The 12 MW Dongfang solar project, owned by Huaneng Hainan Power, was initiated on June 30, 2016, for grid-tied power generation. It adopted 280 W monocrystalline PV modules and Huawei’s Smart PV Solution. The project jump-started the phenomenon of PV plant digitalization. Since Huaneng Hainan Clean Energy’s power plant was enriched with intelligent capabilities in 2017, the energy yield and O&M indicators have skyrocketed to historic levels.
In 2017, when the plant was designed to reach 1,319 utilization hours, actual comprehensive utilization hours reached 1,483, exceeding the planned value by 12.43%. In that same year, on-grid energy was 19.14 million kWh, or 19.77% higher than the planned energy yield (15.98 million kWh), with an annual average performance ratio (PR) of 84.58%.
In 2018, on-grid energy reached 19.05 million kWh, with 1,476 utilization hours, and a performance ratio of 84.43%.
In 2019, on-grid energy increased to approximately 20.56 million kWh, with utilization hours reaching 1,594, and an industry-leading performance ratio of 85.3%.
Huawei says that the Dongfang Power Plant was recognized as a 5A-level PV plant, according to national evaluations and key statistical indicators, for two consecutive years in 2017 and 2018. The plant’s average annual performance ratio exceeded 84.43% over the course of three years, and Huawei says the failure rate was close to zero. Additionally, the annual energy yields exceeded the planned value by approximately 20%.
And 2019 witnessed key breakthroughs. The annual solar irradiance of Huaneng Dongfang Power Plant ranges from 502 x 104 kJ/m2 to 586 x 104 kJ/m2, but it still managed to generate 20.56 million kWh of power in a single year, with 1,594 of utilization hours – a record level of performance.
So why does the energy yield of Huaneng Dongfang Power Plant keep climbing over time? The company says that the answer lies within seven key technologies.
PV module mismatch is usually caused by PV module attenuation, direction, and shading in the morning and at sunset. On the project site, PV module performance may be mismatched due to the shading caused by cloud cover, bird droppings, and water stains following heavy rain in Hainan. All of these factors can contribute to undermining energy yields.
To tackle the problem, Huawei’s smart string inverter solution involves connecting two strings to a single MPPT circuit, and configuring each megawatt with 80 MPPTs. When compared with the central inverter, Huawei’s technology minimizes PV string mismatch, to improve system efficiency.
Wide operating voltage range, extended power duration
As the PV string MPPT features a wide operating voltage range, this in turn enables a longer operating time for the solar inverters, extending the power generation time and further improving the overall yield of the power plant.
Huawei’s smart string inverters use a bipolar topology, which enables the output voltage of each PV module to pass through the DC voltage boost circuit. When DC input voltage is low, the voltage can be boosted to meet the requirements of the bus capacitor. The MPPT operating voltage can range from 200 V to 1000 V. In contrast, a central inverter uses a unipolar topology, and the MPPT operating voltage ranges from 520 V to 1000 V. Therefore, Huawei smart string inverters can work for a longer period of time to generate more power.
No fuse + no vulnerable components = No O&M
Simplicity is an important principle for smart PV design. Simple networking design provides for fewer fault points and lower fault probability throughout the system. “Huaneng Dongfang Power Plant has been running for three and a half years, and has maintained a failure rate of close to zero even in high-temperature environments, characterized by high salt mist as well,” says Yan Zhang, senior product manager at Huawei. The availability of Huawei string inverters has been verified to be 99.996%, according to onsite tests conducted by TÜV.
Prior to their launch, Huawei solar inverters were reportedly required to pass more than 1,400 tests conducted by the Global Compliance and Testing Center (GCTC) to account for scenarios ranging from salt mist and corrosive wet dirt to lightning strikes and high-altitude environments, with temperatures from –60°C to +100°C. This ensured their stable operation across a diverse range of unfavorable environments. “The simple design ensures that the PV plant remains reliable over the long-term,” says Zhang.
Anti-PID technologies prevent losses and ensure safety
The Huaneng Dongfang Power Plant is located just 220 meters off the coast. Therefore, the PV modules have continually operated in a high-temperature, high-humidity environment, in which potential induced degradation (PID) is more frequent.
To resolve this challenge, anti-PID modules are placed in communication boxes. They automatically adjust the output voltage based on the solar inverter voltage, and inject voltage between the phase wire and the ground cable from the AC virtual neutral point to balance the voltage between PV– and the ground, thereby preventing PID from effecting them.
“More importantly, Huawei’s latest PID suppression technology utilizes proprietary technology to build a virtual neutral point through solar inverter circuits,” says Zhang. Compared with traditional solutions that use resistors or inductors to build the neutral point, Huawei’s PID suppression technology represents a major upgrade, reducing compensation loss and making the compensation process safer. “The result is an increased energy yield by more than 2%, and the support for a larger array of more than 5 MW,” says Zhang.
Reduced costs via the replacement of RS485 With PLC
To transmit communication, the Huaneng Dongfang Power Plant uses power line communication (PLC) in place of RS485, which Huawei says reduces the investment required for communications cable deployment and construction.
By applying PLC technology, Huawei says that deployment and commissioning can be completed within two weeks, without the need to dig trenches or bury cables. A single solar PV plant can cover a maximum of 10 km2 on the ground, enabling fast deployment and mobile O&M. Maintenance personnel are also able to use wireless terminals to make video calls with the central control room.
Discrete rate analysis for pinpointing faults
Discrete rate analysis serves as a powerful tool for improving O&M efficiency. For this project, discrete rate analysis detects faulty PV strings, facilitating onsite inspection by O&M personnel. With the analysis, personnel are able to repair low-efficiency solar PV strings in a timely manner, in order to ensure that each PV string in the power plant remains free of defects for an extended period of time.
Smart I-V curve diagnosis
“Smart I-V Curve Diagnosis has proved to be extremely effective when implemented at the Huaneng Dongfang Power Plant,” says Zhang. The scanning for PV string faults of a 12.9 MW PV plant with 1,920 PV strings can be completed within four minutes – covering issues such as hot spots, cracks, and diode short circuits –to enable precise onsite troubleshooting. The detection can be performed online, and a detection report is automatically generated when faults are detected. “The O&M that once required months to complete, can now be fulfilled within mere minutes,” says Zhang.
In 2019, the Smart I-V Curve Diagnosis was upgraded to version 3.0, and all PV strings for a 100 MW PV plant can now be detected within 15 minutes. Additionally, AI and machine learning technologies were integrated to incorporate the experience of Smart I-V Curve Diagnosis and optimize the fault models.
After the conclusion of the project, Huaneng has continued working with Huawei on additional smart PV projects, with a total scale in excess of 1 GW. More than 80% of the projects in the FusionSolar Management System. In August 2019, Huaneng Group and Huawei signed a strategic cooperation agreement, for the establishment of a long-term partnership to promote the further integration of digital information and AI technologies in PV plants, and facilitate further technological progress for benchmark PV plant construction in the grid parity era.