At the end of the attachment, photos of the components of the thermal energy system are shown. Effective collector orifice area – Energy transferred to rock storage – Heat transfer oil charge circuit mass flow rate.
Introduction
- Background
- Obstacles on the way towards the sustainable use of solar energy systems in
- Objectives
- General Objectives
- Technical and Specific Objectives
- Support for collaborative work
- Outline of the thesis report
First, the large size of the country and dispersed settlement patterns make transmitting power to the entire population extremely expensive.” 2 The sun belt is the area of the Earth within approximately ±40 degrees of latitude from the equator.
Summary of literature review in the fields of solar energy and related
Solar energy and its availability
- Solar radiation
- Types of solar radiation
- Solar radiation detection and measurement
- Available clear sky solar radiation
- Solar Radiation Geometry with Respect to Earth and Collector Surface
- Solar Radiation and The Generic Collector Surface
- Sun-Earth-Collector Geometry and Other Related Variables and
- Solar energy collection and tracking configuration
- Solar collectors
- Solar position detection and alignment
- Solar aiming and tracking
The collector surface is tilted by the latitude angle of the location and the normal to the surface is made coplanar with the local meridian. In one of the possible configurations, the axis is made parallel to the earth's axis of rotation (i.e. it is a polar axis) and the corresponding tracking angle becomes equal to the hour angle (ω).
Basic Control theory concepts
- Open loop VS closed loop control system
- System identification, Process model, process behaviour and performance
- System identification and choice of control technique
- Process model
- Process behaviour
- Some Traditional and Advanced Control Techniques
- On-Off Control
- Differential Gap (hysteretic) On-Off Control
- PID Feedback Control System
- Digital Control Systems
- Fuzzy Logic Control
- Finite State Machine Based Control
- Programmable Logic Controllers (PLCs)
On-off control (or also called bang-bang) is one of the most widely used control techniques. A digital controller is a system in the realm of a discrete time, discrete data (input and output) subspace of the generic continuous state space.
Model of the pre-existing solar thermal energy system at UKZN
Models of solar energy systems
Model of the pre-existing solar thermal energy system at UKZN
- System description
- The energy capture subsystem
- The thermal energy storage (TES) subsystem
- Energy utilization subsystem
- Fluid / heat transport
- The Heat Transfer Fluid
- Data acquisition and control subsystem
- Safety considerations
- Summary of physical working principles of the thermal energy system
The receiver steel tube is part of the overall circuit, followed by the heat exchanger fluid in the charging cycle, as shown in Figure 33. As with the receiver, the TES is part of the heat exchanger fluid charging circuit, according to what is shown in Figure 33.
Proposed model for microcontroller based monitoring and control
- Problem definition
- System layout. Inputs and outputs
- Control system design and implementation
- Tracker Controller
- Charging Pump Controller
- Discharging Pump Controller
- Chapter summary
To address the issue of non-deterministic behavior, at this starting point, we prioritized the movement of the hour axis over the declination axis. Either variable will be equal to the desired tracking step size in degrees of arc at runtime. A brief explanation of the methods:. a) When sleep mode is selected, the device is sent to sleep (stopped) regardless of the current tracking error(s).
For the charge pump control, we consider a PID controller at a first stage and a Fuzzy-PID controller at an advanced one.
Design of the experimental prototypes of the microcontroller based
Basic considerations. MCU and other components choice
Hardware design level re-evaluation of input/output requirements
- Analogue to digital conversion inputs
- Thermocouple to digital conversion (TDC) inputs
- Global analogue and digital inputs and outputs requirements
This is the case for the temperatures to be read from the ST-KZN receiver, the TES and the user subsystems. The large number of thermocouple inputs (55) reinforces the need for an external multiplexing solution, regardless of the choice of microcontroller. The following Table 5.3 summarizes the global I/O needs at the MCU port level, including the interface needs (for ADC and TDC) that emerged from the previous discussions.
In Table 5.3, divisible bits are those that can be multiplied by other bits, ie.
Basic system architecture and microcontroller choice
So, for the sake of simplicity and performance, we decided on a 32-bit I/O window applicable to the 40-pin MCU as a good compromise for realizing the first prototype of this solar controller. The resulting system architecture, applicable to any 40 (or higher) pin microcontroller, is shown in Figure 51 below. However, our choice ultimately fell on the Atmel AVR ATmega family of microcontrollers, specifically the ATmega32 MCU, shown in Figure 52 below.
