as their rotational speed is able to match grid frequency, but they exhibit poor efficiency either side of the rated flow. At the larger power scales, this is overcome by using variable inlet vanes and blades, but at the pico hydropower scale this is not viable due to increased cost, unit complexity and reduced system reliability. In all the available reported work, impulse turbines, such as the Turgo or Pelton turbine, are used in a medium- to high-head application environment, as shown in Fig. 1. At low head, impulse turbines are normally avoided as they have a slow rotational speed and are large, but in theory their application at low head should be feasible [6]. Impulse turbines are simple to construct, robust, inherently modular and serviceable, and have good efficiency over a large var- iation in flow rates. Low speed, high-pole number permanent-mag- net generators and variable frequency power electronic converters can be used to interface with a 50/60 Hz grid, overcoming the slow rotational speed issue. Using the criteria described above and application domain, a Turgo turbine was shown in [5] to be a pre- ferred option. Turgo turbines were invented and patented in 1920 by Gilbert Gilkes Ltd. [11] and are mentioned in discussions about impulse turbines [7], but in comparison to the Pelton turbine, there is little published research on this turbine type. As shown in Fig. 2, both Pelton and Turgo turbines generate their torque through the change in momentum of an incoming jet of water. Turgo turbines differ from Pelton turbines by the angle of the incoming water jet. In Turgo turbines the jet enters and exits the wheel plane at an acute angle whereas in Pelton turbines the jet remains in the same wheel plane. Therefore, the water in a Turgo turbine exits from the bottom of the wheel and does not interfere with the incoming jet. This allows the diameter of the wheel to be smaller for a given jet diameter, increasing the rotational speed. Energy Systems & Design Ltd. [10] supplies a Turgo turbine stream engine which can be operated between 3 and 150 m head.