Water consumption solution for efficient concentrated solar power
Deserts and other sun-drenched regions are the ideal location for concentrated solar power plants, but where sunlight is abundant water tends to be scarce. EU-funded researchers are solving this conundrum by developing technologies to comprehensively reduce water consumption, enabling CSP plants to play an even bigger role in addressing the worlds energy and climate change challenges.
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The combination of innovative solutions being developed in the MINWATERCSP project promises to reduce the annual water consumption of an average concentrated solar power (CSP) plant by around 1.4 million m³ equivalent to the household water use of a small European town. The approach will allow CSP technologies to generate renewable power more efficiently, sustainably and cost-effectively, while enabling the development of more plants in areas lacking high-quality water sources.
A holistic combination of next-generation technologies, spanning plant-cooling systems to optimised mirror-cleaning strategies and comprehensive water-management plans, forms the basis of MINWATERCSPs overall solution to address the water consumption challenges of CSP plants, says project coordinator Dr Falk Mohasseb at Kelvion Holding in Germany.
Unlike conventional gas- or coal-fired power stations, CSP plants use mirrors to concentrate solar energy to heat water and convert it into steam; this is then used to turn turbines to produce electricity. Once the steam has done its job, it has to be cooled to condense back into water and start the steam cycle again.
This cooling process accounts for much of the water consumed by CSP plants through evaporation and so-called drift and blow-down losses. As a result, they can use as much as 3 500 litres of water for each megawatt hour of electricity they generate, compared to around 1 000 litres/MWh for modern natural gas-fired power plants.
From wet to hybrid cooling
Rather than using water alone to cool the steam, the MINWATERCSP partners developed a novel hybrid dry/wet cooling system that reduces evaporation losses by as much as 95 % without compromising performance, building on the development of improved energy-efficient fan-based dry-cooling technologies.
Tests show that the deployment of a hybrid cooling system would consistently reduce the net cost of electricity generation over the lifetime of a CSP plant the so-called levelised cost of electricity effectively making CSP plants more efficient and more competitive with other energy technologies. The system is currently being trialled at a full-scale test facility in South Africa belonging to project partner University of Stellenbosch.
Simulations demonstrate that the hybrid cooling system leads to an increased net annual power output from the plant of more than 2 % compared to dry-cooling alone, while meeting the project objective of saving 75 % to 95 % of water use compared to wet-cooling with the same level of capital investment, Mohasseb says.
Additional efficiency gains are being investigated at project partner IRESENs Green Energy Park in Morocco, where innovative technologies are being tested to verify that fouling does not represent a significant problem for the technology.
Efficient mirror cleaning
While cooling is the main consumer of water at CSP plants, it is not the only one. Regular cleaning of the concentrator mirrors also consumes substantial volumes of water, especially in dry, dusty regions. To address this, the project partners are testing improved spray and brush tools at solar thermal plants in Spain which reduce water use by 25 % to 35 %, as well as deploying an automated robot to replace manual cleaning on some types of mirrors.
Combined with a comprehensive water-management plan for CSP plants and the development of an enhanced simulation tool to predict water and waste-water flows, the MINWATERCSP technologies are set to play a major role in the future development of the renewable energy sector with project partners planning to deploy solutions commercially over the coming years.
As a result of the developments in MINWATERCSP, potential impacts include significantly improving technology performance, reducing life-cycle environmental impact, strengthening the European industrial technology base, creating new component manufacturing opportunities, decreasing operation costs and contributing to solving global climate and energy challenges, Mohasseb concludes.