Evaluation of cooling technologies of concentrated solar power plants and their combination with desalination in the mediterranean area

Different alternatives for the effective integration of desalination technologies in the cooling of concentrating solar power (CSP) plants in the Mediterranean area are discussed and evaluated. Two cases are considered where a low temperature multi-effect distillation (LT-MED) plant is integrated into a CSP plant replacing the condenser of the power cycle. In one case, a LT-MED plant is fed by steam at the outlet of the turbine expanded to 70 °C. In the other case a LT-MED is fed by the steam obtained from a thermal vapour compressor (TVC) which uses the exhaust steam of the CSP plant (at 37 °C, 0.063 bar) together with some from the high pressure turbine extraction (17 bar). The two cases are compared with that of a reverse osmosis (RO) unit powered by the electricity produced by the CSP plant. In this case, two different wet cooling technologies, once-through and evaporative water cooling, and a dry air cooling are considered for the CSP plant. Thermodynamic simulations are presented for all cases, together with an economic analysis.     

Concentrating solar power hybrid plants – Enabling cost effective synergies

This paper categorises different concentrating solar power (CSP) hybrid options into light, medium and strong hybrids and discusses the combination of CSP with coal, natural gas, biomass and waste materials, geothermal, and wind. The degree of hybridisation depends on the interconnection of the plant components. Light hybrids create only limited synergies, such as the joint use of a substation, and their cost reduction potential is therefore limited, while strong hybrids share major plant components, such as steam turbine and condenser, and can better match their energy output with electricity pricing.The hybridisation options for CSP with different energy sources are plentiful ranging from feedwater heating, reheat steam, live steam to steam superheating with some options better suited for a specific energy source combination than others. The synergies created in hybrid plants can lead to cost reductions of 50%, better energy dispatchability as well as revenue maximisation.Several CSP hybrid studies exist for coal, natural gas and biomass but these are often investigating a specific hybrid concept. This paper considers several options at a higher level and also includes geothermal and wind which is novel.While the paper focuses on Australia the approach taken and concepts discussed are transferable to other countries.     

A novel power block for CSP systems

Concentrating Solar Thermal Power (CSP) and in particular parabolic trough, is a proven large-scale solar power technology. However, CSP cost is not yet competitive with conventional alternatives unless subsidized. Current CSP plants typically include a condensing steam cycle power block which was preferably designed for a continuous operation and higher operating conditions and therefore, limits the overall plant cost effectiveness and deployment. The drawbacks of this power block are as follows: (i) no power generation during low insolation periods (ii) expensive, large condenser (typically water cooled) due to the poor extracted steam properties (high specific volume, sub-atmospheric pressure) and (iii) high installation and operation costs.In the current study, a different power block scheme is proposed to eliminate these obstacles. This power block includes a top Rankine cycle with a back pressure steam turbine and a bottoming Kalina cycle comprising another back pressure turbine and using ammonia-water mixture as a working fluid. The bottoming (moderate temperature) cycle allows power production during low insolation periods. Because of the superior ammonia-water vapor properties, the condensing system requirements are much less demanding and the operation costs are lowered. Accordingly, air cooled condensers can be used with lower economical penalty. Another advantage is that back pressure steam turbines have a less complex design than condensing steam turbines which make their costs lower. All of these improvements could make the combined cycle unit more cost effective. This unit can be applicable in both parabolic trough and central receiver (solar tower) plants.The potential advantage of the new power block is illustrated by a detailed techno-economical analysis of two 50 MW parabolic trough power plants, comparing between the standard and the novel power block. The results indicate that the proposed plant suggests a 4-11% electricity cost saving.     

