08/05/2018 16:52 SAST | Updated 10/05/2018 10:50 SAST

24/7 Solar Thermal Plant To Be Officially Launched This Month

A solar energy plant that keeps producing electricity after dark and creates jobs in Northern Cape? Believe it, 'cos it's true...

FroukjeBrouwer via Getty Images
A solar thermal energy system using parabolic mirrors to focus the sun's heat on a central pipe containing a "thermal fluid", which is in turn used to boil water and drive a steam turbine that generates electricity.

Spanish multinational Abengoa will officially launch its third large-scale solar thermal plant in South Africa on May 18, near Pofadder in Northern Cape. It is expected to have an impact on the local community and demonstrate the viability of renewable energy as a sustainable source of electricity.

The parabolic thermal installation, Xina Solar One, has a total installed capacity of 100MW and follows the launch of KaXu and Khi, making it the largest such system in Africa.

"Khi, KaXu and Xina Solar One together reach an installed capacity of 250MW of renewable and dispatchable energy, offset 831,000 tons of carbon dioxide emissions every year, and supply upward of 220,000 homes," Dominic Goncalves, vice-president of business development at Abengoa South Africa told News24.

He said that the project delivered 1,300 jobs during the construction phase and is expected to create 80 permanent jobs during the operational phase over the next 20 years.

"Our commitment, after achieving the practical completion of the plant, is to employ 70 percent South African people, although we are focusing on reaching 100 percent," said Goncalves.

Electricity after sunset

Solar thermal plants such as Xina Solar One typically use a set of parabolic mirrors to reflect the sun's rays to tube at the focus of the mirrors, which contains a "thermal fluid" — a mineral salt that remains molten due to the extreme heat, and absorbs more heat while the sun shines.

The excess heat in that molten salt is in turn used to boil water. The resulting steam turns a turbine, generating electricity. The salt keeps emitting heat even after sunset, so the process of creating steam to turn the turbines can continue after dark.

Unlike solar photovoltaic (PV) systems, the solar thermal plants — also known as concentrated solar plants (CSPs) — are therefore able to continue producing electricity overnight, because the molten salt remains hot for hours.

"The efficiency of CSP plants is typically exceeding that of commercial PV installations notably. A direct comparison between those technologies is possible, as both make use of the same resource: solar irradiation," Dr Matti Lubkoll, who teaches solar thermal energy at Stellenbosch University, told News24.

"Wind turbines tend to have a higher efficiency, in terms of converting energy available in the wind into electric power," he added.

This indicates that a time has been reached where a renewable energy technology with base-load capability can produce electricity at lower cost than conventional base-load.

According to the International Renewable Energy Agency (Irena), the levelised cost of electricity from CSPs is higher than PV or wind systems, though the agency was careful to point out that in high sunlight areas, the costs could be significantly less.

"All renewable energy technologies [have] made significant progress, and in 2017 CSP bids elsewhere in the world showed first tariffs below R1/kWh. This indicates that a time has been reached where a renewable energy technology with base-load capability can produce electricity at lower cost than conventional base-load," said Lubkoll.

He said that winning bids for wind power in South Africa came in at "R0.62/kWh and the winning CSP bid at R2.02 per kWh" — comparative to coal at R1.03/kWh in November 2015.

Clean electricity

CSP technology is still a relatively new technology in clean energy production, and the EU-inspired Desertec initiative has so far failed to get off the ground.

The project had aimed to place CSP plants in the Sahara Desert to export electricity to Europe while creating jobs in North African countries.

Irena's "Renewable Energy Technology: Cost Analysis Series on Concentrated Solar Power" report says that globally, renewable energy projects need to be scaled up six times to meet climate goals set out in the Paris Agreement on climate change.

The agency, however, calculates that CSP will make up just four percent of renewable electricity generation, compared to 22 percent from PV and 36 percent from wind, by 2050.

"As deployment of CSP technologies rise, increased maturity follows. Increased deployment will result in component cost reduction and increased maturity in reduced cost of financing, both significantly enabling cost reduction for electricity production cost of CSP," Lubkoll said.

A key challenge for developing CSPs is the state of the transmission network, and Lubkoll highlighted the contrast of the location of projects and the availability of transmission lines.

"In South Africa the best solar resource for CSP plants (actually among the best in the world, second only to the Atacama Desert in Chile) can be found in Northern Cape around Upington. The specific location of CSP plants in this region therefore has to consider the availability of electricity transmission infrastructure."

Energy minister Jeff Radebe recently signed a R56-billion contract with 27 independent power producers, but Goncalves insisted that the contract was not related to the launch of the Xina Solar One project.

He said the "practical completion" of Xina Solar One was in August 2017, meaning that the plant had been working at full capacity for the past eight months.

"We have been looking for the most appropriate date to celebrate an official launch considering agendas, climatology, etc." he said.

Note: this article has been amended to correct technical errors.