Rapid Shutdown for Solar Systems: What You Need to Know
Rapid shutdown is a safety regulation put forth by the National Electrical Code (NEC) requiring solar panels to have switches for cutting off electricity running through your system. Rapid shutdown reduces the voltage of electrical conductors found in wires and cables, protecting your home from quickly catching fire.
Additionally, it protects first responders such as firefighters by enabling them to quickly cut off power in the conductors, making it safe to access the area near your system.
Rapid shutdown for solar systems is only applicable to solar systems mounted on a rooftop. If you are interested in installing solar energy in your home, look no further. Get the best solar panel installation in Orlando from PES Solar and enjoy ideal solar energy panels.
Is Rapid Shutdown Required in All States?
Most states have Rapid shutdown requirements. The requirements are, however, based on the code in effect. Every three years, NEC releases safety electrical system requirements, and the states adopt the regulations at their own time and discretion.
If you live in a state enforcing NEC 2014 or NEC 2017, your solar system must follow the NEC Rapid shutdown requirements for approval. According to NEC 2014, conductors above ten feet from a solar system must be brought down to 30 volts and 240 amperes ten seconds after launching the Rapid shutdown switch.
NEC 2017, on the other hand, requires conductors above one foot to be de-energized and reduced to 80 volts 30 seconds after initiating the Rapid shutdown inside the solar array boundary. Voltage measurements are taken between two conductors and between the conductors and the ground. For conductors outside the solar array boundaries, voltage measurements should not exceed 30 volts 30 seconds after starting the Rapid shutdown system.
Does Your Inverter Have Rapid Shutdown Capabilities?
Some inverters have Rapid shutdown capabilities, while others require additional components to facilitate Rapid shutdown. The standard inverters in the United States are microinverter and power optimizer systems. Both have Rapid shutdown capabilities.
How to Install a Rapid Shutdown Switch
The first step toward installing a solar power system and ensuring it meets the set safety and electrical codes is looking for a qualified installer. Experienced installers have the expertise to design your solar array in compliance with the Rapid shutdown requirements for your state.
If you plan to make changes to a solar panel you installed before your state implemented NEC 2014 or NEC 2017, you must upgrade it to the recent NEC regulations before inspection. Upgrading involves installing a Rapid shutdown system.
Reliable Solar Panel Installation in Orlando
A Rapid shutdown for solar systems is vital for every household. A Rapid shutdown comes with safety benefits, such as protecting your house from fire hazards and safeguarding first responders. Having a Rapid shutdown protocol will help you protect your home investment as you comply with the required safety electrical codes.
There are several energy sources to choose from today. These include solar panels and generators. Having options to choose from is essential to avoid inconveniences during emergencies. To better understand the various available options, learn more about solar panels vs. generators here.
PES solar has a team of professionals with over 20 years of experience in module-level power electronics. We use our expertise to help you get the best devices to boost your solar energy system. Contact PES Solar at (800) 650-6519 to inquire about our services.
About The Author: Austin Miller
With over two decades of experience in the solar and electrical contracting industry, Austin Miller brings a wealth of expertise to the table. As the proprietor of PES Solar, his profound understanding of solar energy and its cost-saving potential is unmatched. Austin’s unwavering passion for the solar sector drives his mission to help businesses and homeowners maximize their savings while embracing renewable energy solutions.
23 NATIONAL ELECTRICAL CODE AND PHOTOVOLTAIC POWER SYSTEMS
Introduction. There have been changes throughout the entire 2023 NEC that may affect the installation of photovoltaic (PV) systems. However, this article will concentrate on the changes in Article 690, Solar Photovoltaic (PV) Systems, Article 705, Interconnected Power Production Sources, Article 691, Large-Scale Photovoltaic (PV) Electric Supply Stations, and Article 710, Stand-Alone Systems, that more directly affect PV systems. These articles are under the purview of Code-Making Panel No. 4, chaired by James J. Rogers.
Climate change is resulting in more frequent weather events, including high winds and rain, tornadoes, hurricanes, flooding, heavy snowfall, and forest fires, resulting in increased numbers of people who have experienced short or long electrical utility outages. This situation is increasing the demand for PV systems that have an energy storage component providing electrical energy during these utility outages. For this reason, changes to Articles 480, Stationary Standby Batteries, and Article 706, Energy Storage Systems, both under the purview of CMP 13 (chaired by Linda J. Little) will also be addressed.
Unfortunately, the definition of Stationary Standby Batteries as batteries remaining in a float charge or near 100 percent state of charge awaiting a discharge event also appears to be applicable to energy storage system batteries. Most PV systems with energy storage systems are utility-interactive, and the batteries remain in the fully charged state until there is a utility outage, sometimes at infrequent intervals or never. The two articles may overlap and be applied in a single system. Here is an example.
