NEC 2017 Primer for Solar Installers: Manufacturers explain how their products meet the updated code

NEC 2017

Jan. 1, 2019, is almost upon us, which means the National Electric Code (NEC) 2017 is almost in effect. Not all jurisdictions will be up to speed (hell, some aren’t even up on NEC 2014 yet), but around 24 states will require compliance immediately. We asked a variety of manufacturers about their NEC 2017-ready products, how they work and any advice they have for solar installers to meet the new code.

This section is from our Nov/Dec issue of Solar Builder magazine. Subscribe for free right here.

Code to know

690.12 Rapid Shutdown of PV Systems on Buildings

PV system circuits installed on or in buildings shall include a rapid shutdown function to reduce shock hazard for emergency responders in accordance with 690.12(A) through (D).

(A) Controlled Conductors. Requirements for controlled conductors shall apply to PV circuits supplied by the PV system.

(B) Controlled Limits. The use of the term, array boundary, in this section is defined as 305 mm (1 ft) from the array in all directions. Controlled conductors outside the array boundary shall comply with 690.12(B)(1) and inside the array boundary shall comply with 690.12(B)(2).

1. Outside the Array Boundary. Controlled conductors located outside the boundary or more than 1 m (3 ft) from the point of entry inside a building shall be limited to not more than 30 volts within 30 seconds of rapid shutdown initiation. Voltage shall be measured between any two conductors and between any conductor and ground.

2. Inside the Array Boundary. The PV system shall comply with one of the following:

(1) The PV array shall be listed or field labeled as a rapid shutdown PV array. Such a PV array shall be installed and used in accordance with the instructions included with the rapid shutdown PV array listing and labeling or field labeling.

(2) Controlled conductors located inside the boundary or not more than 1 m (3 ft) from the point of penetration of the surface of the building shall be limited to not more than 80 volts within 30 seconds of rapid shutdown initiation. Voltage shall be measured between any two conductors and between any conductor and ground.

Know your signs

solaredge

SolarEdge’s SafeDC technology is embedded in its DC optimized solution and as such meets NEC 2017 without any additional components. The existing PV system AC disconnect is used as the initiator. Whenever the inverter or grid is turned off (i.e. AC power), then the DC voltage and current fall below the NEC 2017 thresholds within 30 seconds — each power optimizer is responsible for lowering its output voltage to 1 volt during rapid shutdown activation. This happens both in and outside the array boundary.

“New signs are required to inform emergency responders of the equipment meeting NEC 2017. NEC 2017 requires that equipment used as rapid shutdown devices be listed for rapid shutdown and evaluated according to stringent standards. Installers should check to ensure all equipment is properly listed. For example, inverters and combiners that are used inside or outside the array boundary as rapid shutdown devices must be listed for rapid shutdown in the event that they are used for that purpose,” says Lior Handelsman, founder, VP of marketing for SolarEdge.

HellermannTyton Don’t skimp on labels

HellermannTyton offers a line of NEC 2017 code compliant labels that have been tested to actual real-world conditions for over seven years and through accelerated aging tests, which show the labels will survive decades of exposure [see example of one that did not on the right]. Because of the extensive testing of these solar-compliant labels, HellermannTyton offers a seven-year warranty on all adhesive labels that include the HT check mark and a 25-year warranty on any aluminum labels.

“Many municipalities are very concerned about label life. In this age of OSHA and ANSI compliance, there is increased liability on installers and inspection services. If a label only remains visible for a few years, and if someone gets injured or killed in the process of interacting with the equipment, there can be substantial fines or costly litigation that can affect on-going business,” says Todd Fries, product category manager – identification for HellermannTyton.

Watch for SunSpec certification

sunspec

If you’re unfamiliar with the SunSpec Alliance, it’s time you became familiar. This trade alliance of more than 100 solar and storage stakeholders has been working on information standards for plug-and-play PV system interoperability, but its communication solution for meeting module-level power control and safety (rapid shutdown) with any panel and inverter combination might be its crowning achievement. Look for the logo to the left to find products certified to the SunSpec RSD Specification. Here’s a list of early adopter companies involved in the collaboration and rollout.

