Conduit-hydropower potential in the City of Tshwane water distribution system: A discussion of potential applications, financial and other benefits

Abstract

In water distribution networks, water is often fed under gravity from a higher reservoir to another
\nreservoir at a lower level. The residual pressure head at the receiving reservoir is then dissipated
\nthrough control valves (mechanically or hydraulically actuated), sometimes augmented by orifice
\nplates where there is a propensity for cavitation. There are possibilities to add turbines in parallel
\nand generate hydroelectricity at these locations using the flow and head available.
\nThe benefit of this hydropower generating application is that minimal civil works need to
\nbe done, as the control valves are normally inside a control room/valve chamber. No negative
\nenvironmental or social effects require mitigation, and the anticipated lead times should be short.
\nFrom a topographical perspective the City of Tshwane has a lower elevation than the bulk
\nservice reservoirs of Rand Water, which is the main water supply. Water is distributed through a
\nlarge water system that includes 160 reservoirs, 42 water towers, 10 677 km of pipes and more
\nthan 260 pressure reducing stations (PRS) that operate at pressures of up to 250 m.
\nThe top ten hydropower potential sites in the City of Tshwane water distribution network have
\na total energy generating capacity of approximately 10 000 MWh/a. A number of potential conduithydropower
\nsites have shown promise of short payback periods. The identifying and development
\nof these sites in Tshwane to convert water pressure to electricity is ongoing and exploited further.
\nVarious challenges currently exist with reservoir communication in isolated areas due to
\nvandalism and theft of necessary infrastructure, including electricity cables and solar panels.
\nBecause conduit-hydropower systems can be housed completely inside chambers, vandalism and
\ntheft can be mitigated. Therefore, one of the major benefits of hydropower turbines at these sites
\nis that the hydroelectric potential could be exploited to power telemetry, pressure management,
\nflow control and monitoring/security systems. Alternatively or additionally, other local demand and/or (depending upon the quantum of
\nenergy available) off-site energy demand clusters, or even a municipal or national grid, could also
\nbe serviced by these power stations. The capacity of hydroelectric installations can vary to suit the
\napplication for the amount of power needed or to be generated.
\nShort payback periods, especially when using pumps as turbines, also make conduit-hydropower
\nsystems attractive.