System locations
Solar PV systems can be housed in a variety of locations, and different considerations must be made in each case.
Flat roofs
Tilt-up systems on flat roofs are easy to build and do not require any penetrations, preserving the integrity of the roof material. When installing systems on torch-down roofing products, an additional piece of roofing material is placed under the racking as it is laid down, protecting the roof below. Concrete blocks are fixed to the racking, providing ballast to weigh down the system. Typically, the total weight for these systems is between 0.19 and 0.34 kPa (4 and 7 psf). By budgeting an additional 0.38 kPa (8 psf) into the capacity of the roof support structure, building designers can ensure their roofs will support a solar array.
It should be noted when allocating space for a solar array workers at height in Ontario must remain 1.8 m (6 ft) back from the roof edge unless using fall arrest, per O. Reg. 297/13, “Occupational Health and Safety Awareness and Training,” under the Occupational Health and Safety Act. Regulations in other provinces are similar. Requiring fall arrest for workers installing solar panels slows down the speed of work, resulting in longer construction timelines and increased cost. It is far easier and safer for long-term maintenance to accommodate this setback in the design.
Pitched roofs
Solar arrays can be installed on pitched roofs of all materials. Since ballast is not required, these systems weigh only 0.12 to 0.17 kPa (2.5 to 3.5 psf). Engineers knowledgeable in the field will allow for 0.24 kPa (5 psf) extra pressure when designing a pitched roof to accommodate a solar array.
The easiest systems to install are those on standing-seam metal roofs. By clamping the panels to the seam, one can avoid penetrations. Solar arrays can also be installed on corrugated metal or asphalt shingles. In these cases, the fasteners penetrate the roof material and a flashing is used to prevent any water from entering the building.
Carports
An underused piece of real estate for many buildings is the parking lot. Vast expanses of concrete and asphalt exist for the singular purpose of accommodating parking spaces. Developers are discovering they can generate electricity using solar PV arrays above parking lots, simultaneously providing shade and protection from the elements for vehicles. By creating this win-win situation, carport PV arrays are developing fans among architects, engineers, and developers, not to mention building tenants. However, they do come with unique design considerations, especially given the Canadian climate in which they need to operate.
Designing a parking lot so rows run east-west and spaces run north-south will allow the panels to point due south, making a system covering these spaces more efficient. The tilt of the panels addresses a second, uniquely northern concern with solar arrays in general: snow shedding. Average annual snowfalls across Canada range from 550 to 3350 mm (22 to 132 in.). If this snow stays on the array, production can be significantly reduced. Thankfully, snow clears fairly easily, thanks to the aforementioned tilt and the small amount of heat generated by sunlight on the dark panels.
Unique to the carport scenario is the need to safely dump and clear this snow from the parking lot below. Installing a snow guard, an extra rail along the bottom of the array, will break up sheets of snow or ice as they fall from the panels. Clearing this fallen snow also means the lowest point of the array must be sufficient for snowplow drivers to fit underneath. The drivers will have to navigate the supports as they would any curbs or light standards. However, the solar array itself will not cause an obstruction.
Unlike a roof-mounted solar PV array, where calculations are necessary to confirm the roof will support the added weight of racking, rails, ballast, and panels, a carport solar array is entirely freestanding. The pillars or piles used will have to withstand all loading requirements. A variety of options exist to satisfy this requirement, such as cast-in-place foundations or micropiles.
The benefits of carport solar PV arrays are exciting. Who would not love coming out to a clean car after a snowy day at the office, or a cool car thanks to some shade on a hot summer day? In addition to benefits for individuals, solar PV carports generate electricity that can be used onsite and contribute to the green branding of a location or business. Immediately visible, often from a distance, these structures speak volumes about the dedication of the building owners and tenants.
Building-integrated PV
Integrating solar panels into the building design can increase system capacity above the square footage of the roof. Each application will be slightly different and likely require custom racking solutions. The key to designing a building with integrated solar PV is to consider how close one can get to south, the tilt of the panels (both for snow shedding and production), and the esthetic value of the installation. There will be tradeoffs between visibility and production clients must consider.
Elevated systems
Another method of adding solar PV involves elevating a system above a flat roof. Building a raised substructure for the racking allows the panels to cover the entire roof instead of working around rooftop units. This has the added benefit of providing cooling by shading the roof and allowing air to circulate around the panels, keeping them at a cooler, more optimal temperature.
There is an added cost to developing an elevated system due to the amount of material beyond the typical rails and racking. Elevating a system will cost more than a ballasted system of similar size. However, elevated systems make a statement above the building and provide added visibility of the solar array for passersby. Integrating stub-ups into the building design to install an elevated structure at a later date, or building the substructure for the system at the same time as the building, can reduce labour and engineering costs down the road.
