Designing for solar PV

December 27, 2018

Sunlight shines through a solar carport constructed using panels with a clear backsheet, filtering the light and providing cell visibility from below. All photos courtesy VCT Group[1]
Sunlight shines through a solar carport constructed using panels with a clear backsheet, filtering the light and providing cell visibility from below.
All photos courtesy VCT Group

by Taylor Weber, BID

Gone are the days when architects needed to hide bulky solar panels from view to preserve their vision for the design of a building. Today’s panels and racking solutions have created a world of limitless possibilities where solar photovoltaic (PV) technology becomes a feature and can be integrated into the building design instead of added as an afterthought.

Building considerations

The earlier a solar expert is brought on board, the better. Each building is unique, and through co-operation between architects, engineers, and solar designers, one can arrive at the best possible outcome. Design considerations include the size of system required, the space available for installation, and where solar power use and visibility fits into the project’s priorities.

System size

When considering solar PV for a new or existing building, the first concern is sizing the system to match energy production to building consumption or take full advantage of any incentives or contracts available. The system size will depend on the electricity market in which the team is operating.

In a feed-in tariff scenario, all electricity produced is sold to the grid at a contract price. The size of the system is determined by the contract secured with the local electrical authority. In this situation, installing the largest system for which a contract is available typically results in the quickest payback, as there are efficiencies when installing solar PV at scale. A larger system also provides more flexibility down the road when the contract expires and the production model shifts to net metering, where electricity can be used to offset consumption.

A flat roof with torch-down membrane. Black slipsheets have been placed under the ballasted racking for extra protection.[2]
A flat roof with torch-down membrane. Black slipsheets have been placed under the ballasted racking for extra protection.

In fact, for net metering installations, production is expected to offset consumption. Any electricity generated is used to power local loads first, with excess sent to the grid. Electricity sent to the grid earns credits that can be used to pay for electricity when consumption exceeds solar production. Sizing a system too small in this situation can leave money on the table, as the owner will not produce enough electricity to completely offset consumption. Too large a system ends up giving electricity to the grid for free. Consulting a solar designer and analyzing the client’s electricity usage, or projected usage, is the key to a financially viable solar solution.

Once the desired output of the system has been determined, architects are free to get creative with panel size, style, and placement. A myriad of options will offer similar power outputs. It is up to the architects and engineers to balance this need with the state of the building and client opinions.

Available space

The second consideration when designing for solar power is the space available for and required placement of components. Although solar installations are typically situated on roofs, there are opportunities to take advantage of unique or underutilized spaces to add panels for either production or design requirements. Penthouses, awnings, and parking lots are just a few areas that can be used to expand systems.

Attention must also be paid to the location of other electrical equipment. Inverters to change the direct current (DC) electricity generated to alternating current (AC) for use in the building can be housed outside or inside the structure. A transformer may be needed, depending on the installation. Each of these components requires placement, as well as the ability to run wires connecting the system. Placing everything to ensure minimal distance between components and work to run wire is best done in the building design stage. It is easier to provide conduit and locations for systems at that stage than it is to trench cables and move components down the road.

Design priority

As solar PV technology matures and design options expand, it is possible to specify a unique esthetic for a solar installation. Everything from the colour of frames and backsheets to the tint of the glass or colour of the cells can be selected. This has given rise to the use of solar panels as a design feature instead of simply a generation option, although they may not generate as much electricity as a purpose-built system. Using solar arrays to create awnings, clad a wall, or build shade structures is one way to brand the building and broadcast the green initiatives being undertaken.

Solar carports offer shade and snow protection for vehicles and electricity generation for the building. Electric vehicle (EV) chargers can be integrated as an additional tenant benefit.[3]
Solar carports offer shade and snow protection for vehicles and electricity generation for the building. Electric vehicle (EV) chargers can be integrated as an additional tenant benefit.

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.

A standing-seam roof where racking has been clipped over the ridges, resulting in a fixed system with no roof penetrations.[4]
A standing-seam roof where racking has been clipped over the ridges, resulting in a fixed system with no roof penetrations.

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[5] 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.

In this application, stub-ups from the roof support the structure required to raise the solar photovoltaic (PV) system above the rooftop.[6]
In this application, stub-ups from the roof support the structure required to raise the solar photovoltaic (PV) system above the rooftop.

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.

A 250-kW system where the structure was purpose-built to accommodate raised solar. This creates a unique design feature, while providing shade and cooling.[7]
A 250-kW system where the structure was purpose-built to accommodate raised solar. This creates a unique design feature, while providing shade and cooling.

Esthetic features

While choosing how to integrate and display solar PV, consideration must be paid to the visual attributes of the panels. New options for esthetics mean specifying panels takes more than simply choosing the best production at the lowest price. Frames, backsheets, cell spacing, and even cell colour are customizable and can help achieve the desired effect.

