Architectural PV Design Considerations

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Frameless Lumos Solar Modules
Frameless modules, such as these from Lumos Solar, can visually streamline PV installations.
Off-camber array mounts may maximize PV production, but there are other costs, including the judgment of your neighbors.
Well-designed east- or west-facing PV arrays can make better use of roof space, with a minor reduction in production compared to south-facing arrays.
Even on very low-angled roofs, PV arrays mounted parallel to the roof plane can produce a significant percentage of their potential, with a streamlined appearance.
On all but the flattest roofs, tilt-up racks just add engineering complexity, installation cost, and visual obtrusiveness.
This custom patio array by Florian Solar makes electricity, and provides rain and sun protection.
Solar awnings serve a dual purpose—generating energy and shading windows.
A purpose-built solar carport, optimized for both functions.
Pole mounts and trackers can be positioned to optimize solar exposure.
Ground mounts are unrestricted by roof size or shape.
Putting a PV array on an outbuilding can preserve a home’s architectural lines.
A well-designed, positioned and installed PV array can integrate well into a home’s rooftop.
This overhanging array may have wind-loading problems, besides being unsightly.
Black module frames, dark single-crystalline cells, and black backsheets can help a PV array blend into a dark-colored rooftop.
Frameless PV modules, like these Lumos LSX, offer a modern-looking installation.
Exposed wiring looks bad and is vulnerable to damage.
PV roofing tiles and shingles integrate power production into the roofing material for improved aesthetics.
PV roofing tiles and shingles integrate power production into the roofing material for improved aesthetics.
Amorphous silicon laminates that apply directly to standing-seam metal roofing blend in well, but require additional roofing space to achieve the same energy output as an array that uses standard crystalline modules.
Frameless Lumos Solar Modules

Installation details and new module and racking options are making PV systems aesthetically appealing to a wider range of homeowners. Here are some options for creating great-looking systems.

Orientation

No PV array sticks out more than one that is akimbo to the roof lines. And facing an array due south when no roof surfaces point in that direction can really bring attention to the rooftop. These installations are at the root of what got PV and SHW systems banned in communities that have strict design standards.

If there are west- or east-facing roof slopes available, a PV array can be mounted there at a slightly lower cost compared to spending more money on the customized PV racks and extra labor needed for mounting a south-facing array on a roof facing another direction. The yearly energy losses of east- or west-mounting range from about 20% to 25% (assuming a tilt angle of about 45° or less)—not insignificant, but worth it to many. The losses from southeastern- or southwestern-facing arrays will only be about 10%. The savings in rack costs and labor, if used to buy a slightly larger PV array, would help mitigate the energy losses. (Note: To qualify for some incentive programs, PV systems may need to be oriented/tilted within a certain percentage of ideal, which may rule out extreme east- or west-facing orientations, but may still allow for southeastern or southwestern roof slopes.)

Tilt & Stand-Off

PV arrays produce more energy if their tilt is set to gather the most sunlight. For best annual energy production, that’s usually at an angle about equal to the local latitude. (For instance, an array in Savannah, Georgia, would likely be tilted to 32°.) However, the optimum tilt for some areas is not equal to latitude—for instance, in Seattle (at 48°N), because of its cloudy winters, arrays produce more energy if their tilt is about latitude minus 15° (also about 32°). Because south-facing roofs are rarely sloped at the optimum angle, some arrays use mounts with longer legs at the back to place the modules at the ideal tilt for energy production. This also increases airflow to cool the PV cells. If adjustable legs are used, the experienced system owner willing to risk occasional roof-climbs can make seasonal adjustments to eke out even a few more kWh.

But arrays pitched differently than the roof pitch are subject to wind loading, and the rack and the roof that supports it have to be engineered to handle uplift forces from the wind, making the mounting system more costly. Plus, they draw attention compared to systems mounted parallel to the roof plane.

Because of these factors, most modern installations mount the array parallel to the roof, as a wide selection of racks are available. With this strategy, there is still the need for engineering calculations to determine the number of rail supports and how deep lag screws must penetrate the rafters, but the wind-loading on the building and those attachment points are significantly less. Standoffs keep the array away from the roof surface for good airflow—usually, 6 inches is adequate.

Most south-facing roofs have a slope that is at least in the ballpark of what the ideal tilt angle would be, so yearly energy output differences are marginal. For example, a roof having the common slope of 4:12 is about an 18° angle. If your home is in, say, Columbia, Missouri, the ideal tilt angle to maximize annual production would be 34°. The energy loss from mounting the array parallel to the roof plane (at 18°) versus at the ideal tilt (34°) is only about 3%.

