A review on solar Rankine cycles: Working fluids, applications, and cycle modifications

With the ever-rising paces of fuel consumption and CO2 emission, the urge for renewable energy resources is becoming a challenge in today's world; especially for Iran that has started to reduce its fuel subsidies. The need for electricity and fresh water in the southern coastal regions of the country is increasing with the increase in the population. The high solar radiation level in the region is a promising alternative to mitigate the fuel consumption of the conventional power or desalination plants by the solar thermal source through the concentrated solar technology. In addition, the CO2 emission of the aforementioned plants significantly diminishes by using the molten carbonate fuel cell that is suitable for the CO2 capture. Furthermore, the combination of different power and water technologies, which are operating at different temperatures and pressures, leads to enhance the overall efficiency of the integrated systems. To this end, a novel integrated power/water plant comprising a solar tower, a molten carbonate fuel cell, a gas turbine, a solar Rankine cycle, an organic Rankine cycle, a multi-effect distillation, and reverse osmosis desalination was techno-economically investigated. The multi-objective genetic algorithm was used to find the optimum configuration of the system with the low amount of CO2 emissions, and low unit costs of the electricity and fresh water. The results showed that the most effective parameter on system performance is the operating pressure of the molten carbonate fuel cell. For the optimum configurations of the system, the electricity unit of the cost was found as a value between 0.022 and 0.025 $/kWh. Part of the electricity unit of the cost that is associated with the output power that is generated based on solar thermal energy was obtained as a value between 0.08 and 0.092 $/kWh. In addition, the average unit cost of fresh water was obtained as 1.21 $/m3. The payback period of the system was obtained as 10.44 years if the electricity and fresh water are sold as 0.023 $/kWh and 1.21 $/m3. This can be reduced to 2.88 years for the electricity and fresh water selling prices of 0.069 $/kWh and 1.40 $/m3, respectively. Based on the results, the system with the solar thermal resource will be economically justifiable if the fuel price is increased.

The technical and economic analysis of the dual-purpose power/water Solar Rankine Cycle (SRC) coupled with Multi-Effect Desalination (MED) system was investigated. The influence of using Thermal Vapor Compression (TVC) on the unit costs of the generated power and water was also studied. Due to the population increase in the southern touristic coastal region of Iran and decreasing trend of the fuel price subsidy over the recent years, the government interest is shifting to the use of solar thermal energy and integrating the MED or MED-TVC desalination units with the conventional Rankine cycles, and to apply the solar thermal energy to reduce the fuel consumption. The water production rate of the MED or MED-TVC plants integrated into the SRC can significantly affect the electrical performance and consequently the fresh water and electricity unit of costs which has been rarely reported in the literature. In this regard, a comparison was made between the SRC-MED and SRC-MED-TVC configurations under two different scenarios of 6 and 12 hours of thermal energy storage. The output temperature of the LF solar field was considered to be regulated by defocusing the field mirrors and changing the working fluid mass flow rate. The unit costs of electricity (COE) and fresh water (COW) for both plants were determined under different scenarios of the water production capacities. Based on the results, COE and COW range from 0.20$/kWh to 0.25$/kWh and from 1.25$/ m 3 to 3$/ m 3 , respectively, for different water production rates. Also, for water production rates of more than 80,000 m 3 /day, the SRC-MED plant has lower COE and COW as compared to the S‌RC-MED-TVC plant. While the COE and COW of the SRC-MED-TVC plant are less than those of the other plant for water production rates of less and equal to 36,000 m 3 /day.

The integrated solar energy-driven chiller combined cycle system (SCCC) has a problem of low annual solar energy utilization. The solar thermal efficiency and power output of the traditional integrated solar combined cycle system (ISCC) are limited by the integrated solar mirror field area and Rankine cycle efficiency. This paper presents a new system, on the basis of the combined cycle system with the three pressure HRSG with reheat, the solar energy is integrated into the chiller for cooling the compressor inlet air of gas turbine and the heat recovery steam generator (HRSG) for increasing the power output simultaneously. The Aspen Plus, TRNSYS and EBSILON softwares are applied in this paper to build the models of the overall system. The solar thermal efficiency, annual solar power generation and annual solar thermal efficiency are used to evaluate the performances of the new system, the traditional ISCC system and SCCC system. During the summer solstice, the proportions of solar energy used in cooling and heating are set as 40% and 60% in new system, respectively. The research results show that the new system has a higher power output (406.37MW), thermal cycle efficiency (53.61%) and solar thermal efficiency (48.85%) compared with the traditional ISCC system (385.63MW, 51.67%, and 24.43%, respectively) at the design point. The new system can regulates the proportions of solar energy used in the chiller and HRSG based on the monthly meteorological data, in order to maximize the annual solar energy utilization and annual solar power generation. The new system’s annual solar energy utilization hours (2071h) and solar power generation (25.863GW·h) are far greater than those of SCCC system (1498h, 18.185GW·h, respectively). Therefore, the proposed new system with the simultaneous integrations of solar energy with both the chiller and HRSG not only greatly increases the utilization rate of solar energy, but also has the significant thermodynamic advantages.

