# Ground-Mounted PV



## ricielectric (8 مايو 2010)

MEETING PROJECT GOALS ​The typical PV system’s purpose is to produce the most favorable return on investment, given the constraints of the site. The goals for a specific project, however, should be carefully defined with the owner. Does the owner want to maximize ROI according to time-of-delivery factors per the utility rate schedule? Is there a maximum capacity that is dictated by the utility or other regulatory restrictions that may limit the total size of the project? Are there transmission capacity issues? Energy production estimates are important for any PV system and should be delivered to the owner in the proposal stage of the project to aide in this process. In addition, will aesthetic considerations drive the design of the project? How will other parts of the property or adjacent properties be affected? These considerations are all part of the goal setting process for successful projects.
*Road construction* Road fabric and road base material are used to create access corridors for equipment prior to the start of major construction at this Sunsense Solar ground-mounted installation in Carbondale, CO.*




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*INITIAL SITING ISSUES AND OPTIMIZATION*
If you are siting a ground-mounted system, you need to consider several factors, starting with those most important to the project’s success.
*Plot.* First, identify the property lines. Does the jurisdiction require setbacks from the edge of the property? The envelope allowed for development must be defined early in the process. Ideally, existing drawings done by a surveyor are available through the property owner or available at the local building department. If you must go to the building department, it is probably worth stopping by the planning department to discuss setback requirements, easements or other issues that govern the construction of a ground-mounted solar installation at the site. The building department may have underground utility maps. In addition, it is wise to utilize local “Call Before You Dig” services to have underground utilities identi- fied and marked.
*Civil engineering. *It is important to understand the civil site work necessary for a project early in the process. For example, ground-mounted systems may be subject to storm water runoff mitigation and other environmental reviews that are not typical for roof-mounted systems. If the site must be graded or leveled or if water runoff must be contained in catch-basins, it is important to identify these issues and understand local ordinances and restrictions. Engaging a civil engineer in this effort is advisable on larger systems. Note that permitting and civil construction costs are other factors to consider when designing a ground-mounted system. Understanding these costs upfront may be more difficult with a ground-mounted system than a roof-mounted system. The better the civil site work is defined, however, the better the permitting and construction budgets can be defined.
*Site access. *Access around the site is a big consideration for construction and maintenance. Usually construction machinery needs to move around, and adequate space and pathways are needed to allow the work to flow efficiently. Planning the system for efficient use of labor is important on systems of any size but absolutely crucial on large systems. Mud can be a concern in any construction site during wet times of the year and can also hinder maintenance. A large array should have some well-placed major corridors that allow large construction machinery to enter the site and maneuver as needed. In some cases, it may be necessary to provide enough room for construction machinery traffic both coming and going. Major corridors should be paved with gravel at a minimum.
*Point of common connection.* You should determine the location of the point of interconnection on the property and whether there are capacity constraints on the electrical system. If the point of interconnection is on one corner of the property, does it make sense for the inverter(s) to be located near it, or is it more advantageous to run inverter output-circuits to this location? The answer depends on factors such as the voltage drop difference between the ac and dc parts of the system, inverter accessibility, construction costs and maintenance considerations. Generally, on very large systems more than 100,000 square feet, inverters are located within the array field to reduce voltage drop on the dc side. Many larger systems with central inverters are configured to go direct to medium voltage with a transformer that steps the ac side up to 12.4 kV or higher. It is good practice to plan ahead and locate the electrical system’s major arteries so they are easy to lay out, and to provide a simplified route to the point of interconnection.
