Solar thermal makes inroads

Greencape economic analyst Pieter Janse van Vuuren.

The advantage of solar thermal over solar PV (photovoltaic) is that when the sun stops shining, you still have heat, according to Greencape economic analyst Pieter Janse van Vuuren.

He was speaking at a recent solar heating in agro-processing workshop at the Stellenbosch Institute of Advanced Studies (STIAS).

“The defining feature of a solar thermal system is the collector, and a key selling point is its ability to store energy in the form of heat,” Mr Janse van Vuuren explained, “which means that such a system continues to provide energy when the sun is no longer shining.

“Agro-processing has been highlighted as a key sector for the application of solar thermal since it has a significant energy demand for heat (79 percent), most of which is at low temperatures, less than 160° C,” he said.

“Solar thermal is most efficient and economical at such low temperature ranges, and it is a financially feasible replacement for most fossil fuels, with the possible exception of coal at this stage,” he said.

Existing installations in the Boland which make use of solar thermal for process heat, include the Cape Brewing Company, an artisanal brewery located on the Suid-Agter-Paarl Road near Paarl, and Fairview Cheese, located on the adjacent wine farm, Fairview Estate.

According to Mr Janse van Vuuren, because there is a zero cost increase in energy prices using solar thermal – “sunlight is free” – it is possible for the payback period for a solar thermal installation to be as short as five years. In addition, solar thermal affords significant reduction potential in greenhouse gas emission. “With the carbon tax of R120 per tonne of CO2e awaiting Cabinet approval, this is a significant advantage, particularly for large systems. Similarly, Section 12 income tax rebates are available as energy eff iciency incentives, for large installations as well.”

As the collector panels have no moving parts, solar thermal is also low maintenance, and aside from a periodic “squeegee” to keep them dust free, they simply work. Since none of the materials used to construct the collectors have toxicity of any significance, disposal after the end of useful life is relatively simple and inexpensive.

“Solar thermal is relatively easy to integrate into new buildings, which results in a lowering of installation costs,” he said. “There is significant potential for solar thermal installation in the agri-processing sector, ranging from 425 000m² to 3 758 000m² which translates into 425 GWh to 3 758 GWh per annum.”

Mr Janse van Vuuren presented an info-graphic which compared the average solar irradiation per annum (energy “received” or falling on the earth’s surface per area) with the amount of solar thermal systems installed for South Africa (1 055MWth), Austria (3 5451MWth) and Germany (12 281MWth). In spite of clearly higher solar radiation in South Africa (up to double), Austria and Germany have around three and a half times and 12 times more solar thermal systems installed, respectively.  “The untapped potential for solar thermal in South Africa, is vast,” he said.

But as Mr Janse van Vuuren points out, solar energy is not well understood by potential users. “The technology is perceived to be untested and unreliable,” he said, “and we need clear and transparent communication about the costs, benefits and practical implications of these technologies.”

“The solar thermal industry is still in its infancy, but we need to move along the learning curve for prices to drop, and the agro-processing potential offers a significant opportunity to do so,” he concluded.

MWth, or megawatt thermal, is the thermal energy (heat), measured in megawatts, produced by a heat source, in this case, heat collected from solar radiation by a solar thermal collector.

Visit or call 021 811 0250 for more information about Greencape, a not-for-profit organisation established in 2010 by the Western Cape Government as a special purpose vehicle to support the development of the green economy in the region.