• ABB
• Adesto Technologies
• Canadian Solar
• Celestica Inc.
• Chint Power Systems –
North America
• Delta Products
• Enphase Energy
• ER Solar
• Fronius International
• Ginlong-Solis
• Hansol Technics Co.
• HiQ Solar
• Itek Energy
• Ingeteam
• JA Solar
• LERRI Solar Technology
• Maxim Integrated
• Mersen Electrical Power
• Midnite Solar
• Neo Solar Power
• Omron Global
• OutBack Power
• Phoenix Contact
• SMA
• Samil Power
• Seraphim Solar USA
• Semitech Semiconductor
• Silfab Solar
• Solartec
• ST Micro
• Sungrow
• SunPower
• Sunrun
• Sunpreme
• Suntech Power
• Talesun Tesla
• Texas Instruments
• Tigo Energy
• UL LLC
• Yaskawa Solectrica
• Yingli Solar

sunspec

This is a diagram of how the SunSpec Communication signal for module-level rapid shutdown works.

froniusCompliance doesn’t mean cost

“It is important to know what the actual requirement is and then getting to code compliance in the simplest, most cost-effective way to not put extra financial burden on the customer. We believe that industry standards and innovation will drive down cost and allow customer choice,” says Richard Baldinger, head of marketing for Fronius.

The Fronius Symo Advanced three-phase inverter combines the benefits of the Fronius Symo with the convenience of an open industry standard. Featuring 10 models ranging from 10 kW to 24 kW, the Fronius Symo Advanced meets NEC 2017 compliance in conjunction with the Tigo TS4-F cover via the integrated Power Line Communication (PLC) transmitter that uses the SunSpec communication signal for rapid shutdown. This eliminates the need for any additional communication hardware and provides the most cost-effective option for code compliance.

tigoTigo Energy’s TS4-F (Fire Safety) is a UL-certified multivendor rapid shutdown solution for commercial PV systems that complies with NEC 2017. The TS4-R-F is a simple add-on that retrofits a regular standard solar module with a module-level rapid shutdown device and is compatible with the power line-based SunSpec communication signal for rapid shutdown. Using the existing DC wires between the inverter and module-level electronics as a communication channel significantly reduces installation time.

midnite solarMidnite Solar’s MNLSOB line, in both 600-volt and 1,000-volt models, utilize one transmitter and multiple receivers per system. This product can be used for string or module-level shutdown by using one receiver per string or one per module. They plug directly into the MC4 connectors on your module and, because the MNLSOB transmitter induces a PLC signal into the PV Positive line, there is no additional or new wiring to be done between the transmitter and the receivers. Midnite Solar will be introducing a new SunSpec-compliant MNLSOB by January.

Make no compromises

“There are no additional design requirements to implement shutdown functionality. A designer can build a project for maximum energy harvest, optimal ROI, or with any other goal in mind and simply choose the most cost-effective MLPE to address his or her needs. The shutdown functionality is built into these solutions and does not impact other project considerations. Installers should also be aware of the upcoming release of UL Standard 3741 as another way to comply with NEC 201 690.12 without requiring module-level shutdown by using equipment listed as ‘PV Hazard Control Arrays,’” says Brad Dore, director of marketing for SMA America.

SMA’s Sunny Tripower CORE1 meets the shutdown requirements of NEC 690.12 when paired with a TS4-R-F module-level device. The inverter and MLPE retrofit unit operate on the new SunSpec Power Line Communication (PLC) signal for module-level rapid shutdown. This solution is the most cost-effective way to achieve module-level shutdown. The solution operates on a simple “stay alive” signal broadcast from the inverter over the existing DC wires. The TS4-R-F units will operate while AC power is present, and if AC power is cut via the AC disconnect, the MLPEs lose the “stay alive” signal and de-energize in accordance with code.