A dwelling has a sizable PV system (7 kW AC output) consisting of utility interactive micro-inverters and a string inverter. See photo 1. This PV system AC output feeds all AC circuits in the house, which are also connected to the protected loads AC input/output of a multi-mode utility-interactive inverter. In addition to being connected to the utility service, the multi-mode inverter is also connected to a bank of valve-regulated lead acid batteries (VRLA) rated at 600 kWh. The multi-mode inverter controls the battery charge and discharge processes and the interface with the utility. All the inverters and other equipment except for the batteries are listed under the appropriate Underwriters Laboratory standards. This is not listed energy storage system as covered by Article 706. However, the battery bank meets the requirements of Article 480 and is exempt from the listing requirement because it is installed in a dwelling. But Article 706 covers the various interconnection requirements of the components in the system, and it can be used in conjunction with Article 480 to design, install, and inspect the system.
Sections that remain essentially unchanged from the 2020 NEC will not be addressed.
The text of the 2023 NEC changes will not be fully addressed because of the limitations on the length of this article. The full text of the 2023 NEC is available for viewing on the NFPA website at NFPA.org
ARTICLE 690, Solar Photovoltaic (PV) Systems
Section 690.1, Scope. Informational Notes, Figures 690.1(a) and (b) have been combined into one figure Informational Note, Figure 690.1. This revision adds some clarity by eliminating the interconnections to energy storage systems and showing only the DC PV circuits.
The Definitions in Section 690.2 have all been moved to Article 100, where all the definitions throughout the code will be found.
Section 690.4(B), General Requirements. Additional equipment and acronyms have been added to the list of equipment that must be listed or have a field inspection label applied.
Section 690.4(G), PV Equipment Floating on Bodies of Water. This new section dealing with equipment floating on bodies of water has been added. The section adds additional requirements over those requirements for fixed, land-based PV installations.
Section 690.7, Maximum Voltage, has been broken down into subparagraphs for additional clarity.
Section 690.7(D), Marking DC PV Circuits, has been added dealing with the marking requirements for DC PV circuits. The highest maximum DC voltage in the system must be provided by the installer in one of three listed locations.
Section 690.8(1)(b), Photovoltaic Output Circuit Currents, has been eliminated and the subsequent paragraphs renumbered with some combining of requirements. An Informational Note has been added to indicate that modules that can produce electricity when exposed to light on multiple surfaces are labeled with additional information.
Section 690.8(D), Sizing of Module Interconnection Conductors, has had the name changed to Multiple PV String Circuits and has been divided into subparagraphs for additional clarity.
Section 690.9(C), Source and Output Circuits, has had a name change and is now called PV System DC Circuits. The contents remain the same.
Section 690.9(D), Power Transformers, has had the name changed to Transformers and the current text has been shortened and points to the requirement in Section 705.30 (F). The Exception remains the same.
Section 690.10, Stand-Alone Systems, has been removed, and the requirements are now included in Section 710.15.
The Exception in Section 690.11, Arc-Fault Circuit Protection (dc), has been revised for clarity with subparagraphs.
In Section 690.12, Rapid Shutdown of PV Systems on Buildings, Exception Number 2 has been added dealing with non-enclosed detached structures not requiring Rapid shutdown systems.
Section 690.12(A), Controlled Conductors, has a new Exception dealing with arrays not attached to buildings that terminate on the exterior buildings and PV system circuits installed in accordance with 230.6. These circuits are excepted from the Rapid shutdown requirement.
Section 690.12(B), Controlled Limits, has an additional sentence that says that equipment and systems shall be permitted to meet the requirements both inside and outside the array as defined by the manufacturer’s instructions, including in the listing.
Section 690.12(B)(1), Outside the Array Boundary, has had a few words added to further define the installation of a PV Hazard Control System (PVHCS).
Section 690.12(B)(2), Inside the Array Boundary, has been revised for clarity, and an Informational Note No. 2 has been added following the section.
Section 690.12(C), Initiation Device, has been slightly reworded for clarity, and the Informational Note has been deleted after subparagraph (3).
The contents of Section 690.12(D), Equipment, have been removed and replaced with marking requirements previously found in Section 690.56(C) and retain the title of that section, Buildings with Rapid Shutdown. The requirements for marking and been slightly changed, and the Informational Note now refers to Figure 690.12(D).
The Informational Note for Figure 690.12(D), has now been transferred from its previous location in Section 690.56 (C) to this location.
Section 690.12(D)(1), Buildings with Than One Rapid Shutdown Type, has been added and was previously Section 690.56(C)(1).
Section 690.12(D)(2), Rapid Shutdown Switch, has been added and was previously 690.56(C)(2).
In Part III. Disconnecting Means, Section 690.13 has had (A) Location, broken down into two subparagraphs, (1) Readily Accessible and (2) Enclosures and Doors and Covers. This is essentially a rewrite of the existing requirement that was found in one paragraph.
Section 690.15(A), Location, has been replaced with a new section entitled Type of Disconnecting Means, which has three subparagraphs elaborating on the types of disconnecting means.
Section 690.15(C), Equipment Disconnecting Means, has been revised into four subparagraphs essentially containing the same contents as the previous single paragraph.
