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CSP plant highlights benefits of Fresnel technology

CSP plant highlights benefits of Fresnel technology

Aug 12, 2014

The launch of MTN’s Concentrating Solar Power (CSP) plant has highlighted the benefits of Fresnel technology. This uses the sun to reflect heat from 242 mirror panels to ultimately create air conditioning for MTN’s data centre, converting heat into cold.

Industrial Solar, the German-based supplier of the technology, says that Fresnel technology is used when a water temperature exceeding 130°C is needed. Possible applications cover solar process heating, cooling, thermal power generation, desalination and poly-generation.

“To put this into perspective,” says Frank Major, MD of REACH Renewable, who are engineers for the technology, “the total energy consumption in the European Union is 13,7 TWh of which 28% is used by industry and 67% of this used for heat generation. 27% is used for temperatures between 100°C and 400°C which can be accommodated by Fresnel CSP collectors.”

Due to the broad field of applications of the Fresnel collector, the MTN solar system was built within the “Dena Solar Roofs Programme”  by the German Energy Agency (DENA). The programme supports the solar industry in the Renewable Energies Export Initiative of the Federal Ministry for Economic Affairs and Energy in entering foreign markets.

“Local industry can also be involved. For future CSP Fresnel projects, up to 90% of the value chain can be provided locally. With regards to system components this includes the primary mirrors, steel frame, secondary mirrors, metal frame, absorber tubes, electronics, sensors and belt drive.”

Major says that South Africa has a unique combination of input factors: “It is an emerging market (BRICS), has energy constraints, is highly industrialised, has a renowned research community and has ideal climatic conditions and can play a world leadership role.”

Fresnel rooftop installation
The technology is suitable across a number of industries. In the metal and automotive industries it can be used for drying after the process of painting, electroplating and blueing. In the oil and chemical industries it can be used for injection molding, distillation and oil recovery.

The pharmaceutical industry is able to use Fresnel technology for distillation and injection molding and the paper andtextile industries for bleaching, cooking and drying. The food industry canbenefit from pasteurisation, blanching and cleaning.

Tobias Schwind, CEO of Industrial Solar GmbH, says solar thermal systems can be placed into four categories based on increasing water heating temperatures requirements. Firstly, flat plate collectors, typically used for domestic water heating, space heating and low temperature processing. This heats water to between 40°C and 80°C.

Secondly, evacuated tube collectors are used for solar cooling (single stage) and mid-temperature process heating, producing temperatures of between 90°C – 130°C. Thirdly, when temperatures are required between 130°C and 220°C, Fresnel technology is used.

Fourthly, utility scale power generation and industrial process heating requires heat between 250°C and 450°C. Along with other concentrating solar technologies the Fresnel technology will also address these requirements.
The basic principal of Fresnel technology is based on  a troughcollector design, whereby the trough is cut into almost flat mirror sections, which are tracked uniaxially to focus the sunlight onto a stationary absorber tube. A typical installation will consist of primary and secondary mirrors as seen in the diagrams below.

For rooftop installations, such as at MTN, the Fresnel technology offers a low wind load, good weight-spread, high ground usage and has no north-south alignment requirements. Maintenance is low because flat glass is easy to access and clean and the components are reliable. The primary mirrors are made of flat glass vs. aluminium, giving durability and reflectivity. The system comprises of high-quality vacuum absorber tubes and can provide precise temperature and power control with no stagnation.

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