Optimum power from a solar thermal power plant using solar concentrators

In this paper, the optimum temperature of operation of a solar concentrator and thus the maximum power obtained from a solar thermal power plant has been calculated. Results are plotted graphically and discussed.     

Optimization of low temperature solar thermal electric generation with Organic Rankine Cycle in different areas

The presented low temperature solar thermal electric generation system mainly consists of compound parabolic concentrators (CPC) and the Organic Rankine Cycle (ORC) working with HCFC-123. A novel design is proposed to reduce heat transfer irreversibility between conduction oil and HCFC-123 in the heat exchangers while maintaining the stability of electricity output. Mathematical formulations are developed to study the heat transfer and energy conversion processes and the numerical simulation is carried out based on distributed parameters. Annual performances of the proposed system in different areas of Canberra, Singapore, Bombay, Lhasa, Sacramento and Berlin are simulated. The influences of the collector tilt angle adjustment, the connection between the heat exchangers and the CPC collectors, and the ORC evaporation temperature on the system performance are investigated. The results indicate that the three factors have a major impact on the annual electricity output and should be the key points of optimization. And the optimized system shows that: (1) The annual received direct irradiance can be significantly increased by two or three times optimal adjustments even when the CPC concentration ratio is smaller than 3.0. (2) Compared with the traditional single-stage collectors, two-stage collectors connected with the heat exchangers by two thermal oil cycles can improve the collector efficiency by 8.1–20.9% in the simultaneous processes of heat collection and power generation. (3) On the use of the market available collectors the optimal ORC evaporation temperatures in most of the simulated areas are around 120 °C.     

Techno-economic evaluation of concentrating solar power generation in India

The Jawaharlal Nehru National Solar Mission (JNNSM) of the recently announced National Action Plan on Climate Change (NAPCC) by the Government of India aims to promote the development and use of solar energy for power generation and other uses with the ultimate objective of making solar competitive with fossil-based energy options. The plan includes specific goals to (a) create an enabling policy framework for the deployment of 20,000 MW of solar power by 2022; (b) create favourable conditions for solar manufacturing capability, particularly solar thermal for indigenous production and market leadership; (c) promote programmes for off grid applications, reaching 1000 MW by 2017 and 2000 MW by 2022, (d) achieve 15 million m² solar thermal collector area by 2017 and 20 million by 2022, and (e) deploy 20 million solar lighting systems for rural areas by 2022. The installed capacity of grid interactive solar power projects were 6 MW until October 2009 that is far below from their respective potential.     

A novel auto-cascade low-temperature solar Rankine cycle system for power generation

A novel auto-cascade low-temperature solar Rankine cycle (ALSRC) system is proposed. Compared to the single stage low-temperature solar Rankine cycle (SSLSRC) system, the ALSRC system is different because it consists of two solar collectors, two expanders, a regenerator, and an internal heat exchanger (IHE). The working fluid for the ALSRC is the zeotropic mixture Isopentane/R245fa. The main advantages of the ALSRC system is that heat from the exhaust stream of the expanders are reclaimed twice, once using an IHE and another time using a regenerator. System parameters such as regeneration, mixture composition, the outlet temperature of the low temperature solar collector, and the inlet temperature of two expanders are investigated to determine their effects on thermal efficiency. Results showed that with a regenerator, the thermal efficiency of the ALSRC system using a mixture of 0.32 R245fa by mass was significantly higher than that of the SSLSRC system. It was determined that regeneration, the mixture composition, and the outlet temperature of the low temperature solar collector are all important factors that affect the system’s thermal efficiency.     

