Devices and Methods for De-Energizing a Photovoltaic System
The 2014/2017 changes to §690.12 of the National Electrical Code (NEC) require that all photovoltaic (PV) systems installed in or on buildings include a ‘rapid shutdown’ mechanism which reduces the voltage within 1 inch of an installed module to less than 80V within 30 seconds of rapid shutdown initiation. Currently this requirement is challenging to achieve in a cost-effective manner. However the National Renewable Energy Laboratory (NREL) has invented and developed a prototype device which quickly and reliably de-energizes PV modules in compliance with §690.12 and is projected to cost ~$0.01/WattDC to install. This change in the NEC is related to problematic emergency situations. For example, if a building with a rooftop PV system catches fire, firefighters must shut down the PV system before they enter the building. Because the PV system continuously converts light to electricity, the PV system cannot be shut down simply by disconnecting the breaker. Even if the alternating current is shut down past the inverter, the direct current (DC) circuit between the PV modules and the inverter is still live. This is particularly problematic if there is structural damage to the residential or commercial building or the circuit. For example, live wires may be in contact with additional conductive surfaces (e.g., metal supports and pooled water), posing significant hazards to firefighters and other first responders. To address this problem, firefighters often shut down PV systems by hauling tarps up to the roof of the building and placing them over the PV modules to block incident light from reaching the solar/PV panels and thus preventing the conversion of light to electrical energy. This technique is both time-consuming and dangerous. Therefore it would be advantageous to provide a method of de-energizing a PV system that is fast and safe and can be automatically triggered/set. The ability to rapidly de-energize PV modules in the event of an emergency is of great interest to PV system owners and the fire-fighting community. This is particularly true in the United States following introduction of PV safety shutdown provisions in the 2014 National Electric Code (NEC) and follow on in the 2017 NEC. The approach taken for this Phase I SBIR engages the system frame ground in a way that identifies whether individual PV circuits should be de-energized at the module level and can be designed and implemented to automatically de-energize and switch off without the need for a centralized signal or control to do so. Such a central signal or control could be compromised or disabled during an event such as a fire or natural disaster such as a fire, earthquake, tornado, hurricane, etc.; whereas the proposed innovative The overall goal of this Phase I DOE SBIR is to create a family of safety PV products including and initially focused on NEC to §690.12 2017 compliant Rapid PV De-Energizers that can be incorporated in new PV installs and easily retrofitted into existing PV systems including those grandfathered and not compliant with NEC §690.12 2017. We have demonstrated a very low cost module level rapid device and method for de-energizing a PV system based on the work done by Dr. Chris Deline of NREL and enhanced and improved by InnoSys in Phase I of this SBIR. We have extensively tested this circuit including emulated and actual PV/solar cells.
- Research Organization:
- Innosys Inc.
- Sponsoring Organization:
- USDOE Office of Energy Efficiency and Renewable Energy (EERE), Renewable Power Office. Solar Energy Technologies Office
- Contributing Organization:
- InnoSys, Inc.
- DOE Contract Number:
- SC0018833
- OSTI ID:
- 1571817
- Type / Phase:
- SBIR (Phase I)
- Report Number(s):
- DE-SC0018833; 8019757399
- Country of Publication:
- United States
- Language:
- English
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