Streamline to ground

Section 690.43 states that “Exposed noncurrent-carrying metal parts of PV module frames, electrical equipment, and conductor enclosures of PV systems shall be grounded in accordance with 250.134 or 250.136(A), regardless of voltage.”

brilliant rack

Brilliant Rack racking systems feature mounting connections with serrated bolts that ensure the most effective metal-to-metal contact for proper bonding connections. These connections are essential for dispersing any electrical charge, providing multiple pathways to soil in compliance with Section 250.92 B. This reduces the danger of equipment damage or human injury should the rack become electrically charged through equipment malfunction, human error or lightning strike. Independent testing has demonstrated Brilliant Rack systems are capable of dispersing higher currents through the system into soil, and that the serrated bolt and nut are likely to maintain this connection better over a long period of time than WEEB clips.

sunmodo

SunModo’s ground lug, self-bonding clamps and self-bonding rail splices meet the requirements found in NEC 2017. The basis of the self-bonding system is its patented stainless-steel floating bonding pin, which is designed to be captive in the mounting components and provides a bonding path from the PV panel frames to the rails and rail splices and finally to the ground lug. The Ground Lug is compliant with both UL 467 and the equipment grounding requirements 690.43. The self-bonding system is for use with PV modules that have a maximum series fuse rating of 30A.

 

 

Rooftop Adder Table removed

quick mount pv

“The Rooftop Adder Table that has affected the ampacity calculations for conductors that are run at a specified distance above a rooftop has been deleted. This table generally hasn’t been well accepted by electrical personnel since its addition to the NEC several years ago. Because of the deletion, if raceways are kept at least 7/8 of an inch above the rooftop, there should no longer be a need for upsizing conductors and increasing costs,” says Randy Barnett, safety compliance professional for the NFPA.

Quick Mount PV has two NEC 2017-ready products in its classic conduit mount and conduit mount for tile. When used in conjunction with a standard off-the-shelf conduit hanger, the conduit is raised in excess of the minimum 7/8-in. off the roof surface, which is new in NEC 2017. These mounts are designed to lift electrical conduit off the roof to protect wiring from overheating. These mounts use Quick Mount’s proprietary waterproofing technology to seal the roof penetrations, and aluminum and stainless steel parts are used to secure the electrical conduit for the life of the system.

— Solar Builder magazine

Market Driver: When augers, ground screws make economic sense for solar contractors

 

auger-ground-screw

The use of augers and ground screws has been of interest in mounting solar systems for some time, and for the right size job, they offer smaller solar contractors an opportunity to grow their business.

Small site factors

For one, with smaller PV systems, one may not need to spend money on a soil engineering analysis and the cost to permit the design separately. The typical soil type in an area may be known from experience. Perhaps local experience with other construction such as a home foundation or a water line installation can provide clues to the soil type.

A method used by some contractors is to use a hammer drill and ground rod available from an electric supply store and see how easily the rod can be driven into the earth. If the rod hits solid rock 6 inches below the surface, or if the rod is very hard to drive, this could either disqualify the use of ground driven foundations, or in some cases lead to using ground screws rather than augers.

Additionally, many counties and states have published maps showing the soil types for many locations. Other sources of data are well sites where there is often a record by the foot of the surface to depths much greater than one would drive a ground-mount.

Selecting a ground-mount

Once a determination has been made as to the type of soil at a site, the installer should select a ground mount to use at a site. If the soil type is not heavily compacted and not rocky, one can consider the use of augers. Most typically, a ground auger driven 7 to 10 ft. will suffice for most 3- and 4-row landscape arrays.

If the ground is compacted, made up of heavy clay, or has small rocks within the first 10 ft., then a ground screw would probably be a better choice. Ground screws offer lower torque when driving them into the soil and are less likely to break in harder ground. However, in soft, loamy soils a ground screw will not provide big pullout values compared to an auger.

If the ground is too rocky, other options such as post and concrete, ballasted arrays, or rock anchors may be a better alternative. Experience with ground arrays will greatly help in the selection of a ground mounting system.

Driving ground mounts

Some form of tractor or track machine is required to drive ground-driven foundations. These machines are easy to rent and use, and depending on the volume you are doing, worth owning. Small arrays with only 8 or 12 posts are probably not worth the investment, but between that and larger arrays that require a specialized company to drive the mounts, there is a sweet spot that makes financial sense.

