For a long time, the high cost of photovoltaic power generation has always been one of the obstacles restricting the rapid development of the PV industry. How to effectively reduce the cost of PV systems, improve power generation efficiency will continue to be the core issue of the future development of photovoltaic industry. At present, the mainstream of photovoltaic modules and related components are based on the DC voltage 1000V designed and manufactured , the cost and efficiency of power generation are also difficult to meet the needs of large-scale photovoltaic power plants and large-capacity power plant, so the development of photovoltaic products have been associated 1500V is a trend.
Strengths of 1500V Standard
1500V high voltage components and auxiliary electrical equipment means that lower system cost and higher power generation efficiency, and will become the new darling of the photovoltaic industry.
After the DC input voltage is increased, each string can be connected to additional components, increasing the string length of 50%, reducing the amount of direct current to the inverter using a cable, the number of combiner box inverters can also be reduced. At the same time, the power densities of electrical equipment, such as combiner boxes, inverters, transformers, increase, volume decrease, workload of transportation and maintenance reduce, which all will help reduce the cost of photovoltaic systems.
From the perspective of system, higher input and output voltage level can be expected to reduce system efficiency AC and DC side line loss and low voltage side winding losses of transformer, the power station can increase 1.5-2%.
The challenges brought about by 1500V Standard
The 1500V system will reduce the safety and reliability of electrical system, while increasing the PID and other risks. Therefore, in manufacturing 1500V PV modules have to be considered the main backplane PD, electrical connectors and electrical insulation and other factors affect the component reliability and security. While its main difficulty lies in the selection of materials, like enterprises should choose a better quality, more demanding and harsh junction boxes, backplanes, connectors, etc.
The requirements on inverters in 1500V are higher. Some issues must be taken into account: insulation, clearances as well as the potential breakdown voltage when increased after discharge and others. Therefore, the inverter needs to adopt more complex topologies and a higher voltage level power devices and DC switch.
After the voltage was raised to 1500V, the safety of the system performance requirements is higher. Various from AC, there is no zero-crossing point for DC, in the event of leakage, it will cause a major accident. So choose a suitable 1500V DC switch is critical to enhance the security of the entire system.
Outlook on 1500V Standard
Since 2013 , the major focus of PV panel manufacturers have transferred R & D 1500V PV modules , and now Canadian Solar , Trina , JA and others have been developed 1500V PV panels. Huawei, Sungrow, and Omnik are developing new inverters for the 1500V module. It is reported that the International Electrotechnical Commission (IEC) launched 1500V components trial standards and in the near future will transition to a mandatory standard. Parties message indicates that future this will become a new industry standard. With respect to 1000V system, 1500V has been a qualitative leap, but also means that the PV modules and components must meet a much higher standard than the current technical requirements and quality requirements.
The importance of and how to select DC switch for PV application?
Solar photovoltaic systems use DC switch is as important protection device, which directly affect the safety, reliable operation of the PV system and stability of the entire PV system power and income. The importance of selecting a suitable DC switch is self-evident, especially in the 1500V DC photovoltaic system. PV systems suitable switch guarantee a safe, stable, reliable operation, and security in installation, maintenance, repair.
In Germany, the Netherlands and some other European countries, the inverter is requested must configure built-in DC switch. In the UK, India, Australia and other countries, photovoltaic systems must install an enclosure DC switch. With the domestic photovoltaic policy gradually clear, the new installed capacity of photovoltaic power plants increased year by year, especially in the current distributed photovoltaic systems launched, personal household roof PV systems will become increasingly popular. Currently on the domestic market, the so-called photovoltaic DC switch is actually an AC switch or improved products, rather than a true Photovoltaic systems DC switch with safe arc extinction, high-power cutoff function. These switches do not have these features, when off, easy to produce heat, leakage and sparks, severe cases may even burn out the entire PV plant. So the selection of qualified photovoltaic DC switch will be crucial.
DC 1500V system voltage as new technology concepts, need inverters, cables and other components manufacturers to participate and cooperate. Among them, the DC switch is the most important component of a photovoltaic system, as security safeguards, whose rated current and voltage will also have an impact on the selection of photovoltaic systems. DC switching voltage and current are determined by the series connected current and voltage of disconnected PV array. Thus, in the system selection, we need to make sure the system current and voltage, and then select the appropriate photovoltaic DC switch. Generally, voltage of PV systems may reach 1000V, the future or will reach 1500V, you need to disconnect the current assembly according to brand and power of PV module, and connection mode in photovoltaic system.
Since 1500V system voltage design will become the main trend in system selection, the DC switching voltage parameters need to be concerned about. Current common DC switches can disconnect 1000V DC, but rarely 1500V. The latest data on the DC switching shows switch manufacturers abroad who can provide the maximum DC voltage 1500V is few including IMO, China currently only PROJOY.
It is reported that PROJOY latest PEDS series and IMO SI series PV-specific maximum DC voltage are up to DC switch 1500V, a European DC X100 series 1000V, X60 only 600V.
Figure 1：Comparison among PROJOY PEDS / IMO SI / A European X Series
Higher system voltage standard in addition to the DC switching voltage and current proposed new requirements, but also to switch the operating temperature, IP class. At -25°C ~ + 70°C ambient temperature PROJOY PEDS series switches can be loaded, IMO SI series switches work can work at + -40°C ~ 65°C environment, only -20°C ~ + 70°C for this European products. Better protection level, PEDS switch is up to IP66 rating, but China had no other switch manufacturers can do this level of protection.
As a small branch of the photovoltaic industry, perhaps PV DC switch did not get enough attention, but its position in the PV system is self-evident. Only by constantly insight into new industry standards, better service for the entire system can be achieved.
Due to the advantages of 1500V DC access significantly, with mature applications in metro and wind power in the future it will be favored by investors. Also with the Jiuquan-Hunan ± 800 kV HVDC transmission project started, UHV grid has entered into full speed, large-scale construction of the new phase. PV DC output characteristic itself is bound to be popular and to explore the direction of research, such as how to achieve HV PVDC direct access to ultra-high voltage or high voltage DC transmission system, as well as low-voltage DC network or flexible DC distribution issues. High Voltage Products will be the future technology trends, which will be the new technical challenges faced by the PV module, inverter, as well as DC switch manufacturers.