Thinking out of the dam: pipeline power

‘People think that because South Africa is a dry country, there is not a lot of opportunity for hydropower,’ says water engineer Marco van Dijk, ‘but it is actually low-hanging fruit.’

Particularly ripe for the picking is conduit hydropower (CH), which involves placing turbines in existing pipelines and water systems. Its potential application for South Africa will be demonstrated on 31 March at the launch of a flagship pilot project at the Brandkop Reservoir in Bloemfontein.

The project, known as the Bloemwater Conduit Hydropower Plant, is the result of a collaboration between the Water Research Commission (WRC) and the University of Pretoria’s Department of Civil Engineering, where Van Dijk is a researcher and lecturer.

He explains how CH works: ‘In pipelines, excess pressure is usually dissipated by means of a pressure reducing valve (PRV) that opens and closes automatically to control water flow. We all have such valves in our houses, just upstream of the geyser, so that municipal water pressure can be reduced to household pressure.

‘The mechanical energy dissipated in this way usually goes to waste. But if the PRV is replaced by a turbine connected to a generator, the excess water pressure can be converted to electricity.’

He says that this simple system can be used wherever there is excess pressure in a pipeline. Pipelines supplying water reservoirs and waste water outlets are prime targets, and the electricity generated can be used on site, put back into the grid, or used to power something specific, like remote monitoring or logging equipment.

‘At Brandkop, where the CH plant generates 96 kilowatt, we wanted to produce enough electricity to supply Bloemwater’s head office with renewable power,’ says Van Dijk.

He explains that this project is a research effort that assesses the feasibility of CH, and that other municipalities can learn from it. The WRC has produced reports for this purpose and Van Dijk’s project team and his students have published their findings. He hopes the information generated will inform policies that will make the uptake of CH easier and more widespread.

It is already quite straightforward to implement. ‘Unlike other power plants, with CH there is no need to apply for a water-use licence or, in most cases, to perform an environmental impact assessment, which can be very expensive and cumbersome.’ It also doesn’t require precious water to be released from dams as is the case with conventional hydropower and the turbines are readily available.

It is thus not only environmentally friendly, but also economically viable, robust and convenient.

‘We have determined that the City of Tshwane could potentially produce two megawatt from five sites and Rand Water could generate 15 megawatt from four sites. Johannesburg Water also has potential to generate a significant amount of power,’ says van Dijk.

With such a high potential output in just two regions within Gauteng, there is clearly huge scope for CH implementation throughout the country.