Section 690.15(D) is now called Location and Control. It is revised and expanded the previous requirements into four subparagraphs providing additional details.
Significant revisions have been made in Part IV, Wiring Methods and Materials.
Section 690.31(A), Wiring Methods, now includes four subsections, (1) Serviceability, (2) Where Readily Accessible, (3) Conductor Ampacity, and (4) Special Equipment.
Table 690.31(A)(B) is now renumbered as Table 690.31(A)(3)(1).
Section 690.31(B), Identification and Grouping, has been revised and expanded to three subsections, (1) Conductors of Different Systems, (2) Identification, and (3) Grouping. The changes include additional material and better clarity.
Section 690.31(C)(1), Single Conductor Cable, has been revised and expanded with additional requirements into three subparagraphs.
Section 690.31(C)(2), Cable Tray, has been expanded to include three subparagraphs dealing with single conductor PV wires smaller than 1/0 AWG.
Section 690.31(D), Direct-Current Circuits on or in Buildings, has been revised and changed. The previous subparagraph (1) concerning flexible wiring methods has been removed. Subsection (1) is entitled and now addresses Metal Raceways and Enclosures and Subsection (2) Marking and Labeling contains the same material as the previous edition of the code.
A new Section 690.31(G), Over 1000 V DC, has been added and has three subparagraphs.
Part V. Grounding and Bonding.
Section 690.41(A), PV System Grounding Configuration, has minor rewording for clarity.
Section 690.42, Point of System Grounding Connection, has been retitled Point of PV System DC Circuit Ground in Connection and has been slightly expanded with two subsections, (A) Circuits with GFDI Protection and (B) Solidly Grounded Circuits.
Section 690.43(A), Photovoltaic Module Mounting Systems and Devices, has been slightly shortened and added an Informational Note.
The title of Section 690.43(C), With Circuit Conductors, has been changed to Location. An additional sentence adds clarity.
In the first sentence of Section 690.47(A), Buildings or Structures Supporting a PV System, the reference has been changed to 690.40(B) instead of Part III of Article 250.
Part VI. Source Connections. This part was previously entitled Marking.
The sections related to PV Rapid Shutdown in this part have been moved to 690.12.
There are three sections in this part now. Section 690.56, Identification of Power Sources, refers to the requirements in article 705.10. Section 690.59, Connection to Other Sources, refers to the requirements in Parts I and II of Article 705. The contents of Section 690.72, Self-Regulated PV Charge Control, have not been changed.
Article 691 Large-Scale Photovoltaic (PV) Electric Supply Stations. See photo 3.
691.1 Scope. Informational Note No. 1 now has a reference to Section 691.4.
The Definitions in 691.2 been moved to Article 100.
691.4 Special Requirements for Large-Scale PV Electric Supply Stations. Two new subparagraphs been added to the section and an Informational Note No. 2 addresses minimum size requirements.
Section 691.9, Disconnecting Means for Isolating Photovoltaic Equipment. The Informational Note has an updated reference to NFPA 70E-2021 and the reference to NFPA 70 E-2018 has been deleted.
Section 691.10, Fire Mitigation. This title has replaced the previous title Arc-Fault Mitigation and an Informational Note has been added.
ARTICLE 705 Interconnected Electric Power Production Sources.
Section 705.1, Scope. A second Informational Note has been added to this section.
The Definitions in Section 705.2 have been moved to Article 100.
A new Section 705.5, Parallel Operation, has been added with two subsections: (A) Output Compatibility, and (B) Synchronous Generators. Subsection B has an Informational Note referring to IEEE 1547 and UL 1741.
Section 705.6, Equipment Approval, has been revised and two Informational Notes have been added.
Section 705.10, Identification of Power Sources, has been restructured and expanded for clarity with additional requirements.
Section 705.11 has been re-titled to Supply-Side Source Connections.
Section 705.11(A) has been completely rewritten and now is entitled Service Connections and now has three subsections.
Section 705.11(B), Conductors, has been expanded and now has three subsections.
Section 705.11(C), previously titled Overcurrent Protection, has been changed to Connections [previously 705.11( D)] and significantly expanded with three subparagraphs: (1) Splices or Taps, (2) Existing Equipment and, (3) Utility-Controlled Equipment.
Section 705.11(D) is now Service Disconnecting Means with new content.
Section 705.11(E) is now Bonding and Grounding with new requirements.
Section 705.11(F) is now Overcurrent Protection and has been significantly reduced in size from the previous edition of the code by referring to Article 230 requirements.
Section 705.12, Load Side Source Connections, has been significantly revised with modified requirements by combining requirements into only two large subsections, (A) Feeders and Feeder Taps, (B) Busbars.
Section 705.13 has been retitled Energy Management Systems (EMS) with reduced requirements from the previously titled Power Control Systems.
Section 705.20, Source Disconnecting Means, has modified and added requirements.
Section 705.25, Wiring Methods, has some wording changes and minor additions for clarity. An Informational Note has been added.
