Elsevier

Energy Policy

Volume 39, Issue 7, July 2011, Pages 4391-4398
Energy Policy

Costs of reducing water use of concentrating solar power to sustainable levels: Scenarios for North Africa

https://doi.org/10.1016/j.enpol.2011.04.059Get rights and content

Abstract

Concentrating solar power (CSP) has the potential to become a leading sustainable energy technology for the European electricity system. In order to reach a substantial share in the energy mix, European investment in CSP appears most profitable in North Africa, where solar potential is significantly higher than in southern Europe. As well as sufficient solar irradiance, however, the majority of today's CSP plants also require a considerable amount of water, primarily for cooling purposes. In this paper we examine water usage associated with CSP in North Africa, and the cost penalties associated with technologies that could reduce those needs. We inspect four representative sites to compare the ecological and economical drawbacks from conventional and alternative cooling systems, depending on the local environment, and including an outlook with climate change to the mid-century. Scaling our results up to a regional level indicates that the use of wet cooling technologies would likely be unsustainable. Dry cooling systems, as well as sourcing of alternative water supplies, would allow for sustainable operation. Their cost penalty would be minor compared to the variance in CSP costs due to different average solar irradiance values.

Highlights

► Scaling up CSP with wet cooling from ground water will be unsustainable in North Africa. ► Desalination and alternative cooling systems can assure a sustainable water supply. ► On large-scale, the cost penalties of alternative cooling technologies appear minor.

Introduction

About eight tons of CO2 are emitted each year on average by every citizen of the European Union (U.S. Energy Information Administration (EIA), 2009). This is the result of an energy-intensive lifestyle, mainly relying on burning fossil fuels for energy generation. The consequences are experienced by the whole planet as global climate change (Solomon et al., 2007). An increase in average air temperatures and hence the frequency and intensity of extreme weather events, such as floods or droughts, will threaten human life more and more during the upcoming decades (Parry et al., 2007). One way to counteract this development efficiently is to restructure the energy sector by replacing fossil energy resources with renewable ones, making energy generation sustainable and reducing CO2 emissions substantially (Metz et al., 2007).

There are many visions of how Europe could obtain its energy sustainably. While their time horizon, emission goal and technology preferences can differ widely, there is relative consensus that if we want to achieve a sustainable energy market by the mid-century, transformation must begin over the next few years (Knopf et al., 2010, Van Vuuren et al., 2010). One energy technology that could play a major role in a fast and efficient transformation to renewables is concentrating solar power (CSP). Already in commercial operation today and equipped with affordable energy storage capacities for either peak or baseload power generation, CSP has the economic and technological potential to become a leading energy technology in future (Khosla, 2008, Lorenz et al., 2008, Pitz-Paal, 2005). But to make the most efficient use of solar energy, deserts are the preferred location for CSP plants. Several researchers have suggested that for CSP to supply sufficiently large amounts of power to the energy mix, the European electricity grid would need to expand southwards to the Sahara, allowing new cooperation and transition possibilities for both North Africa and Europe (Battaglini et al., 2009, MacKay, 2009, Patt, 2010). Two recent political and private sector initiatives in this direction are the Mediterranean Solar Plan (2008) and the Desertec Industrial Initiative (2009), respectively. This increasing interest of European energy policy leads to the need of proactive investigation of potential adverse environmental consequences of such large-scale projects, making local resource studies from North Africa of interest for Europe.

While CSP has great potential, one issue that has arisen in its development, especially in the United States, is its sustainability in the very desert environments to which it is most suited (Pitz-Paal, 2005). In contrast to other renewable technologies like photovoltaic (PV) or wind, CSP requires a considerable amount of water, mainly for cooling purposes, when using recirculating wet cooling, a characteristic this technology shares with other thermal power technologies. While coal or nuclear power plants show a similar water demand, natural gas plants require only up to a fourth of that (cf. U.S. Department of Energy (DOE), 2006, U.S. Department of Energy (DOE), 2009). Some renewable energy experts argue that this water demand constrains the large-scale development of wet-cooled CSP in desert regions; either they would consume too much water in an area with by definition very low water resources, or, when using more expensive alternative cooling systems, like dry cooling, CSP could not become cost-competitive with other energy technologies (Carter and Campbell, 2009, Hogan, 2009, Woody, 2009, Patel, 2010).

We investigate the validity of this argument for the case of large-scale investment in CSP in the Sahara, starting with four case studies from Morocco to Egypt, and then scaling up to a regional level where CSP could meet a substantial part of the future electricity demand of both regions, North African and Europe. We focus on growth scenarios that include power production for the European market because here the potential social and political ramifications of unsustainable water use are the most acute.

Section snippets

Background

Concentrating solar power technologies use an assembly of mirrors that reflect and concentrate solar thermal energy to heat up a fluid that then impels a conventional steam power cycle for electricity generation. Heat storage capacities, mostly involving the use of molten salt, allow running the steam turbine after the sun goes down, and during periods of cloudiness. Parabolic trough (PT) and central tower (CT) are the most mature technologies at present, with CT showing highest thermodynamic

Methods

As the water demand of a plant depends on its precise location, its access to water resources as well as its climate, we examine four representative locations for CSP plants in North Africa. For each location, we identify appropriate cooling technologies for both central tower and parabolic trough plants. We compare wet cooling systems with dry cooling (integrating direct and indirect technologies) as well as with hybrid (two wet cells added to the dry cooled condenser) and spray cooling

Case study results

Water demand at all four sites averages 2240 (CT) or 3180m3/GWh (PT) with the hottest sites showing highest water demands. Hybrid systems require about 360–380 m3/GWh on average and naturally dry-cooled system stay stable at 300/340 m3/GWh. Until 2050 these requirements increase with climate change under an A1B scenario on average by about 2% (45 [CT]–60 [PT] m3/GWh) for wet-cooled systems and 1.5–3% (5–15 m3/GWh) for hybrid-cooled CT systems or 2–3% (7–15 m3/GWh) for PT.

Integrating the three

Discussion

Concentrating solar power has the potential to become an important source for the future energy mix of Europe and North Africa. All types of CSP plants require a certain amount of water, while PT plants still require about 40% more water than CT technologies. Our study investigated regional environmental and economical drawbacks of CSP technologies that could hinder a large-scale development in North Africa. For CSP in desert regions, the energy-water nexus is a key issue when targeting a

Acknowledgments

Funding for this work was received from the European Climate Foundation. We would like to thank Michael Hogan, Herbert Formayer, Zoltán Szabó and Juan Ignacio Burgaleta for providing data and valuable assistance, as well as stakeholder participants at two workshops, held in Potsdam, Germany, in March 2010 and Hammamet, Tunisia, in June 2010, for presenting useful insights. Any remaining errors are those of the authors.

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