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Interesting Technology Updates -Click on a title below

  • - A radical idea to get a high-renewable electric grid

    This is an interesting approach to optaining very high penetration of renewables such as photovoltaics and wind.  At present most large installations operate under Power Purchase Agreements (PPA) wherein the economics are based on a sell all output at predetermined prices. This contrasts with standalone systems wherein the system size Read More
  • - Breakthrough Batteries Powering the Era of Clean Electrification

    - Breakthrough Batteries Powering the Era of Clean Electrification Battery Storage Costs Drop Dramatically, Making Way to a New Era. A recent Rocky Mountain Institute (RMI) report continues to confirm that clean electrification through batteries is advancing at impressive rates. Very interesting report: Breakthrough Batteries- Powering the Era of Clean Electrification Read More
  • - Interesting Technology

    An assortment of links to interesting information   Semiconductor Nanowires Could Double the Efficiency of Silicon Solar Cells A p/n semiconductor junction is not the only way of converting sunshine into useful electrical energy.  Light consists of a flow of photons of various energy levels (colors).  See this article-Solar Cells.  Nanowires Read More
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Testing

Rapid Shutdown of Photovoltaic Module Series Strings
With the increasing number of Photovoltaic (PV) power systems being installed on buildings and the concern of emergency first responders (firemen) that these high voltages on buildings represent a hazard to first responders, the National Electrical Code (NEC) has added requirements intended to address this hazard. Many PV power systems use a design with many series connected PV modules (termed ‘strings’) to simplify wiring and increase efficiency. Presently these systems can use strings with cold open circuit voltages of up to 600 volts DC on residences, up to 1000 volts on non-residential buildings, and up to 1500 volts in utility scale installations. The problem is that even if the wires from the PV array are disconnected, high voltages remain and emergency responders could be exposed to high voltages even if all electrical power is shut off for the building.

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To address this hazard, the NEC added Section 690.12 Rapid Shutdown of PV Systems on Buildings in the 2014 edition. The requirements were refined in the 2017 edition. Methods and designs for achieving the proper rapid shutdown are not addressed by the NEC but instead are addressed in the product standards (such as UL Standards) for this type of equipment. The figure below from the September/October issue of Solar Pro magazine (see solarprofessional.com) illustrates the requirements.

Rapid Shutdown of Photovoltaic Module Series Strings (2)

Rapid Shutdown of Photovoltaic Module Series Strings

With the increasing number of Photovoltaic (PV) power systems being installed on buildings and the concern of emergency first responders (firemen) that these high voltages on buildings represent a hazard to first responders, the National Electrical Code (NEC) has added requirements intended to address this hazard. Many PV power systems use a design with many series connected PV modules (termed ‘strings’) to simplify wiring and increase efficiency. Presently these systems can use strings with cold open circuit voltages of up to 600 volts DC on residences, up to 1000 volts on non-residential buildings, and up to 1500 volts in utility scale installations. The problem is that even if the wires from the PV array are disconnected, high voltages remain and emergency responders could be exposed to high voltages even if all electrical power is shut off for the building.

To address this hazard, the NEC added Section 690.12 Rapid Shutdown of PV Systems on Buildings in the 2014 edition. The requirements were refined in the 2017 edition. Methods and designs for achieving the proper rapid shutdown are not addressed by the NEC but instead are addressed in the product standards (such as UL Standards) for this type of equipment. The figure below from the September/October issue of Solar Pro magazine (see solarprofessional.com) illustrates the requirements.


 

RapidShutdown2014 vs 2017

There are many ways that the PV industry is addressing these requirements:

Module Level Electronics (MLE), the inclusion of electronic devices within the PV modules:

  • Micro Inverters, one per PV module (or sometimes for 2 modules), to produce AC power from the PV array area. Due to inverter requirements, these inverters must shut down any time the AC power is disconnected or fails (utility outage).
  • Power conditioners for each PV module that are controlled by the central inverter and are designed to shut down whenever the inverter is shutdown.
  • Other shutdown devices such as small remote switching devices, controlled by the inverter or a separate rapid shutdown switch..

Array rapid shutdown devices that are placed within the array boundary and disconnect the PV array whenever the inverter is shutdown.

Inverter location – simply placing the string inverter close to the PV array, within the array boundary. Inverters are being designed to allow such low profile mounting.

In Arizona there is no state wide building code, cities and counties determine the applicable codes and versions of codes.  For instance, Phoenix is now on the 2017 version of the NEC and the 1' boundary applies, while Scottsdale is on the 2014 version of the NEC and the 10' boundry applies. The installer will have to obtain building permits and follow the applicable code version.

 

Activating rapid shutdown:  PV systems installed following either the 2014 or 2017 versions of the NEC will have a reflective label (left image) near the electrical service showing the switch that will put the PV system in shutdown mode.  This label may be either on the AC disconnect (center image- for systems that shutdown upon loss of the utility connection) or on a separate switch (right image).  PV systems using micro-inverter and installed following earlier NEC versions may not be labeled.

PV RAPID LABELLNF222RL AC DiscRapidShutdownSw

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     This is your source for solar and renewable energy information in Arizona. Explore various technologies, including photovoltaics, solar water heating, solar architecture, solar cooking and wind power. Keep up to date on the latest industry news. Follow relevant lectures, expositions and tours. Whether you are a homeowner looking to become more energy efficient, a student learning the science behind the technologies or an industry professional, you will find valuable information here.
  • About The Arizona Solar Center

    About The Arizona Solar Center Arizona Solar Center Mission- The mission of the Arizona Solar Center is to enhance the utilization of renewable energy, educate Arizona's residents on solar technology developments, support commerce and industry in the development of solar and other sustainable technologies and coordinate these efforts throughout the state of Arizona. About the Arizona Solar Center- The Arizona Solar Center (AzSC) provides a broad-based understanding of solar energy, especially as it pertains to Arizona. Registered Read More
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