Diego-César Alarcón-Padilla

Techno-economic Analysis

This chapter describes a steady-state sensitivity analysis based on a design point, considering each of the four configurations proposed in Chap. 5. This approach deals with a simulation-based analysis that allows estimation of overall efficiency over a wide range of boundary conditions to determine which cogeneration system is the most optimal in terms of capital cost (overall efficiency is directly related to the solar field size required). The analysis was performed for the three existing cooling technologies: once-through, evaporative water cooling and dry air cooling (except for the case in which a low-temperature (LT) multi-effect distillation (MED) unit replaces the condenser in the parabolic-trough concentrating solar power [PT-CSP] plant). The specific electric consumption (SEC) and the exhaust steam temperature were taken as inputs to be varied for a wide range of conditions that cover all the locations between the Mediterranean basin and the Arabian Gulf and match the three cooling systems considered. The simulations were carried out using the models described in Chaps. 3, 4 and 5. The study evaluated in which cases the PT-CSP + MED configurations are more efficient than the PT-CSP + RO configuration. Note that the results given in this chapter are valid only for parabolic-trough solar technology; thus, they could change for a different solar technology. Finally, a detailed techno-economic analysis is described for two representative locations in the Mediterranean basin and the Arabian Gulf, with the aim of determining the most suitable configuration and refrigeration system in each location. Specific operating conditions were established for each location, based on similar studies and information from real plants.

Integration of a Desalination Plant into a Concentrating Solar Power Plant

This chapter addresses the description and thermodynamic analysis for the integration of desalination plants into the power cycle described in Chap. 4. The systems chosen for this study combine a Concentrating Solar Power plant using parabolic-trough collector technology for electricity generation with various desalination plants, giving rise to what is known as a parabolic-trough concentrating solar power and desalination (PT-CSP + D) plant. The description of the PT-CSP plant, based on the Andasol-1 (Blanco-Marigorta et al., 2011) commercial plant, is detailed in Chap. 4, showing all the model equations. The desalination technologies selected to combine with the PT-CSP plant were multi-effect distillation (MED) and reverse osmosis (RO), as discussed in Chap. 1. On one hand, the simultaneous production of water and electricity using an RO plant connected to a CSP plant seems the simpler option. On the other hand, the integration of a low-temperature MED (LT-MED) plant is an interesting alternative because it allows replacement of the conventional power-cycle condenser by using exhaust steam as the thermal energy source for the desalination plant. However, to satisfy demand, while providing a certain performance, the LT-MED plant inlet temperature should be around 70 °C (corresponding to 0.031 bar absolute), meaning that the steam does not completely expand through the turbine and therefore the power-cycle efficiency is low compared with a stand-alone electricity-generating plant. This is the reason why another alternative to the MED plant, MED with thermal vapour compression (TVC), is considered. In this case, the steam expands completely in the turbine until it reaches the permitted value for the condenser conditions. However, part of the steam circulating through the turbine is extracted and used as high-pressure steam; this, together with the low-pressure steam coming from one of the MED effects, generates the inlet steam required in the first stage of the desalination plant. Moreover, in this study, a new concept of CSP + MED plants is evaluated (which, until now, has not been studied in published works), a thermally fed LT-MED plant with steam coming from a thermocompressor (LT-MED + TVC). In this case, the low-pressure steam (the entrained vapour) used by the thermocompressor comes from the exhaust steam of a PT-CSP plant instead of one of the MED effects. In each of the systems studied, desalinated water production is evaluated as well as the power and efficiency of the dual thermal solar power and desalinated water cycle.

Steady-State Modelling of a Parabolic-Trough Concentrating Solar Power Plant

This chapter describes the modelling of a parabolic-trough (PT) concentrating solar power (CSP) plant that produces electricity. To do this, the modelling of the solar field itself is explained first and then the power cycle, consisting of a reheat Rankine cycle, with steam as the working fluid. This power cycle will be used subsequently to be coupled to a desalination plant, creating what is known as a dual-purpose solar power/water cogeneration plant.

Steady-State Modelling of a Low-Temperature Multi-effect Distillation Plant

This chapter describes the development of a mathematical model of a vertically stacked, forward feed (FF), low-temperature multi-effect distillation (LT-MED) plant. The model was developed by taking into consideration the same design and operational characteristics as the pilot multi-effect distillation (MED) plant at Plataforma Solar de Almeria, in the southeast of Spain. The model has been validated, comparing the results of the model with the experimental data from the pilot plant.

Combined Fresh Water and Power Production: State of the Art

This chapter deals with the combined fresh water and power production by concentrating solar power (CSP) and desalination plants (CSP + D). First, the cogeneration of electricity and desalinated water from conventional power plants is described to provide a better understanding of the integration processes. Later in the chapter, the CSP plant technologies available are described, focusing particularly on parabolic-trough collectors. Finally, the latest studies related to CSP + D plants and the existing refrigeration systems within CSP plants are expounded.

State of the Art of Desalination Processes

The integration of the desalination processes into concentrating solar power plants (CSP + D) is nowadays the best alternative to solve simultaneously the water scarcity problems and the depletion of fossil fuels. Most of the regions facing fresh water shortages have high insolation levels and are located close to the sea, with more than 70 % of the world population living in a 70 km strip bordering the sea. Therefore, the use of solar energy for the simultaneous fresh water and electricity production is maybe the most sustainable solution.