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Planning a Solar-Ready Roof

By Marcy Marro Beginning this year, the California Energy Commission’s new energy-efficient standards require solar ready roofs for all newly built residential and commercial structures. While home and building owners will not be required to install photovoltaic (PV) panels at the time of construction, buildings will need to be equipped for future PV installation. The… Continue reading Planning a Solar-Ready Roof

Beginning this year, the California Energy Commission’s new energy-efficient standards require solar ready roofs for all newly built residential and commercial structures. While home and building owners will not be required to install photovoltaic (PV) panels at the time of construction, buildings will need to be equipped for future PV installation.

The best time to think about a solar roof plan is during the design stage. Pre-planning a solar-ready design is a must for an installation during build or in the future. This entails developing a solar-ready review, which focuses on optimizing the design and power production while minimizing the initial and long-term costs.

Components of a solar ready review include:

Orientation

To maximize power production of a PV system, building orientation is a very important factor. When steeper slopes are involved, south-facing roof surfaces are best. If a south orientation is not possible, southwest or southeast can also be viable options. Orientation is not as important for low-slope roofs 5 degrees or less.

PV modules are normally installed planar to the roof surface on steep roofs, and planar or very slightly tilted on low-slope applications. Aggressive tilting is seldom done anymore due to economic considerations and adverse wind effects. Tilted systems are still used in very northern geographies or on some roofs not oriented to the south. It is a delicate balance of increased cost versus increased power production.

In theory, the best pitch is the latitude of the job site, but in practice this is seldom done.A lower pitch than optimum is not as critical as orientation; the difference in power production is nominal. The increase in power production is not usually worth the premium cost of unusually steep pitches, unless the steeper slope is also an intentional design element.

Shading

The best design for a solar system is an unobstructed roof area with no shading. Building components such as plumbing stacks, skylights, chimneys and parapets can create shadows on the solar system. Consideration should also be given to any trees or future buildings that could cast a shadow on the system.

Attention to all the details in designing a solar system is crucial to achieve the most power production and to run an accurate return on investment (ROI) for the system.

With a basic ROI, the system designer and owner can accurately evaluate whether PVs makes financial sense. (Figure 1)

Example case ROI analysis:

• Net system cost after tax credit: 236,250
• What year do you go cash positive? Year six
• Positive cash flow for balance of service life: ROI
• At the end of 25 years (warranted period for solar modules) produced a ROI of 450,230,377
• If the system goes 35 years (still producing power) produced a ROI of 450,940,377

Roofing Material vs. Service Life

Generally, the warranted life of solar modules is 25 years, but actual service life may reach 35-plus years. The roof’s service life should exceed the service life of the solar system. Otherwise the roof must be replaced, necessitating the de-commission, removal and re-assembly of the solar system.

It is vital to understand the relative costs of the roof asset (the mounting platform) and the solar asset (the revenue generator). Let’s consider an example of a new TPO roof of significant size that is covered with PV. The initial cost of the roof is approximately 3/sq. ft. Calculating the value of the solar array at about 12 watts per square foot and a typical cost of 5000.50/watt, the cost of the array is 30/sq. ft. The aggregated cost is 33/sq. ft. But the TPO roof is a 15-year roof and will have to be replaced during the life of the solar system.

When re-roofing is required after 15 years, the cost of reroofing is not only the cost of the new roof, but also the cost of dismantling and reassembling the solar array, in addition to the loss of power production during the process. Estimating the re-roof cost at 5000/sq. ft. and the cost of removing and reinstalling the solar array at 13/sq. ft., the total is 15/sq. ft. for the complete re-roof.

The aggregated cost of this total system over time is now 48/sq. ft. for a total 30-year system.

Compare this to the cost of using standing seam metal roofing. Instead of expensive ballasted or penetrating racking systems required for the TPO roof, standing seam roof clamps can be used to mount the system without penetration. This provides as much as 15 percent lower costs than mounting costs on membrane roofs.

