Class trip to Palmiet

The 2015 Masters class of the University of Cape Town’s Energy Research Centre recently went on a fieldtrip to Eskom’s Palmiet hydro electric pumped storage power plant near Gordon’s Bay in the Western Cape. The tour consisted of a presentation given at the plant’s visitor’s centre as well as a tour through the inside of the plant itself, including the operator’s control room. The basic operation of the power plant and the way in which it generates electricity was explained as well as why these types of plants are very important and helpful for an electricity grid. The minimization of the environmental impact of the plant’s construction and operation in a sensitive natural biosphere was explained as well as how the plant assists in augmenting the local water supply reservoirs through its pumping capabilities. Palmiet has two separate but identical 200MW units for a total capacity of 400MW. Construction of the plant started in 1983 and was completed 5 years later in 1988.

Palmiet structure with bottom “Koggelberg” reservoir (left) with top “Rockview” reservoir (right)

A pumped storage scheme generates electricity in a similar way to a classic hydro-electric power plant with a few key differences. It similarly makes use of a dam of water, allowing the water to flow through a tunnel and through a turbine – the turbine is connected to a generator which as it rotates generates electricity for the national grid. The main difference however is that the pumped storage scheme doesn’t have a continuous natural flow of water, instead it makes use of 2 separate dams or reservoirs to store the water. The power plant lets the water flow to generate electricity but it can also use electricity from the grid and reverse the turbines into pumping mode, transferring the water from the bottom reservoir to the top reservoir to be used again when needed. The plant is almost completely underground with just small surface building. These concepts are demonstrated in the animation below.

Pumped Storage animation
Pumped Storage Plant: Basic Operation Schematic
Shaft Coupling between Turbine (bottom) and Generator (top). The turbine and generator themselves are enclosed and not visible here.
Shaft Coupling between Turbine (bottom) and Generator (top). The turbine and generator themselves are enclosed and not visible here.

The power plant effectively acts as a large energy storage device. The benefit of this is that the plant can provide valuable energy during peak periods of demand while using the excess cheaper energy available at night to pump water for storage. The plant also has the capability to start, stop and vary its power output very quickly compared to other power plants, another essential capability for balancing the power grid. The plant can also run in “synchronous condenser mode” which allows the plant to assist in balancing the frequency and voltage on the grid. This type of plant can also add significant benefit in balancing the variable energy generated from the increasing amount of renewable energy sources being connected to the grid. The plant could for example store excess solar energy generated during the day and provide energy during peak demand after the sun sets. The plant can generate continuously for a maximum of 32 hours before the top dam is emptied, however this would take approximately 45 hours to pump back up. The plant manages its water levels using a weekly schedule, mostly generating during peak hours of the week and using the weekend to replenish its water levels (load shedding has sometimes occurred on the weekend to provide electricity to ensure there is enough water available for the week to come).

The Palmiet pumped storage scheme finds itself in the middle of a very sensitive environmental area of the Cape Floral Kingdom, specifically in the Koggelberg Biosphere Reserve. The Cape Floral Kingdom is found uniquely in the Western Cape of South Africa and forms one of the only 6 floral kingdoms known to man. The project is said to have set up environmental controls before commencing with construction and followed them strictly throughout to minimize the environmental impact of the plant during construction and operation. The plant also allows for other benefits to be provided as the plant can augment the water supplies of the Steenbras Reservoir via the Rockview dam by pumping water up from the lower Koggelberg dam (Shown below). Eskom has agreements with the Department of Water affairs for how this water transfer should be managed correctly and effectively.

Map of the area with various dams shown