Best practices for roof-mounted photovoltaic systems

By AXA XL Property Risk Consulting Technical Advisor, Germany & APAC Marc Van de Velde

Is your company considering installing photovoltaic (PV) solar panels on the roofs of one or more of its facilities? Or perhaps it already has.

If so, it is hardly alone. According to the International Energy Association (IEA), PV solar generation increased by a record 22% in 2021 and “is becoming the lowest-cost option for new electricity generation in most of the world.” The IEA also noted that the residential and commercial/industrial sectors—also known as distributed PV—accounted for 28% and 19% of new solar PV capacity, respectively, in 2021. As the IEA put it, “… generous policy incentives drove record distributed PV capacity additions in China, the United States and the European Union in 2020-2021.”

These “generous policy incentives” include the Inflation Reduction Act, which the U.S. enacted in August 2022, and the steps many European countries are taking to accelerate growth in solar PV capacity. The French law for the Acceleration of the Production of Renewable Energy adopted on 10 March 2023 states that existing outdoor car parks of more than 1,500 square meters must be equipped with solar panels on at least half of their surface, with some exceptions (Art 40). These new solar PV systems are expected to generate as much electricity as ten nuclear power plants.

Two broad sets of risk

The escalating demand for PV panels is helping drive a booming renewable energy market as governments, corporations and individuals confront the increasingly urgent need to transition to a low-carbon economy.

However, it isn’t all upside. Although large, flat roofs on industrial and commercial buildings present a massive opportunity for PV systems, building owners/managers must address two broad issues to ensure the panels and associated components are installed correctly and will operate safely in a variety of conditions:

Making sure that the structural integrity of the building isn’t compromised and that adding these new materials and components won’t threaten the performance of other critical building elements or systems.
 Implementing appropriate measures and taking reasonable precautions to prevent fires, and when one occurs, having processes and procedures in place to lessen the damages and the risks to firefighters.

 Solar PV best practices

Solar PV systems comprise individual photovoltaic cells, pre-assembled into modules or panels, that absorb and convert sunlight into electricity. Other system components include a solar inverter to convert the output from direct to alternating current, plus cables, cable connectors and junction boxes. Many systems today also incorporate solar tracking devices to improve overall performance and an integrated battery to store excess electricity.

Given the rapidly growing pace with which these relatively new technologies are being deployed, AXA XL’s Risk Consulting team has developed detailed guidance to help building owners/managers understand and minimize the unique risks associated with installing and operating solar PV panels on the roofs of existing commercial or industrial structures. Also known as “building-applied” (BAPV) systems, these are the most common distributed PV application types used today. The key points are summarized below.

Although the provisions covered in this publication also apply to new construction, it was developed primarily for building owners/managers looking to retrofit existing buildings with BAPV systems. Also, it doesn’t address the issues with ground-mounted installations found in utility-type plants or building-integrated technologies (BIPV), where panels or thin film materials are integrated into the building envelope.

Roof requirements

With rooftop mounted applications, first and foremost, the existing roof cover/insulation should be assessed considering, e.g., its current condition, expected remaining lifetime and signs of damage. Because of the increased fire risk, BAPV systems shouldn’t be installed on roofs containing combustible insulation materials. Also, the expected lifetime of a PV system is at least 20 years, and upgrading or repairing the roof will be complicated after a system is installed. However, adding a BAPV system could represent an opportunity to upgrade the roof and lessen fire risk by replacing combustible insulation—including building panels with combustible cores—with non-combustible materials. (The fire risks associated with a building containing a solar PV system and non-combustible insulation are still substantially less than in a building without solar panels and with combustible insulation materials.)

The roof deck/roof supports should be inspected and analyzed to ensure they can handle the additional load of the PV system plus expected snow/ice load, hail size and wind speeds. Also, the system design should include elements to facilitate snow removal in places with heavy snowfalls.

Minimizing fire risk

Installing a BAPV system means transforming an empty, typically barren patch of roof into what is essentially a power generation station comprising electrical wiring, junction and combiner boxes, inverters and control equipment, all of which can fail and cause fires. Moreover, as we reported in a previous article, firefighters face new, unique challenges when fighting fires in buildings equipped with PV systems.

Since most PV fires won’t self-extinguish and will require some manual intervention, these systems shouldn’t be installed on roofs outside a fire department’s reach because of the building height, layout/configuration, or other factors. Also, most roofs lack fire detection and suppression systems, so there might be considerable delay in fire department notification.

AXA XL would also recommend that companies review their plans/designs with local fire brigades including, importantly, the location of the disconnection means, plus the inverters and cables that can’t be de-energized. Turning the system “off” is critical to removing the risk of electrical shocks when applying water to the fire. However, that only stops the current flowing from the panels into the building’s electrical system; the panels themselves can continue to produce power if the fire occurs during the day. As a result, firefighters battling blazes in buildings with solar panels need to be continuously aware of electrical shock hazards.

Other considerations

The material also includes general guidance on various issues related to the design, installation and operation of solar PV systems. For example:

You should only use PV panels that comply with relevant internationally recognized electrical performance and safety standards and have an approval/listing from an independent testing laboratory such as TUV, UL, FM or CSTB.Make sure that the installation doesn’t compound possible snow or rain accumulation that could, in turn, affect roof stability.You should not install panels over or next to drains and other roof installations that require regular maintenance and inspection

It also covers specific parameters including:

Size and spacing considerations, e.g., the minimum borders between the panels and other building elements or housing battery storage systems separately from plant operations.The proper placement of cables, cable connectors and related components including junction and combiner boxes.Provisions for minimizing undetected ground faults or DC arc faults. These have caused many of the losses in PV installations and can be triggered by poor installation practices, faulty designs, insulation degradation, or water ingress into system components.

In sum, the AXA Group, AXA XL and AXA XL Risk Consulting are committed to supporting the transition to a low-carbon economy and applaud our clients’ efforts to reduce their CO2 emissions, including by retrofitting existing facilities with solar PV systems. We hope the best practices we have developed will help clients better understand the issues and implications of these installations and ensure that they are designed, installed and operated safely and efficiently.