The evolution of smart PV
A new generation of smart PV power plant technologies is emerging that offers increasingly sophisticated remote O&M capabilities, greater plant reliability and improved energy yields.
If the PV module is the engine room of a solar array, the inverter and associated control technologies form the brain. As the penetration of PV generation grows, so too do the management challenges that come with accommodating that power on the grid, and inverters are evolving to become ever more sophisticated to meet the demands of grid operators and customers alike.
A further challenge presented by the growth of PV is the increasing size and geographic dispersal of solar fleets. Plant owners in large countries such as China or the US face significant logistical difficulties in operating and maintaining their fleet, simply because of the distributed nature of their assets. Managing on-theground teams becomes a more costly exercise, and again innovations in power control and communications technologies are helping minimise the amount of manual intervention required to keep a plant running optimally.
The emerging generation of solar power plants enabled by the increasingly sophisticated inverter and control technologies has been dubbed “smart PV”. In the smart PV power plant, the whole process of the PV power plant deployment, from the construction to O&M, is optimised and innovated. Digital information, internet and PV technologies are brought together to optimise initial investment, lower O&M costs, improve the electric energy yield and increase the return on investment.
At its heart, a smart PV plant is one in which manual intervention is reduced through the implementation of fully automated operation. A smart system can automatically discover, diagnose and rectify faults, thereby improving the electric energy yield, lowering O&M costs and increasing system revenues. The three planks of a smart PV system are automation, informatisation and intelligence.
Automation means reducing on-site manual operations through the use of components that cannot be damaged and which thus minimise on-site diagnosis or manual repair. Traditional automation solutions have faced a variety of issues that have made them more costly. For example, the traditionally large size of devices has meant they require heavy-lifting equipment, resulting in high installation costs.
Traditional solutions also use external fans for cooling. External fans present various issues such as noise, poor reliability and high replacement or maintenance costs. Meanwhile, the inverter equipment room requires periodic cleaning, because accumulated dust or salt spray can cause device failures. Experts need to visit the site for troubleshooting. Frequent and lengthy O&M is required, and once a fault occurs, the losses incurred can be huge.
By removing damageable components, integrating complex functions, and removing components and operations that require maintenance, the smart PV power plant has a simpler overall architecture. Generally, the smart PV solution makes the power plant construction easier by simplifying the design, shortening the construction period and simplifying the relationship between spare parts.
Informatisation refers to high-precision, intelligent detection on strings, the high-speed, high-reliability and low-cost transmission of that data, as well as highreliability storage and monitoring of background data.
Traditional solutions have typically had large data granularity, low detection precision and low transmission reliability. Furthermore, no string monitoring is available for centralised or distributed inverters, while only current detection is available for the centralised inverters.
The smart PV solution supports high-precision string detection. Advanced power line communication (PLC) and 4G wireless communication technologies are used for intra-array transmission and intra-powerstation communication. High-precision sensors are used for string detection. By means of a high frequency differential compensation algorithm and highprecision factory calibration, the detection precision reaches 0.5%. The smart PV solution can accurately monitor two-dimensional information of the string voltage and current. In addition, the smart PV solution can monitor the string status in real time, automatically generate alarms for anomalies and accurately locate string faults.
The use of 4G wireless communication technology for intra-power station communication offers various advantages: with respect to function, the coverage of a single station can reach 80 square kilometers, the transmission delay is smaller than 50ms and smooth expansion of the power plant is supported. With respect to engineering and O&M, optical fibers and ditching are not required, and therefore troubleshooting and maintenance become simple. With respect to management, mobile internet, smart PV terminals, drones and remote expert support work in a collaborative manner to ensure efficient O&M.
Intelligence involves using big data analysis to enable problems to be detected quickly and the correct O&M solution chosen. The intelligence aspect of the smart PV solution encompasses three main strands:
1. Active mining of low-efficiency components to achieve preventive maintenance: This enables the operating state of power plants to be proactively optimised for plant owners, especially those with a large number of plants, taking both maintenance and operation of the plants into consideration.
Discrete analysis is performed for all strings and devices to identify abnormalities for which no alarm is generated. For example, for a hot streak, the system may not generate any alarm, but the efficiency of this string is lower than that of other strings. Therefore, you can locate this string by means of discrete analysis.
In addition, you can also evaluate devices by performing comparison analysis and measuring long-term device efficiency and faults. The evaluation results can be used as references for future device selection and solution design.
2. Remote maintenance – unattended or few-person attended: The power plants do not require any on-duty personnel on site. Monitoring and analysis are carried out at the central headquarters. When a fault occurs, the system sends alarms and rectification suggestions to the on-duty personnel, who can rapidly handle the issues by following the system instructions.
