Non-Imaging Concentrator based Solar System Operations & Maintenance Manual

Transcription

1 Non-Imaging Concentrator based Solar System Operations & Maintenance Manual UNDP-GEF Project on Concentrated Solar Heat Ministry of New & Renewable Energy Government of India November, 2014 Prepared By: lr;eso t;rs MNRE MSA RENEWTECH F O U N D AT I O N

2 Index Acknowledgement...3 About This Manual Working Principle Module Components Module Specification Module Connection Reflector Specification Maintenance and Precaution Receiver Receiver Components Receiver Specification Maintenance and Precaution P & I Diagram of Connection Operation Check list Start-up Procedure Shutdown procedure Maintenance Troubleshooting

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4 Acknowledgement This document is the result of active mentorship, support and inputs from the following individuals: Dr. S.K. Singh, MNRE Dr. A.K. Singhal, MNRE-UNDP Project Management Unit Dr. R.P. Goswami, MNRE Shri Pankaj Kumar, MNRE-UNDP Project Management Unit Dr. Deepak Gadhia, Founder of Gadhia Solar Ltd. And Director of MSA RenewTech Foundation Shri Kailash, Technician at Solar Energy Center, Gurgaon 3

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6 About This Manual This document describes a typical non-imaging solar thermal system and the procedures needed to operate and maintain it successfully. The document is intended primarily for instructors, supervisors and engineers to train the site-level technicians. The document maintains a focus on the practical day-to-day tasks of operating a non-imaging system. The design of the system and the engineering considerations behind its operation are not covered unless they have a direct bearing on operational decisions. 5

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8 1. Working Principle To make an image, all the parallel light rays should be concentrated at a single point. Non-Imaging collectors are the collectors which can t make the image (of sun). Compound Parabolic Collector (CPC) is a well-known kind of non-imaging collector. In CPC, parallel light rays get focused at two points instead of one. 1 st Parabola Receiver 2 nd Parabola Figure 1: Basic Shape of a Compound Parabolic Concentrator (CPC) Basic shape of the Compound Parabolic Concentrator (CPC) is illustrated in the figure. The name, Compound Parabolic Concentrator, derives from the fact that the CPC is comprised of two parabolic mirror segments with different focal points as indicated in figure. The focal point (B) of 1 st parabola lies on 2 nd parabola, whereas the focal point (A) of 2 nd parabola lies on 1 st parabola. The two parabolic surfaces are symmetrical with respect to reflection through the axis of the CPC. The receiver tube place is AB. 2. Module CPC modules are similar to flat plate collector. It has a fixed structure and hence does not need to track the sun. CPC reflectors are fixed at a tilted base. And the receivers are placed at the focal points of each reflector. Figure 2: Sun s Declination The angle of CPC from the horizontal is called tilt angle. The output of the system is directly related to the tilt angle. To get maximum output, incident angle 1 should be zero. Since the sun s declination. a. During summer (Tilt angle = Latitude angle ) b. During winter (Tilt angle = Latitude angle ) c. Throughout the year (Tilt angle = Latitude angle) 7

9 2.1. Components There are three main components in the module. 1. CPC Reflector 2. Evacuated receiver tube 3. Supporting structure Header Tilted base Receiver tube Tilt angle Figure 3: Components of a Compound Parabolic Concentrator 2.2. Module Specification Table 1. Module Specification Specification Unit Value Aperture surface area 2.33 m 2 No. of tubes 14 No. Collector length m Collector width m Collector depth 0.12 m Gross area 2.62 m 2 Collector weight 41.2 Kg Optical efficiency 46.4 % Collector capacity 2.31 l 1 st degree heat loss (a1) kw/m 2 K 2 nd degree heat loss (a2) kw/m 2 K 2 Max. permissible operating pressure 10 Bar Stagnation 1000W/m2 radiation C Tube connection Series Glass tube material Borosilicate glass 3.3 Absorber coating material Reflector material Collector frame material Insulator material Working fluid Aluminium Nitride Aluminium Aluminium grey (natural anodized / A6CO) Thermic wool Water 8

10 2.3. Module Connection Modules can be connected in parallel as well as series. Series connection increases temperature while parallel connection increases flow rate. Series Connection Parallel Connection Figure 4: Series and Parallel combination of the Modules of a Compound Parabolic Concentrator 3. Reflector Usually the non-imaging reflectors are CPC reflectors. It is made up of a metal sheet with high reflectivity (90% to 95%). Reflector reflects the maximum amount of sun s radiation towards the receiver. Reflector should be cleaned frequently in order to achieve good reflectivity Specification Table 2. Reflector Specification Specification Unit Value Aperture surface are m Collector area m Reflectivity % 93 Reflector material Reflector type Aluminum Compound parabola 3.2. Maintenance and Precaution 1. Regular cleaning is a requisite 2. Prevent reflectors from dents and scratches 9