Section 705.28, Circuit Sizing in Current, has been revised with additional material related to Energy Management System (EMS) with multiple subsections in the Power Source Output Maximum Current Section (A) and several exceptions in the Conductor Ampacity Section (B).
Section 705.30, Overcurrent Protection. This section has been extensively revised and expanded and now includes subsections (A) through (F).
Section 705.32, Ground-Fault Detection, has a few words added in the text and in the Exception for clarity.
Part II. Microgrid Systems
Section 705.50, System Operation, has a few words added for clarity and two Informational Notes have been added.
Section 705.70, Microgrid Interconnect Devices (MID), has subparagraph (3) modified for additional clarity.
Section 705.76, Microgrid Control System (MCS), is a new section dealing with the subject equipment in four subparagraphs and an Informational Note.
Part III. Interconnected Systems Operating in Island Mode.
Section 705.80, Power Source Capacity. This new section is a single paragraph dealing with the sum of all power source outputs.
Section 705.81, Voltage and Frequency Control. This new section is a single paragraph requiring island mode sources to be compatible with connected loads.
Section 705.82 Single 120-Volt Supply. This new section contains information and warnings about overloading neutrals on three wire circuits supplied by 120 V sources.
ARTICLE 710 Stand-Alone Systems
Section 710.6, Equipment Approval, has had a few slight modifications for clarity and Informational Note has been deleted.
Section 710.10, Identification of Power Sources. This section has had a few modifications for clarity and the Exception has been deleted.
Section 710.10(F), Back-fed Circuit Breakers, has been deleted and replaced with the previous 710.10(G), Voltage and Frequency Control.
ARTICLE 480, Stationary Standby Batteries.
Section 480.1, Scope. The section now includes the minimum size of standby battery as 1 kWh. An additional Information Note now refers to Article 706, and the existing Informational Note has an additional reference.
Section 480.2, Definitions, has now been moved to Article 100.
Section 480.4(A), Corrosion Prevention. The Informational Note has now been merged into the text.
Section 480.7(A), Disconnecting Means, has a few words changed for clarity.
Section 480.7(G)(1), Facilities with Utility Services and Stationary Standby Batteries, as a slight wording change in the title and the removal of a reference to Section 712.10.
ARTICLE 706, Energy Storage Systems.
Section 706.1, Scope, has additional standards referenced Informational Note No. 3.
Section 706.2, Definitions, has been moved to Article 100.
Section 706.7, Commissioning and Maintenance, has been divided into two sub-sections entitled (A) Commissioning and (B) Maintenance. It is noted that commissioning does not apply to one- and two-family dwellings.
Section 706.8, Storage Batteries, has been removed from this article.
Section 706.15, Disconnecting Means, has been expanded significantly with increased content and requirements. Subsection titles have been revised and an additional Subsection E has been added with substantial content.
Section 706.20(A), Ventilation. Informational Notes in this section have been substantially revised.
Section 706.31(A), Circuits and Equipment. This section has received significant amounts of additional information and an Informational Note.
Section 706.31(B), Overcurrent Device Ampere Ratings, no longer has a reference to Article 240.
Section 706.40, General, has been slightly revised, and an Informational Note added.
Section 706.50, General, has been revised slightly for clarity.
Section 706.51, Flywheel ESS (FESS). This is a new section with four numbered paragraphs.
John Wiles retired in April 2013 as a Senior Research Engineer at the Southwest Technology Development Institute at New Mexico State University. However, he works part time as 25% employee and continues to assist the PV industry, electrical contractors, electrical inspectors, and purchasing agencies in understanding the PV requirements of the National Electrical Code (NEC). He is an active member on six UL Standards Technical Panels. John served as Secretary for the PV Industry Forum involved with Article 690 of the NEC. Over 30 submissions were accepted for the 2011 NEC and 55 proposals were submitted for the 2014 Code. He drafted the text for Article 690 in the 2005 NEC Handbook and 2008 NEC Handbook. Fieldwork involves balance of systems design for PV systems, inspections and acceptance testing of PV systems, test and evaluation of PV components, and the design and installation of data acquisition systems. He bought his first codebook in 1960 and installed his first PV system in 1984. He lived in an off-grid, PV/wind-powered home (permitted and inspected, of course) with his wife Patti, two dogs, and a cat for more than 16 years. His retirement home currently has a 8.5 kW utility-interactive PV system will full-house battery backup and now has three dogs and two cats. He writes the “Perspectives on PV” series of articles for the International Association of Electrical Inspectors in their IAEI News magazine and has published an IAEI book on PV and the NEC for inspectors and plan reviewers. He has a Master of Science Degree in Electrical Engineering.
Decoding Solar Panel Output: Voltages, Acronyms, and Jargon
For those that are new to solar power and photovoltaics (PV), unlocking the mysteries behind the jargon and acronyms is one of the most difficult early tasks. Solar panels have many different voltage figures associated with them. There is a good amount to learn when it comes to solar panel output.