The cost of a mid-sized, low-slope commercial standing seam roof is about 4/sq. ft. But the metal standing seam roof outlives the solar, avoiding all costs of roof replacement. And the savings in mounting costs more than offsets the premium cost of the roof.

Consequently the aggregated initial cost with the standing seam metal roof is approximately 31/sq. ft., making the aggregated cost of ownership over the life of the solar system 31/sq. ft. for the metal roof vs. 48/sq. ft. for the TPO.

So when you look at the roof (the mounting platform) and the solar system (the revenue generator) as a single asset, the initial costs are lower when using a standing seam metal roof versus any other roof type. And the long-term costs are much, much lower.

Ready to go solar?

At every level — corporate, state, national — solar energy is seen as an attractive solution to augment power in a clean environmental-friendly way. This article takes a look at the basic factors to be considered to self-test the feasibility of a rooftop solar PV system installation, before calling the experts for the detailed site survey.

Here is the basic checklist to see if you are ready to go solar.

General checks

• Shadow-free: To maximize the sunlight during the day, make sure that your rooftop is clear of encumbrances which might block solar panels. For maximum efficiency, the roof needs to be clear to get sunlight throughout the day. For this, as far as possible, the rooftop must be free from shadows of trees or adjoining buildings, especially from the south. Also, consider what may create a shadow or shade in the future, such as growing trees or new buildings.

Rooftop checks

Rooftop checks is another important criterion that needs to be inspected to see if you are ready to go solar. To begin with, the load carrying capacity of the rooftop should be checked beforehand. The solar panels with structure typically weigh 15 kg per sq. m. This weight varies depending on the technology and type of structure. Hence, make sure the rooftop is strong enough to bear the load of the plant. Additionally, the presence of multiple and scattered ventilators, HVAC, skylights on the roof may considerably reduce the usable area for a solar power plant.

• Metal Roof: Metal rooftops are best suited for solar plants as they are typically heavy and can bear the load of a plant. However, if the rooftop is damaged, then it becomes difficult to install solar panels on them. The orientation of the rooftop is also critical as it plays a role in determining panels expos due to the sunlight. If the rooftop is curved, then the number of panels that can be installed would go down due to reduced space. Typically, solar panels are designed to handle wind pressure up to 150 kmph. So consider the wind speed on your rooftop while making the final decision to go solar.
• Asbestos roof: As they are brittle in nature, it is not advisable to install rooftop solar power plants on them. The solution is to replace the asbestos rooftop with a metal one, which is better suited for solar generation.

Ground mount checks

Selecting a site for a ground mount solar installation is based on many considerations, such as whether the photovoltaic plant is close to the grid, and whether the process for obtaining a grid connection agreement is transparent and predictable.

• Basic requirements: 1) Access to the land 2) A level ground 3) Soil strength at the location, where the solar plant has to be installed and 4) Obtaining mandatory regulatory permits and ensure there are no zonal restrictions.
• Tracking Arrays: The output of a ground mount solar power system can be increased by having the system track the sun as the sun moves across the sky on a daily basis and adjust the tilt of panels to the seasonal solar path, instead of being fixed in one orientation.

As part of our regular site evaluation process, CleanMax does an extensive check to make sure you’re ready to go solar. Our engineers have often, come up with innovative solutions to handle the trickiest of rooftops ensuring complete safety compliance.

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Our “solar 101” series is designed to guide prospective residential and commercial solar customers in their quest for the right solar system.

We’ll break down the decision-making process into bite-sized pieces so you can navigate the process and feel good about your choices.

We’ll FOCUS on the most common type of residential or commercial installation: a system attached to a roof.

And to get started, we will look at how to evaluate the age and condition of your structure’s roof. Is it old? Is it new? Wait… didn’t we just replace the roof not too long ago?

If your roof is less than five years old (or better yet, if it is brand new) then this is a perfect time to install solar. Solar installed on a newer roof is low maintenance, and will age gracefully over the years!

