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Dienstag, 11. Juli 2017

Smart and Getting Smarter: China's View of the Future of PV Power Plants

Smart and Getting Smarter: China's View of the Future of PV Power Plants

 
As the private sector increasingly takes on the task of installing solar PV in China, growth is happening quickly. Last year China installed more solar capacity than any other country in the world at 34 GW, beating the US’s 14 GW and Europe’s 6.9 GW.
Neck and neck with the growth of PV is the growing use of digitization within the power industry. Manufacturers are installing cloud-connected sensors on equipment so that it can be remotely analyzed and controlled. And as this “internet of things,” or IOT, becomes ubiquitous in the power industry, so too will smart power plants.
Lead image: Aerial view of the Desert Sunlight power plant in California. Credit: Jamey Stillings via Flickr.
At the intersection of IOT and solar PV is the “smart PV power plant,” a concept that the government of China would like to see implemented across the country, according to its recently published Guiding Opinions on Promoting the Development of “Internet Plus” Smart Energy, which sets a goal of increasing the proportion of renewable energy, promoting the clean and efficient use of fossil fuels, and advancing the energy market through industrial upgrades.
Definition of a Smart PV Plant
A smart PV plant has less need for manual intervention because it operates automatically. A smart plant can automatically identify, diagnose, and repair faults, thereby increasing the electric energy yield, lowering O&M costs, and boosting revenues. A smart PV system must go through three stages in its development: automation, information gathering, and intelligence.
Automation refers to reducing on-site manual operations with components that cannot be easily damaged and require no on-site expert diagnosis or manual repair. Information gathering refers to high-precision, intelligent detection on strings; fast, reliable, secure, and low-cost transmission of that information; and high-reliability storage and monitoring of background data. Intelligence means using big data analysis to detect problems and offer O&M suggestions. Intelligence can enable remote expert guidance based on remote mobile O&M, preventative maintenance, and automatic data reporting at different levels based on an automatic report system.
Inside a Smart PV Plant
The intelligence of a smart PV plant derives from three distinct layers: the bottom layer, the intermediate layer, and the top layer.
The bottom layer contains hardware devices and is equipped with a smart PV controller. The controller can precisely monitor each PV string and independently detect each channel of input voltage and current, laying a basis for accurate fault location detection and O&M efficiency improvement. Multi-channel maximum power point trackers (MPPTs) allow for refined energy management. High-precision sensors ensure higher data precision and improve the electric energy yield and maintainability of plant systems.
At the intermediate layer is the smart PV plant O&M system that includes smart PV monitoring and production management. The systems are interconnected so that the information management system and all sub-plants communicate. An integrated computer monitoring system is deployed on the unified communication platform to monitor the running status of each device of the plant.
The top layer is the group headquarters or a regional centralized O&M center, which can manage plants in a centralized manner, increasing the electric energy yield and reducing management costs. Based on a cloud computing platform, the O&M center supports data access capabilities for managing tens of gigawatts and hundreds of geographically dispersed solar PV plants. It can store hundreds of terabytes of data for 25 years and ensures data security by means of a well-established rights control and authentication mechanism. It can analyze the implementation status of annual or monthly power generation plans for each power plant as well as the O&M investment, to help group executives make decisions. The O&M center can also summarize the production data of multiple plants, perform fusion analysis, and develop a set of KPIs (key performance indicators) that help evaluate the operating and health status of various plants to quickly identify weakness and offer improvement suggestions.
At 1-GW this solar PV project in Yanchi, Ningxia, China is the largest in the world. Credit: Huawei. 
Why Smarter is Better
Compared with traditional plants, the smart PV power plant has a variety of advantages:
Higher IRR: The internal rate of return (IRR) of the smart PV plant is more than 2 percent higher than traditional plants, according to our data. 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.
Zero Maintenance: The smart PV plant is capable of running maintenance-free for 25 years. With an IP65 rating, 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, sand, and salt spray on component lifetime is reduced. The system is maintenance-free because it is not equipped with any damageable components, or any components that need to be replaced periodically (such as fuses and fans). Components and the entire system are designed for 25-year reliability. This combined with rigorous verification tests removes the need to replace system components throughout their lifecycles and ensures reliable and economical operation.
Increased Power Output and System Reliability: The actual usage of the installed capacity of the PV plant is high. Our data shows that compared to traditional power plants, the annual mean number of failures of the smart PV plant is decreased by 30 percent. The probability of system failures that affect the electric energy yield is one-tenth that of traditional solutions, and maintenance costs after the warranty period are one-fifth those of traditional solutions, according to our calculations.
A traditional PV plant essentially uses a serial connection. Faults of any component (such as DC combiner boxes, DC power distribution cabinets, heat dissipation and auxiliary power devices for equipment rooms, and plant inverters) result in either partial or complete PV power generation loss. Unlike the traditional PV plant, a smart PV plant is a distributed parallel system with a simpler structure. Faults of a single inverter will not affect the operation of other devices. The system is easy to install and maintain because it is small and lightweight, and has spare parts for the whole machine available onsite. These aspects dramatically improve the availability of the system.
String-level smart monitoring and multi-channel MPPT technologies ensure a visible, credible, manageable and controllable plant. The smart PV controller can independently detect voltage and current of each string with precision over ten times greater than that of a traditional smart combiner box solution, laying the groundwork for accurately locating string failures and improving O&M efficiency.
Upgradable: When superior components become available or the operating environment changes, the smart PV controller software with backward compatibility can be used to remotely upgrade the system online. This removes the need for the replacement of online devices.
Grid-friendly: Because it has the advantage of high-speed processing capability, high sampling and control frequency, and control algorithms of the smart controller, the smart PV plant can proactively adapt to grid changes, achieve better multi-parallel control and a higher harmonic quality of the grid connection. This allows it to better satisfy grid access requirements and improves its adaptability to adverse grid environments.
Safety: Based on a no-DC junction design, the smart PV 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 plant avoids safety and protection 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 component electric potential, the smart PV plant can actively adjust the system working voltage, so that the system can have positive grounding voltage without grounding the negative electrode of solar panels, thereby effectively eliminating the PID effect. The detected leakage current is greater than 30 mAh since the negative electrode of the solar panels is not grounded and there are residual current detection circuits in inverters.
Smart PV Plants are the Way Forward
The driving force behind the internet is user experience and the one and only way for PV enterprises to grow and prosper is to adopt the same thinking. As China’s PV industry matures and scenarios in which PV plants operate are increasingly diversified, improving the electric energy yield and ensuring safety is key for plant owners.
PV power plant intelligence can not only provide suitable solutions for plants deployed in different regions and different scenarios, but can also reduce O&M costs and increase revenues. The smart PV plant has become an important part of China’s smart energy industry system and a new trend of development in the PV field.
Jeff Yan is a senior product manager at Huawei.
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