Types of solar panel voltage:
- Voltage at Open Circuit (VOC)
- Voltage at Maximum Power (VMP or VPM)
- Nominal Voltage
- Temperature Corrected VOC
- Temperature Coefficient of Voltage
- Measuring Voltage and Solar Panel Testing
Voltage at Open Circuit (VOC)
What is the open circuit voltage of a solar panel? Voltage at open circuit is the voltage that is read with a voltmeter or multimeter when the module is not connected to any load. You would expect to see this number listed on a PV module’s specification sheet and sticker. This voltage is used when testing modules fresh out of the box and used later when doing temperature-corrected VOC calculations in system design. You can reference the chart below to find typical VOC values for different types of crystalline PV modules.
Voltage at Maximum Power (VMP or VPM)
What is the Max Power Voltage of a solar panel? Voltage at maximum power is the voltage that occurs when the module is connected to a load and is operating at its peak performance output under standard test conditions (STC). You would expect to see this number listed on a modules specification sheet and sticker. VMP is at the place of the bend on an I-V curve; where the greatest power output of the module is. It is important to note that this voltage is not easily measured, and is also not related to system performance per se. It is not uncommon for a load or a battery bank to draw down the VMP of a module or array to a few volts lower than VMP while the system is in operation. The rated wattage of a PV module can be confirmed in calculations by multiplying the VMP of the module by the current at max power (IMP). The result should give you [email protected] or power at the maximum power point, the same as the module’s nameplate wattage. The VMP of a module generally works out to be 0.5 volts per cell connected in series within the module. You can reference the chart to find typical VMP values for different types of crystalline modules.
What is the voltage of a solar panel? Nominal voltage is the voltage that is used as a classification method, as a carry-over from the days when battery systems were the only things going. You would NOT expect to see this number listed on a PV module’s specification sheet and sticker. This nomenclature worked really well because most systems had 12V or 24V battery banks. When you had a 12V battery to charge you would use a 12V module, end of story. The same held true with 24V systems. Because charging was the only game in town, the needs of the batteries dictated how many cells inside the PV should be wired in series and or parallel, so that under most weather conditions the solar modules would work to charge the battery(s). If you reference the chart, you can see that 12V modules generally had 36 cells wired in series, which over the years was found to be the optimum number for reliable charging of 12V batteries. It stands to reason that a 24V system would see the numbers double, and it holds true in the chart. Everything worked really well in this off grid solar system as the and evolved along the same nomenclature so that when you had a 12V battery and you wanted solar power, you knew you had to get a “12V” module and a “12V” controller. Even though the voltage from the solar module could be at 17VDC, and the charge controller would be charging at 14V, while the inverter was running happily at 13VDC input, the whole system was made up of 12V “nominal” components so that it would all work together. This worked well for a good while until maximum power point technology (MPPT) became available and started popping up. This meant that not all PV was necessarily charging batteries and that as MPPT technology evolved, even when PV was used in charging batteries, you were no longer required to use the same nominal voltage as your battery bank. String inverters changed the game for modules, as they were no longer forced in their design to be beholden to the voltage needs of deep cycle batteries. This shift allowed manufacturers to make modules based on physical size, wattage characteristics, and use other materials that produced module voltages completely unrelated to batteries. The first and most popular change occurred in what are now generally called 18V “nominal” modules. There are no 18V battery banks for RE systems. The modules acquired this name because their cell count and functional voltage ratings put them right in between the two existing categories of 12V and 24V “nominal” PV modules. Many modules followed with 48 to 60 cells, that produced voltages that were not a direct match for 12V or 24V nominal system components. To avoid bad system design and confusion, the 18V moniker was adopted by many in the industry but ultimately may have created more confusion among novices that did not understand the relationship between cells in series, VOC, VMP, and nominal voltage. With this understanding, things get a lot easier, and the chart should help to unlock some of the mystery.
The temperature-corrected VOC value is required to ensure that when cold temperatures raise the VOC of an array, other connected equipment like MPPT controllers or grid tie inverters are not damaged. This calculation is done in one of two ways. The first way involves using the chart in NEC 690.7. The second way involves doing calculations with the Temperature Coefficient of Voltage and the coldest local temperature.
Temperature Coefficient of Voltage
What is a solar panel temperature coefficient? The temperature coefficient of a solar panel is the value represents the change in voltage based on temperature. Generally, it is used to calculate Cold Temp/Higher Voltage situations for array and component selection in cooler climates. This value may be presented as a percentage change from STC voltages per degree or as a voltage value change per degree temp change. This information was not easily found in the past, but is now more commonly seen on spec pages and sometimes module stickers.
Measuring Voltage and Solar Panel Testing
How do I measure voltage on a solar panel? Voltages can be read on a solar panel with the use of a voltmeter or multimeter. What you’ll see below is an example of a voltmeter measuring VOC with a junction box. This would be the view from the back of the PV module. Using a multimeter is the best way to measure solar panel output.
When researching solar panel output, it can be overwhelming to understand the different voltage figures and acronyms used. For those new to solar power and photovoltaics (PV), decoding the terminology can be a challenge. In this blog post, we will break down the basics of solar panel output, including voltage, acronyms, and jargon, to help you get up to speed.