GIS-based assessment of combined CSP electric power and seawater desalination plant for Duqum—Oman

This paper investigates the potential of implementing combined electric power and seawater desalination plant using concentrated solar power technologies for Wilayat Duqum in Oman. Duqum is going through a considerable urban, touristic and industrial expansion and development. GIS solar radiation tools are used to select the most appropriate site for the plant location. There are basically two different options to combine concentrated solar electric power with seawater desalination. The first option is to combine a CSP plant with a thermal desalination unit, exploiting the exhaust heat of the steam cycle to drive a thermal desalination unit. The second option is to exploit only the electricity output of the CSP plant with a reverse osmosis desalination unit. The paper deals with both options and shows where each of the concepts has advantages considering local conditions: the quality of the input water, the demand of freshwater and/or potable water, social and economic aspects, the environment and others.     

太阳能热发电产业发展障碍分析

太阳能热发电是将太阳能转化为热能,通过热功转化过程发电的技术。目前商业化的太阳能热发电项目在全球逐步推进。然而我国的太阳能热发电处于产业化起步阶段,相关产业链上的产品还处于试制和产业化的前期阶段,关键技术产品仍需要进一步验证。我国太阳能直射辐射资源的调查体系,不能满足日益发展的太阳能资源开发利用需求,同时也缺乏电站整体系统设计、系统集成、建设以及运营的能力和经验。太阳能热发电相关检测体系、标准体系还是空白,无法验证我国生产的产品的性能和可靠性。为了推动太阳能热发电的产业建设和发展,需要政策层面上重点鼓励、支持太阳能热发电的技术研发,示范工程的建设,以此带动市场规模的扩大。     

Performance assessment of a solar hydrogen and electricity production plant using high temperature PEM electrolyzer and energy storage

This paper investigates the performance of a high temperature Polymer Electrolyte Membrane (PEM) electrolyzer integrated with concentrating solar power (CSP) plant and thermal energy storage (TES) to produce hydrogen and electricity, concurrently. A finite-time-thermodynamic analysis is conducted to evaluate the performance of a PEM system integrated with a Rankine cycle based on the concept of exergy. The effects of solar intensity, electrolyzer current density and working temperature on the performance of the overall system are identified. A TES subsystem is utilized to facilitate continuous generation of hydrogen and electricity. The hydrogen and electricity generation efficiency and the exergy efficiency of the integrated system are 20.1% and 41.25%, respectively. When TES system supplies the required energy, the overall energy and exergy efficiencies decrease to 23.1% and 45%, respectively. The integration of PEM electrolyzer enhances the exergy efficiency of the Rankine cycle, considerably. However, it causes almost 5% exergy destruction in the integrated system due to conversion of electrical energy to hydrogen energy. Also, it is concluded that increase of working pressure and membrane thickness leads to higher cell voltage and lower electrolyzer efficiency. The results indicate that the integrated system is a promising technology to enhance the performance of concentrating solar power plants.     

Thermal energy storage technologies and systems for concentrating solar power plants

This paper presents a review of thermal energy storage system design methodologies and the factors to be considered at different hierarchical levels for concentrating solar power (CSP) plants. Thermal energy storage forms a key component of a power plant for improvement of its dispatchability. Though there have been many reviews of storage media, there are not many that focus on storage system design along with its integration into the power plant. This paper discusses the thermal energy storage system designs presented in the literature along with thermal and exergy efficiency analyses of various thermal energy storage systems integrated into the power plant. Economic aspects of these systems and the relevant publications in literature are also summarized in this effort.     

The thermal efficiency improvement of a steam Rankine cycle by innovative design of a hybrid cooling tower and a solar chimney concept

In the present work, a dry cooling tower and a solar chimney design are recombined in order to increase the thermal efficiency of a steam Rankine cycle. The rejected heat from the condenser into the dry cooling tower supplemented by the solar radiation gained through its transparent cover are the sources of wind energy generation that is captured by a wind turbine which is located at the beginning of the chimney. In this research a case study for a 250 MW steam power plant of Shahid Rajaee in Iran has been performed. A CFD finite volume code is developed to find the generated wind velocity at the turbine entrance for a 250 m dry cooling tower base diameter and a chimney height of 200 m. Calculations have been iterated for different ambient temperatures and solar irradiances, representing temperature gradient within day length. A range of 360 kW to 3 MW power is obtained for the change in the chimney diameter from 10 to 50 m. The results show a maximum of 0.37 percent increase in the thermal efficiency of a 250 MW fossil fuel power plant unit; which proves this design to be a significant improvement in efficiency of thermal power plants, by capturing the heat that is dissipated from dry cooling towers.     

