Development of a Pico conduit-hydropower turbin within a city's water distribution system

Abstract

Energy is the lifeblood of worldwide economic and social development. In recent years, South Africa (SA) has experienced local energy shortages that have resulted in interruptions in the supply of electricity, referred to as “load shedding”. During such times, the monitoring and operation of water infrastructure become problematic. In combination with a culture of vandalism and theft of infrastructure components that have resale value, infrastructure becomes inoperable at an ever-increasing rate. Equipment functionality and levels of bulk water service delivery could be maintained through the development of alternative energy-generation methods in all spheres of the South African national, provincial, and local government.

Because of the energy shortages in SA, localised alternative energy-generation methods are being adopted to maintain the management and control of water systems. The solutions involve utilising energy more efficiently, optimising existing systems, and seeking new approaches for supplying electricity to water supply infrastructure. The introduction of small hydroelectric turbines and generators at strategic places where there excess pressure exists in the water supply and distribution system, is a relatively simple energy solution to recapture some of this renewable energy. This could typically be done at existing pressure-reducing stations (PRS) or anywhere along the pipeline, by extracting hydroelectric energy to meet a specific demand, without compromising the main functioning of the supply system.

A number of water authorities throughout the world have realised the potential of conduit hydropower and have implemented generating schemes. In SA, there are 257 municipalities and several water supply utilities. All of these municipalities own water supply distribution systems that could be considered for hydropower installations. Fortunately, a number of conduit hydropower opportunities exist within City of Tshwane (CoT), due to its geographic location relative to the country's main water sources.

In CoT, water is distributed through a large water system that comprises 165 reservoirs, 39 water towers, 10 863 km of pipes, and more than 280 PRSs – some of which are operating at pressures of up to 250 m. The current reality is that regular load shedding results in a loss of control over parts of the water supply network. Retrofitting a hydroelectric turbine in an existing system, is a solution to address the constant demand for electricity at specific locations. This will ensure that communication with reservoirs – not only in isolated areas – for various operational, maintenance, and infrastructure management reasons, is maintained. This includes telemetry, pressure management, flow control and 24-hour monitoring and security systems.

In this study, a pico conduit hydropower turbine was developed and the application and the installation of a retrofit conduit hydropower unit into a city’s water distribution system was explored. The entire retrofitting process is described, with examples of three of the four types of conduit hydropower developments in CoT. A novel conceptual hydroelectric turbine generator was designed to be retrofitted easily in an existing valve chamber. The prototypes tested in this study resulted in the development of a pico hydropower unit (PHU) at a competitive cost. These PHUs could be applied in water lines, installed in series (inline) with the main water lines.

An inline pressure wheel (IPW) was developed and tested extensively over a period of four months to a point where the first commercial PHU (IPW2) was ordered for installation in CoT at the Klipgat Hospital Reservoir. This unit generates adequate electricity from the water network before discharging into the reservoir. A simplified control system manages the generated power to store sufficient power to run the equipment on-site and shuts down automatically when not needed, to prolong system life. The operation of this commercial IPW will be monitored and data will be collected during operation to evaluate the unit’s performance and to contribute to future studies. The results could be used to improve the design and effectively of the commercial IPW series.