Rapid Shutdown
Rapid shutdown was introduced by the National Electrical Code (NEC) as a way to provide a solution for firefighters and emergency responders to de-energize solar systems. The National Fire Protection Association (NFPA) has also stressed the importance of a reliable shut down system. The function of rapid shutdown systems are intended to protect firefighters and the need to safely control the voltage coming from the solar system when a fire or other emergency ensues. In a solar system when an inverter is shut off, the DC connection from the system continues to function, meaning the connections are still live, producing a shock hazard to emergency responders. In response to the NECs regulations, solar system providers have come up with different solutions. At Ollo, we strive to implement the most effective and reliable shutdown system for our customers. One type of shutdown system used is a string-based inverter system, which connects groups of solar panels, each string connects to a single inverter where electricity is converted from DC to AC. The other option is a microinverter, which is an inverter about the size of a Wi-Fi router, installed underneath each solar panel on the roof. What Ollo has done is compare and contrast all the different types of systems, where we found a certain type of micro-inverter would benefit our customers more than any other system.
While string inverters have benefits, we found that implementing the shutdown system through the string system could be problematic. To start string inverters do not inherently meet the NEC 2014 Article 690.12 standards. A rooftop switch disconnect can shut off a PV system, but opening a disconnect switch may not reduce shock hazard on PV systems. On the PV array side of the disconnect switch, DC voltage still exists during daylight hours. On the other side of the disconnect switch, capacitors and parallel array circuits are connected to the string inverter and can keep the circuit energized after the disconnect switch is opened. Adding a rapid shutdown function to string inverter systems would require the removal of the rooftop junction box and replacing it with a rapid shutdown box. Also having to run conduit and control wire between the controller and junction box. String systems also face the challenge of the inverter system only performing as well as its lowest-performing panel. Every panel operates at the same capacity as the lowest producing panel, making small obstacles like shade have a big impact on energy production.
Microinverters already conform to the 2014 NEC article 690.12. This is because most systems will de-energize when the power from the grid is disrupted. Microinverters convert low voltage DC to AC voltage to integrate with utility grid AC voltage. When the PV system is disconnected from the grid, the MLPE’s stop producing AC voltage and cuts off voltage to the home and the grid. The problem with conventional microinverter systems is that when one system fails the whole system fails. Think about the system like Christmas lights, when one bulb fails every bulb after that fails. The solution is a microinverter that connects to more than one solar panel. This minimizes the risk of failure in energy production and rapid shutdown. The rapid shutdown has to pass through every single microinverter in a conventional system. In the system used by Ollo, the rapid shutdown process has to pass through fewer inverters making the risk of malfunction exponentially less than traditional systems.
In all solar technology, the regulations are constantly changing, making it a challenge for providers to keep up with the latest technology. We pride ourselves on being fluid to changing technology and welcome new methods and systems that benefit our customers. Our team has taken action to implement these microinverters in our projects to make solar power more economical, user friendly, and safe for all involved. Having fewer points of connection leaves less room for error in emergency situations. Fast-acting emergency responders need fast-acting technology to be able to perform their job in a safe and efficient manner. Ollo has taken all these factors into consideration and found a solution that not only benefits our customers but also our first responders.