On site experimental evaluation of a low-temperature solar organic Rankine cycle system for RO desalination

The paper presents the on site experimental evaluation of the performance of a low-temperature solar organic Rankine cycle system (SORC) for reverse osmosis (RO) desalination. This work is a research step forward to the experimental evaluation of the SORC under laboratory conditions, where the system was tested using an electric brake as load and an electric thermal heater as heat supply. The difference is that solar collectors have been applied as heat supply and there has been a realistic investigation of the performance of the system under the conditions implied by solar energy. The thermal energy produced by the solar collectors’ array evaporates the refrigerant HFC-134a in the pre-heater-evaporator surfaces of the Rankine engine. The superheated vapour is then driven to the expander, where the generated mechanical work produced from expansion drives the high-pressure pump of the RO desalination unit. The superheated vapour at the expander’s outlet is directed to the condenser and condensates. Finally, the saturated liquid at the condenser outlet is pressurized by a positive displacement pump and the thermodynamic cycle is repeated. A special energy recovery system of Axial Pistons Pumps (APP) has been integrated into the RO unit to minimise the specific energy consumption. The results prove that the above concept is technically feasible and continuous operation is achieved under the intermittent availability of solar energy. However, considerably low efficiency has been observed, in comparison with the results taken under controlled thermal load. Nevertheless, it becomes apparent that further optimisation work is required to improve the system efficiency. The research work has been done within the framework of COOP-CT-2003-507997 contract, partly financed by EC.     

Solar hybrid steam injection gas turbine (STIG) cycle

Solar heat at moderate temperatures around 200 °C can be utilized for augmentation of conventional steam-injection gas turbine power plants. Solar concentrating collectors for such an application can be simpler and less expensive than collectors used for current solar power plants. We perform a thermodynamic analysis of this hybrid cycle. High levels of steam-to-air ratio are investigated, leading to high power augmentation compared to the simple cycle and to conventional STIG. The Solar Fraction can reach up to 50% at the highest augmentation levels. The overall conversion efficiency from heat to electricity (average over fuel and solar contributions) can be in the range of 40–55% for typical candidate turbines. The incremental efficiency (corresponding to the added steam beyond conventional STIG) is in the range of 22–37%, corresponding to solar-to-electricity efficiency of about 15–24%, similar to and even exceeding current solar power plants using higher temperature collectors. The injected water can be recovered and recycled leading to very low water consumption of the cycle, but a very low cost condenser is required to make water recovery feasible.     

Dynamic Modeling of a Parabolic Trough Solar Thermal Power Plant with Thermal Storage Using Modelica

Concentrating solar power (CSP) technology with thermal energy storage is a renewable and emerging technology. In this work, dynamic models for analyzing and evaluating energy storage concepts and its interaction with the solar field and the power block have been developed. A physical model of a 50 MW CSP plant has been implemented in the modeling language Modelica. The models are developed in a modular, flexible structure with a well-defined interface to easily replace and test modules of various detail and complexity. Models include turbine island, steam generator, solar field, and thermal energy storage system. In addition, a decentralized control configuration has been developed. Results have been successfully validated against the reference plant key steady-state data. Dynamic response of the power block has shown expected behavior, and transient durations were comparable with settling times predicted in literature. Furthermore, the performance of the plant has been evaluated during a typical summer day including effects such as variation of solar irradiance, charging and discharging the heat storage system, and dumping excess heat in the solar field. The summer day scenario results agreed with published performance of the plant.     