The machine used will need some form of rotary head such as the small Bobcats used to dig holes for pole buildings and fence posts. Alternately, some farm tractors have a rear-mounted rotary

driver used for fence posts that may be used.
Most equipment rental yards can supply a small track machine normally used with a hole-digging auger. With the hole-digging auger removed, an adaptor can be used to mate the drive head to fit augers and ground screws. A 2 in. hex adaptor that fits the machine can be purchased by the installer if not available from the equipment rental yard with the machine.

The amount of torque required to drive a ground mount should not be more than a nominal 3,000 lbs. If more torque is required, or if the mounts are breaking, than the wrong mount was selected. If augers break, a ground screw should have been used. If ground screws break, then a non-driven mount should be used.

If occasionally a mount breaks due to an undetected boulder or other issue, a traditional post and concrete mounting should be used. In the case of Groundwater, a 50-kW project in Portland, Ore., where over 400 augers were used, eight anchors broke due to large sporadic rocks and were replaced with eight concrete-mounted posts.

Calculations and measurements

There are many resources available covering the use and calculations for commercial construction using augers and ground screws. These include Chance Hubble manuals, and other commercial suppliers of augers. However, there are some general guidelines one can follow summarized below.

Augers have a pitch determined by the blade angle. Our auger is a 10-to-1 auger. Using a 10-to-1 auger, each ft lb of torque driving the auger provides approximately 10 times the uplift capability when driven to 10 ft of depth. For example, if an auger is driven with 500 lbs of torque to 10 ft. the pullout will be approximately 5,000 pounds. Typically, augers are driven much harder, resulting in tested pullup values of 20,000 to 30,000 lbs. Most often, augers driven in reasonable soil values will dramatically exceed the pullout values actually required to resist pullout or overturn of the array.

In the case of ground screws, they are typically applied to more dense soils and solids with rock intermixed. A ground screw should not be used in solid rock.
Ground screws in hard soils have pullout values of 1,500 to 5,000 lbs at a depth of 5 ft., however this estimate is entirely based upon the soil density. The use of ground screws in soft soils will not provide a satisfactory base for a solar array.

The use of a torque measurement gauge is recommended as an additional check on the drive torque and resulting pullout capability. Some modern machines one can rent or buy have a built-in torque gauge. Additionally, there are devices that can mount between the hydraulic head and the ground mount to measure the torque. However, a careful operator will have some sense of the amount of effort required to drive the ground mounts, and in most cases can successfully install and drive ground arrays without a torque head.

Cliff Schrock is an engineering consultant with SunModo.

 


On the Scene

Ready to rack

AP Alternatives’ Ready Rack mounting hardware is designed for both large utility-scale projects and small commercial projects. The small helical anchors and quick-install cross bracing make the simple system robust even for high wind zones. The mini-tilt brackets are adjustable and allow for quick field alignment of the post height. This allows the anchor posts to be installed rapidly and any terrain variation can be accounted for by simply adjusting the tilt bracket up or down to achieve the best aesthetics on an ungraded site. This system is nimbly installed with an attachment that fits on a skid steer.

— Solar Builder magazine

When augers, ground screws make economic sense for solar contractors

SunModo solar auger

A small Bobcat 331 being used to drive a 10 ft auger using the technique of advancing upon the auger to vertical as it is driven.

The use of augers and ground screws has been of interest in mounting solar systems for some time, and for the right sized job, they offer smaller solar contractors an opportunity to grow their business.

Ground conditions

For one, with smaller PV systems one may not need to spend money on a soil engineering analysis and the cost to permit the design separately. The typical soil type in an area may be known from experience. Perhaps local experience with other construction such as a home foundation or a water line installation can provide clues to the soil type.