The preference was based on some comparative advantages of the ATmega32, such as the robust and simple architecture of the AVRs, more memory and I/O resources (from the ATmega32), ease of prototyping: use of through-hole plating technology, more tolerant operation (related to ESD and moisture sensitivity), simple programming languages and development tools, low costs, local availability (including that of development tools), etc.
Final architecture, schematic and components layout diagrams
- Basic considerations
- Final system architecture
This is to take advantage of its higher memory and I/O handling capabilities, although it is slightly more expansive and not fully pin and feature compatible with the ATmega32 subfamily, which would require small (most likely software level) changes. Although the choice was the ATmega32, the design began with the ATmega8535 (pin and feature compatible except for JTAG) and gradually moved to the ATmega16 and finally to the ATmega32 as memory requirements evolved. The architecture and functions of the various ICs and components chosen to implement the generic diagrams in Figure 49 and Figure 50, including their data sheets/application notes; and.
The final system architecture, developed from the one in Figure 51 as a result of its development over the ATmega32 and other selected components, is presented on the diagram of Figure 54.
Implementation Schedule
General: all the theoretical and practical considerations discussed in previous sections, as well as basic and technical concepts in electronics, digital systems and computer science and CADD/CAE/CAM. Although all schematics and component layouts will be presented, we see no absolute need to do so for PCB track layouts. It is important to note that these boards are easily identified on the overall system architecture shown in Figure 54, as they are highlighted in the same color as in the block diagram below.
Circuit diagrams
- Main board circuit design considerations
- Main board’s circuit schematics, components and pcb layouts
- ADC board circuit design considerations
- Alignment board circuit design considerations
- TDC board circuit design considerations
- Tracker’s board circuit design considerations
- Charging and discharging pumps circuit design considerations
- Power supply unit (PSU) board design considerations
The alignment board (light and gravity sensors) contains 4 photodiodes (OPT301M), physically arranged to allow fine alignment with the sun tracking dish. This information is fed back to the tracking controller to correct the dish position angle accordingly; Different connectors are used to connect the thermocouples, the motherboard and the power supply.
To interface it with the ADC, we wired the potentiometer to act as an angle to voltage converter (0-2900 to 0-5V).
Chapter summary
The real time monitoring and control program (ST-RTOP)
Real time control program generic characteristics
ST-RTOP’s characteristics
The ST-RTOP as a control framework
ST-RTOP Structural diagram
The following sections also show other generic flowcharts that show the functionality of some of the individual subcomponents of the diagram in Figure 72. It sets the flags in time, which are then used to trigger the execution of the corresponding tasks within the endless loop of the main function.
Description of some of the main software components
- Description of some system control and timing functions
- The timer tic and system timing and synchronization
- The real time clock (RTC) software interface implementation
- The arbitration of the use of shared resources. The semaphores
- The console user interface (the keyboard and the LCD)
- The Keyboard software interface implementation
- The LCD software interface implementation
- Analogue to Digital Conversion interface functions
- Thermocouple to Digital Conversion interface functions
- The sun tracking interface implementation
- The tracking interface mathematical model software implementation
- Tracker’s Finite state machine controller software implementation
- The PID controller software implementation
- The MCU side data logging software interface implementation
The bit position is equal to the user ID which is equal to its priority in using the corresponding resource;. f) Bit 0 of the semaphore flag word is the busy flag: when 0, the resource is free, otherwise, the resource is busy => someone is using it;. AD conversion for K-type thermocouples (Thermocouple to Digital Conversion) is scheduled, triggered, and synchronized by the timer-based task scheduler/trigger discussed in Section 6.5.1.1 ("Timer Tick and Timing and System Synchronization Interface" ). The other 2 (SD and M2M) were not implemented. 2) The data recording format chosen and used is "comma separated values" (.CSV), which is easily read and processed by many packages, including spreadsheet processors such as Microsoft Excel.
Details can be found in the files datalogger.c on page 164 and datalogger.h on page 164 of Appendix A.