What are solar amps and watts?
Solar amps and watts are two measurements of the amount of electrical energy that a solar panel produces. Solar amps (A) measure the rate of electric current produced by a photovoltaic cell, while solar watts (W) measure the amount of power delivered to an electrical load. Both solar amps and watts are related to the efficiency rating of residential solar panels. The higher the efficiency rating, the higher the number of solar amps and watts produced.
There are many types of 60-cell solar panels on the market for home solar applications, each with varying efficiency ratings and amp/watt outputs. High efficiency panels are capable of producing more solar watts than low-efficiency panels, although they tend to cost more upfront. By choosing the right panel, homeowners can ensure that their solar array is producing enough power to meet their electricity needs.
Why do solar panels have so many voltages associated with them?
Solar panels have a variety of voltage figures associated with them due to the different types of solar panels, their placement in a solar panel system, and their power production. The most common type of rooftop solar panel uses a direct current (DC) and produces a low voltage. This low voltage is typically between 20 and 40 volts, depending on the specific type of panel. To increase the voltage output, multiple solar panels can be wired together in a series or parallel connection, or both, depending on the specific solar energy system.
When solar panels are connected in a series, the voltages are added together. This means that connecting two 20-volt solar panels in series would yield a total voltage output of 40 volts. Connecting three panels in series would result in a 60-volt output, and so on. This method is often used when the total voltage needs to be higher than what a single panel can provide.
In contrast, when solar panels are connected in parallel, the wattage is added together. This means that connecting two 10-watt solar panels in parallel would yield a total wattage output of 20 watts. Connecting three panels in parallel would result in a 30-watt output, and so on. This method is often used when the total wattage needs to be higher than what a single panel can provide.
The voltage output of a solar panel also depends on its power production, which is measured by the manufacturer at Standard Test Conditions (STC).
What does STC mean?
STC is defined as an irradiance of 1,000 W/m2 and cell temperature of 25 degrees Celsius. Because real-world conditions are rarely equal to STC, the actual power output of a solar panel may differ from its rated output. This is why it’s important to understand the various voltages associated with your particular solar energy system to ensure it meets your needs. To determine solar panels rated output, you need to know two figures: the solar panel wattage (measured in watts) and solar panel efficiency (measured in percent). Solar installation involves connecting solar panels to a photovoltaic system that can use or store the generated electricity. The efficiency rating of solar panels varies depending on factors such as environment, angle, and geographic location, but typically ranges between 15–20%. Knowing what wattage solar panels generate helps determine their overall performance in terms of power production for any given solar installation project. Understanding the various voltages associated with solar energy systems can be challenging for those new to the technology but once you’ve grasped this knowledge, you’ll have the knowledge you need to make informed decisions about your own solar energy installation.
How many size should my solar panel be?
When choosing a solar panel size, you must consider your energy needs and the hours of sunlight available in your area. The size of the solar panel will determine how much electricity it can produce, measured in kilowatt hours (kWh). Your energy needs will determine the type of solar panel that you need.
If you’re looking to produce a specific amount of electricity, the total number of solar panels that you need will depend on their wattage rating. Generally, the higher the wattage rating, the more electricity it will generate. You can calculate how many solar panels you need to meet your energy requirements by dividing your kWh requirement by the wattage of each panel.
For example, if you have an energy requirement of 10 kWh per day and you are using solar panels with a rating of 250 watts, then you would need 40 solar panels.
When choosing the size of your solar panel, make sure to consider the hours of sunlight available in your area as well. The more sunlight available, the fewer solar panels you’ll need to meet your energy requirements.
In summary, the size of the solar panel that you need depends on your energy needs and the hours of sunlight available in your area. You can calculate how many panels you need to meet your energy requirements by dividing your kWh requirement by the wattage of each panel.
Line Side Tap vs. Load Side Tap: Everything You Need To Know
If your solar photovoltaic (PV) system produces more electricity than you can use, the excess is sent to the grid where it flows to your neighbor and their neighbor and so on. The process of connecting a solar PV system to the larger electric grid is called interconnection and it’s often the final step in the solar panel installation process.
The physical connection between your solar system and the grid can be made either with a line side tap or a load side tap. If you have no idea what that means, read on. This article is designed to explain the basics in a way that doesn’t require you to be a licensed electrician or have a degree in electrical engineering.
Interconnection Specialists Required
There are very specific codes and regulations that need to be followed in order for your grid-connected solar PV system to pass inspection and receive the all-important permission to operate from the utility.
That means you need both interconnection specialists designing your system and electricians well-versed in line side tap and load side tap interconnection techniques doing the actual installation. Reputable solar partners like Velo Solar will have both on their team, and they’ll recommend which interconnection technique is appropriate for your situation.
Electrical Engineering 101
We’re assuming that if you’ve read this far, you’re not an electrical engineer or an electrician who already understands this. That said, what follows will make a lot more sense if we establish some basic definitions. First, let’s talk about some of the components of your existing electrical system and your solar system.