A method used by some contractors is to use a hammer drill and ground rod available from an electric supply store and see how easily the rod can be driven into the earth. If the rod hits solid rock 6 inches below the surface, or if the rod is very hard to drive, this could either disqualify the use of ground driven foundations. In some cases this could lead to using ground screws rather than an augers. Additionally, many counties and states have published maps showing the soil types for many locations. Other sources of data are well sites where there is often a record by the foot of the surface to depths much greater than one would drive a ground driven mount.

Selecting a ground mount

Once a determination has been made as to the type of soil at a site, the installer should select a ground mount to use at a site. If the soil type is not heavily compacted and not rocky, one can consider the use of augers. Most typically, a ground auger driven 7 to 10 ft. will suffice for most 3 and 4 row landscape arrays.

If the ground is compacted, made up of heavy clay, or has small rocks within the first 10 ft., then a ground screw would probably be a better choice. Ground screws offer lower torque when driving them into the soil and are less likely to break in harder ground. However, in soft, loamy soils a ground screw will not provide big pullout values compared to an auger.

If the ground is too rocky, other options such as post and concrete, ballasted arrays, or rock anchors may be a better alternative. Experience with ground arrays will greatly help in the selection of a ground mounting system.

SunModo augers

Auger being driven at Groundwater site with Bobcat 337

Driving ground mounts

Some form of tractor or track machine is required to drive ground driven foundations. These machines are easy to rent and use, and depending on the volume you are doing, worth owning. Small arrays with only 8 or 12 posts are probably not worth the investment, but between that and larger arrays that require a specialized company drive the mounts, there is a sweet spot that makes financial sense.

The machine used will need some form of rotary head such as the small Bobcats used to dig holes for pole buildings and fence posts. Alternately, some farm tractors have a rear mounted rotary driver used for fence posts that may be used.

Most equipment rental yards can supply a small track machine normally used with a hole digging auger. With the hole digging auger removed, an adaptor can be used to mate the drive head to fit augers and ground screws. A 2 inch to hex adaptor that fits the machine can be purchased by the installer if not available from the equipment rental yard with the machine.

Figure 4 – Drive adaptor to convert from hydraulic head on rental machine to 2 inch ground mount.

The amount of torque required to drive a ground mount should not be more than a nominal 3000 pounds. If more torque is required, or if the mounts are breaking, than the wrong mount was selected. If augers break, a ground screw should have been used. If ground screws break, then a non-driven mount should be used.

If occasionally a mount breaks due to an undetected boulder or other issue, a traditional post and concrete mounting should be used. In the case of Groundwater a 50 kW project in Portland Oregon, where over 400 augers were used, 8 anchors broke due to large sporadic rocks and were replaced with 8 post and concrete mounted posts.

Auger and Ground Screw Guidelines

This post is an excerpt of this full guideline from SunModo, which clears up the confusion surrounding the use of augers and ground screws. To view the entire white paper, enter the info below.

Calculations and measurements

There are many resources available covering the use and calculations for commercial construction using augers and ground screws. These include Chance Hubble manuals, and other commercial suppliers of augers. However, there are some general guidelines one can follow summarized below.

Augers have a pitch determined by the blade angle. Our auger is a 10 to 1 auger. Using a 10 to 1 auger, each ft. lb. of torque driving the auger provides approximately 10 times the uplift capability when driven to 10 ft of depth. For example, if an auger is driven with 500 pounds of torque to 10 ft. the pullout will be approximately 5000 pounds. Typically augers are driven much harder, resulting in tested pullup values of 20,000 to 30,000 lbs. Most often, augers driven in reasonable soil values will dramatically exceed the pullout values actually required to resist pullout or overturn of the array.

In the case of ground screws, they are typically applied to more dense soils and solids with rock intermixed. A ground screw should not be used in solid rock.

Ground screws in hard soils have pullout values of 1500 to 5000 pounds at a depth of 5 ft., however this estimate is entirely based upon the soil density. The use of ground screws in soft soils will not provide a satisfactory base for a solar array.

The use of a torque measurement gauge is recommended as an additional check on the drive torque and resulting pullout capability. Some modern machines one can rent or buy have a built-in torque gauge. Additionally, there are devices that can mount between the hydraulic head and the ground mount to measure the torque. However, a careful operator will have some sense of the amount of effort required to drive the ground mounts and in most cases can successfully install and driven ground array without a torque head.

