Why Design Solar-Ready Buildings?
Solar-ready buildings allow for future solar installations without the need for expensive adjustments and retrofits. Many existing buildings aren’t a good fit for rooftop solar due to orientation, roof size, shading or other factors. It can be incredibly expensive, or even impossible, to retrofit these buildings in a way that makes solar viable. Even new buildings may need substantial improvements to capitalize on their solar potential.
This can be avoided by including solar production as a design criteria in the building plan, not adding it after the fact. A few simple changes to the design of a building can make adding solar more predictable and less expensive.
Building orientation, roof layout, space for PV equipment and knowledge of local zoning and regulatory requirements are all important factors to address. NREL has published two detailed reports here and here detailing the specific technical considerations, which we’ll summarize below.
Building Orientation & Shading
Anywhere north of the equator, PV systems perform best when facing due south. With this in mind, sloped roofs will work best with one south facing side. While flat roofs are more straightforward, they are still susceptible to shading from nearby buildings and trees. Even small amounts of shading can decrease solar production, so finding a clear area for the solar array is crucial.
A contiguous rectangle of solar panels is the most efficient layout, maximizing the system size and reducing load on the roof. A building must have enough flat, unobstructed roof space to accommodate this. With today’s current solar technology, we typically estimate that 10,000 square feet of unobstructed roof space can fit a 126kW solar array (which would produce around 148,600kWh here in Minnesota). For example, take a look at these office and multi-family residential projects.
Plumbing & exhaust vents, chimneys and other rooftop equipment can interfere with the placement of a solar array. These obstructions should be minimized when possible, and clustered together on the north side of the roof to save space. A good rule of thumb is to place an obstruction twice as far away from the array as the obstruction is tall, to avoid any shading.
A ballasted solar array can add between 3 to 10 pounds per square foot of load to a building’s roof. The ballast is needed to counteract potential wind uplift. This additional weight should be accounted for when determining the roof’s load capacity. This is another reason that it’s helpful to cluster your rooftop units and other obstructions together in a spot away from the solar array. Having to work around those elements will change the layout of the system, and increase the load on that particular area of the roof.
The color and material of the roof can also impact solar performance. White TPO membrane roofs, which provide increased reflectivity, can boost solar energy production up to 15% when bifacial modules are used.
Your roof is a long-term investment and maintaining the existing warranty is key. Before selecting a roof material and manufacturer, it’s good to look into what is required to install solar on top of that membrane and how the warranty will be maintained. Most, if not all roof manufacturers have a process in place to retain the roof warranty after a solar installation, but the requirements (and associated costs) can vary widely.
Designing the building’s main electrical panel to accommodate solar without utility upgrades will also make interconnection easier. A good rule of thumb is to allow for 100 amps of electrical gear for every 100kw of solar. So a 1MW rooftop solar array would require the ability to connect a 1,000 amp service to the electrical gear, via a disconnect or breaker integrated into the gear.
Identifying where the inverters and other solar electrical equipment will be located (on the roof or near the main electrical panel) should be part of the building design process. Ensure that adequate space is left at whichever location is chosen, and there is easy access for future maintenance. We recommend leaving 15 linear feet available for new solar equipment.
Zoning, Permitting & Policy
Zoning laws, permitting requirements and their potential impact should be understood during the building planning process. These rules can cover the potential height of new neighboring buildings, how close a solar array can be to the edge of the roof or if there are historic preservation protections in place.
Depending on the location of the building, there may be system size limits or interconnection restrictions that impact the solar system design. For example, in Xcel Energy territory in Minnesota, solar systems can be net metered up to 120% of a building’s energy usage or 1MW, whichever is reached first. Most other utilities in Minnesota only allow net metering up to 40kW. Similarly, knowing which federal, state and utility incentives are available will help maximize the solar project’s positive financial impact.
Let’s Talk About Solar-Ready Buildings
Overall, there is a lot to consider when designing a solar-ready building, but the long term benefits are more than worth the extra planning. Impact Power Solutions has been helping organizations implement solar projects for over 30 years. If you’re interested in learning more about designing a solar-ready building, or want to see how solar can work for your organization, reach out to us today!