Finding Potential Sites for Small-Scale Hydro Power in Uganda: a ...

o Then the water flows from the forebay tank or reservoir down a closed pipecalled the penstock. The penstock is often made of high-density materials andexposes the water to pressure; hence the water comes out of the nozzle at theend of the penstock as a high-pressure jet. The recommended head, or thevertical drop from the beginning to the end of the penstock, for small-scalehydropower schemes should at least be 20 meters. A drop of 20 meters or morealso means that the amount of water needed to produce enough power for thebasic needs of a village is quite small.o The power in the jet, called hydraulic power or hydropower, is transmitted to aturbine wheel, which changes it into mechanical power (see section 3.2.2). Theturbine wheel has blades or buckets, which cause it to rotate when they are struckby water. Hydro-turbines convert water-pressure into mechanical shaft power,which can be used to drive an electricity generator, a grain mill or some otheruseful device. Via the tailrace in the powerhouse, the water returns back to theriver from where it was taken.o An electronic controller is connected to the generator. This matches the electricalpower that is produced, to the electrical loads that are connected. The “load” isthe appliances and machinery, which are energized by the hydro scheme. This isnecessary to stop the voltage from going up and down. Without a load controller,the voltage changes as lights and other devices are switched on and off.o The distribution system, or the power lines connects the electricity supply fromthe generator to the houses. This is together with the penstock, the mostexpensive parts of the system (Fraenkel et al., 1991; Maher & Smith, 2001;www.microhydropower.net)3.2.2 PowerWhen discussing a hydropower project, the power concept can be divided into threedifferent types, hydraulic, mechanical and electrical power, which will have threedifferent values. The hydraulic power will always be more than the mechanical andelectrical power, because some power is lost as it is converted from one form to another,as can be seen in Figure 3.4 (Maher & Smith, 2001). It is also important not to confusethe words “power” and “energy”. Power is the energy converted per second i.e. the rateof work being done. Energy is the total work done in a certain time (Fraenkel et al.,1991).18