According to the data, from January to May 2018, Chinese new PV grid-connected installed capacity was about 13~14GW, of which distributed PV installed capacity exceeded 10GW, a year-on-year increase of 150%. China has long been the world's number one photovoltaic power.
Under such a large installed capacity of photovoltaics, problems related to product quality, PV solar panel mounting installation specifications, and post-operation and maintenance have emerged in recent years. Among them, the DC high voltage problem in photovoltaic systems has been increasingly valued by the entire industry.
What is the risk of rescue?
“Scattering risk”, as the name implies, is the risk that exists in the rescue process. How can there be a risk of rescue in the PV system?
In the photovoltaic system, the solar modules are arranged in an array in series, and the entire series of line voltages are accumulated, generally reaching a high voltage of 600V to 1000V. When the system is running for many years, the wire is easily exposed after the insulation of the wire is corroded, and it is very easy to generate a DC arc, which penetrates the air and causes a fire. When a fire caused by an electric arc or a fire caused by other causes occurs, the DC side has a voltage as long as there is light. Especially when the DC side reaches a high voltage of 600V~1000V or more, the danger is self-evident. Fire fighting work is very dangerous, firefighters can not be rescued, otherwise there will be a risk of electric shock.
In summary, there is a “rescue risk” in the PV system.
Foreign safety regulations for “rescue risk”
Due to the consideration of photovoltaic safety, government fire safety agencies, insurance companies, and power grid companies around the world have successively issued corresponding policies on fire safety in photovoltaic systems.
Foreign countries have a relatively mature understanding of photovoltaic fire safety. There have been “National Fire Control Regulations”, which require firefighters to maintain a minimum safety distance when they rescue fires with PV systems. Firefighters must not perform rescue work within a safe distance.
The National Electrical Code, NEC, introduced the NEC2014 690.12 "Component-Level Self-Shutdown Solution" standard in 2014, and revised it in 2017 to require "component-level shutdown" in photovoltaic systems. The new NEC 2017-690.12(B)(2) requirements are effective as of January 1, 2019. Germany, Australia, Italy and other countries have also introduced corresponding regulations, clearly requiring the addition of DC cut-off devices between inverters and solar panel mounting bracket components in photovoltaic systems.
"Component level shutdown" solution
The essence of solving the "risk of rescue" is to eliminate the presence of DC high voltage on the roof. The “component-level shutdown” solution, which is the installation of component-level shutdown devices in photovoltaic systems, is believed to be the best choice.
Component-level shutdown devices currently include: power optimizers and intelligent control shutdowns. A photovoltaic system with a power optimizer and a shunt is equipped with a component-level shutdown function that shuts down the connections between each solar mounting structure component in the event of a system fire and eliminates the DC high voltage present in the array. Firefighters can carry out rescue work without threatening the personal safety of firefighters and solving the risk of rescue of photovoltaic systems.