11 4. Receiver Receiver absorbs the maximum amount of sun s radiation, reflected by the CPC reflector. For good absorptivity, receiver should be cleaned properly. It is a very complex but crucial part of the collector. Cross-section view of receiver is shown in the figure below. (A) Copper Pipe Holder (B) (C) (D) Figure 5: Cross-section View of the Collector Tube of a Compound Parabolic Concentrator 4.1. Receiver Components 1. Copper Tube: It is the innermost part of the receiver. It is U-shaped copper tube. As shown in figure, one end of the tube is inlet (for cold water) and the other end is outlet (for hot water). Figure 6: Flow of the Water in Copper Tubes of a Compound Parabolic Concentrator 2. Copper Tube Holder: It s a circular hollow pipe which holds the U-shaped tube. It is generally made up of Aluminum. 3. Inner Glass Tube: It is a cylindrical glass pipe with a high heat absorption coating. It increases the overall absorptivity of the receiver. It is also called absorber glass tube. 4. Outer Glass Tube: This is the outermost glass tube and hence is tough and thick. The main function of the outer glass pipe is to maintain vacuum, which thereby reduces conduction heat loss. It also provides safety to the inner glass tube. Connection: In a CPC module, receiver tubes are connected, either in parallel or series. 10

12 4.2. Receiver Specification Table 3. Receiver Specification Specification Unit Value Tube length m 1.4 Receiver absorptivity % 92 1 st degree heat loss (a1) kw/m 2 K nd degree heat loss (a2) kw/m 2 K Glass tube, (diameter external / diameter internal / wall thickness / tube length) Tube connection mm Parallel 47/36.2/1.6/15 03 Glass tube material Borosilicate glass 3.3 Absorber coating material U shape Tube material Aluminium Nitride Copper 4.3. Maintenance and Precaution 1. Regular cleaning is a requisite 2. Prevent receiver from overheating. Never expose receiver in sun without significant flow of water. 3. Always cover the collector with tarpaulin, when it is not in use. 5. P & I Diagram of Connection Figure 6: P & I Diagram of Connection in a Compound Parabolic Concentrator Working Figure 6 shows the process flow of the system. The water from the expansion / storage tank (H) is pumped by using a feed pump (A) into the solar field inlet (B) and the hot water comes out from the solar field outlet (C). Hot water will go to process via 3-way valve (D). After transferring the heat to the process, it will go to expansion tank (for maintaining pressure). In solar plant there are two mode of operation: 1. By-Pass mode (A-B-C-D-G-H): If hot water output at C does not have enough temperature (for process) then it directly goes to expansion tank via 3-way valve. In morning time, when solar radiation is low, the solar plant is operated in pass mode and the water is circulated in solar field till it achieves the temperature for process. 2. Pass Mode (A-B-C-D-E-F-H): If hot water output at C has enough temperature (for process), than the 3-way valve (D) will pass the hot water to the process and from process to expansion tank. 11

13 6. Operation 6.1. Check list Table 3. Check List Sr. No. Equipment Condition Location 1 Reflector & Receiver Cleaned Field 3 Pump suction valve Open 4 Pump discharge valve Open Field/ pump house Field/ pump house 8 Water level in expansion tank Sufficient Field 9 Nitrogen pressure in expansion tank As per design Field 10 Vent valves Closed Field 11 Drain valves Closed Field 12 Electricity (voltage & phase) 440V, 3 phase synchronized with pump Control panel 6.2. Start-up Procedure 1. Switch On the electric supply switch in control panel. 2. Start the feed pump. Keep an eye on water flow rate. 3. Once the flow gets stabilized, remove the tarpaulin cover from the collector. 4. Keep a watch on output temperature and pressure. 5. After achieving desired temperature, open output valve to start the process Shutdown procedure 6. Take the most recent reading of temperature, pressure and flow indicators. 7. Cover all the collectors with tarpaulin. 8. Monitor input and output temperature of field. 9. Wait for temperature to get stabilized (inlet temperature (B) ~ outlet temperature (C). 10. Switch Off the pump and control panel. 11. Close all the inlet and outlet valve of solar field. - For long term shut down, drain all the water from solar field. Afterwards cover the solar field properly 7. Maintenance 1. Check for leakages and verify that enough solar heat transfer fluid is in the system; furthermore, flush and clean the system with the help of filling station. 2. Ensure all the connections and mounting elements are secured tightly. 3. Visually inspect all collectors for probable defects. 4. Pressure check the expansion vessel and all safety devices. 5. Check all moveable and electrical components. 6. Check the tanks for their reliability and security. 7. Replace the damaged tube as soon as possible as it can affect the output adversely. 8. Oil and grease the pump motor as per routine or as per manufacturer s instruction. 12

14 8. Troubleshooting Table 4. Troubleshooting a CPC Problem Possible Cause Solution Pump is operating fine, but temperature at flow and return is same. Also, the pump is very hot. Low heat gain in the system. The temperature at collector is higher than that of tank but the pump is not working. There is no sound coming from the pump. There might be some air in the system and/or the valves are closed The insulation pipe might be faulty. There could be high heat loss in the system. The water circulation controller is bad There is no power Either the controller is not working properly or the temperature difference is too large Maximum temperature is already achieved There might be some deposits in the bearing of the shaft of the pump which might be blocking it. Broken pump Check the pressure of the system. Flush the solar system completely and open all the valves Thoroughly check the system layout. This includes collector connection, shading, pipe insulation, clock timer, and flow controller system Check all the electrical connections and fuses to ensure uninterrupted power supply Check temperature sensor and controller. Minimize the temperature difference Check temperature. Correct the settings if needed Try switching to maximum rotation speed for a short interval. If it does not work, unblock the rotator by putting screwdriver into slot and turning the blades of the pump manually. Replace the pump 13

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