Frames

Frames provide the structure of the panel, enclosing the glass, cells, and backsheet and supplying a point at which to fix panels to racking. Typically, a plain aluminum frame is used, clearly delineating the edges of each panel. The aluminum can also be black anodized to create a sleeker array. With black frames, individual panels are not as easily visible, and the array blends more naturally into a dark rooftop. Black-framed panels typically cost the same as regular aluminum frames.

One can take things a step further by opting for frameless panels. By sandwiching cells between two sheets of glass, these panels eliminate the need for a frame. Although they add esthetic value, it can be difficult to find an appropriate racking system to clamp down frameless panels.

Backsheets

The backsheet of a PV module is typically a polyvinyl fluoride film designed to withstand the effects of temperature, moisture, and ultraviolet (UV) radiation panels must endure during more than 25 years of service. In addition to protecting the cells and electronics within, choosing a backsheet has an impact on performance and esthetics.

Like frame material, backsheets can make panels stand out, blend in, or act as a feature. White and black backsheets show through the spacing between cells. White backsheets highlight the cell structure, while black ones create a sleeker look, especially when used in conjunction with a black frame. A clear backsheet or glass-on-glass panel allows the cells to be seen from both sides of the array and allows light to filter through between the cells. This creates unique opportunities for solar panels in awnings, gazebos, or carports to become a visual feature and create unusual lighting effects.

Solar design integrated at evolv1, the first project to receive a Zero Carbon Building–Design certification from the Canada Green Building Council (CaGBC). The roof is a 264-kW feed-in tariff system, while the 504 kW of panels on the carports provide power directly to building occupants.[8]
Solar design integrated at evolv1, the first project to receive a Zero Carbon Building–Design certification from the Canada Green Building Council (CaGBC). The roof is a 264-kW feed-in tariff system, while the 504 kW of panels on the carports provide power directly to building occupants.

The choice of backsheet and frame will also affect performance of the panel due to internal reflection and heat generated. According to Fraunhofer USA’s 2010 presentation at Intersolar North America, three per cent of incident sunlight is reflected from a white backsheet. Some of this is recaptured due to internal reflection. Using a black backsheet instead of white reduces the reflection, resulting in a loss of production. In matching solar modules from a single manufacturer, choosing a black backsheet decreases the quoted efficiency by one per cent.

Customizing the cells

In addition to the materials framing the panels, manufacturers now offer customization for cell spacing and colour. The options are virtually endless, limited only by a designer’s imagination. Coloured cells, beyond the typical blue and black of traditional silicon, are turning solar panels into a more adaptable building material. Varying the spacing between cells, when done in conjunction with a clear backsheet, allows for manipulation of light and shade when used as an awning or a carport.

The power of solar

As the solar industry continues to evolve, one can look forward to seeing more unique applications of the technology. Moving beyond solar power as an afterthought, architects and developers can integrate solar arrays into their building designs. By taking advantage of panel options as design elements and using underutilized spaces to make an impact, design/construction professionals can help solar arrays stand out and make a building unique, in addition to generating renewable energy for many years to come.

[9]Taylor Weber, BID, is the marketing co-ordinator for VCT Group. He promotes the use of solar power as both an energy-generation option and a design practice. Since 2008, VCT Group has been developing solar PV installations, helping clients with energy management, and promoting the transition to electric vehicles. The company has built more than 13 MW of solar projects for clients and manages more than 10 MW with a value of $30 million. Weber can be reached at tweber@vctgroup.com[10].

Endnotes:
  1. [Image]: https://www.constructioncanada.net/wp-content/uploads/2018/12/Clear-Backsheet.jpg
  2. [Image]: https://www.constructioncanada.net/wp-content/uploads/2018/12/Torch-Down.jpg
  3. [Image]: https://www.constructioncanada.net/wp-content/uploads/2018/12/Car-Port.jpg
  4. [Image]: https://www.constructioncanada.net/wp-content/uploads/2018/12/Pitched-Metal-Roof.jpg
  5. Average annual snowfalls: http://climate.weather.gc.ca/climate_normals/index_e.html
  6. [Image]: https://www.constructioncanada.net/wp-content/uploads/2018/12/Elevated-Truss-2.jpg
  7. [Image]: https://www.constructioncanada.net/wp-content/uploads/2018/12/Elevated-Truss.jpg
  8. [Image]: https://www.constructioncanada.net/wp-content/uploads/2018/12/evolv1.jpg
  9. [Image]: https://www.constructioncanada.net/wp-content/uploads/2018/12/Taylor-Weber-Profile.jpg
  10. tweber@vctgroup.com: mailto:tweber@vctgroup.com

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