Rapid Shutdown – Safety First
Although not mandated by federal law, the National Electric Code (NEC) has been adopted by many state and local authorities responsible for building and construction safety. With over a century of history, the NEC is routinely updated to keep up with technology and suggest best practices.
For example, starting in 2019, the NEC recommends new guidelines that reflect the changing adoption of solar design, where systems implemented with microinverters and with string inverters with power optimizers require new safety procedures.
In its most basic form, Rapid Shutdown refers to designs and installation procedures that allow the solar power generation source to be isolated quickly from the circuit. Solar panels must be disconnected in order to reduce or eliminate shock hazards in emergency situations. The photovoltaic reaction in solar panels continues as long as the front surface is exposed to light. The more potent the exposure, the more solar power is produced. Rapid shutdown breaks the circuit, indirectly “turning off” the panels from a point downstream in the power circuit. The panels themselves are still electrically “hot”.
Perhaps most importantly, these protocols are key to keeping a grid-connected solar energy system safe in the event of a grid power outage. Whether a person intervenes to purposefully cause a shutdown or the reaction is automatic due to grid faults, the designed response is the same.