Cliff Schrock is an engineering consultant with SunModo.

— Solar Builder magazine

Four energy dense solar mounting systems for C&I rooftops

SunModo SunBeam

sunmodo

As a permanent part of the building and roof structure, the SunBeam system eliminates any abrasions, moss build up and need of system removal for roof repair or re-roofing. In addition, it provides shading of HVAC equipment, increasing efficiency and faster temperature response. Twenty-year warranty.

Material: High-grade aluminum and 304 stainless steel hardware. Anchor-only attachment.

How it maximizes energy density: The SunBeam system elevates above obstructions such as HVAC, pipes and vents. By spanning over roof obstructions such as HVAC, pipes and vents, the system takes full advantage of the available roof surface thereby maximizing the PV system size. The system can be easily adjusted to account for the multiple roof pitches on site.

Everest Solar D Dome R²

everest

The D Dome R² system is an east/west commercial flat roof solution. The third generation of this product is now rail-less with only five major components and minimal hardware. It sits at a fixed 10-degree pitch and allows for 3.5-in. inter-row spacing. Twenty-year warranty.

Material: Aluminum, ballast with attachment optional. The ballast blocks sit under the panels.

How it maximizes energy density: Everest Solar Systems believes east/west systems are more efficient south of the tropic of cancer. First, an east/west system practically eliminates inter-row spacing which allows more modules on the roof, thus increasing module density. On one internal study, Everest compared a the production of a 10-degree south-facing system with its east/west system in southern California at different azimuths. The south-facing fit 88 modules and had a 14 percent decrease in at the 225-degree azimuth. The D Dome R² system reached 108 modules in the same space and had less than 0.1 percent change between all azimuth angles.

Solar Mounting Solutions

sms

SMS Racking consists of only three major parts that arrive with all hardware pre-inserted allowing for quick single tool installation. The THRU-ITT integrated wire management system allows wiring to remain organized and protected by running wires east-west and north-south internally. Since this racking design does not rely on the panel for integrity, installers can complete racking and wire installation independent of the panel. Twenty-year warranty.

Material: G90 coated steel and optional galvanized steel, aluminum, powder-coated. Ballast only.

How it maximizes energy density: SMS developed an Excel spreadsheet that determines the optimum row-to-row spacing based on the selected solar module, optimum tilt angle, solar azimuth angle, and the altitude angle all specific to install location. By optimizing the length of row-to-row spacers, the SMS system can greatly reduce the amount of redundant material, which in turn will reduce racking cost and avoid installing the modules in a high shadow region. The racks are designed with minimal distance between modules in the east/west direction to eliminate unused area.

Ecolibrium EcoFoot5D and EcoFoot2+

ecolibrium

EcoFoot5D 5-Degree and EcoFoot2+ 10-Degree speed installation and simplify logistics for flat-roof installs. Main components are: a base, pre-assembled clamps (integrated bonding without washers) and a wind deflector. The system is black, ASA-PC, UL Listed Resin with a 25-year warranty mounted with ballast, attachments or a mix.

How it maximizes energy density: EcoFoot5D 5-Degree delivers 18.4 percent more power than the 10-degree system and lowers cost per watt. The system maximizes roof density while maintaining the ease and simplicity of EcoFoot. The modular base is small at 7 in. x 16.7 in., and inter-row spacing is a dense 9.9 in., creating a tightly packed array. Stackable bases enable up to 290 kW per pallet, resulting in fewer pallets and minimized shipping, storage and onsite crane use.

— Solar Builder magazine

Degrees of Separation: How to mount commercial rooftop PV systems to maximize energy

Ecolibrium EcoFoot system

Ecolibrium EcoFoot system

On commercial rooftops, design trends are all about maximizing energy density. Module selection is a huge factor there, but so are the layout and tilt decisions — figuring out the perfect shape and tilt to mount as many modules as possible without compromising their performance.

