating the voltage, current and rotation speed of the turbine, the efficiency of the turbine could be found and a graph plotted. Once the graph was plotted, it was clearly seen that the turbine was not at its most efficient when at full power, instead at half power (this was then explained to be the case for the majority of turbines) and at that point had an efficiency of 37.75%. This reduction in efficiency could be down to various features of the systems such as the bends in the pipe decreasing the speed and increasing the friction on the water. The friction through the system of the pipework on the water creates a dynamic pressure, which was 0.4bar small (2.6) than that of the static pressure (3.0).

As mentioned previously, as well as powering the turbine, the water is also used as for drinking and cleaning for the whole of the site. As the water in the reservoir is not safe to use, when fed down the pipework, some is separated into a sand bank where the water will filter through the sand, removing the bacteria over a matter of days, finally releasing to be used on site.

APPLICATION TO PROJECT