Note, the discussion that follows assumes a single-phase system.
Of note, there are a few variations of the ‘single phase’ configuration, based on the number of wires. Three-phase systems, often found in factories or large office buildings have slightly different considerations, though the concept is the same.
You can think of the main electrical panel, otherwise known as the service panel, as the switchboard for the electricity that flows into your business. There are two main service wires that come into the panel’s main breaker from the utility connection after first passing through the meter. Each carries 120-volts of power. Flipping the main breaker off stops the flow of electricity to your entire facility.
After flowing through the main breaker, the electricity next comes to the two busbars in the panel. Busbars (also commonly spelled bus bars or bussbars) distribute the electricity to the two columns of circuit breakers in the panel.
The panel will likely have 120-volt circuit breakers, also known as overcurrent protection devices (OCPD), that are connected to one busbar or the other. Depending on what you’re powering, you may also have 240-volt breakers that are connected to both bus bars. Each should be labeled allowing you to shut off the power to a specific part of your facility if necessary (showroom lights, workshop, exterior lights, etc.).
Because there are a finite number of spaces in each panel for circuit breakers, your business may have one or more subpanels that are fed by the main panel. Subpanels can be the same size and work the same way as your main panel. They likely provide power to a certain area of your facility, such as a workshop.
Every solar PV system includes an inverter that converts the direct current (DC) electricity generated by your solar system to the alternating current (AC) electricity used to power your facility and its equipment.
Understanding Line Side and Load Side
Throughout this article, we’ll be discussing the concepts of line side and load side. Here’s how to differentiate between the two: the line side supplies power while the load side uses the power; your utility power meter or main breaker is typically the line of demarcation between the two.
In short, the current could be on the line side or the load side of your electrical system, depending on where it is at the moment. For example, if it’s in between the main meter and the main electrical panel, it’s on the line side. The instant it comes out of the main panel and into your building it’s considered load side.
So, with that basic information in mind, let’s talk about the two ways you can connect your solar system to the grid.
Load Side Taps
With a load side tap, your solar inverter is wired directly to your electrical panel through a circuit breaker. When you have more power than you need, it flows from that breaker through the bus bars, the main breaker, the meter, and then ultimately out to the grid.
Any electrician will tell you that working on a live (or electrified) system is dangerous. When connecting the solar inverter to the panel, the electricity must be shut off.
This is easily done with a load side tap because all you have to do is flip the main breaker in the main panel to the off position; once you’ve done that, then everything from the panel on in is de-energized. As we’ll discuss in a moment, a line side tap is a more complicated process.
Load side taps are common for residential systems and smaller commercial systems.
When designing your solar system, the provider must consider the 120% rule. This rule was established by the National Electrical Code (NEC) to identify how much power can be safely back-fed through the load side of the existing electrical panel. Of note, the 120% rule covers 2 out of about 6 ways that a load-side interconnection can be sized. While it is one of the more popular methods, there are situations where another of the 6 rules could be used, allowing you to exceed what would have been possible using the 120% rule.
Every service panel has a capacity limit, which is determined by the busbar rating and is measured in amperes (amps). If the current flowing through the panel exceeds the capacity rating, there is a chance that the busbars can melt, creating a fire hazard.
The NEC’s 120% rule says that the sum of the solar breaker and the main service panel breaker can be no more than 120% of the busbar rating. In other words, given that the main breaker matches the rating of the busbar (which is often the case), the solar breaker can be no more than 20% of the main electrical panel breaker rating.
For example, if your panel has a 200 amp busbar rating and a 200 amp main breaker, the 120% rule is calculated as follows:
In this scenario, the solar breaker can only be 40 amps, which is fine for most residential systems, but insufficient for most commercial solar arrays.
Exceeding the 120% rule is dangerous and neither the inspector nor the utility will allow your system to be connected to the grid in that way.
EPC 2.0 – A MODERN AND FLEXIBLE APPROACH TO COMMERCIAL SOLAR.
Different Rules May Apply
It’s important to note that there are still some commercial and industrial applications that adhere to the 100% rule established by the NEC in 2005.
Additionally, more recent editions of the NEC say that the solar breaker must be at least 125% of the system output. For example, if your solar inverter output is 32 amps:
In the scenario above, a 32 amp inverter would not cause the system to exceed the 120% rule. However, if the output of the inverter is 34 amps, you would need a 42.5 amp solar breaker (341.25), which would exceed the 120% rule.
Your solar provider will help you understand how the NEC rules apply to your situation.
Downsizing the Main Breaker
If your system will exceed the 120% rule, one solution is to downsize the main breaker. For example, if your main breaker is 175 amps versus 200, the equation looks like this:
The smaller main breaker means your connected solar system can safely output 65 amps of power. This could be a viable approach if your load, or the amount of power you need at once, doesn’t exceed 175 amps. If it does, you’ll be tripping circuit breakers which will be a nuisance.
