Questions About Home Rooftop Solar Systems? MRA Experts Have Answers
- Metal Roofing Alliance
- 4 days ago
- 5 min read
Investing in a home rooftop solar system can be a major undertaking so it helps to be armed with the answers. From basic terminology and installation questions, to selecting roofing material, here are the answers to what you need to know when it comes to choosing and installing a residential rooftop solar system.
Part I. Understanding the technical terms
Q: What does Photovoltaic (PV) mean?
A: Photovoltaic refers to a device that converts sunlight directly into electric energy. Form factors include:
A “cell” is the smallest denominator of a solar collector.
A “modular” are cells arranged in rows and columns and laminated together. A modular has 60 to 72 plus cells wired together (often the size of a large flat screen TV).
A “string” is a larger denominator of a solar collector consisting of multiple modules. String size is usually limited to about 12 modules.
An “array” is the largest, consisting of one string or hundreds of strings connected.
Q: What’s the difference between insolation and irradiance?
A: These are the two different names for quantifying the amount of sunlight reaching an area (usually expressed in the number of sun-hours hitting the solar system per day, month or year based on historical data for the location). The number of sun-hours multiplied by the wattage produced by the system equals the power production in kilowatt-hours. A pyranometer is used to measure solar irradiance or insolation.
Q: What do Crystalline silicone or flexible thin film mean when it comes to solar production?
A: These are the two main types of solar modules available. Crystalline can be monocrystalline, polycrystalline or a combo. Flexible thin film is fully-adhered amorphous silicon to a flexible plastic backing but also can be rigid, sandwiched between glass. Because they produce the most power per square foot of surface, 90% of roof mounted solar panels are crystalline modules. Each adds approximately two to three pounds per square foot of collateral load. Thin films are much lighter and can be adhered to some roof types but require a new, clean surface.
Part II: Rooftop Installation Questions
Q: What is “tilt angle” and why is it important for solar placement?
A: The solar community uses tilt angle to determine the position of the solar panel while the roofing community uses “pitch.” A lower tilt angle than optimum is not as critical as the panel orientation.
Q: How do I know if my house can maximize solar energy?
A: Factors such as shadows caused by tree or building obstructions and directional orientation all play a role, along with tilt angle and pitch. Work with a qualified engineer and solar installer to determine proper placement and opportunities for maximizing your home’s solar collection during the initial project planning and permitting stages.
Q: What is a fully ballasted solar system?
A: For flat roofs, ballasted systems require racking to hold solar modules in place. Racking often includes tilt capabilities to orient modules to maximize solar collection.
Q: Do low slope roofs require a special type of solar system?
A: Lower sloped roofs may require reduced ballast, which involves similar racking or framing components, but can be enhanced by proprietary aerodynamic foils, reducing the amount of needed ballast. Mechanically attached systems are also possible with low-slope and flat roofs and are often used with pre-existing construction. Again, an engineer or certified installer can help you design a system that will allow you to maximize solar collection based on your home’s characteristics.
Q: How do I maximize my rooftop solar system investment?
A: First, make sure your roof is ready and won’t fail before your system does. Solar panels last an average of 25 years. Your roof needs to be able to last at least that long because having to disassemble, replace or repair a roof and reassemble your system can quickly wipe out any energy saving you may have realized due to expensive added labor and material costs. Also, make sure the roof you choose is energy efficient. It doesn’t do much good to produce solar energy only to have it leak out of the house due to an inefficient roof or lack of insulation/proper ventilation. Metal roofs not only make a great platform for rooftop solar systems but help ensure produced energy isn’t wasted.
Part III: Differences Between Roofing Materials
Q: Does the type of roof make a difference when it comes to solar system installation?
A: Yes. The roof is the solar mounting platform. The service life of the roof should always exceed the service life of the solar system. If a roof fails before the system, it can necessitate the decommission, removal and reassembly of the solar system, which can cause serious financial and logistical impact. Here’s a breakdown of different roofing material and solar system considerations:
Asphalt: Asphalt usually involves stand-off mounts secured into the roof trusses with lag screws. Special flashing kits are used to reduce water leakage around penetration site. Typically, only the highest-quality asphalt roofs can last longer than a solar system, with many failing prematurely especially in regions with extreme climate conditions.
Tile: Like shingles, a sub-flashing is required underneath along with a special top flashing, and mounting hardware. Danger of tile breakage during installation is likely, so cost significantly increases.
Metal: Metal roofs are ideal for solar installation as they are strong, weather-tight, durable and can last 50-plus years—longer than solar systems themselves—offering exceptional protection for a solar system investment. They can support framed, rack mounted and thin film laminate (which require a clean and smooth surface, free of imperfections). Solar systems can be mounted on metal without requiring any perforations in the roof, which substantially reduces the possibility of leaks. Installation also is fast and efficient, resulting in further cost savings for materials and labor.
Q: There are different types of metal roofs. What’s best for a solar system?
A: All quality metal roofs work well with residential solar systems, but here are a few things to note:
Standing seam metal roofs: This style utilizes unique non-penetrating seam clamps to anchor PV modules and all other ancillary roof-mounted equipment (accessories such as wire chases, combiner boxes, roof walkways and other ancillary attachments including satellite dish antennas). Non-penetrating seam clamps allow for quicker and more economical solar panel installation compared to traditional methods. Non-penetrating seams also greatly improve wind uplift resistance by limiting the possibility of clip disengagement. Stainless steel mounting disks can withstand severe conditions and are compatible with brass mounting clamps for copper roofs. Clamp manufacturers such as S-5! offer tremendous resources for educational resources and training. For easy low maintenance, consider a metal roof with a high-quality, long-lasting painted finish.
Pre-formed metal panels: Also allow for solar attachments that do not penetrate the roof (same as standing seam).
Stone-coated metal roofs: A stone-coated metal roof is made from steel or some other metal; the metal is then coated with stone chips and attached to the steel with an acrylic film. For homeowners who want the style of more traditional roofing materials—yet need a more durable roof to protect their solar roofing system investment—stone-coated offers many of the advantages of standing seam metal roofs. Like standing steam, stone-coated metal roofs match perfectly with solar system installation requirements and offers other important benefits, including light weight, exceptional performance and durability, wildfire protection, hail strike resistance, high wind protection and more.
A solar PV rail system mount bracket that maintains water-tight integrity of stone-coated metal roofs is essential for proper installation. Stone-coated metal roofing manufacturers, such as Decra and Boral, recommend a variety of training and installation resources from solar rail mount system companies including Quick Mount PV and Solar Roof Hook.