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Transmission study.* If the project is a typical net-metered system, determining the size of existing switchgear and service type is no different from any other PV system. The difference comes with systems that are owned by a utility or selling energy directly to the utility through a power purchase agreement. The project developer or owner often does this due diligence prior to the system designer’s involvement, but sometimes the designer is asked to do this task. A transmission study may be necessary for large systems, but that is beyond the scope of this article.
*Performance optimization.* In addition to broad siting concerns, energy generation optimization should be considered early in the project. You need basic optimization studies to determine tilt angle and row spacing for the array. Pay close attention to the trade-off between higher tilt angles, closer to latitude, that might allow for greater yearly energy harvest and the additional space required between rows to minimize self-shading.
Analyses done by many in the industry over time have generally indicated that latitude minus 10°–15° is a good compromise tilt angle in a multiple-row fixed-tilt ground-mounted system. Most systems are designed to allow some self-shading loss between rows in the heart of the winter— typically between 1% and 3% of yearly production. The additional space required to eliminate row shading is not usually practical. One rule of thumb for row spacing is to complete a sun elevation calculation for December 22 and allow 1–3 hours around solar noon before shade reaches the bottom edge of the active collector surface. One option for achieving this is to undertake a careful study with a shading analysis tool, like a Solar Pathfinder or Solmetric SunEye, using an object placed to the south of the tool in the general location of the array. Software programs, 
like PVSyst or PV*SOL Expert, make in-depth shade studies possible.   
System designers who want to get more sophisticated in this regard may also consider the bypass diode operation of the module under shaded conditions and set up the stringing of the circuits to reduce system losses. For example, if possible, string the source circuits so that the shading of the lower 30%–50% of the bottom module reduces system voltage in a way that still allows the inverter to power point track. This may allow the system to harvest a little bit more energy per year. It is also worth considering time-of-delivery factors in terms of the electric rate schedule that the site is metered under to allow the owner optimal return on investment. Certain rate schedules incentivize energy delivery at high-demand times of the day or year. Designing a system to take advantage of these higher rates influences the angle and orientation of the array. If summer afternoon production is highly incentivized, for example, the system may deliver a better return on investment with a lower tilt angle and orientation more to the west. Many production modeling software programs offer performance analysis and optimization tools. (See “Production Modeling for Grid-Tied PV Systems,” April/May 2010, SolarPro magazine.)
*ADDITIONAL SITING ISSUES*
Once initial siting and optimization studies are complete, additional siting issues become important considerations, including security; wind zone, snow zone and seismic zone classifications; and soil properties.
*Security.* A ground-mounted PV system is generally quite easy to see and access. Unfortunately, this makes it an appealing target to thieves. A system that is less visible presents less of a target; every opportunity should be taken to obscure the system from the casual passer-by. However, only so much can be done to hide a solar system in the middle of a big field. System owners should be made aware of the potential for theft early in the development to allow them to be part of the solution and prepare for the expense that this may entail. A fence is a good place to start. Not only is it helpful to prevent theft, but also safety concerns and code requirements make a fence a veritable must-have for ground-mounted systems.
Large-scale systems may employ a network of cameras, sensors and lights—and sometimes a security patrol. Smaller systems often cannot justify this added expense. If you think that a system location requires more protection than a fence can offer, you can consider using tamper-proof and proprietary-driver fastener systems that make disassembling the system challenging. For example, mounting-system manufacturer Schletter sells specifically sized steel spheres that can be driven into the cavities of socket-head hex bolts used for module clamping to make the modules very difficult to remove. The flip side of this is the added difficulty involved in removing modules for legitimate reasons. Proprietary-driver fasteners allow the contractor to service the array without allowing wrench-wielding thieves access.