Awning or Patio Cover

Several array mounting methods avoid the home’s rooftop altogether. The first—PV awnings—have the added advantage of providing shade. Many PV modules are about the same length as purpose-built window awnings, making them an attractive choice for shading windows on south-facing walls. Plus, using adjustable awning supports can make seasonal tilting easy—either to increase system output, or to decrease and increase shading as the season and solar gain needs dictate.

A PV awning system can be pricey, as the method may require custom engineering to match the mounts to the building attachment means, array weight, and local wind loads. Beefed-up hardware and attachment methods must handle all the cantilevered weight that tries to pull the array away from the building, and there is often increased labor involved in mounting custom systems. Assuming the awning is to be on the south side of the building, the energy produced should nearly match what a south-facing roof-mounted system would produce. The exception is when the sun’s arc sweeps to the northeast or northwest, producing shade on the array by the building itself.

Another place where an array can serve two functions—producing energy while providing shade—is over a patio. Custom-designed PV patio structures are becoming more common, and some installation companies are specializing in their design. Whether this solution is practical depends upon where the patio is situated. Most patio shading structures do best if located facing south. But if on the other sides of the building, the tilt (negative on a north patio) and building shading will affect output significantly, and the array will likely be in the building’s shade for significant portions of the day, especially in winter.

Solar carports can be another way to get more value out of your PV array investment. If the right spot is available, you can orient and tilt the structure for optimum solar gain and keep your cars out of the weather.

Bifacial modules, which produce power from both the back and front, can be an excellent fit for patio and carport applications. They allow some filtered light to pass through the array, providing soft lighting underneath. If a light-colored surface is used underneath, this can reflect light back to the underside of the array, helping to augment power production.

On the Ground

Other alternatives to roof mounting are ground and pole mounts. These methods are usually selected when the roof is not available due to shading or orientation problems, but are a viable aesthetic choice.

These methods transfer the aesthetics issues to another area of the property, where they can be dealt with in other ways. If desired, shrubbery or decorative fencing can hide these arrays, as long as it is not close enough to cause shading problems on the modules. The National Electrical Code requires preventing access to the wiring of these arrays. Often, the solution is a fence—though such an access-prevention fence is likely to be too close to the array to hide it sufficiently.

With these mounts, ideal tilt and orientation are easy to set and, as long as there are no buildings or trees making shade, production can be maximized. Ground mounts and pole mounts are available in a wide range of configurations, ready to accept the modules of your choice. Some inverters can be mounted at or on the mounting structure, eliminating the need to find a spot at the home. Access to the arrays for installation, adjustment and maintenance is usually easier than on a roof—ground and pole mounts are ideal for the tinkerer who wants to adjust the array’s tilt seasonally. Trackers are also an option for properties with wide-open solar access (ideally from dusk to dawn). By keeping the array pointed at the sun all day—without human intervention—trackers help maximize energy output.

But for all of these options (ground, pole, and tracking) extra excavation and installation labor is usually required for poured and reinforced concrete footings, and for the conduit ditches to the home. And the cost of aesthetic fencing or landscaping must be considered, which will vary depending upon what is acceptable to the homeowner. So while potential energy output is equal to or even greater than a rooftop system, cost for the simplest mount and protective fencing will be more than a roof-mounted system.

Outbuildings

Mounting a PV array on a shed, garage, or other outbuilding can keep the lines of a home aesthetically pleasing. As with ground and pole mounts, this can transfer the aesthetics issue to other areas of the property, which might be more visually isolated from the home’s main viewshed. Depending upon the outbuilding site, array energy output and cost is about the same as for a roof-mounted system on the home with similar solar access, though trenching and conduit to the home might increase the system’s cost. If the outbuilding is purpose-built, then the roof orientation and slope can be constructed for ideal solar access.

Rooftop Fitting

Assuming that the roof is the chosen site for an array to be mounted parallel to the roof plane, the array’s size and placement can make a difference in its overall appearance. For example, centering an array on an area of unbroken roof surface looks more symmetrical than placing it to one side or the other, or segmenting it to avoid dormers, chimneys, or plumbing standpipes. If an array is significantly smaller than the roof surface, then some people feel that it looks better closer to the ridge than down by the eaves—but like all aesthetic considerations, there is a lot of personal opinion involved. 

