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Savvy farmers on the Fish River harness hydropower

Home Infrastructure Energy – Power Generation Savvy farmers on the Fish River harness hydropower

WITH an adequate head of water, sufficient flow rates and minimal seasonal variation, the Fish River system is generating power for farmers to run their energy-hungry operations without interruption.

Managing director at I&F Engineering, Ian de Jager, has been building hydropower stations in South Africa since the mid-2000s. The company has installed plants in Mpumalanga, the Western Cape and is commissioning its fifth project on the Fish River in the Eastern Cape in November.

A hydroelectric power plant’s generation potential is a function of the water source’s flow rate – the volume of water per second  –  and the head of the water source to the turbine. The head is an indication of elevation between the source and the turbine outlet (pressure generated in the pipe) similar to a water pump’s grading.

De Jager gives the example of a plant near Cradock where the water flow is 5m3/s and there is a head of 9m, 350 kW of electricity is generated.

De Jager says he works with a minimum head of 5m. If the head doubles and the flow rate stays the same, the power generated is twice as high – and it’s the same for a situation in which the flow rate doubles and the head stays constant.

De Jager says the stations on the Fish River have heads between 18m and 40m. “Water is released from the Gariep Dam, so there is a constant flow. Typically, water is diverted via a canal along the contour line and then through a penstock (pipeline) to the turbine before being fed back into the river system.”

Two-year process

Projects take about two years to complete. “We start by researching the history of the river and create a flow duration curve for the water source. Based on that information, we can decide what size turbine is most viable for the project.”

De Jager says that the first year of the project is spent securing a water license, completing an environmental impact assessment and applying to Eskom to feed into the grid.

The build starts in the second year. “There are many companies that manufacture turbines. They design the turbines to run at maximum capacity depending on the maximum and minimum flow rates and the head available. I use mostly Cross Flow turbines manufactured by Ossberger which is based in Weissenburg, Germany as I find their turbines to be simple yet robust. They handle variable flows at an efficiency of about 85%, which is perfect.”

“Ossberger designs the whole system, including the turbine, generator, panels and gearbox, which they ship to South Africa. We connect the completed hydro plant to the farmers’ private grid, or the Eskom grid and do the commissioning. The actual installation takes about two weeks after the civil works are completed.”

Advantages of hydropower

The hydroelectric plants generate power with a pure sine wave just like the Eskom grid because it makes use of generators. There is no need for an inverter and, because the power is generated and available 24/7, no batteries are needed for storage.

Another major advantage is hydropower generation’s high capacity factor. De Jager says that with solar, the capacity factor is 25% and for wind, it is 23%. This means that for 100 kW of installed capacity, plants only generate 25% and 23% of the installed capacity. This means that instead of 100 kWh you only generate 25 kWh for solar on average.

“Depending on the water flow, hydro’s capacity factor can be up to 90% as in the case of plants on the Fish River system near Cookhouse. I normally design to a capacity factor of around 60% minimum. To maintain high efficiency, the size of the turbine is reduced if the seasonal flow becomes too low. But that depends on the payback period that the client has decided on,” de Jager says.

Return on investment

In the Cookhouse area, where customers are paying the Blue Crane Municipality tariffs, the investment in a hydro plant can pay off in just two years. For Eskom direct clients, it can take around four years. “With an expected lifespan of at least 50 years, hydroelectric power generation makes financial sense,” says de Jager, who wonders why there aren’t more hydro plants at dams and weirs in South Africa.

De Jager says his company installed a 2,300 kW hydro plant near Franschhoek which wheels power to commercial users through the Eskom grid. “All that’s required is a suitable site as hydros are site-specific and the plant needs to be built near the water source.” He says it’s also possible for investors to build hydropower stations on any suitable site and wheel energy to clients, similar to solar farms.

De Jager says there is Increasing demand for hydro power stations but that the concept is not always understood. “A big river is not enough. A drop in elevation is needed so that the relationship between the water’s flow rate and head is sufficient to drive a turbine to make the project viable.”

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