Steam temperature stability in a direct steam generation solar power plant

Direct steam generation (DSG) is one alternative to the current oil-based parabolic trough solar thermal power plants. Within the German research project ITES, the dynamic behavior of a DSG collector field and the interactions with the conventional power block are assessed in detail. A transient solar field model developed by DLR is used to simulate the steam temperature behavior. Artificial irradiance disturbances as well as real irradiance data are used as input to the system. The resulting main steam temperature gradients are then analyzed by Siemens considering the standards for steam turbines.This paper presents the transient simulation results of the steam temperature as well as the corresponding results of the steam turbine analysis. It is found that the occurring temperature gradients are challenging for a safe turbine operation, if a conservative control system is used. Therefore, the use of an additional thermal inertia to stabilize the steam temperature is suggested. Its impact is also analyzed and discussed in this paper.     

Performance of a direct steam generation solar thermal power plant for electricity production as a function of the solar multiple

This paper describes the influence of the solar multiple on the annual performance of parabolic trough solar thermal power plants with direct steam generation (DSG). The reference system selected is a 50 MW_e DSG power plant, with thermal storage and auxiliary natural gas-fired boiler. It is considered that both systems are necessary for an optimum coupling to the electricity grid. Although thermal storage is an opening issue for DSG technology, it gives an additional degree of freedom for plant performance optimization. Fossil hybridization is also a key element if a reliable electricity production must be guaranteed for a defined time span. Once the yearly parameters of the solar power plant are calculated, the economic analysis is performed, assessing the effect of the solar multiple in the levelized cost of electricity, as well as in the annual natural gas consumption.     

Operating temperatures of linear solar concentrators for optimum power output

In this paper, operating temperatures of linear solar concentrators for optimum power output have been calculated considering the operating temperature, emissivity of absorber and wind velocity dependence of the heat loss factor. Results are presented graphically and discussed.     

Off-design performance analysis of a closed-cycle ocean thermal energy conversion system with solar thermal preheating and superheating

This article reports the off-design performance analysis of a closed-cycle ocean thermal energy conversion (OTEC) system when a solar thermal collector is integrated as an add-on preheater or superheater. Design-point analysis of a simple OTEC system was numerically conducted to generate a gross power of 100 kW, representing a base OTEC system. In order to improve the power output of the OTEC system, two ways of utilizing solar energy are considered in this study: (1) preheating of surface seawater to increase its input temperature to the cycle and (2) direct superheating of the working fluid before it enters a turbine. Obtained results reveal that both preheating and superheating cases increase the net power generation by 20–25% from the design-point. However, the preheating case demands immense heat load on the solar collector due to the huge thermal mass of the seawater, being less efficient thermodynamically. The superheating case increases the thermal efficiency of the system from 1.9% to around 3%, about a 60% improvement, suggesting that this should be a better approach in improving the OTEC system. This research provides thermodynamic insight on the potential advantages and challenges of adding a solar thermal collection component to OTEC power plants.     

INDITEP: The first pre-commercial DSG solar power plant

This paper presents the conceptual design of the first solar power plant using Direct Steam Generation (DSG) in a parabolic-trough solar field. Experience and know-how in the DSG process acquired during the DISS project were applied in designing the solar field of this plant. The 5-MWe plant is composed of a DSG parabolic-trough solar field connected to a superheated steam Rankine power cycle. The solar field produces 410 °C/70-bar superheated steam. Detail engineering of this plant is currently underway within the framework of the INDITEP project, which is promoted by a German-Spanish consortium with the financial support of the European Commission (Contract No. ENK5-CT-2001-00540). The main design objective is to assure high operational flexibility and reliability. This is the reason why a robust superheated steam turbine has been selected, though the efficiency of its power block is modest.     

Component exergy analysis of solar powered transcritical CO<Subscript>2</Subscript> rankine cycle system

In this paper,exergy analysis method is developed to assess a Rankine cycle system,by using supercritical CO2 as working fluid and powered by solar energy.The proposed system consists of evacuated solar collectors,throttling valve,high-temperature heat exchanger,low-temperature heat exchanger,and feed pump.The system is designed for utilize evacuated solar collectors to convert solar energy into mechanical energy and hence electricity.In order to investigate and estimate exergy performance of this system,the energy,entropy,exergy balances are developed for the components.The exergy destructions and exergy efficiency values of the system components are also determined.The results indicate that solar collector and high temperature heat exchanger which have low exergy efficiencies contribute the largest share to system irreversibility and should be the optimization design focus to improve system exergy effectiveness.Further,exergy analysis is a useful tool in this regard as it permits the performance of each process to be assessed and losses to be quantified.Exergy analysis results can be used in design,optimization,and improvement efforts.     

