Figure 1: Schematic diagram of solar furnace components
“With the inherent ruggedness, accuracy, scalability, and platform network integration of CompactRIO, Compact Fieldpoint, and NI Compact Vision System, we can develop a reliable, distributed application within the time limit of the project.”
– Roberto G. Galàn, Centro de Investigación en Matemáticas AC
Develop a distributed control and data acquisition system that can control all subsystems of the high-radiation flux solar furnace.
Use NI LabVIEW graphical system design software, LabVIEW Real-Time, LabVIEW FPGA and LabVIEW vision development module, and NI CompactRIO, Compact Fieldpoint and NI Compact Vision System hardware platform to develop the control and data acquisition system of high radiant flux solar furnace.
Dr. Norberto Flores – Centro de Investigación en Matemáticas AC
Roberto G. Galàn – Centro de Investigación en Matemáticas AC
Because of its location in the sun, Mexico is an ideal place to use solar technology. The area’s annual average sun exposure exceeds 5.5kWh/m2. High-quality solar resources make this area an ideal choice for the implementation of concentrated solar technology (CST), which can be used to generate electricity or produce solar hydrogen fuel.
In order to promote the development of CST in Mexico, CIE Energy Research Center built a high radiant flux solar furnace (HRFSF). HRFSF makes it possible to use solar radiation in basic application research and the development of industrial production processes. The main purpose of HRFSF is to develop thermoelectric solar tower components for central tower power plants. Another purpose is to process and manufacture advanced materials, and make them embody the thermophysical, mechanical and optical characteristics of materials exposed to sunlight.
We need a control and data acquisition system to operate all integrated components of HRFSF. The Industrial Mathematics Department of CIMAT (Mathematics Research Center) cooperates with CIE staff to jointly perform the task of developing a control system.
High radiant flux solar furnace(HRFSF) Components
The High Radiant Flux Solar Furnace (HRFSF) is mainly composed of the following three components: a condenser, a heliostat and shutter (see Figure 1). The condenser lens is the core of the system, and its function is to concentrate solar radiation to a very high level, thereby reaching high temperatures (up to 3000°K) in the focal area. The condenser is placed in a solar furnace and does not move; all movement required to track the sun needs to be performed by the heliostat. This is done to obtain a static focus area, which provides a more easily controlled environment for conducting experiments. The performance of the furnace depends on the ability of the heliostat to accurately track the sun. The shutter partially opens and closes at different angles to control the amount of radiation allowed to enter the system. It is worth mentioning that HRFSF includes a heliostat covering an area of 81 square meters, a shutter covering an area of 42.2 square meters, and an optical condenser composed of a 409 hexagonal first surface polished glass mirror.
In addition to the above components, there is also a mobile platform that can accurately locate the experiment at different points in the focus area. The data acquisition system is also used to monitor different experimental variables, such as temperature, pressure flow, solar radiation and concentrated radiation flux distribution. The experiment of the cooling system is also necessary. In addition, the weather monitoring station is integrated in the system, except for the heliostat, cooling system and some solar radiation and wind speed sensors, all other furnace components are located inside the entire furnace structure.
We chose the NI platform for the control and data acquisition system because it enables the development of all control, data acquisition, and vision functions through an intuitive and flexible development environment.
With the inherent ruggedness, accuracy, scalability, and platform network integration of CompactRIO, Compact Fieldpoint and NI Compact Vision System, we can develop a reliable, distributed application within the time limit of the project.
There are 1 PXI computer in the control system, 4 NI cRIO-9074 integrated system controllers, 1 cFP-2120 controller with cFP-BP8 backplane, and a CVS-1450 connected to Ethernet. The distribution of furnace frame components is shown in Figure 2:
The heliostat is controlled by the NI cRIO-9074 integrated system controller, which has two NI 9505 servo modules to control the two heliostat motors. One of them is used for azimuth movement, and one is used for height movement. The solar tracking equation can be used to obtain the position of the heliostat, which can calculate the solar vector based on the position of the latitude and longitude of the heliostat. By understanding the solar vector, we can accurately determine the position and height angle of the heliostat.
We use a 2000 p/r encoder for feedback control, combined with the heliostat gear box, to control the position of the heliostat. We use limit switches and NI 9421 source digital output module to detect the safe position of the heliostat. We also manually customize the angle of the heliostat.
The heliostat control system uses a 16-bit IEEE 1394 camera to take pictures of the focus area to obtain visual feedback. This also determines the exact position of the sunspot and can make slight adjustments to the position of the heliostat. Use NI CVS-1450 to acquire and process images.
We use cRIO-9074 controller, NI 9505 module and NI 9421 module to control the shutter. The NI 9505 module controls the open area by controlling the shutter motor. The motor is connected to the gear box and feedback is obtained from the 2,000 p/r decoder. The NI 9421 module is used to read the limit switch, which can determine the starting position of the shutter. There is a similar system setting for positioning the platform in the focus area. However, this system has three motors that control the motion axis, so that we can accurately position the platform.
Our cooling system transports water to the experimental device on the positioning platform. The system is also controlled by another cRIO-9074 controller. The CompactRIO program starts the water pump, monitors the level of the water storage tank, and controls the proportional valve through an NI 9265 analog output module to adjust the water flow. We also use NI 9472 and NI 9421 modules to control the cooling system. Since the pump and water tank are located outside the furnace structure, we use two NI WAP-9071 wireless bridges to communicate with the CompactRIO controller. One is located inside the cooling system control box, and one is located inside the furnace structure.
We communicate with the weather station through an integrated web server. We monitor many environmental variables, but the most concerned is direct radiation and wind speed. The former can indicate the best time to experiment in the furnace. If the heliostat is not in a safe position, it may be damaged by excessive wind speed, so the latter is also very important.
We use shared variables published on the network to exchange data between the subsystem and the central control system. The central computer is the host of the shared variable engine. We use shared variables to develop fast and reliable communication without affecting the safety of the system and the speed of the control loop.
THRFSF has conducted multiple experiments and is operating normally. We will add more equipment to the furnace next year. HRFSF is a research tool. We hope to use clean and renewable energy from the sun to develop new materials and new technologies for the production of electricity.
Since HRFSF is used in various experiments, the data acquisition system must be flexible. We choose various analog input modules in the Compact FieldPoint family of products to cover a wide range of input signals. We can adjust the input module configuration through the central control system to suit the specific needs of any experiment.