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**Wind, snow and seismic zones.* Factors such as environmental loads and weather conditions in the project area, including wind and snow, determine the system’s structural design. Chapter 16 of the _International Building Code (IBC)_ defines loads as they pertain to structural designs. Note that some areas have special design considerations. In general, wind loads tend to govern the structural design of a solar project, but wind loads are not the only loads that should be considered. Check with the local building department to ensure that the wind, snow and seismic zones in the area are consistent with the engineer’s assumptions.
Dave Helmich, principal at D/PM Engineering, advises: “In the US, the model codes prescribe various load combinations that must be considered in every analysis and design. Depending on which system you use in the _IBC_, there are seven or eight of these combinations. Not all of the combinations are relevant to the design of a mounting rack. For example, live loads, earth pressure and crane loads are not involved. As a practical matter, this normally involves dead load, wind load, seismic and snow loads. Ice loads must be considered similarly to dead loads where applicable, and the designer should consider both positive and negative pressure loads.”
Consult with the module manufacturer for any special requirements for mounting in locations with snow and ice. In general, avoid situations where snow is allowed to pile up on top of a module. In areas with significant amounts of snow, the array height should be high enough that the expected highest snow level does not reach the bottom edge of the lowest module. If you are designing a system in a high-snow area, you may want to specify an array with higher tilt angles to facilitate easier snow shedding. Some PV modules have higher load ratings and can withstand high snow loads. Also be aware that most module frames have drain holes that are intended to allow water to flow freely through the frame and out. If the racking design obstructs these drain holes, water may collect and freeze, possibly damaging the module.
*Soil properties. *The greatest variable in a ground-mounted system is likely the cost of the foundation. This is greatly affected by soil conditions, which must be assessed to determine foundation design and depth. Subsurface conditions are crucial to any foundation that requires driving or excavation of the soil. The bearing pressure characteristics of the soil, significant presence of rocks and soil corrosivity are all important factors that affect foundation design and cost. It is therefore useful to do some preliminary research at the site. If you are preparing to work on a ground-mounted system, you may also want to review Chapter 18 of the _IBC_ to brush up on some of the design criteria applicable to foundations.
An existing geotechnical report on your site is always preferable, but many times this is not available. The local building department may have some prior classifications of soils in the area. Consulting with a civil engineer or geotechnical engineer familiar with the region may also be helpful in understanding local soil conditions. Similarly, a geotechnical engineer may be able to provide a preliminary reconnaissance assessment. D/PM Engineering’s Helmich explains: “For very preliminary assessments, the _International Building Code_ and its predecessor codes contain a helpful table. Table 1806.2 puts soil materials in one of five classifications, ranging from clay and clayey material to crystalline bedrock. Where building officials deem there to be special problems, they can require a detailed geotechnical report based on sampling to more precisely characterize materials.”
If you are a contractor submitting a proposal on a groundmounted PV project, it is wise to have a clause in the contract that protects you against unforeseen subsurface conditions like rocks or subsurface water. On larger sites, a geotechnical study is usually necessary. When used in conjunction with good design engineering, this reduces the overall foundation cost by reducing uncertainty and allows you to limit the foundation size to what is necessary given the soil conditions. “Where there is great variation or known problem soils, it is good practice to secure a full geotechnical report on any size project,” says Helmich. “For smaller projects, a better approach may be to utilize _Code_ default values. The _IBC_ is deemed conservative, and this conservative assessment may cost less in construction than the added cost of a geotechnical investigation.” Contractors should work with owners in the early stages of a project on when and how soil classification is accomplished so that uncertainty about soil conditions does not become a problem during construction. “Remember,” Helmich adds, “that soils have tremendous variation in characteristics spatially, in three dimensions. This is an important reason to secure advisory services locally to attempt to eliminate costly surprises during construction.”


