Concentrated Solar Power (CSP) Plant to Co-generate Water for Namibia

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Concentrated Solar Power (CSP) Plant to Co-generate Water for Namibia

Concentrated Solar Power (CSP) is suited to regions with good solar resource. Here’s how it can solve related water scarcity.

A research study from Stellenbosch University finds that a 100 MW concentrated solar power (CSP) plant adapted to also “co-generate” water via multi-effect distillation (MED) would potentially be financially viable for Namibia given a world class solar resource at Arandis, where state utility NamPower plans a solar park close to the demand.

Including multi-effect distillation would add relatively little extra cost to that of a standalone CSP plant in Namibia, the authors of Integrating desalination with concentrating solar thermal power: A Namibian case study find in a study published at  Renewable Energy  in January 2018.

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The proposed solar thermal energy would be dispatchable day or night (red and orange thermal storage tanks) and include thermal desalination. Credit: Ernest Dall

CSP is the thermal form of solar that makes electricity by powering a conventional power block, but instead of fossil fuel, uses just sunlight. (How CSP delivers solar at night.)

The feasibility study for Namibia comes in the context of much CSP+desalination research and development by major CSP research centers globally, including MIT and the Cyprus Institute, which successfully demonstrated a prototype for Mediterranean islands in 2008, and CIEMAT in Spain, that leads the IEA/SolarPACES Task VI: where it researches and coordinates international researchers, and Germany’s DLR, which has summarized the range of CSP+desalination technologies explored.

Pros and cons for Namibia

This proposed 100 MW CSP+desalination plant would be more expensive than the existing desalination plant just north of Swakopmund, which uses grid-powered reverse osmosis, the study estimated.

However, co-generation of electricity and water would have additional benefits over the current grid-powered reverse osmosis plant. One advantage of this proposal is that it simultaneously generates electricity, while the current plant consumes Namibia’s scarce electricity.

With thermal energy storage the study’s CSP+desalination plant would provide dispatchable solar to supply 15% of Namibia’s peak demand into the evening, giving the small sunny nation greater energy independence from its neighbors, and reducing its carbon footprint, helping it meet its 2030 70% renewable energy target.

With a small population, 2.5 million, Namibia’s peak load was around 656 MW in 2017, of which 347 MW is supplied – albeit seasonally – by local hydro power from the Ruacana Hydropower Scheme.

“In 2017, Namibia imported approximately 60% of its annual electricity from surrounding countries. Most is from South Africa’s power utility, Eskom, and that’s mostly coal,” said the research study’s co-author, Ernest Dall.

Dall received a bursary for his Masters in Mechanical Engineering at Stellenbosch in South Africa from NamPower, Namibia’s national electric utility, and is now an engineer in its Power Systems Development division.

“I luckily had the option to choose my research topic and I wanted to do something looking at future issues that do not just affect Namibia, but issues that are global, and that is basically electricity and water scarcity, which if you think about it, go hand-in-hand in desalination,” he related.

Namibia is already water stressed. The United Nations projects it will become vulnerable by 2025.

Relatively little additional cost to add desalination to a CSP plant

“There is a synergy between power generation and desalination of seawater,” explained Dall. “The desalination plant effectively replaces the condenser in the Rankine cycle, whilst the Rankine cycle in turn provides a ready source of low grade heat for desalination.The concept hinges on utilizing that waste heat from your CSP plant and trying to use that as a heating source.”

The profitability of co-generating both electricity and water is equivalent to that of a CSP plant only generating power.The added cost is minor, about 13%. The solar field would be oversized in relation to the power block, and both operations would be simultaneous.

“You can do both at once, generate electricity and desalinate water,” said Dall. “Because the desalination plant functions as the dry cooled condenser – the one is dependent on the other. One in fact cannot function without the other one unless there’s a redundancy added in the system.”

Water sales would subsidize electricity production, as water prices are relatively high

“Water is considered a precious commodity in Namibia with prices seen to rise in the past resent years. We experienced a drought now for a few years and I don’t believe that water prices will decline anytime soon.” CSP+desalination could be attractive in similar water-stressed nations, Dall said.

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Paper : J.E. Hoffmann, E.P. Dall, Integrating desalination with concentrating solar thermal power: A Namibian case study, published at  Renewable Energy  in January 2018.

http://www.solarpaces.org/wp-content/uploads/DALL- namibia -PAPER.pdf

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