But what if your roof is old or leaking, and will soon need to be replaced? That’s also an ideal opportunity, because it allows your roofers to coordinate with your solar developer to install the best system overall.

But what if your roof is somewhere in between?

Customers often have a problem adding solar panels to roofs that are middle-aged. A typical roof has a 25-year life expectancy, so roofs in the range of 8 to 20 years present a dilemma of wasting many costly “roof years.”

For instance, a 250,000-square-foot white thermoplastic (TPO) roof on a commercial structure might cost 5/sq. ft.—on the order of 450.25 million–to replace. That amounts to roughly 50,000 per roof year. So, if you “give up” five years, that’s 250,000.

And while a homeowner’s dollar amounts are much lower, the dilemma is just as real.

When unsure of what to do because your roof is in that pesky middle-aged range, use this approach to quickly determine the dollar value of the roof’s age:

Expected Roof Lifetime – Age of the Roof = Leftover Roof Life

Divide Leftover Roof Life by Expected Roof Lifetime. (This gives the percentage of the roof’s remaining value)

Multiply that percentage by the cost of the new roof

The dollar amount that results offers a way of figuring out what you may be willing to pay for clean electricity from solar. If that number hurts as the check is written, maybe wait a few years. But not always! Especially not if you’re someone who cares about the environment. In fact, you might purposely decide to spend a little extra for the opportunity to reduce your environmental impact.

And, sometimes, depending on solar incentives and bank financing rates, it actually makes economic sense to replace a roof early. So use the formula as a guide, but weigh it against your other goals and factors.

As a start, get quotes from both roofing and solar contractors. When you compare the total cost of both investments to the long-term electricity savings you stand to realize from the solar system, you can get a good idea of your projected electricity savings.

Obviously, the combined payback period for a new roof and a new solar system is much longer than a solar system’s payback on its own. However, a solar power system pays for itself in a way that asphalt shingles and TPO simply can’t.

Seen from a different angle, buying a roof with a solar system is almost the same as getting a free roof!

Subsequent articles will dive into important questions such as how to find and vet contractors, how to size the system, and what expenses to expect related to hardware, fees, and labor. We also will show how rebates and tax incentives provide a boost to ROI, and how banks now see solar projects as ideal for lending.

This content is protected by copyright and may not be reused. If you want to cooperate with us and would like to reuse some of our content, please contact: editors@pv-magazine.com.

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Commercial Solar Guy is a commercial utility solar developer, general contractor for commercial and residential solar, as well a consultant. We construct projects in MA, RI, NY, and soon PA.

Solar–ready building requirements can bring rooftop PV to new markets

Sunlight Electric worked with the architect to design this barn for solar. The installer suggested the larger south-facing roof and the architect oriented the building for best sun exposure.

For long-tail solar installers, good local solar policy is crucial to business success. One trending policy initiative, solar-ready building requirements, helps eliminate barriers to local solar adoption and creates business opportunities in tough markets.

Solar-ready building requirements compel builders to make solar installation easier on new builds, whether rooftop PV will be installed now or in the future. These requirements aim to cut the costs that come with retrofitting buildings for solar and encourage building owners to consider solar as a real possibility.

NREL published a guide to help cities and states pursue solar-ready guidelines or mandates in 2012. The organization highlights six different areas that should be addressed by solar-ready legislation: determining the optimal solar system placement on a roof, accounting for building orientation and shading; minimizing obstructions in roof design; considering PV install and equipment needs such as pre-installing mounting brackets; making initial PV design considerations such as system size; researching policy factors like net metering and how they may impact a future system; and discussing zoning and permitting requirements such as solar access laws or historical preservation regulations.

Example of site layout impacts on solar potential. NREL

The state of California and cities of Orlando, Florida, and Tucson, Arizona, along with others, have incorporated solar-ready requirements in commercial or residential building codes. Some have done so in pursuit of SolSmart designations, a program run by The Solar Foundation that distinguishes cities and counties that are “open for solar business.”