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## ricielectric (8 مايو 2010)

FOUNDATION AND RACKING SYSTEMS ​With information on geotechnical and civil issues, you can now choose the foundation and racking type. The foundation design, in some cases, may dictate the racking type, since some racking designs are limited to a few foundation types or are better suited to one type. Choosing the right foundation and racking type for a site is among the biggest design decisions to be made.



FOUNDATION TYPES
Most solar installers have experience with cast-in-place concrete footings for ground-mounted systems. On a small system, this may be the best option. As system sizes get larger, there are usually compelling reasons to consider alternate foundation types, including ballasted foundations, driven-steel piles and ground screws. (See Table 1.)
Ballasted foundation. This is a good option when the soil is difficult to penetrate or has considerable rocks or subsurface contaminants. Even the uncertainty of what lies below may make a ballasted foundation preferable. Precast concrete is probably the most common option. For example, Conergy and SunLink both offer ground-mounted systems that use precast concrete footings as the primary foundation option. Robert Miros, vice president of engineering for SunLink, explains the benefits: “Ballasted footings are a very simple design element for contractors to work with. SunLink can ship all the parts needed for a system on a truck to the site, and an entire array can be built with a few wrenches.” Alternatively, there are designs that specify filling a container with rock or other materials.
Care should be taken with a ballasted foundation to allow for some soil settling, erosion or heaving. A large area of rigidly linked racking on multiple-ballasted foundations could be subject to stresses with soil movement. SunLink solves this problem with racks that are attached to only two foundations and have adjustability built in. As Miros states, “This not only allows contractors to create a level array during construction, but adjustments can also be made in the future if soil settling is an issue over time.”
Ballasted foundations do, however, have limitations when it comes to sloped or uneven terrain. Work with the mounting-system manufacturer and the civil engineer to make sure that the mounting system can accommodate the slope and relative change in the finished grade.




Driven-steel piles. On many larger projects these days, driven-steel piles—generally, steel beam or pipe—are increasingly the foundation of choice. While many designers in the US are just discovering these products, German and Spanish project developers have had great success with them. The advantages include speed of installation, accuracy of placement, lack of cure time and low cost when employed on a large scale. For these reasons, many large-scale systems use driven-piles when possible.



Specialized machinery is often needed, so a smaller project may not be able to benefit from the lower costs that economies of scale bring. The fixed cost for bringing pile-driving equipment and personnel with the necessary expertise to the site generally equates to a high cost per unit on small projects.
Ground screws. Helical piers and ground screws are another type of pile foundation. A smaller site may be able to take advantage of a ground screw, which can be driven by small construction machinery, like a small front-end loader fitted with the appropriate attachment. StrateGen Consulting’s Edgett notes, “An earth screw can allow savings over concrete piers, without the need to bring in a pier driver.”
RACKING TYPES
For the lowest risk and, typically, lowest cost approach, purchase a racking system from a reputable manufacturer with a good track record in supplying commercial product to the industry.
Preengineering is just one of the benefits of working with equipment available from reputable manufacturers. Many mounting-system manufacturers have done extensive testing to validate that their designs hold up to expected loads. Their designs may also allow for field adjustments that make up for inaccuracies in the locations of foundations. These installation efficiencies are another benefit of working with quality, commercially available racking systems. Schletter, SunLink and Unirac, for example, along with other racking manufacturers, have taken pains to minimize the number of tools and the level of construction expertise needed to assemble their systems. The tools typically needed are limited to wrenches or impact drivers.
Some contractors, nevertheless, choose to design and implement their own racks on a per project basis, either in an effort to reduce cost or to meet certain design constraints of the project. This effort certainly can be successful. However, if you implement a custom rack, you should be well aware of the additional engineering costs and liabilities involved in validating its structural integrity. Though a racking system may appear simple to design and execute, many elements can be overlooked and lead to more expensive and lengthy projects. In general, contractors are better served by working with commercially available products. (See Resources.)
Sharp Electronics demonstrated a prototype ground-mount racking system at Solar Power International 2009 intended for use with its new thin-film module on utility-scale projects. “Sharp realized that to achieve the installed costs necessary to attain grid parity in the coming years, work needed to be done to lower the installed cost of solar power systems,” says Steve Meredith, Sharp’s senior product engineering manager for commercial and utility solar. “Sharp’s new thin- film PV technology is likely to be deployed in many large-scale ground-mounted systems, and we wanted a way to ensure that this product could be integrated as easily and inexpensively as possible.”




