SIMULATION OF SOLAR THERMAL CENTRAL RECEIVER POWER PLANT AND EFFECT OF WEATHER CONDITIONS ON THERMAL POWER GENERATION

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1 International Journal of Mechanical Engineering and Technology (IJMET) Volume 8, Issue 2, February 217, pp , Article ID: IJMET_8_2_4 Available online at ISSN Print: and ISSN Online: IAEME Publication SIMULATION OF SOLAR THERMAL CENTRAL RECEIVER POWER PLANT AND EFFECT OF WEATHER CONDITIONS ON THERMAL POWER GENERATION Sandhya Jadhav Research Scholar, Bharati Vidyapeeth Deemed University College of Engineering, Pune, India Dr. V. Venkat Raj Former Director, Health Safety and Environment Group, Bhabha Atomic Research Centre, Mumbai, India ABSTRACT Mathematical model is presented for prediction of thermal losses from central receiver solar thermal power plant. Results obtained are verified with evidence from solar experiments. Code is developed for studying the effect of variation of weather conditions i.e. variation of incident solar radiation, wind speed and ambient temperature during the entire year on the thermal performance of receiver. Thermal losses have its effect on efficiency of the receiver and hence the overall cost of solar thermal to electric power. Radiation and convection losses are the major components of thermal losses. Simulation is done for weather data of Jaipur city of India. Key words: Central receiver solar plant, external receiver, thermal losses, simulation. Cite this Article: Sandhya Jadhav and Dr. V. Venkat Raj. Simulation of Solar Thermal Central Receiver Power Plant and Effect of Weather Conditions on Thermal Power Generation. International Journal of Mechanical Engineering and Technology, 8(2), 217, pp INTRODUCTION In central receiver solar thermal power plant (CRSTPP), the incident solar rays from the sun are concentrated and reflected by heliostat field onto a receiver mounted at the top of a tower. Heat transport fluid flowing through the receiver tubes gets heated up by absorbing the incident energy on the receiver and is used to produce steam which drives the turbine. The CRSTPP requires a large space for installation and the components are costly. To carry out experimentation, it becomes costly and time consuming. Therefore experimental work has shown the necessity to master user friendly modeling tools and simulation to reduce the effort and time required. Tools can be of great help in predicting the performance of components of plant and also plant as a whole. It also helps in plant optimization. Several codes have been developed since 197s. According to different specifications and needs of power plants, these softwares can be modified and adopted for simulation. In the literature, some software for energy balance and performance analysis of entire power plant are available. DELSOL developed by 27 editor@iaeme.com

2 Sandhya Jadhav and Dr. V. Venkat Raj Kristler in 1986 is a performance and design optimization software developed by using FORTRAN 77. Although receiver radiation and convection losses are also calculated, the detail is probably insufficient for use in receiver evaluation, thus only flux density calculation capabilities are used for receiver analysis. SOLERGY developed in 1987 used FORTRAN 77 for simulation of the plant. Code is developed using Visual Basic for studying the thermal performance of the central receiver solar thermal power plant for different amount of solar radiation received during the entire year. The code developed simulates the operation and annual power output of a solar central receiver power plant using an actual simulated weather data recorded at time intervals of 1 hour. It calculates the net electrical energy output including parasitic power requirements over 24 hrs a day. It has subroutine for each major plant system, receiver, thermal energy storage and turbine. Annual plant performance is found by adding the performance at every considered time step. For each time step, the heliostat field concentrates the incident solar radiation and directs it on to the receiver placed on the top of the tower. On receiving the adequate amount of solar radiation from the heliostat field, the receiver starts working. The operation of the receiver depends upon the power received from the heliostat field and the previous receiver status. The lower receiver power limit is set by the minimum flow rate that the receiver flow valves can handle. If the power to the receiver is greater than the receiver thermal rating, the input is decreased to the thermal rating, by heliostat defocusing. All thermal power from the receiver is delivered to thermal storage tank, provided that storage tank can accept it (i.e. until storage tank is full). The turbine operates, after a specific level in thermal storage is achieved. 2. THERMAL LOSSES IN THE RECEIVER In Solar thermal power plants, heat loss can significantly reduce the efficiency and consequently the cost effectiveness of the system. It is therefore vital to fully understand the nature of these heat loss mechanisms. The magnitude of the thermal losses varies and it depends on the receiver type, geometry and size. Apart from receiver configurations weather conditions also play a significant role in thermal losses of receiver. Therefore it becomes important to study the effect of incident solar flux, ambient temperature and wind speed. Thermal losses in receiver are due to conduction, convection and radiation processes. Experimental works have shown that conduction losses are very small. Therefore neglecting thermal power loss due to conduction, the total thermal power lost by the receiver is the summation of loss due to radiation by the receiver and loss due to convection by the receiver. These losses account for most of the receiver thermal losses resulting from calculation. They are evaluated in the receiver simulation model. 3. EFFECT OF VARIATION IN WEATHER CONDITIONS Variation of incident flux, wind speed and ambient temperature affects the performance of receiver and hence thermal losses from receiver. Therefore, effect of variation in incident flux, wind speed and ambient temp is studied Variation of Incident Solar Radiation Incident Flux in W/m Jan March May July Sept Nov Month Figure 1 Monthly average incident flux in W/m 2 for Jaipur editor@iaeme.com