Often, homeowners want to maximize the amount of energy their systems produce, which means filling as much of the roof surface with as many PV modules as possible. Local fire codes dictate whether or not you can install modules to the roof edges, or must leave space for access around the array. Many codes require at least 3-foot setbacks at the top and to one side of the array, but these stipulations can vary. Aesthetically, hanging PV modules or rack rails over any of the edges of the roof surface can look sloppy. If there is not enough room on the roof for standard efficiency modules to produce the amount of energy desired, then one option is selecting modules with a higher conversion efficiency. Using the highest-efficiency modules can increase array cost by about 7 to 12%.

Modules come in many different sizes, but most are rectangular, with width-to-height ratios between 1:2 and 11/2:2. A variety of sizes makes it possible to more closely tailor an array to the roof space. For example, a 40- by 18-foot  roof could accommodate three rows of 10 modules that each measure 39 inches wide and 59 inches tall, while allowing a 3-foot path to each side and 3 feet of access at the top. Choosing a 39- by 65-inch module (of the same wattage) means that only two 10-module rows would fit. Even if oriented in a landscape format, only 24 modules could be accommodated.

Module Aesthetics

If you want to go all-out in attempting to match your array to the roof, there are a few options. Modules with black frames and black back-sheets meld visually with a dark-colored roofing surface. A handful of modules are available with bronze frames, which may be a good match for clay roof tiles or brown-colored shingles or metal. Verification of efficiency differences between white and black-colored components aren’t available, but since black absorbs more of the sun’s heat, expect a little loss in efficiency.

Another aesthetic choice is the dark, more matte-like cells found in single-crystalline modules versus the sparkly appearance of multicrystalline cells. When comparing standard single crystalline versus multicrystalline modules, the differences in energy output and cost between the two are negligible, although the efficiency gap will be between 3% and 5% when comparing multicrystalline or standard single crystalline to high-efficiency single-crystalline modules. A less common type of cell, amorphous, has its own dark, matte appearance. This type of PV technology is mostly used in building-integrated PV (BIPV) applications (see page 51), but is also available in framed and frameless modules. Amorphous modules are cheaper, but produce much less power per square foot, which means twice the surface area or more to accommodate an amorphous array as compared to a crystalline silicon array.

Installation Quality

Your installer’s experience, knowledge and attention to detail can make a significant difference in how a finished system looks. This includes neatly laid out or hidden conduit runs; no visible wiring; no rack rails protruding from the array edge; and making sure the array is centered in open areas and square with the roof. An experienced installer will not use unflashed L-brackets as feet, but will select the properly flashed standoffs to hold the array. A conscientious installer will also work with you through the various module choices, weighing the financial and energy costs versus benefits of all the different aesthetic approaches.

BIPV

Building-integrated PV is often touted as the holy grail of PV systems, as they can blend into the structure and, in some cases, replace roofing materials (such as shingles or tiles). The most commonly found BIPV products are amorphous silicon PV laminates, which fit between the ribs of standing-seam metal roofs, and PV shingles designed to replace some of the asphalt shingles on a standard roof. Another product that has gained popularity is crystalline silicon solar tiles, meant to replace flat cement tiles.

These products are finding acceptance in the solar housing tracts that are popping up around the country. These houses are being built to sell to the masses, and not the solar-savvy individual, so the feeling among builders is that the house must appear as “typical” as possible. For now, the products have higher cost and spotty availability—not as many are made (economy of scale) compared to standard PV modules. The products’ labor costs can be higher as well, because they require additional product-specific installation training and the accompanying learning curve.

Most PV installations have plenty of airflow around the modules, which helps keep cells cooler and producing energy more efficiently. Because of restricted airflow, especially behind the cells, BIPV products tend to operate at higher temperatures, decreasing the cells’ production. For example, solar tiles will produce 3% to 5% less energy than conventional roof-mounted arrays.

Some large architectural projects, like skyscrapers and other business buildings, are specifying PV technology integrated into glazing and other building features. Generally, the designer works with the manufacturer to obtain custom-produced modules—which are not available to homeowners. For more information on BIPV and other PV aesthetics, see “Residential Building-Integrated Photovoltaic Systems” in HP130.

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Michael Welch is a senior editor for Home Power, and a long-time energy activist and off-gridder who is satisfied with the purely functional beauty of the solar-electric systems on his home and office.

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