Other racking companies offer specific ground-mount options for different market segments. Unirac, for instance, segments the solar market into residential or small commercial projects and large-scale or utility-scale projects and offers different ground-mount products in each category. Unirac’s U-LA ground mount, a familiar option to solar contractors in the US, is a pipe-based product intended for systems under 500 kW, while its new ISYS ground-mount system, based on an I-beam design, is aimed at systems 500 kW and higher. Unirac believes that a different approach for large ground-mounted systems allows for parallel workflow or specialization between different installation teams and achieves greater installation efficiencies. This specialization of labor functions is like an assembly line where each worker can maximize productivity by focusing on a discrete task. According to Juan Suarez, director of engineering at Unirac: “Parallel assembly is a key component in larger systems. It is going to be the primary differentiator among successful large utility projects.”
Schletter adds foundation design and installation to its racking products by owning and operating pile-driving equipment and providing soil testing and qualification. The latter is part of its service to certify system designs to the specific project location. According to Sven Kuenzel, the company’s senior sales manager: “Schletter is able to deliver a truly fully engineered system to our customers. On every single project, we do pullout tests with our post and provide a full geotechnical report. We deliver wet-stamped structural calculations and drawings, reviewed and certified by a licensed engineer in the project state.”






ADDITIONAL CONSIDERATIONS

Whatever foundation option and racking system is chosen, taking the following considerations into account contributes to a project’s success.
Ease of installation. It is important to consider the working conditions of the installation crew. The height of the rack and how modules are attached to it are crucial factors in determining the speed of installation. Needing ladders or lifts generally slows a project down, so it is essential to scrutinize the racking configuration, including the necessary working height for crewmembers to fasten racking pieces and modules.
Thermal expansion. The racking system should be designed to take into account thermal expansion. Expansion joints should be built into long sections of racking to prevent thermal cycling from stressing the rack or the modules. Modules should not be butted tightly together on the rack; their frames expand in hot conditions, which could cause them to impart stress on one another and possibly damage or destroy the module laminates. Steel and aluminum have quite different expansion coefficients. A rack made of aluminum needs expansion joints far more frequently than does a steel rack.
Corrosion. Foundation and racking system corrosion is another issue to consider for a specific site. In most cases, driven-steel piles should be hot-dip galvanized to mitigate corrosion. It is important to characterize soil conditions at the site to determine if additional means are necessary to protect the foundation. In highly corrosive soil, the steel in the foundation may require additional protective coatings; a steel-driven pier may need epoxy coating in addition to hotdip galvanization; rebar within a cast-in-place concrete footing may need epoxy coating or galvanization.
Design compatibility. The intended application must be consistent with the PV module manufacturer’s approved conditions of use as described in the module installation manual. Different manufacturers have different mounting and clamping requirements, and module load ratings can vary depending on the mounting configuration.
ELECTRICAL DESIGN ISSUES ​Next, consider the electrical design issues, including inverter and combiner box locations, code compliance issues and lightning protection.



