Thermal energy storage is a primary research area in the solar thermal energy research group (STERG). One thermal storage concept uses particular types of rock found in areas assumed to be suitable for CSP plants. This thermal storage concept is a component of the SUNSPOT cycle (Stellenbosch UNiversity Solar POwer Thermodynamic cycle) which uses a gas and steam turbine to produce electricity based on demand and at a high efficiency.

Kenny Allen is a PhD student working on the rock storage concept. As part of his research, he organised a rock collection expedition to collect samples of rock that may be suitable for this application. He has collaborated with the geology department at the university and has studied detailed geology and solar maps of South Africa to plan the expedition. Paul Gauché, also a PhD student and coordinator of STERG, accompanied Kenny to learn more about the regions of interest and to help with the sample collection. The expedition has just ended after covering a little over 2,000 km between Stellenbosch and to where the Kalahari sand dunes just begin.

With a focus on particularly sunny parts of the country, many samples were collected. These samples will be tested for thermal and mechanical properties to determine if any of the rock types can be used in a CSP plant. As part of the testing, the samples will undergo accelerated temperature cycling up to 1,000°C in a newly acquired kiln. If some of the rock types survive this testing, future expeditions will be done to collect more of those types or others may need to be explored.

Ultimately, the plan would be to provide thermal storage to CSP plants across the country to keep them generating power 24 hours a day. A quick estimate on how much rock is needed shows that 25 GW of electrical power (Eskom’s current capacity is around 40 GW) can be produced 12 hours per day (the average length of a night) using an amount of rock that would fit into a sphere with a radius of 100m. That is somewhat smaller than this monolithic looking outcrop somewhere near Springbok.

The breath-taking scenery and wonderful hospitality of the Northern Cape was an added bonus! To see all photo’s, please to go this link at Picasaweb.