Alternatively, your solar provider could replace your existing panel with a model that has a higher rating, though this can cost between 20,000 to 50,000 in a typical commercial building. Velo Solar can provide this upgrade service if needed.
Because of the current cost and availability of electrical equipment for commercial solar systems, line side taps are becoming increasingly common with large solar systems as a cheaper alternative.
Line Side Taps
With a line side tap, also called a supply side connection, the solar inverter is connected to a PV service fused disconnect and/or a solar only circuit breaker panel, which in turn is connected to a junction box. The junction box sits in between the main meter and the main service panel and houses the connections between the main breaker, the utility meter, and the solar system.
The PV service fused disconnect, sometimes called the fusible AC disconnect, is most commonly used when your solar array has a single large inverter. In the case of a multiple inverters, a PV panel and a fused disconnect are both used, as required by code and the utility.
The advantage to this approach is that it allows you to install a supply side connection that is limited only by the amperage of the existing panel. That means that if you have a panel rated for 200 amps, your line side tap connection can also be as much as 200 amps.
With this type of installation, the inverter is essentially wired into the system before the main panel. That means you can’t just flip a circuit breaker to interrupt the power coming into the building, making the installation more complicated.
As previously discussed, with a load side tap you can flip the main breaker, shutting off the power to the system and rendering it safe for the electricians as they make their connections.
The line side method requires your solar provider to work with the utility to disconnect your facility from the transformer (the typical connection point between your business and the grid) before the interconnection process can start.
This process, often called pulling the meter, prevents electricity from flowing to the electrical system, so that it’s safe to work on.
Understanding Rapid Shutdown Requirements for Solar
Most US states require solar energy systems to have Rapid shutdown devices. The remaining states will follow soon enough as they switch to more recent versions of the National Electrical Code (NEC).
But what exactly is the Rapid shutdown requirement and how do you stay compliant? This article will walk you through it.
What Is Solar Rapid Shutdown?
Solar Rapid shutdown devices enable rooftop solar systems to de-energize quickly in an emergency. Without them, there’s no safe way to turn a solar system off. Because even if the inverter is off, solar panels still generate power whenever the sun is shining.
So if there’s been an emergency, and you’ve called firefighters, there usually isn’t time to figure out how to deal with live solar conductors.
That’s why Rapid shutdowns became an electrical safety requirement in the National Electrical Code (NEC). The main purpose is to keep first responders safe from exposure to live electricity sources.
Differences Between NEC 2014 and NEC 2017
A new version of NEC code is released every 3 years. While the most recent one was released in 2020, 18 states still use NEC 2017. over, when it comes to Rapid shutdown requirements, there aren’t any significant differences between NEC 2017 and NEC 2020.
Rapid shutdown requirements first appeared in NEC 2014 and became more specific in NEC 2017. So let’s take a closer look at the differences between NEC 2014 and NEC 2017.
Rapid Shutdown Device Location
- NEC 2014: Makes no mention of the location of the device that starts the Rapid shutdown process.
- NEC 2017: Clarifies that the Rapid shutdown initiation device must be in a readily accessible location outside the building.
Distance From the Solar Array
- NEC 2014: PV conductors inside a building, more than 10 feet from the array or more than 5 feet long, must be shut down to 30 volts or less within 10 seconds of Rapid shutdown initiation.
- NEC 2017: PV conductors inside a building, more than 1 foot from the array or more than 3 feet long, must be brought down to 30 volts within 30 seconds. Conductors within the array must be brought down to 80 volts within 30 seconds.
Why Is Rapid Shutdown Required for Solar?
As mentioned, Rapid shutdown is required as a fire safety measure. In the unfortunate event of a fire, first responders typically get on the roof to access the upper floors and vent smoke out of the building.
If there’s sun, your PV array is generating voltage which could be dangerous to firefighters who need to FOCUS on putting out the fire without worrying about the potential dangers of high-voltage PV conductors. A Rapid shutdown system removes this danger with a single switch or button.
How to Meet the Solar Rapid Shutdown Requirements
The first step is to determine which version of the NEC code is enforced for solar installations in your city or county.
If it is NEC 2014 or higher, a Rapid shutdown system will be required. Then, the easiest way to meet Rapid shutdown requirements is to install a system that is already listed or field labeled with Rapid shutdown capabilities. For example, the SolarEdge system incorporates DC optimizers at every solar panel, while Enphase incorporates microinverters installed at every panel. These devices shut off the power around and within the solar array at the flip of a switch, so there is no need for additional equipment.
You still have options if you want to install a more traditional central inverter. For NEC 2014 compliance, include a Rapid shutdown device on the roof at the edge of the PV array and link it to the switch at ground level.
To meet NEC 2017 requirements, install module-level equipment to manage the Rapid shutdown at each solar panel. Remember, you need to install it at the same time as the solar panels.
Install a NEC-Compliant Solar System
When in doubt, reach out to our experts to ensure that your solar installation will comply with Rapid shutdown requirements. They will walk you through the whole process of choosing the right equipment for your project and ensuring your solar energy system complies with NEC.