Pairing the right racking system with a flat-roof space opens up a world of possible equations. Use a racking system that will position the panels to maximize the energy output, which includes the tilt angle, inter-row spacing and the direction the panels will face. As always, geography matters. For one, the roof’s azimuth, or the direction the pitch faces. For a perfect south-facing system, the azimuth should be 180.

But new systems are tweaking the traditional. East/west systems are becoming popular below the tropic of cancer. Designers are playing more with tilt angles, with the general trend moving toward 5-degree tilt — likely to reduce inter-row shading without compromising the number of modules used or resulting in too much soiling.

“Rooftop energy density is maximized by fitting more panels on the roof using a 5-degree racking system,” said Jonah Coles, product solutions manager, Ecolibrium Solar. “The key to fitting more panels on the roof is to use racking with a small footprint and narrow inter-row spacing. The combination packs in panels, yet the inter-row spacing is wide enough to allow for the working room needed for ease of installation and post-installation maintenance.”

RELATED: Why energy density matters — and three ways to maximize it

But the tilt decision isn’t one-size-fits all. Everest Solar Systems notes tilt angle efficiency correlates to latitude — the higher the latitude often requires a higher tilt. The latitude in Hawaii, for instance, allows a system to be virtually flat, but there needs to be enough tilt to keep the rain from pooling and to keep dust off the modules. Brandon Gwinner, regional sales manager, SunModo, puts that minimum at a 4-degree tilt.

SunModo Sunbeam

“The tilt degree is dependent on the region/location and optimum output based on TSRF,” he says. “The minimal tilt degree racking systems are typically to maximize the number of modules you can get on a roof without your rear post being 8 ft off the roof and to get the most energy density/power density per the project.”

There are also some wind/snow load considerations that can keep tilt below a certain height/tilt degree, as well as parapet walls and billowing of wind. The installer has to find the balance between production and engineering capabilities.

Also, installers looking to maximize production in summer months should consider using lower tilt angles than installers looking to maximize production in winter months. In snowy northern climates, Everest Solar recommends a 10-degree system tilt angle, which is better for shedding snow, plus the wider inter-row spacing allows more room for snow to land without piling up and casting a shadow or covering the modules.

“If you can hit your power goal with a 10-degree system, then 10-degree would be the system of choice. If not, 5-degree racking can enable a successful system when 10-degree wouldn’t fit enough panels to generate enough power,” Coles said.

Commercial installations have significantly more requirements than residential installations, so understanding jurisdictional requirements at the onset of the project will make the process go smoothly. Some states, like Oregon, do not require extra engineering when the tilt is under 18 in. on the back edge of the array, based on a prescriptive path. So, cost analysis vs. ease of permitting is a factor for tilt decisions too.

The inter-row spacing issue

Tilted PV panels cast shadows on the rows of modules behind them, necessitating a gap between rows to minimize the effects of production loss due to shadows cast on panels in anterior module rows. Here are a few ideas to mitigate the impact of this phenomenon on your PV installation via Peter Abou Chacra, engineering consultant, SunModo.

  • Reduce the tilt of your south-facing array. For peak energy production on a per-module basis, PV modules have an ideal incident angle with solar rays emanating from the sun. For some installations, however, it may make sense to reduce the tilt of the modules to a less optimal incident angle. Though this means less production on a per module-basis, it can mean a significant increase in the daily unshaded collection time for the array. This gain in effective collection time can offset the losses caused by a sub-optimal tilt for the module itself. Using software dedicated to modeling and analyzing a system’s performance at a different tilt angle and inter-row spacing should figure out the best path.
  • Locate your system on a south-facing slope. Even a five-degree inclination can have a marked impact on the amount of inter-row spacing required. This can significantly increase the number of modules you can fit in a given area.
  • Consider 3-in-landscape or 4-in-landscape monoslope installations. Coupled with a low tilt, this strategy can reduce inter-row spacing significantly on a given installation since modules on the same structure and slope don’t require significant spacing between them. This can be particularly effective if you can gradually elevate the anterior monoslope PV structures as you work your way north through the site.

— Solar Builder magazine