3 Simulation of Solar Thermal Central Receiver Power Plant and Effect of Weather Conditions on Thermal Power Generation The total solar incident flux obtained in year 27 in Jaipur is shown in Fig.1. It is observed that most of the sunny days of the year the incident flux received is 9 W/m 2 as. On rainy seasons and cloudy days it is zero. Therefore the effect of variation of incident flux is studied for the values ranging from to 9 W/m 2. As most of the days in the year, wind speed is observed to be 4m/s and the ambient temperature to be 3 C, therefore these values are considered for simulation. Thermal power loss due to radiationin MW th Incident flux in W/m 2 Figure 2 (a) Variation in thermal losses due to radiation with increase in incident flux Thermal power loss due to Convection in MW th Incident flux in W/m 2 Figure 2 (b) Variation in thermal losses due to convection with increase in incident flux Thermal Power in MW th power absorbed net power Power loss Incident flux in W/m 2 Figure 2 (c) Variation in thermal power with increase in incident flux Increase in solar radiation increases the receiver temperature and hence the loss due to radiation also increases. It can be observed from Fig.2a that the radiation loss increases considerably, almost 4 times when incident solar radiation increases from 1 W/m 2 to 9 W/m 2. Thermal loss due to convection on the other hand increases by only a small amount i.e. only by.6 MW th as shown in Fig 2b. Due to the increase in thermal losses, the total loss in the receiver increases with increase in flux intensity as shown in Fig 2c. As the flux intensity increases, the net power absorbed by the receiver increases but as there is increase in losses, net power generated and the overall efficiency of the receiver is almost constant and is within a range of 78% to 82% editor@iaeme.com

4 Sandhya Jadhav and Dr. V. Venkat Raj 3.2. Variation in Wind Speed It is observed that the average value of wind speed is more than 1.5 m/s in all the months as shown in Fig 3. Hourly data of weather however shows that on many hours of the day, there is no wind i.e. wind velocity is zero m/s. The maximum value of wind speed is observed to be 15.4 m/s. Therefore for simulation, wind velocity is varied from m/s to 2 m/s. As most of the days in the year, solar incident flux is observed to be 7 W/m 2 and the ambient temperature is 3 C, therefore the solar incident radiation is taken to be 7 W/m 2 and ambient temperature is assumed to be 3 C for simulation. Wind speed in m/s Jan March May July Sept Nov Month Figure 3 Monthly average wind speed in m/s for Jaipur. With input values stated earlier, the performance of receiver is studied under varying values of wind velocity from m/s to 2 m/s. Power loss due to radiation (P R ) remains constant as it is independent of wind speed and is MW and variation in heat loss due to convection is observed, thus affecting the total power loss and net power generated from receiver along with the efficiency of the receiver. Heat transfer Coefficient in W/m 2 K Power Loss due to Convection in MW th Velocity of wind in m/s Velocity of Wind in m/s Figure 4 (a) Variation of heat transfer coefficient with variation of speed Figure 4 (b) Power loss due to convection with variation of wind speed Net power generated in MW Velocity of wind in m/s Efficiency of Receiver Velocity of Wind in m/s Figure 4 (c) Variation in net power generated with variation of wind speed Figure 4 (d) Variation of efficiency of receiver with variation of wind speed 3 editor@iaeme.com

5 Simulation of Solar Thermal Central Receiver Power Plant and Effect of Weather Conditions on Thermal Power Generation The results obtained are plotted to visualize the impact of wind speed. Fig No 4a shows that the heat transfer coefficient increases with the increase in wind speed and the thermal power loss due to convection also increases with wind speed as shown in Fig 4b. It can be seen that after wind speed of 5m/s, power loss due to convection increases sharply. It is observed, at m/s wind velocity, the net thermal power generated in the receiver decreases with increase of wind speed. This shows that there is 8.9% of reduction in net thermal power for increase of wind speed from m/s to 2m/s as shown in Fig No.4c. Decrease in receiver efficiency due to increase in heat loss is also observed from 81.35% to 74.1% as shown in Fig No.4d Variation of Ambient Temperature Ambient Temperature in C Month Figure 5 Monthly average ambient temperature in C for Jaipur. Fig No.5 shows the average ambient temperature for all the months of the year 27 for Jaipur city. It is observed that the average value of ambient temperature is more than 18 C in all the months, above 35 C on sunny days and as low as 2 C on winter days. The highest temperature is observed as 45 C. Therefore for simulation, ambient temperature is varied from C to 45 C. The solar incident radiation is taken to be 7 W/m 2 and wind speed is assumed to be 4m/s. The values of thermal losses obtained after simulation show that with increase in ambient temperature, convection loss increases very slowly and radiation loss decreases. Thus net power decreases as well as the efficiency also decreases by a very small amount. In general, there is little impact of ambient temperature on the thermal performance of the receiver. Thermal power loss due to radiation decreases by very small amount as shown in Fig No.6a. This happens due to large difference between the receiver temperature and ambient temperature. Small increase in ambient temperature affects the radiation loss by negligible amount. Thermal power loss due to convection decreases sharply for the increase in ambient temperature from C to 45 C as shown in Fig.No.6b. The decrease in loss due to convection is.2mw th. Since there is decrease in thermal power loss due to both, convection and radiation, the net thermal power of receiver increases as shown in Fig.No.6c. Same pattern is observed for increase in efficiency of the receiver as shown in FigNo.6d. The efficiency of the receiver increases as net thermal power of the receiver increases editor@iaeme.com

