Precise String Monitoring
For the traditional central solution, the monitoring data is acquired from the DC combiner. However, the projects built recently have been using combiner box without string monitoring. All the data collection is relying on the central inverter DC input, and the precision can only achieve 3%. Moreover, there are hundreds of strings connected to the central inverter. It’s very difficult for operators to do the troubleshooting among thousands of PV panels. As the low accuracy of the detection components, the string current and voltage cannot truly reflect the string current and voltage. Without precise monitoring of current and voltage, the inverter cannot track the maximum power point (MPP), which will cause energy loss. For the traditional central solution, the monitoring data is acquired from the DC combiner. However, the projects built recently have been using combiner box without string monitoring. All the data collection is relying on the central inverter DC input, and the precision can only achieve 3%. Moreover, there are hundreds of strings connected to the central inverter. It’s very difficult for operators to do the troubleshooting among thousands of PV panels. As the low accuracy of the detection components, the string current and voltage cannot truly reflect the string current and voltage. Without precise monitoring of current and voltage, the inverter cannot track the maximum power point (MPP), which will cause energy loss.
Furthermore, without string monitoring, it cause big trouble during the commissioning of the project and lifetime O&M. The results generated by the background monitoring system based on such voltage and current values are not instructive, and the resulted mis-judgment will cost lots of unnecessary workloads and materials for troubleshooting. The system shutdown in troubleshooting process will affect the power generation.
In Huawei’s latest Smart PV Solution as the editor knows , the detection precision of Hall Effect sensors can reach 0.5%, which is six timesbetter than that of the smart combiner box in terms of detecting the voltage and current of PV strings, through high-frequency difference algorithm compensation and high-precision instrument calibration. Moreover, the string status can be monitored in real time, alarms are automatically generated in the case of errors, and faulty PV strings can be accurately located.
Stable communication technologies
In the Smart PV System, data is transmitted among PV arrays over power line carrier communication (PLCC) while transmitted inside the PV plant over 4G wireless communication, which contributes to more precise smart string detection.
PLCC substitutes for RS485, dramatically improving the transmission rate from 9.6 bit/s (19.2 kbit/s at most) to 200 kbit/s. By using power cables as transmission channels, no dedicated cables need to be routed, which saves the expense on communications cables and construction by 0.01 RMB/W. The RS485 solution, by contrast, requires complex construction and underground cable routing. The PLCC solution features high reliability and excellent maintainability, because AC power cables are used for transmission and only faulty modules need to be replaced when the communication fails. Whereas, an RS485 communications cable is likely to be connected incorrectly, and a broken connection affects part of the communication. If a cable is broken, you need to dig it out and replace it. In general, PLCC can eliminate the use of communications cables and improve the reliability.
Nowadays, as the PV plant installation environment become more and more complex, increasingly customers choose 4G wireless communications technology in the PV Plant. This technology constructs an intelligent management network and brings the following advantages for the PV plant:
• A single PV plant can cover an area of up to 80 km2, the transmission delay greater than 50ms and plant capacity able to be expanded smoothly.
• No ditches need to be dug to route optical cables, faults can be located, and the maintenance is easy.
• The mobile Web, SUN2000 app, unmanned aerial vehicles, and remote experts work cooperatively for efficient O&M.
A 20MW PV plant using Huawei 43KTL inverters have been commissioned smooth in May. Problems found on the strings, like reverse connection, ground fault, panels breakage have been solved easily by the string monitoring interrogated in the inverter. Only 2 person took 1 week to take all the activities.On the contrast, one 30MW Project using central inverters take more than months to track the fault cables with more than 5 operators. Therefore, the monitoring system can find the real fault and correct the fault in time to increase power generation and improve the operation and maintenance efficiencies.
Smart I-V scanning
Smart I-V scanning allows the inverter to export I-V curves, deploys algorithms on the management system, and analyzes data. It also identifies modes to scan all PV strings of a PV plant and identify hidden PV module faults.
For instance, Huawei’s SUN2000-43KTL requires only 1 second to finish scanning and 10 minutes to output a report including data about a PV array in one-click mode, with no testing personnel and experts onsite. This greatly lowers the labor and cost requirements for testing. Test personnel are forewarned about PV module faults using smart PV string diagnosis, and the health status of the PV plant can be estimated comprehensively to achieve proactive maintenance. The diagnosis precision and efficacy have been certified by TÜV.
A successful trial was carried out at Huanghe Hydropower, finding that 0.17% of PV modules in a PV array were faulty. The big difference is based on Huanghe Hydropower’s previous spot-check ratio of 0.3%, 97.6% of these faulty PV modules would have escaped detection.The online I-V curve detection function enables the features and health status of PV strings of large-scale PV plants to be inspected. This facilitates O&M by detecting and processing low-efficiency PV strings, improving energy yields, and preventing faults from propagating. The online I-V curve detection function brings four key benefits:
Benefit 1: Timely Discovery of PV Module Faults
• All PV modules in the PV plant are scanned rapidly and periodically through annual inspection, detecting faulty PV strings. Timely processing of the faulty PV strings helps improve energy yields and prevents faults from propagating.
• Carrying out I-V tests for PV strings with low output power on an irregular basis helps detecting and preventing faults.
Benefit 2: Inspection Quality Improvement
• The I-V curve can be used to accept PV modules after a PV plant is constructed, detecting faulty products, improving PV plant quality, and reducing acceptance cost.
• Tests the faulty PV strings reported by the system by combining the I-V curve detection result. This significantly improves PV plant inspection efficiency and fault detection rate, as well as lowering inspection workload.
Benefit 3: High Automation
• One-click remote operation greatly reduces PV plant test intensity, requirements on test personnel, and test cost.
• Automatic analysis of I-V curves lowers requirements on test personnel.
• Automatic generation of reports reduces workloads for test personnel.
Benefit 4: Mining the Value of Historical Data
• The system automatically collects statistics about PV string fault types and attenuation rate based on PV modules and historical runtime. Using the collected statistics, it provides suggestions for the future construction of the PV plant.
• When the array attenuation rate changes rapidly or a certain type of faults propagates throughout the system, the PV plant owner can adjust the O&M policy accordingly. This improves O&M efficiency, reduces costs, and increases the plant PR.
PV modules function as the main body of a PV system, making PV module quality a vital consideration. Huawei’s smart I-V scanning technology is a significant step toward freeing PV plants of the consequences of PV module faults.
Summary
All in all, precise string monitoring help totroubleshooting at the first place and reduce the O&M cost, with high preciseand smart I-V scanning technology, Huawei FusionSolar Smart PV Solution is the first choice for power plant construction.