Performance analysis of an Integrated Solar Combined Cycle using Direct Steam Generation in parabolic trough collectors

The contribution of solar thermal power to improve the performance of gas-fired combined cycles in very hot and dry environmental conditions is analyzed in this work, in order to assess the potential of this technique, and to feature Direct Steam Generation (DSG) as a well suited candidate for achieving very good results in this quest. The particular Integrated Solar Combined Cycle (ISCC) power plant proposed consists of a DSG parabolic trough field coupled to the bottoming steam cycle of a Combined Cycle Gas Turbine (CCGT) power plant. For this analysis, the solar thermal power plant performs in a solar dispatching mode: the gas turbine always operates at full load, only depending on ambient conditions, whereas the steam turbine is somewhat boosted to accommodate the thermal hybridization from the solar field.     

Production of enriched methane by a molten-salt concentrated solar power plant coupled with a steam reforming process: An LCA study

Enriched Methane is a gas mixture consisting of methane and a certain amount of hydrogen (10–30%vol) that finds out several applications such as fuel of Internal Combustion Engines (ICEs). To produce EM, a steam reforming reactor whose heat duty is supplied by a molten-salt stream heated up by a concentrating solar power (CSP) plant can be used, in order to generate the hydrogen steam by solar energy. In fact, molten salts at temperatures up to 550 °C can allow to reach the necessary thermal level inside the reactor to promote steam reforming reaction.     

Comparative studies of augmentation in combined cycle power plants

The attractive features of a combined cycle (CC) power plant are fuel flexibility, operational flexibility, higher efficiency and low emissions. The performance of five gas turbine‐steam turbine (GT‐ST) combined cycle power plants (four natural gas based plants and one biomass based plant) have been studied and the degree of augmentation has been compared. They are (i) combined cycle with natural gas (CC‐NG), (ii) combined cycle with water injection (CC‐WI), (iii) combined cycle with steam injection (CC‐SI), (iv) combined cycle with supplementary firing (CC‐SF) and (v) combined cycle with biomass gasification (CC‐BM). The plant performance and CO₂ emissions are compared with a change in compressor pressure ratio and gas turbine inlet temperature (GTIT). The optimum pressure ratio for compressor is selected from maximum efficiency condition. The specific power, thermal efficiency and CO₂ emissions of augmented power plants are compared with the CC‐NG power plant at the individual optimized pressure ratios in place of a common pressure ratio. The results show that the optimum pressure ratio is increased with water injection, steam injection, supplementary firing and biomass gasification. The specific power is increased in all the plants with a loss in thermal efficiency and rise in CO₂ emissions compared to CC‐NG plant. Copyright © 2013 John Wiley & Sons, Ltd.     

Operating cost and water economy of mixed air steam turbines

In this work an economic evaluation of the operating cost and the water economy of the various commercial MAST (mixed air steam turbines) technologies is carried out. For the water requirements the analysis takes into account either the use of a reverse osmosis desalination plant or the use of a water recovery condenser. The two simulation tools used are the IPP (independent power producers) optimization algorithm and the CAROC (computer aided reverse osmosis calculations) optimization algorithm. Both software tools take into account the capital cost, the fuel cost and the operation and maintenance (O&M) requirements of each candidate scheme (MAST plant or RO desalination plant accordingly) and calculate the least cost configuration. The results indicate that when natural gas is used as a fuel it is more cost effective than gasoil. Also, by the integration of water recovery condenser the operating cost is slightly less than in the case of the use of a reverse osmosis desalination plant. Lastly, the least cost MAST technology is the LOTHECO cycle (LOw Temperature HEat COmbined cycle) with natural gas.     