Solar-ready requirements can be a step toward a full solar mandate on new builds like California’s, which went into effect this year. New York also adopted a solar mandate for new buildings and existing buildings undergoing certain significant roof renovations in 2019.

Solar-ready requirements can also be a way for states that weren’t solar-friendly to give the technology an opening, like in St. Louis, Missouri. At the end of 2019, the city passed legislation requiring all commercial, residential and multi-family construction to be built solar-ready — with elements including a roof that can handle the added load, a reserved space on the electrical panel and, possibly most importantly, an obstruction-free space on the roof for adequate solar capacity.

A retrofit solar installation in St. Louis by EFS Energy.

St. Louis rooftops are often small to begin with, so obstructions combined with fire code setbacks have made solar installation a challenge until now, said Paul McKnight, board member of the Missouri Solar Energy Industries Association (MOSEIA) and CEO of installation company EFS Energy. He thinks the new code could help solve old problems with installations in the city.

“There’s a lot of relatively heavily shaded areas, there’s a lot of trees in the region, and then when you do have an open roof space, there’s always obstructions,” McKnight said.

Another issue he’s faced is pushback from code officials when trying to install solar on historic buildings, which are numerous in Downtown St. Louis. He hopes the new rules help make solar more accepted in these cases too.

“Having this more overarching goal and having solar-ready zones, I think there will be a lot less pushback from other authorities on where [solar] can go, so I think it’s good in that respect,” McKnight said.

EFS has not done many solar installations in the city, but McKnight is hoping this law opens more possibilities.

When solar-ready goes wrong

Missouri’s solar advocacy group MOSEIA was not directly involved in creating the solar-ready legislation, and a few exceptions to the rule are written vaguely, making it potentially easy for builders to get out of it if they really wanted to, McKnight said. He’s also concerned that code officials may not be prepared to enforce the rules due to their lack of knowledge about solar.

Even in the No. 1 solar state of California, solar-ready rules haven’t had much oversight, according to Rob Erlichman, president of installation company Sunlight Electric.

A Sunlight Electric installation for Ganau America in Sonoma County. Solar was planned in the new construction.

“We have seen over 17 years at least half a dozen times where we had proposed solar, the customer has said, ‘Great, I want to get my structural engineer to sign off on this,’ and the structural engineer comes back and says, ‘Yeah, no can do, the building needs to be reinforced,’” Erlichman said.

In all of those instances, Erlichman’s own engineers took a second look and determined it was in fact structurally sound enough to handle a solar load.

“I’m sure they’re all super capable licensed structural engineers, but if you’ve never done solar before and you’re not doing it five days a week, you don’t really understand how to interpret the code,” Erlichman said. “So, as a result, we’ve seen plenty of the ‘solar-ready’ situations involve over-engineering a building, which makes no sense and is a waste of money, or we’ve seen the opposite happen.”

In one example of the opposite, an international food service company told Sunlight Electric its new under-construction warehouse was being built to be solar-ready. When Erlichman looked at the building plans, he saw the steel support columns were actually too thin to support a solar load. Since he caught the error early in construction, the company had time to up-size them so solar would work.

“If we didn’t ask, then it would have been a tragedy. To reinforce those columns after the fact would probably have made it prohibitive,” Erlichman said.

In addition to load-bearing capacity, he said the ideal solar roof is made of 20-year single-ply membrane for strength and added energy efficiency. Electrical infrastructure must also be planned for to ensure a smooth solar installation later.

“If I were made national wizard for solar, in addition to ensuring that the structural integrity is adequate but not overly designed, I would want to make sure that there’s a set of standards associated with how to build the electrical infrastructure to properly prepare for solar,” Erlichman said.

Solar-ready without a mandate

Sean Price, director of commercial sales for Virginia-based installer Sigora Solar, said although there’s no requirement for constructing solar-ready buildings in the company’s home state yet, he’s seeing a trend of more building owners choosing to design net-zero buildings with solar or at least leave the option for future solar via solar-ready design.