3. Accurate fault locating, reduced diagnosis error rate and improved O&M efficiency: Based on the high-precision string-level detection of the smart PV controller, the system can detect faults in a timely manner. By analysing databases, the system can accurately locate a specific faulty device and propose handling suggestions based on preset measures and O&M experience.
Inside the smart PV power plant
The intelligence of the smart PV power plant derives from three distinct layers: bottom layer (hardware intelligence, including intelligence of PV components, inverters, and power distribution devices), intermediate layer (intelligence of production monitoring and management and optimal power generation control), and top layer (major region decision-making).
1. Bottom layer: This layer contains hardware devices and is equipped with a smart PV controller. The controller can precisely monitor data of each PV string and independently detect each channel of input voltage and current. In this way, the detection precision is improved, laying a basis for accurate fault locating and O&M efficiency improvement.
2. Intermediate layer: This contains the smart PV power plant O&M system that includes the smart PV monitoring system and production management systems. An integrated computer monitoring system is deployed on the unified communication platform to monitor the running status of each device of the power plant.
3. Top layer: This layer contains a group HQ or regional centralised O&M centre, which can manage power plants in a centralised manner, increasing the electric energy yield and reducing management costs. Based on the cloud computing platform, the O&M centre supports the data access capabilities for managing tens of gigawatts and hundreds of power plants, geographically distributed in various areas. It can analyse the implementation status of annual or monthly power generation plans of each power plant as well as the O&M investment, to help group executives to make decisions and summarize production data of multiple power plants.
The benefits of smart PV
Compared with traditional power plants, the smart PV power plant has the following advantages:
- Advanced technologies such as multi-channel MPPTs and multi-modal MPPTs reduce the loss caused by component attenuation, shadow sheltering, inconsistent engineering and installation, inconsistent terrains and DC voltage drop. The system performance ratio reaches 83% or higher. Compared with the traditional PV solution, the average electric energy yield of the smart PV power plant is improved by 2% or more and the internal rate of return by 3% or more.
- The smart PV power plant supports 25-year reliable and maintenance-free running. The smart PV controller supports isolation between internal and external environments, so that components are running in a stable environment, and the impact of external factors such as temperature, wind and salt spray on component lifetime is reduced; the system is not equipped with any damageable components, or any components that need to be replaced periodically.
- The actual usage of the installed capacity of the PV power plant is high. Compared with that of the traditional solution, the annual mean number of failures of the smart PV power plant is decreased by 30%. The probability of system failures that affect the electric energy yield is only one-tenth that of the traditional solution, and maintenance costs after the warranty period are only one-fifth that of the traditional solution.
- The string-level smart monitoring and multichannel MPPT technologies ensure a visible, credible, manageable and controllable power plant. The smart PV controller can independently detect voltage and current of each string, laying the groundwork for accurately locating string failures and improving O&M efficiency.
- The smart PV power plant supports upgrade and evolution. When components advance technologically or the running environment is changed, the PV controller software can be used to remotely upgrade the system online.
- The smart and active grid-adaption technologies adopted by the smart PV power plant offer grid-friendliness. Advantages such as high-speed processing capability and control algorithms of the smart controller enable the smart PV power plant to positively adapt to changes of grids and better satisfy grid access requirements.
- By reducing the DC power transmission distance, the smart PV power plant achieves safe power transmission. Safety transmission and protection of DC power are important and difficult. Based on a no-DCjunction design, the smart PV power plant implements remote-distance power transmission by outputting DC current from the strings to inverters. Then, the inverters convert the DC current to AC current. In this way, the smart PV power plant avoids the safety issues caused by DC power transmission and reduces potential safety risks caused by DC arc discharge.
- Component power attenuation caused by the potential-induced degradation (PID) effect greatly affects the ROI. By using a smart controller to automatically detect the component electric potential, the smart PV power plant can actively adjust the system working voltage, so that the system can have positive grounding voltage without grounding the negative electrode of the solar panels, thereby effectively eliminating the PID effect.
Huawei’s string inverter integrates high-accuracy residual current detection (RCD) to protect the circuit; this effectively limits the contact current when staff accidentally contact PV+, and at the same time RCD cuts off the leakage circuit to protect the circuit itself and ensure safety.
PV power plant intelligence can not only provide suitable solutions for power plants deployed in different regions and different scenarios, but can also reduce O&M costs and increase revenues. The smart PV power plant will play an increasingly important role in the future deployment of solar around the world.