太阳能热力发电的生命周期分析

应用生命周期分析法(LCA),对塔式太阳能热力电站所用设备材料的生产、运输、电站基本建设等3个过程进行了分析,分别计算出3个过程中的能耗及其对环境的影响,并与燃煤发电进行了比较。结果表明．太阳能热力电站每发电10MWh,即可节省能源3．78t标准煤,少向大气排放粉尘、CO2、NOx、SO2分别为498．7,9 933,49．94,78．75kg。太阳能热力发电具有显著的节能和环保效益。     

Performance and design optimization of a low-cost solar organic Rankine cycle for remote power generation

Recent interest in small-scale solar thermal combined heat and power (CHP) power systems has coincided with demand growth for distributed electricity supplies in areas poorly served by centralized power stations. One potential technical approach to meeting this demand is the parabolic trough solar thermal collector coupled with an organic Rankine cycle (ORC) heat engine.The paper describes the design of a solar organic Rankine cycle being installed in Lesotho for rural electrification purpose. The system consists of parabolic though collectors, a storages tank, and a small-scale ORC engine using scroll expanders.A model of each component is developed taking into account the main physical and mechanical phenomena occurring in the cycle and based on experimental data for the main key components.The model allows sizing the different components of the cycle and evaluates the performance of the system. Different working fluids are compared, and two different expansion machine configurations are simulated (single and double stage).     

A parabolic dish/AMTEC solar thermal power system and its performance evaluation

This paper proposes a parabolic dish/AMTEC solar thermal power system and evaluates its overall thermal–electric conversion performance. The system is a combined system in which a parabolic dish solar collector is cascaded with an alkali metal thermal to electric converter (AMTEC) through a coupling heat exchanger. A separate type heat-pipe receiver is selected to isothermally transfer the solar energy from the collector to the AMTEC. To assess the system’s overall thermal–electric conversion performance, a theoretical analysis has been undertaken in conjunction with a parametric investigation by varying relevant parameters, i.e., the average operating temperature and performance parameters associate with the dish collector and the AMTEC. Results show that the overall conversion efficiency of parabolic dish/AMTEC system could reach up to 20.6% with a power output of 18.54 kW corresponding to an operating temperature of 1280 K. Moreover, it is found that the optimal condenser temperature, corresponding to the maximum overall efficiency, is around 600 K. This study indicates that the parabolic dish/AMTEC solar power system exhibits a great potential and competitiveness over other solar dish/engine systems, and the proposed system is a viable solar thermal power system.     

Improved solutions for temperature and thermal power delivery profiles in linear solar collectors

For the conversion of absorbed sunlight into useful thermal power, we demonstrate that the profiles of absorber temperature, fluid temperature and thermal power delivery along linear solar collectors can be solved in closed form even when the collector heat-loss coefficient is far from constant over the collector operating range. This analytic solution eliminates the errors inherent in earlier approximate solutions, and makes the dependence of collector performance on component properties transparent. An example for a realistic solar concentrator illustrates the improvement in prediction accuracy.     

A hybrid power generation system: solar‐driven Rankine engine–hydrogen storage

This paper reports on the feasibility of a hybrid power generation system consisting of a solar energy‐driven Rankine engine and a hydrogen storage unit. Solar energy, the power for the hybrid system, is converted into electrical power through a combination of a solar collector, a tracking device to maintain proper orientation with the sun and a Rankine cycle engine driving an electrical power generator. Excess electricity is utilized to produce hydrogen for storage through electrolysis of water. At the solar down time, the stored hydrogen can be used to produce high‐quality steam in an aphodid burner to operate a turbine and with a field modulated generator to supplement electric power. Case studies are carried out on the optimum configuration of the hybrid system satisfying the energy demand. A numerical example based on the actual measured solar input is also included to demonstrate the design potential. Copyright © 2001 John Wiley & Sons, Ltd.     