A Sunlight Electric installation for affordable housing community Mercy Housing in Sacramento. Solar was planned in the new construction.

He said the biggest solar-ready considerations for building owners is designing roofs that are structurally capable of handling the additional load of solar panels and making sure the roof has a long warranty.

“In the event that a building isn’t ready today or for whatever reason it’s just not in the cards for the near future, having that kind of proactive planning is always beneficial,” Price said.

Axium Solar of Texas has worked on some solar-ready new builds as well, most notably the Austin Central Library. The builder wasn’t sure it would install solar immediately but prepared for it anyway.

“Sometimes the solar might be an alternate, and depending on the bid and the budget that comes in, they may decide to keep it or take it out of the scope but they’re at least putting in the infrastructure just in case,” said Eric Cotney, VP of Axium.

The library ultimately decided to add solar while the building was under construction.

Cotney said there have been other new building projects where engineers have consulted with Axium to understand what size conduits to use and how to adequately prepare for solar.

Whether it’s mandate-driven or a building owner’s personal choice, preparing new construction for solar in the future is a good investment that cuts solar install costs later and increases the technology’s reach.

I have been advocating for “solar ready” roofs in new construction for many years. It is a forward-thinking concept and just makes sense. I have also been involved with the roofing industry for 4 decades. An important ingredient of “solar ready” involves choice of roof type. I have strong disagreement with what one of your contributing authors considers the “best solar roof”. With module service life in the range of 30 years, single ply membranes empirically do not have service life consistent with that of the solar modules mounted to them. When that membrane roof expires in 15 or 20 years the costs of dismantling solar, re-roofing and re-assembly of the array are astronomical. While inverter replacement is normally included in the solar financial proforma, roof replacement is not. It certainly should be. It is a real cost of ownership for most roof types. Metal roofing (especially standing seam) on the other hand has a service life between 50 and 100 years, depending on the metal type. It is non-combustable (Class-A), virtually maintenance-free and enables penetration-free and ballast-free mechanical attachment that is easily tested and engineered to virtually any service load criteria desired. It is also environmentally friendly with 100% recyclability and the highest recycle rate of any construction material. Because standing seam metal roofs also have built in, “free rails” (up-standing seams every 12″-24″), the cost of adding rails can be obviated. In fact, the total mounting cost for metal is actually much lower than for any other roof type. The solar array has a cost and value many times that of the roof. Inferior roof types diminish the real value of solar. Roof and solar should always be considered as a single asset. Putting an expensive P.V. plant on a membrane, or asphaltic roof is like putting a Ferrari engine on a Volkswagen chassis– who would do that?

Further, it seem solar issues should be incorporated into the design and orientation of all structures. Fore example, one does not need the summer sun blasting through south Windows in the Texas summer. But that sun renders a lot of KW or BTU on a sunny winter day in Wisconsin. What about solar hot water for showers or heating? Etc. Thanks Jim Johnson Greenfield Mo

“The state of California and cities of Orlando, Florida, and Tucson, Arizona, along with others, have incorporated solar-ready requirements in commercial or residential building codes. Some have done so in pursuit of SolSmart designations, a program run by The Solar Foundation that distinguishes cities and counties that are “open for solar business.” In “requiring” a solar PV ready roof to be constructed as part of the construction code, then it should also take into account the wind loading factor the roof will endure when solar PV is installed. This “should” decrease the soft costs required by cities and counties for “proper design construction” of a roof with solar PV installed. Some counties require a sign off of a Civil Engineer and an Electrical Engineer, before a permit is allowed to start the installation. If the building code has this as the specification, then it should be approved before the building has begun. “Whether it’s mandate-driven or a building owner’s personal choice, preparing new construction for solar in the future is a good investment that cuts solar install costs later and increases the technology’s reach.” This would be the codicil of the construction industry’s “measure twice, cut once”.