Researchers in Qatar have looked at the extent to which cleaning robots reduce the yield of solar power plants due to the shades they produce on the panels. They found that the orientation of the modules has a huge effect on the shadow effect.
“Cleaning robots are now used in almost all solar PV plants in the desert, and they usually operate during the day, creating a moving shadow over the PV modules,” said Benjamin Figgis, lead author of the study. pv magazine. “We did a field study in Qatar to measure how the robot’s shadow affects PV production in real time and see if hot spots are created.”
The researchers conducted a series of clear-sky tests using the commercial robot Nomadd Desert Solar Solutions on different solar PV system configurations at the QEERI test facility in Doha, Qatar, at a tilt angle of 22 degrees. They looked at three main factors: module design, module orientation, and robot speed.
They specified that the DC current and voltage of the PV array were recorded at 4 Hz from several minutes before passing the robot to several minutes. The current was measured by passing a coiled DC cable through a 10 A/75 mV shunt resistor and measuring the voltage drop with the same data logger. String DC power (P) was obtained by multiplying the voltage and current values.
They explained that the response speed of the inverter is the most critical factor as the robot moves quickly over the modules. They also noted that the robot takes the same amount of time to traverse the string regardless of module type or orientation.
Through their analysis, the academics found that module orientation has a huge impact on shadow effects.
“In landscape, string current and power dropped sharply as the robot passed, while strings with shape modules had little effect,” Figgis said. “This was well explained by the layout of the bypass diodes in the modules. Fortunately, there were no signs of hot spots in the cells, although the bypass diodes did get hot if the robot stopped for a while.”
Figgs also explained that the inverter’s maximum power point tracking (MPPT) algorithm had trouble coping with the robot’s moving shadow—sometimes it increased the string voltage, sometimes decreased it, and it took about a minute to restore the MPP. the robot left the group. “In the tested configuration, one robot pass reduced the day’s solar energy yield by about 0.16% with landscape modules. With the portrait modules, the loss was almost zero,” he further explained.
The researchers also found that the power drop was greater for full-cell modules than for half-cut panels, and that heating of the module’s bypass diode occurred if the robot stopped on the module, but not while the robot was moving.
“The main lessons learned were that if a PV plant is designed with cleaning robots in mind, their shading losses can be minimized by a vertical module layout, which is usually the case with single-axis trackers,” Figgs concluded. “In landscape systems, it’s best to run robots at night, even before dew forms.”
The results of the study can be found in the study published in “The effect of robot moving shadow cleaning on the PV string”. Solar energy.
In January, the same group published a study assessing the extent to which cleaning robots could threaten the physical integrity of solar panels. They found that the cleaning machines have a very minimal effect and that modules of the same size cause about the same amount of vibration.