中低温废热发电的思路与方法

在工业生产过程中,存在着大量具有一定温度品质的热能被放散。实践中,可以通过某种设备系统将其回收利用,既节约了宝贵的一次能源,又改善了环境质量。中低温废热发电就是回收废热而生产二次优质能源的一种方法。     

Economic analysis of power generation from parabolic trough solar thermal plants for the Mediterranean region—A case study for the island of Cyprus

In this work a feasibility study is carried out in order to investigate whether the installation of a parabolic trough solar thermal technology for power generation in the Mediterranean region is economically feasible. The case study takes into account the available solar potential for Cyprus, as well as all available data concerning current renewable energy sources policy of the Cyprus Government, including the relevant feed-in tariff. In order to identify the least cost feasible option for the installation of the parabolic trough solar thermal plant a parametric cost–benefit analysis is carried out by varying parameters, such as, parabolic trough solar thermal plant capacity, parabolic trough solar thermal capital investment, operating hours, carbon dioxide emission trading system price, etc. For all above cases the electricity unit cost or benefit before tax, as well as after tax cash flow, net present value, internal rate of return and payback period are calculated. The results indicate that under certain conditions such projects can be profitable.     

Wind effect on the performance of a solar organic Rankine cycle

The effects of wind, ambient temperature and solar radiation on the simultaneous productions of mechanical work and heat by a solar Rankine cycle are studied. The on site experimental study uses the pentafluorobutane R365mfc as working fluid in a system consisting of a small-scale single glazed flat plate collector, a micro turbine, a condenser and a pump. The theoretical study focuses on the prediction of the optimum operating temperature of the collector according to the solar radiation, the temperature of air and the wind speed. Then, the total production of mechanical and thermal energy is calculated during a sunny day for which various wind speeds are simulated. The results highlight the effect of wind on the corresponding production and they also establish the value of the recommended evaporating temperature according to weather conditions.     

Performance evaluation of solar chimney power plants in Iran

The solar chimney power plant is a simple solar thermal power plant that is capable of converting solar energy into thermal energy in the solar collector. In the second stage, the generated thermal energy is converted into kinetic energy in the chimney and ultimately into electric energy using a combination of a wind turbine and a generator. The purpose of this study is to evaluate the performance of solar chimney power plants in some parts of Iran theoretically and to estimate the quantity of the produced electric energy. A mathematical model based on the energy balance was developed to estimate the power output of solar chimneys as well as to examine the effect of various ambient conditions and structural dimensions on the power generation. The solar chimney power plant with 350 m chimney height and 1000 m collector diameter is capable of producing monthly average 1-2 MW electric power over a year.     

Concentrating solar thermal power as a viable alternative in China's electricity supply

Study of low-carbon and pollution renewable alternatives for China revealed that concentrating solar thermal (CST) electric power generation was underemphasized in China's renewable energy plan. The analysis shows the competitive viability of CST: (1) China has the key prerequisites to make CST power generation economical including high-quality insolation and appropriate land, (2) CST's proven history, scale, and dispatchability makes it a good utility-scale power option, especially in the economically underdeveloped Western regions, (3) while CST power is currently more expensive than coal-fired electricity on a nominal basis, when costs of externalities are accounted for, CST, at 11.4 US cents/kWh, can become 57% cheaper than scrubbed coal and 29% cheaper than nuclear power, (4) CST power continues dropping in cost due to economies of scale and technological improvements and can potentially realize a levelized electricity cost of around 4 cents/kWh within ten years, (5) it would significantly rise in competitiveness if and when China completes the extensive smart grid for connecting its solar-abundant western regions with the high-demand eastern regions, (6) CST has the potential to positively impact Western China's economy, but proper policy and deal structure must be in place to ensure that the local community shares the benefit.