The PC side data logging program
Chapter summary
Description of Experimental Setups
Experiments performed
The schedule of experiments
No. Brief description of the experiment. i) Measure the maximum mean angular velocities of the tracking axes and (ii) assess whether the newly built system performs basic real-time control functions of the sun tracker above the plant: sun tracking dish assembly. Tracer control with temperature logging attempts. i) Evaluate whether the newly built system is capable of performing basic sun tracker control while simultaneously reading and recording thermocouple temperatures and other system variables, and (ii) evaluate how sun tracking positively affects heat collection.
Description of experimental setups
- Setup of experiments 1: Basic data acquisition and logging experiments
- Setup of experiments 2: Thermocouple data acquisition and logging
- Setup of experiment 3: The “ice to boiling” experiment
- Experimental setup description
- Expected results
- Setup of experiment 4: “Basic Tracker control functionality experiments”
- Setup of experiments 5: Integrated tracker control with temperature
The data logging is performed by the data logging MCU software component and the DatalogWinlink PC side program, all described in the previous Chapter VI. TD conversion is performed by the MAX6675 TDC and data is read by the MCU via the SPI bus and temporarily stored in a buffer in RAM. The data is read and temporarily stored in a buffer in the MCU's RAM and shortly afterwards sent to the PC via serial port RS232.
TD conversion is done and the data is read from the MCU via the SPI bus and temporarily stored in a buffer in RAM.
Results and Discussion
- Results of the basic data acquisition and logging experiment (using the MCU’s
- Ambient temperature acquisition and logging, on the 13/Aug/07
- Results of the thermocouple data acquisition and logging experiments
- Thermocouple temperature acquisition experiment A, on the 23/08/07(9h)
- Thermocouple temperature acquisition experiment B, on the 23/08/07
- Results of the “ice to boiling” experiment, held the 23/Jul/08
- Results of the “basic tracker control functionality experiments”
- Basic sun tracking experiment (A), on the 23/Jun/09
- Basic sun tracking experiment (B), on the 24/Jun/09
- Results of the integrated tracker control with temperature logging experiment,
- Chapter summary
The value of the actual declination angle (green curve) was initially around -210 (point A, 850min). The actual hour angle value (purple curve) was approximately 00 from the start (point B to E). From point E onwards, the saucer moves westward at full speed until it reaches the set point (at point G, about 854 minutes of the time axis); . 7) From the experimental data, we found that the value of the angular velocity of the hour axis between points E and G is 0.170/S (approximately 100/min).
In Figure 98, the curves represent a portion of the solar tracking experiment carried out on 24 June.
Conclusions and outlook of further work
The roadmap and the main obstacles faced
Conclusions. Achievements and failures
Recommendations
Tracker->status = TRACK_STATE_IDLE; // remain idle Tracker->Forward = FsOut(TrackerMode); //status outputs Tracker->Reverse = FsOut(TrackerMode);. Tracker->status = TRACK_STATE_MOVING_SOUTHWARD; .. case TRACK_STATE_MOVING_EASTWARD: //= move backward; actual hour angle decreases // .. rotational motion along the Earth). File: Datalogger.c (source code of MCU's side c datalogging functions). float*)&(ADC_LastSample[0][ADC_xmuxAddr_PyrHeliometer_Vi]), LOG_FIELDTYPE_FLOAT};. float*)&(ADC_LastSample[0][ADC_xmuxAddr_Trackers_Vout]), LOG_FIELDTYPE_FLOAT};. float*)&(ADC_LastSample[0][ADC_xmuxAddr_Trackers_Iout]), LOG_FIELDTYPE_FLOAT};. float*)&(ADC_LastSample[0][ADC_xmuxAddr_SouthAlignPHDiode]), LOG_FIELDTYPE_FLOAT};. float*)&(ADC_LastSample[0][ADC_xmuxAddr_NorthAlignPHDiode]), LOG_FIELDTYPE_FLOAT};. float*)&(ADC_LastSample[0][ADC_xmuxAddr_NTCambientTemp_Vi]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TRcvrIn]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TRcvrSurfIn]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TRcvrOut]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TRcvrSurfOut]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TESin]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TESout]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevA1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevB1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevC1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevD1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevE1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevF1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevG1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevH1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_TES_LevI1]), LOG_FIELDTYPE_FLOAT};. float*)&(TDC_LastSample[0][TDC_xmuxAddr_PlantAmbientTemp]), LOG_FIELDTYPE_FLOAT};.
