National Instruments hardware and software has helped a Spanish factory optimise its solar panel production process, from purifying silicon ore to manufacturing and testing the final product. Alberto Cortes and Ricardo Silla of manufacturer Siliken Renewable Energy explain
Sunlight is the most plentiful natural resource. Because the sun is not subject to the same supply limitations as fossil fuels and it is available nearly everywhere, it is increasingly being used as a free, clean source of renewable energy.
Our engineers at Siliken Renewable Energy work to help harness this abundant resource and address escalating environmental and energy concerns. As a company we have grown to become one of Spain’s largest manufacturers of photovoltaic (PV) solar cells, which we use to convert sunlight into electricity.
Siliken differs from other PV cell manufacturers because we handle all aspects of solar cell development including silicon purification, panel manufacturing, verification, and installation. NI products play an important role in our research and development process to innovate and produce new technologies and to test every solar panel we produce.
Optimising the silicon purification process
Typically, the silicon purification process consists of converting the chemical element to a silicon compound — which we can more easily purify by distillation than in its original state — and then converting that silicon compound back into pure silicon. At our facilities we use a novel, patented silicon purification process that is approximately 40 per cent cheaper than traditional methods. To increase further the efficiency of our new process, we began optimising the standard control equipment already in place at the facility that we built using the NI PXI platform, LabVIEW FPGA Module, sound and vibration software, and vision software.
Because we purify the silicon at temperatures hotter than 1000degC, we 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, we conduct a remote analysis of the images to measure the size of large amounts of purified particles as they are produced.
At the same time, we need faster control loop rates to measure the flow and pressure parameters of the purified silicon. Using the NI PXI-4472 dynamic signal acquisition module, we can monitor vibration levels to ensure that they never surpass predefined security levels, thus avoiding system instability that could cause the reactor to break. We 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
When we began manufacturing solar panels, our end-of-line test system consisted of a boxed scope that we used to perform manual testing. With our new PC-based system based on LabVIEW and an NI PCI-6220 multifunction M Series data acquisition (DAQ) board, we integrated the 'closing' of the solar modules into a semi-automatic process. Using a LabVIEW front panel as the human machine interface and the DAQ board to help perform the operation, this application essentially 'closes' the module once the solar cells are inside.
After we assemble the solar panels, we must perform I-V characterization tests to verify the power output of every module to ensure that each one produces the stated power. Performing these tests is rather complex because we have to administer a known quantity of light to each panel so we can simultaneously determine both the voltage and current draw of the panel. To accomplish this, we developed a method that only uses a single 10ms pulse of light. When the light pulse is administered, we acquire 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, we performed these tests with greater accuracy and significantly increased our throughput. In the past, we conducted this process using multiple sequential tests. In addition, while the previous I-V curve we used consisted of 30 points, we now use more than 2000 points for I-V characterization testing, thus providing more precise calibration parameters. As a result, we received recognition for providing the best advertised-to-actual performance ratio for panel output.
Beyond solar cell manufacturing
In addition to solar panel production, we are 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 we began manufacturing our invertors, we developed a prototype using NI CompactRIO and an NI TPC-2006 touch panel computer. We are 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.