6 Sandhya Jadhav and Dr. V. Venkat Raj Power loss due to radiation in MW th Figure 6 (a) Power loss due to radiation with variation of ambient temperature Power loss due to convection in MW th Figure 6 (b) Power loss due to convection with variation of ambient temperature Net thermal power in MW th Efficiency of receiver Figure 6 (c) Variation in net power generated with variation of ambient temperature Figure 6 (d) Variation of efficiency of receiver with variation of ambient temperature 4. CONCLUSION It is observed that, the thermal losses due to radiation increases considerably with the increase in incident flux. It is seen that due to variation in flux intensity the receiver temperature varies and hence the mean temperature which results in variation of the working fluid properties. The net thermal power generated in the receiver decreases with increase of wind speed. There is 8.9% of reduction in net thermal power for increase of wind speed from m/s to 2m/s. The efficiency of the receiver increases as net thermal power of the receiver increases with increase in ambient temperature. Out of these three weather parameters; incident solar radiation is the most affecting parameter for thermal losses and hence generation of thermal power. REFERENCES [1] A. Sobin & W. Wagner. Central collector solar energy receivers. Solar Energy, Vol.18, pp-21-3,1976. [2] Clifford K. Ho, Software and codes for Analysis of Concentrating Solar Power Technologies, Sandia Report, December 28. [3] James E. Calogeras and Larry H. Gordon, Storage Systems for Solar Thermal Power, in Proceedings of Thirteenth Intersociety Energy Conversion Engineering Conference San Diego, California, August 2-25, editor@iaeme.com

7 Simulation of Solar Thermal Central Receiver Power Plant and Effect of Weather Conditions on Thermal Power Generation [4] L.J.Yebra, M. Berenguel, S. Dorando and M. Romero, Modelling and Simulation of Central Receiver Solar Thermal Power Plants in Proceedings of the 44th IEEE Conference on Decision and Control and the European Control Conference, Spain Dec 12-15, 25. [5] M. Castro, J. L. Presa, J. Diaz, J. Peire, A. F. Baker, S. E. Faas, L. G. Radosevich & A. C. Skinrood. Central receiver & storage systems evaluation. Solar Energy Vol. 47, No3, pp , Printed in U.S.A,1991 [6] Magal, B. S., Solar Power Engineering, Tata McGraw Hill Publishing Company Limited, Second Print [7] Ortega, J., J. Burgaleta, M. Tellez, Central Receiver System (CRS) Solar power plant using molten SALT as heat transfer fluid, Journal of Solar Energy Engineering (Transactions of the ASME), Vol. 13, No. 2,, pp (6 pg), May 28. [8] Robert Z. Litwin, Receiver System: Lessons Learned from Solar Two, The Boeing Company, Canoga park, CA, SANDIA National Laboratories, March 22. [9] Romero, M., R. Buck, J. Pacheco, An Update on Solar Central Receiver Systems, Projects, and Technologies. ASME Journal of Solar Energy Engineering Vol.124, pp , May 22. [1] S. P. Sukhatame, Solar thermal power generation, in Proc. Indian Acad Sci (Chem Sci.), Vol. 19, No. 6, pp Dec [11] Winter, C. J., R. L. Sizmann, L. L. Vant, - Hull (Eds.), Solar Power Plants Fundamentals, Technology, Systems, Economics (New York: Springer Verlag) 25 [12] Zhihao Yao, Zhiheng Wang, Zhenwu Lu & Xiudong Wei, Modeling and simulation of the pioneer 1 MW solar thermal central receiver system in China, Renewable Energy Vol. 34, 29, pp [13] Alo Mikola, Teet-Andrus Kõiv and Mikk Maivel. Production of Domestic Hot Water with Solar Thermal Collectors in North-European Apartment Buildings. International Journal of Mechanical Engineering and Technology, 7 (1), 216, pp [14] Jadhav Sandhya Dilip and Dr. V. Venkatraj, Thermal Losses in Solar Central Receiver, International Journal of Mechanical Engineering and Technology, 4(6), 213, pp editor@iaeme.com