Combining wind farms with concentrating solar plants to provide stable renewable power

We evaluate the extent to which a combination of wind power and concentrating solar power (CSP) may lead to stable and even baseload power by taking advantage of: 1) spatiotemporal balancing of solar and wind energy resources and 2) storage capabilities of CSP plants. A case study is conducted for the region of Andalusia in Spain. To this end, spatiotemporal variability of modeled CSP and wind capacity factors in a 3-km spatial resolution grid were analyzed based on principal component analysis (PCA) and canonical correlation analysis (CCA). Results reveal that renewable baseload power can be obtained in the study region by locating wind farms and CSP plants using balancing patterns derived from CCA and PCA. In addition, the power fluctuation reduction attained from these patterns was substantially higher than those obtained by interconnecting randomly-located wind farms and CSP plants across the study region. Results were particularly meaningful for the winter season. Upon considering storage capability of the CSP plants, results proved better. The main difference was a higher firm capacity value associated with spring and summer seasons. For the other seasons, the contribution of thermal storage capabilities of the CSP plants to stable power proved less relevant.     

Thermodynamic analysis of an LNG fuelled combined cycle power plant with waste heat recovery and utilization system

This paper has proposed an improved liquefied natural gas (LNG) fuelled combined cycle power plant with a waste heat recovery and utilization system. The proposed combined cycle, which provides power outputs and thermal energy, consists of the gas/steam combined cycle, the subsystem utilizing the latent heat of spent steam from the steam turbine to vaporize LNG, the subsystem that recovers both the sensible heat and the latent heat of water vapour in the exhaust gas from the heat recovery steam generator (HRSG) by installing a condensing heat exchanger, and the HRSG waste heat utilization subsystem. The conventional combined cycle and the proposed combined cycle are modelled, considering mass, energy and exergy balances for every component and both energy and exergy analyses are conducted. Parametric analyses are performed for the proposed combined cycle to evaluate the effects of several factors, such as the gas turbine inlet temperature (TIT), the condenser pressure, the pinch point temperature difference of the condensing heat exchanger and the fuel gas heating temperature on the performance of the proposed combined cycle through simulation calculations. The results show that the net electrical efficiency and the exergy efficiency of the proposed combined cycle can be increased by 1.6 and 2.84% than those of the conventional combined cycle, respectively. The heat recovery per kg of flue gas is equal to 86.27 kJ s^?1. One MW of electric power for operating sea water pumps can be saved. The net electrical efficiency and the heat recovery ratio increase as the condenser pressure decreases. The higher heat recovery from the HRSG exit flue gas is achieved at higher gas TIT and at lower pinch point temperature of the condensing heat exchanger. Copyright © 2006 John Wiley & Sons, Ltd.     

Solar tower power plant in Germany and future perspectives of the development of the technology in Greece and Cyprus

Since the 80s power production with solar thermal power plants has been a way to substitute fossil fuels. By concentrating direct solar radiation from heliostats very high temperatures of a thermal fluid can be reached. The resulting heat is converted to mechanical energy in a steam cycle which generates electricity.High efficiencies and fast start-up are reached by using air as a heat medium, as well as using porous ceramic materials as solar receiver of the concentrated sunlight.In Germany the construction of a 1.5 MW_e solar tower power plant began in 2008. It is operational since December 2008 and started production of electricity in the spring of 2009.In Greece and Cyprus, countries with high solar potential, the development of this competitive solar thermal technology is imperative, since it has already been implemented in other Mediterranean countries.     

Modeling the potential for thermal concentrating solar power technologies

In this paper we explore the tradeoffs between thermal storage capacity, cost, and other system parameters in order to examine possible evolutionary pathways for thermal concentrating solar power (CSP) technologies. A representation of CSP performance that is suitable for incorporation into economic modeling tools is developed. We also combined existing data in order to estimate the global solar resource characteristics needed for analysis of CSP technologies. We find that, as the fraction of electricity supplied by CSP technologies grows, the application of thermal CSP technologies might progress from current hybrid plants, to plants with a modest amount of thermal storage, and potentially even to plants with sufficient thermal storage to provide base load generation capacity. The regional and global potential of thermal CSP technologies was then examined using the GCAM long-term integrated assessment model.