Inverter location. The location of the inverter or inverters in a system can be an important design consideration. On a small system it might make sense to group inverters together near the point of interconnection, perhaps mounting small inverters on the north side of the racking within the array field. The method just needs to be consistent with the NEMA rating of the inverter. Larger systems are more likely to have large central inverters located throughout the array, centralized to the circuits that are feeding them to minimize voltage drop.
It is also a good design practice to keep inverters out of the direct sun and rain, limiting heat from solar gain and premature corrosion from moisture. Inverter manufacturers offer enclosures for this purpose—like the PV Powered Power- Vault, the Satcon Prism, or the PV Box from Schneider Electric— generally for megawatt block sizes, that keep inverters in a ventilated yet enclosed space out of the elements. An enclosed inverter that is kept out of direct sun and rain, away from pests and excessive dust, is bound to have fewer problems and last longer.
Locating a grounding electrode system near inverters is advisable; if the inverter is to be placed on a concrete pad, it is a good idea to create a grounding electrode system there by providing a concrete encased electrode or a ground ring in accordance with _NEC_ Article 250.
Combiner box location. Combiner boxes should be kept in the shade to prevent fuses inside the box from heating to the point of nuisance tripping. Combiner boxes should carry the appropriate NEMA rating for the way they are mounted. Their location should be easily accessible for servicing. Output circuits should easily transition into trenches. It is a worthwhile investment to ensure the disconnect is adjacent to or integrated into the combiner boxes; this facilitates service and increases safety during maintenance. In fact, a new Article 690.16 provision in the 2011 _NEC_ will require a disconnecting means “on PV output circuits where overcurrent devices ( fuses) must be serviced that cannot be isolated from energized circuits.”
Wire management. Typically the string or source-circuit wiring going into the combiner box is in free air, mechanically attached to the racking system. The PV output circuit, or feeder, from the combiner box is then fed into a system of trenches that runs either to an external array recombiner box or the inverter, which may contain an integrated subcombiner. When wire runs are in free air behind the array, it is good practice to avoid securing large bundles of wire together to avoid co-heating and reducing the rated ampacity of the conductor. _NEC_ Table 310.17 assumes that a conductor in free air can be cooled by convection; a conductor in the middle of a large bundle is, therefore, not technically in free air.
Circuits run in free air should be neatly secured to prevent them from swinging in the wind, being caught by snow or ice or being damaged by any sharp edges. They should also be accessible for commissioning and troubleshooting. Unfortunately, wire management on PV systems is generally an afterthought, and system designers are challenged to find quality products that can make their job easier. Schletter, however, offers wire-management clips that fit extrusion channels in its racks as an accessory; other companies, such as Hellermann Tyton, are beginning to manufacture wire-management accessories aimed at the PV market.
Where the system voltage is greater than 30 V and connectors are readily accessible, _NEC_ Article 690.33(C) requires the use of lockable connectors that need a tool to separate the connection. Similarly, Article 690.31(A) requires that current-carrying conductors in PV source circuits with system voltages greater than 30 V in readily accessible locations be installed in raceways. The latter is generally not practical. Therefore, conductors in free air need to be made inaccessible. On ground-mounted arrays, this is generally accomplished by enclosing the array within a fence with a locked gate. 




Does securing an array behind a locked gate supersede the need for a locking connector? The _NEC_ seems to indicate so, since the connectors are inaccessible in this condition. But some inspectors may insist on a locking connector on the module and other free-air connections regardless. Work with your local inspector early in the process on this issue to remove any uncertainty. It may also be possible to make system conductors inaccessible by erecting barriers to enclose the back and sides of the rack on smaller arrays where a fence is not possible or is unsightly.
Grounding. Make certain that module frames and racking are grounded per _NEC_ requirements and per the module manufacturer’s installation manual guidelines. Check with the mounting system manufacturer for any grounding requirements specific to the system. There should be a continuous ground path maintained throughout the array. Lightning protection is important to consider. Certain areas of the country have a higher lightning risk, and you should be aware of the lightning risk inherent in the area where the system is to be located.
The _NEC_ has two different concerns in the area of grounding. On one hand, equipment grounding is required to protect against shock or fire hazard. This ensures that a PV system is disabled in the event of a ground fault, for example. Grounding for lightning protection, on the other hand, keeps any metallic part in the array referenced to ground so that a charge is unlikely to build up on the structure during an electrical storm. Many systems are well grounded by virtue of the foundations that the modules are mounted to. Proving that to the satisfaction of an owner or inspector, however, may be less straightforward.
Certain foundation designs may be better for grounding a system than others. For example, it is possible that a ballasted foundation be effectively isolated from ground, depending on the conditions of the site. While the foundation can incorporate grounding by design or by coincidence, additional grounding means are also worth considering. Concrete used as a foundation, for example, may or may not be able to adequately serve as a grounding electrode. In any case, it is relatively easy to install some well-placed ground rods throughout the site. A good location for ground rods is right next to combiner boxes. A grounding electrode conductor is then run between the ground rod and the ground lug in the combiner box. Ideally, the designer, with the help of an electrical engineer experienced in lightning protection, specifies a grid of grounding electrodes. Always verify that the racking and module frames are continuously connected with properly rated hardware.