Multi-objective design of reverse osmosis plants integrated with solar Rankine cycles and thermal energy storage

In this study, we experimentally explore the performance of using alcohol/water mixtures in a solar Rankine cycle system with an evacuated tube collector. The effects of the operating pressure and the composition of the working fluid on the temperature at exit of the solar collector and the heat transfer efficiency of the evacuated tube are investigated. Thermal resistance analysis is also performed to evaluate the heat losses of the evacuated tube. As the content of ethanol heightens, the lower latent heats and the lower boiling temperatures lead to a higher superheat at the exit of the evacuated tube, resulting in greater heat loss. On the other hand, ethylene glycol/water mixtures are unable to be heated beyond saturation at higher operating pressure, which eliminates their potential to be used in a solar Rankine cycle. Comparing to water, ethanol/water mixtures work very well because of its capability to produce dry, highly-superheated steam for the work-output device.

Reverse osmosis desalination powered by photovoltaic and solar Rankine cycle power systems: A review

Assessment of Direct Steam Generation Technologies for Solar Thermal Augmented Steam Cycle Applications

A comparative study between parabolic trough and solar tower technologies in Solar Rankine Cycle and Integrated Solar Combined Cycle plants

A Hybrid Electric and Thermal Solar Receiver

Thermodynamic analysis and optimization of an integrated Rankine power cycle and nano-fluid based parabolic trough solar collector

Solar power generation has emerged as one of the most rapidly growing sources of renewable energy. The solar thermal system with a Rankine cycle used to harness solar energy and generate electricity from a low temperature heat source is an emerging technology. The major drawback of solar thermal power generation is its poor efficiency, which is around 10% to 15%. Although prior attempts to improve the efficiency of the solar thermal system and use of Nano fluids in heat transfer applications have been carried out, very little work has been carried out using Nano fluids in Rankine cycle systems. Thus, the objective of the research undertaken was to primarily improve the efficiency of a small-scale solar thermal system by selecting working fluids, optimizing the system parameters and using Nano fluids with improved heat transfer properties for capturing heat. Thermodynamic simulation tool Aspen Hysys was used to carry out simulations of the Rankine and Regenerative Rankine systems. The system was simulated with combinations of Dowtherm-Cu O/Ag/Al2O3/TiO2 as the heat transfer fluid, and n-butane, n-pentane, n-hexane, or R-134a as the working fluid. System parameters such as mass flow, temperature, and pressure were optimized to obtain maximum power output and efficiency, keeping the system constraints and practicality in mind. The use of Nano fluids improved heat transfer to the working fluid in the heat exchanger by a maximum of 50%. The efficiency of the basic Rankine cycle was determined 16.03% for n-pentane, 14.90% for n-hexane, 13.83% for n-butane, and 9.82% for R-134a as the working fluid. Further, the use of regeneration improved the efficiency of the system by 6%, 3 %, 7% and 2% respectively. Highest efficiency of 27.96% was obtained when 6% volume concentration of Al2O3 was used in the heat transfer fluid, and n-pentane was used as the working fluid in the Regenerative Rankine cycle.

A review of sustainable solar irrigation systems for Sub-Saharan Africa

Solar thermal energy technologies and its applications for process heating and power generation – A review

Development of a geothermal-flash organic Rankine cycle-based combined system with solar heat upgrade

Qatar declared that by 2020, at least 2% of its electrical power generation should be by solar energy. This means that solar power plants (SPPs) of at least 640 MW capacity should be added, and be operational by 2020. Among the SPP alternatives to be built are: stand-alone solar Rankine cycle operated by parabolic trough collectors, photovoltaic power stations, and integrated solar combined cycle (CC). In this paper, the main characteristics and equipment of CC operating in Qatar and other Gulf area are illustrated. Then, the integration of the CC with solar field to become ISCC is introduced, and its merits are given. Then the ISCC is integrated with multi-stage flash desalting units to produce both electric power and desalted seawater. The addition of solar increases the solar steam, and thus, the capacity of both the steam turbine and desalination units. The additional cost of adding 55 MW capacity to the CC by solar energy is less than the 60% of stand-alone SPP with Rankine cycle having the same capacity.