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Human eye inspired control of a smart solar reactor from sunrise to sunset

Contact Information

University: KU Leuven, Belgium

Team Members (with year of graduation): Lode Van den Langenbergh (June 2015) and Cedric Ophoff (June 2015)

Faculty Adviser: Nesrin Ozalp

Email Address:

Submission Language: English

Project Information

Title: Human eye inspired control of a smart solar reactor from sunrise to sunset

Description: We have developed a novel solar reactor coupled with an iris mechanism which enables the reactor temperature remain constant from sunrise to sunset by mimicking human eye reaction to light. A closed loop control system using NI hardware and software was designed to calculate and control the required optimum iris opening area from a given incoming solar energy and a desired internal temperature of the reactor.

Products: Due to the complexity of the iris/reactor mechanism and the control algorithm of such unsteady and nonlinear systems, a good number of iterations for the physical prototype might be needed, which is a very time consuming, requiring significant space allocation in the lab and expensive. Virtual prototyping feature of the National Instrument’s Control and Simulation module helps in overcoming this problem by providing hardware-in-the-loop simulation and control simulations. This reduced the number of iterations through the physical prototype, and streamlined design and deployment processes. The products that are being used in this system are:

  • LabVIEW® 2014
  • Control simulation module
  • Mathscript module
  • PID and Fuzzy Logic toolkit
  • Compact RIO (NI 9030)
  • Two 16-channel thermocouple modules (NI 9214)
  • A four-channel analog input (NI 9215)
  • A four-channel analog voltage output (NI 9263)
  • A bridge analog voltage input (NI 9237)
  • Stepper motor with integrated controller and driver which communicated through a USB to RS-485
  • Detection of high flux radiation coming from solar simulator by connecting heat flux gage to NI 9237 through NI 9949 adopter

A closed loop control system was designed to calculate the required optimum aperture area from a given incoming solar flux and a given internal temperature of the reactor.


cRIO assemby for Heat Flux measurements

The Challenge: Solar energy can be utilized in various thermochemical processes in order to turn intermittent solar energy into a storable chemical form. These solar thermochemical processes are housed in a solar reactor and provide reduced or emission free production of various fuels and commodities. However, one of disadvantages of using concentrated solar power for thermochemical processing in a solar reactor is the transient nature of the solar energy due to the position of the sun. Especially in solar thermochemical processing, it is crucial to maintain constant or semi-constant temperatures inside the solar reactor. If the solar reactor temperature can be kept constant, then the process efficiency is kept almost constant regardless of the changes in solar flux from sunrise to sunset.

The Solution: At our laboratory, we have developed a mechanism inspired from the human eye; specifically the iris. Our foregoing numerical results from optical, thermodynamic, and heat transfer simulations show that correctly varying the aperture diameter with respect to transient incoming solar flux densities facilitates the maintenance of quasi-constant temperature distributions inside the reactor *.

* Ozalp, N., Toyama, A., Jayakrishna, D., Rowshan, R., Al-Hamidi, Y. Effect of camera-like aperture in quest for maintaining quasi-constant radiation inside a solar reactor. ASME Journal of Mechanical Design, 2011, 133(2), 021002.


Iris and Solar Reactor assembly

Explain how your project works: This iris mechanism is developed to adjust itself against the changes in solar flux by increasing its diameter when the flux level is low, and by decreasing it when the flux level is high. Such mechanical behavior has the potential to achieve semi-constant temperatures inside a solar reactor according to the theoretical results. With this new mechanism, called “smart iris aperture”, the heat loss due to changes in solar energy levels can be substantially minimized. The iris mechanism is driven by a closed loop control system to adjust the area where solar energy enters the reactor.

We developed a control system based on single input single output (SISO). The input is the difference (fault) between the set point value which is desired temperature inside the reactor and the feedback temperature which is process value. The output value is determined by a PID controller and MPC system representing the aperture area. The output value and the necessary hardware drive the iris mechanism until the desired area is achieved. This loop is repeated to minimize the fault between the set point and feedback value.

Each control iteration, the MPC algorithm solves an optimization problem based on measurements of the current states. The MPC computes the following adjusted output variables and sends the first input value (of the optimization problem) to the actuator. In physical terms, the control system is built of three main parts: the sensors, the controller and the drive train. The selection of each component has an influence on the accuracy, precision, reliability and speed.   

Explain the benefits using LabVIEW and NI tools:

Feedstock control is done by the controller which sends steering signal to the mass flow controller. The mass flow controller opens and closes an electromagnetic valve depending on the input signal and then gives feedback to the main controller. Embedded systems from National Instruments provide real-time simulations, the motor control and data acquisition. Compact RIO hardware platforms are divided into three internal components: (1) the real-time controller, (2) the field programmable gate array (FPGA), and (3) the interchangeable c-modules. Communication between the real-time controller and the FPGA passes through PCI bus which provides reliable and fast data transport.

The c-modules are plugged in the chassis and may communicate with the real time controller and the FPGA. FPGA is a reconfigurable silicon chip made out of thousands of logical cells containing smaller hardware elements like flip-flops, lookup tables etc. Each of these logical cells includes several inputs and outputs. Developers are to configure the integrated circuit by use of hardware based software languages. The FPGA module creates the possibility to configure these integrated circuits in the LabVIEW environment. This results in fast and easy way to acquire high performance FPGA programs.

National Instruments™ LabVIEW offers flexible and fast graphical programming language which exceeds in parallel programming and build in error handling functions. Secondarily, the help functions and example finder can be used to ease up the programming. Add-on modules provide full control strategy: (1) System Identification module, (2) Control and Simulation module and (3) Real-Time module, which are used to create the closed control system to accommodate the transient nature of the sun. The present test application is made of three c-modules:

(1) Thermocouple module, (2) Analog voltage in module, and (3) Analog voltage out module.


Solar Simulation  (Heat Flux measurement)

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Nominate Your Professor

We would like to nominate our professor for her dedication to find innovative solutions to world’s pressing problem such as energy and environment, and her extensive use of NI hardware and software to achieve these goals. Prof. Ozalp gave us the opportunity to do our Masters thesis on the development of an iris mechanism (Cedric Ophoff) and closed loop control mechanism (Lode Van den Langenbergh). She was new at KU Leuven and has built the lab from scratch together with us in 1 year.  The lab is now equipped with state-of-the-art controls tools by NI and has high temperature experimental setup utilizing a 7 kW solar simulator. Although it was a lot of hard work to start from scratch and come to the point that we are, this was an excellent learning and growing opportunity for us. We picked each and every tool in the lab with her and closely observed her dedication to research with never ending effort. The main effort in that period was the selection of NI equipment and learning programming in LabVIEW which she valued tremendously and we used extensively for every measurement. Use of NI tools created such an exciting ambience in the lab combined with the innovative spirit to excel in research. Her continuous follow-up and constructive feedback made our thesis very high quality. She encouraged us to submit a conference paper on our thesis and we have accomplished our first peer-reviewed conference paper accepted for publication in archival conference proceedings and presentation at the American Society of Thermal and Fluids Engineers (ASTFE) conference in August 2015, in New York. We appreciate her vision and her trust in us to enroll in this international competition organized by the National Instruments (NI) which has not been tried by previous students at our campus.    

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