Surge arrestors. The topic of some lively debate in the solar industry, a surge arrestor is, in theory, supposed to establish a high-resistance load path for an induced surge—usually a surge due to lightning—to prevent it from causing widespread damage to the sensitive parts of a PV system, like the modules and inverters. Surge arrestors’ effectiveness is not universally accepted, however. While surge arrestors could reduce the potential for an electrical storm to damage a solar array, do not count on them as the sole means of lightning protection.
Trenching. Try to minimize trench distances, when possible. Planning a simple, logical trench system early in development is the best means to achieve this. One good method is locating an inverter central to the array block that feeds into it and running the trenching from the system coincident to the roadway leading to the inverter. Trenching throughout the array can be tricky, since trenches need to stay away from rack foundations in order not to disturb the soil right next to the foundation. A trench next to a foundation could reduce the soil’s bearing pressure at this location and reduce the foundation’s load capacity. Helmich of D/PM advises: “For an embedded-pier type of system, I believe the near edge of a trench should be kept a horizontal distance away from the near edge of a pier equal to the depth of the trench. Piers are designed to resist horizontal forces based on the lateral bearing resistance of the soil. If the soil cannot be relied upon, it throws the design into question. Trench backfill quality is sufficiently uncertain that this standard should be heeded on most projects.”
Using direct-burial cable in trenching for a large array is certainly worth considering since the cost savings can be attractive, but it is not without complication. The contractor must have sufficient expertise to work with direct-burial cable, and the cables must be properly protected and installed per _NEC_ requirements. The cables are more susceptible to damage from rocks or other debris in the soil, especially in areas where heavy equipment may drive above it. Also, if there is a problem, the cables have to be dug out rather than pulled.
SUCCESS IN THE LARGE-SCALE MARKET ​As system sizes increase, designers and contractors have more opportunity as well as more liability. Effectively planning and executing large ground-mounted systems present different challenges. StrateGen Consulting’s Edgett explains: “Material savings is less important on small systems. If a part can adapt to multiple modules, loads or situations, it is often worth the small cost increase on that part to allow the flexibility. Large systems, however, should take advantage of their size in order to decrease cost. Cost is king on large systems. Every part should be analyzed for wasted material or labor, because the cost of the analysis is so much less than the cost of the hardware and installation.” The focus on cost savings, however, should be tempered with attention to careful engineering to ensure that a design decision intended to save a few pennies per unit does not lead to a future redesign costing thousands of dollars.
Dr. Neway Argaw, vice president of engineering for the renewable energy division at Quanta Services, points out the need for integrating the supply chain into the process: “In order to execute a successful project, it is critical to bring everyone along the supply chain to the table in order to optimize the staging and delivery of the project. Industry professionals are used to thinking as craftsmen. To bring the costs of projects down to achieve higher market penetration, however, we need to think more like manufacturers. We need to be creating assembly plants in the field.” Argaw sees more subassemblies coming to the site prefabricated, allowing for an efficient process flow and a reduction in waste that needs to be dealt with at the site.
Juan Suarez of Unirac also believes that preassembly will be crucial to gain efficiencies in large-scale systems. “Pushing labor from the field to a controlled environment is going to be one of the most significant contributors to lowering the levelized cost of energy,” he says.
Robert Miros of SunLink believes that racking system manufacturers need to work more closely with PV module manufacturers to offer a variety of integrated solutions that achieve the cost savings in materials and labor needed to allow the industry to grow more rapidly. Citing the computer industry as an example, Miros states: “PV module manufacturers today are guarded about releasing specifics on the mechanical load limits of their products. Hard disk drive manufacturers had to provide a lot of information to computer manufacturers in order to allow that industry to achieve the efficiencies necessary to experience rapid growth.”
Considering the projected growth for the solar industry, we are likely to see considerable improvements in the technology and processes used to construct ground-mounted PV systems, especially as designers and contractors learn lessons from executing these projects.


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