Sunlight is the most plentiful natural resource. Because the sun is not subject to the same supply limitations as fossil fuels and is available nearly everywhere, it is increasingly being used as a free, clean source of renewable energy. Engineers at Siliken Renewable Energy work to help harness this abundant resource and address escalating environmental and energy concerns. As a company, it has grown to become one of Spain's largest manufacturers of photovoltaic (PV) solar cells, which it uses to convert sunlight into electricity.
Siliken differs from other PV cell manufacturers because it handles all aspects of solar cell development including silicon purification, panel manufacturing, verification and installation. National Instruments' products play an important role in the research and development process to innovate and produce new technologies and to test every solar panel Siliken produces.
Optimizing the Silicon Purification Process with NI Products
The typical silicon purification process consists of converting the chemical element to a silicon compound, which Siliken can more easily purify by distillation than in its original state, and then converting that silicon compound back into pure silicon. At Siliken's facilities, they use a novel, patented silicon purification process that may become 40 percent cheaper than traditional methods such as the Siemens' process. To further increase the efficiency of its new process, Siliken began optimizing the standard control equipment already in place at the facility that the company built using the NI PXI platform, LabVIEW FPGA Module, sound and vibration software, and vision software.
Because Siliken purifies the silicon at temperatures hotter than 1,000C, it used an NI PXI-1422 digital image acquisition module to acquire images of the purified silicon particles as they are fed out of the purification reactor. Next, with NI vision software, Siliken conducts a remote analysis of the images to measure the size of large amounts of purified particles as they are produced. At the same time, faster control loop rates are needed to measure the flow and pressure parameters of the purified silicon. Using the NI PXI-4472 dynamic signal acquisition module, Siliken can monitor vibration levels to ensure they never surpass predefined security levels, thus avoiding system instability that could cause the reactor to break. Siliken chose to use the highly integrated LabVIEW and NI PXI platform and conducted two separate critical tasks using a unified solution.
Solar Panel Manufacturing and Quality Testing Using NI Hardware and Software
When Siliken began manufacturing solar panels, its end-of-line test system consisted of a boxed scope used to perform manual testing. With its new PC-based system based on LabVIEW and an NI PCI-6220 multifunction M Series data acquisition (DAQ) board, the company integrated the “closing” of the solar modules into a semiautomatic process. Using a LabVIEW front panel as the human machine interface (HMI) and the DAQ board to help perform the operation, this application essentially “closes” the module once the solar cells are inside.
After the solar panels are assembled, the company must perform I-V characterization tests to verify the power output of every module to ensure each one produces the stated power. Performing these tests is rather complex because the company has to administer a known quantity of light to each panel so it can simultaneously determine both the voltage and current draw of the panel. To accomplish this, Siliken developed a method that only uses a single 10 ms pulse of light. When the light pulse is administered, it acquires the I-V of the panel to calculate its power in watts.
Using NI CompactRIO, LabVIEW FPGA and an NI PCI-6122 S Series multifunction DAQ board, Siliken performed these tests with greater accuracy and significantly increased its throughput. In the past, it conducted this process using multiple sequential tests. In addition, while the previous I-V curve used consisted of 30 points, the company now uses more than 2,000 points for I-V characterization testing, thus providing more precise calibration parameters. As a result, Siliken received recognition for providing the best advertised-to-actual performance ratio for panel output.
Beyond Solar Cell Manufacturing
In addition to solar panel production, Siliken is also manufacturing essential equipment such as solar panel inverters, which are used primarily to change direct current to alternating current via an electrical switching process. Before it began manufacturing invertors, Siliken developed a prototype using NI CompactRIO and an NI TPC-2006 touch panel computer. The company is also using CompactRIO to conduct research in other renewable energy fields such as hydrogen fuel cells, and NI CompactDAQ for wind power research because these platforms offer compelling operational advantages and shorter development times than other traditional control and test tools.