Florida's Winds Create  Installation Problems for 
Solar Water Heating and Photovoltaic Modules on Buildings 

Wind speeds in Florida, among the highest in the nation, are capable of creating loads on solar equipment installed on buildings that exceed the allowable or "design" capacity of solar water heating collectors and photovoltaic modules. Building Codes require that components to be installed in or on buildings be tested or certified for obvious safety reasons. The testing establishes the allowable load that solar, and other equipment (components & Cladding) attached to, or installed on, buildings can withstand to ensure the safety and integrity of the installation. Building Codes and associated standards such as ASCE-7 (American Civil Engineers Minimum Design Loads for Buildings & Structures) develop methods to determine the magnitude of the loads created by wind. They also establish the "allowable" loads that must not be exceeded for safety reasons on buildings and associated components, such as the solar equipment installed on the roof, walls, etc. of buildings. Code Officials typically verify that a solar installation uses components that have been fully certified and/or designed in compliance with wind loads as well as the myriad of other health and safety issues related to construction during the permitting process .

In order to address this issue, manufacturers of solar equipment have their equipment tested by Nationally accredited laboratories to determine the structural capacity of their equipment. Solar water heating system manufacturers have been having solar collectors tested for years and submitting them to Metro Dade for Product Approval. Photovoltaic manufacturers have their modules undergo mechanical (structural) testing as part of the module certification process. The testing essentially establishes a "test load" which is used to establish the allowable load that the equipment can be subjected to. The load established by the manufacturer, based on expectations of performance, is used during the mechanical (pressure) testing to establish the "design" load which in Florida will be 50% of the "test" load. The design load is the maximum allowable load on the component. In the case of some equipment, notably photovoltaic modules, the test load established by the manufacturer is too low for installation on many buildings in Florida. The wind loads in Florida approach and sometimes exceed the solar collectors or modules "allowable" or design load for an installation on residential buildings. Installation of Solar systems on commercial or industrial buildings can be more problematic because of the higher wind loads on taller buildings that often requires specialized installation documents (designs) developed by Structural Engineers to meet the wind load requirements.

Photo courtesy of Solar Design Inc.

The wind creates forces (loads typically expressed in pounds/square feet, PSF) on all of the building surfaces and any equipment including solar equipment attached to it. The force of the wind creates positive loads on the surfaces as well as the negative or uplift loads visible in the picture. The most common damage from high winds results from the uplift load, the result of which are graphically illustrated in the picture. Wind load on collectors and modules installed on a roof are not only a function of the speed, they are a function of the surrounding area (Exposure Area), the height of the collector, the location of the collector on the building, how the equipment is attached to the building and what it is attached to.

The wind load on a solar array installed at ground level will be significantly less then the wind load on a collector installed on the roof of a building because the wind speed, and the associated load, increases with the height above the ground. A solar collector installed on a roof at its edge must be able to withstand a higher load than a collector located in the central area of the roof. A collector or module installed on a high rise commercial building such as a Condo or Office building will have a significantly higher load by virtue of it's height. Solar equipment should be designed to take the loads it will be subjected to and properly attached to the building structure in order to be a "safe" installation and be "Permitted". As many of us say in this area, this is not "rocket science", it's simply a matter of doing it right in the first place, perhaps attaching the collector in a stronger manner (using larger hardware (bolts etc.,) and/or number of connections) and/or locating solar equipment in areas that would be expected to have lower design loads.

The installation requirements for solar equipment (collectors and modules) are clearly detailed in the Florida Building Code that has specific requirements and procedures that can be used to ensure a safe installation. The solar equipment must be tested to determine it's Mechanical Capacity to resist the forces of the wind. The solar equipment must be properly attached to the Main Force Resisting System (MFRS-Building structural system)to ensure the entire installation will meet or exceed the site specific wind load. The wind speeds and resultant loads vary throughout the state as can be seen on the wind speed map below. Recent (July 2007) changes in the Florida Building Code (FBC) expanded the Wind Borne Debris Region, effectively increasing the design wind loads in the coastal areas by requiring areas with wind speeds 120 MPH or more to be designated Exposure C increasing the design wind load up to 40% for many residential installations. This change increased the design load on many buildings in the coastal areas impacting both residential and commercial installations.

Wind loads increase significantly with height, and can be problematic for solar applications on high rise Commercial and Industrial (C&I) Buildings in coastal Florida where winds loads will be significant. The wind loads on solar equipment on tall buildings can readily exceed the design uplift load or capacity, typically 50 to 55 pounds per square foot (PSF) of the typical solar water heating collectors. A recent review of construction documents for solar thermal and electric installations on a ten story commercial building in the central area of the state, for example, found that the design wind load approaching 100 PSF. If the installation was to be evaluated using ASCE-7 2005, which will become effective in Florida in the near future, the load could approach 125 PSF depending upon the location of the equipment, significantly above the allowable load for the solar components. These are the types of issues that need to be addressed if the sunshine state is to utilize solar energy.

The Solar industry in Florida faces a significant barrier over the structural issues. At the present time Solar thermal collectors sold in the state have been tested using procedures developed by Metro Dade years ago have design (maximum allowable) wind loads of 50 to 55 PSF. Actually, solar thermal collectors must be tested at two times the design load following Metro-Dade's procedures, adopted in the Florida Building Code in the Test Protocols in order to verify the allowable design loads. Solar thermal collectors may need to be installed differently or beefed up in the future. Solar electric (photovoltaic ) systems however are another story.

Photovoltaic (PV) modules have not been tested (Mechanical Tests)to the same levels (test pressures) as solar thermal collectors. The majority of PV modules have been tested (for uplift) in accordance with the UL Standards up to 2,400 PASCAL's (50 pounds/Sq. ft or PSF). Modules tested to pressures of 50 PSF have an allowable design (wind) load of only 25 PSF, 50% of the test pressure in Florida. A quick glance at the Tables for Components and Cladding on roofs with a mean roof height of 30 Feet in the FBC or ASCE-7 will quickly point out the limitations of a design load of 25 PSF

PV modules with allowable wind loads of 25 PSF can not be installed on the roof of most buildings in the coastal regions throughout Florida and they will not be readily "Permitted" on the high-rise buildings at all unless test loads are increased and/or structural designs that can provide improved structural capacity are developed and signed and sealed by a Florida Registered Engineer. This is a real problem that needs to be addressed by the PV Industry.

At the present time many Solar Contractors, Distributors and Manufacturers are experiencing difficulties in the permitting process because of structural issues and/or concerns raised by Building Officials related to the installation of solar applications and their attachment to the buildings. PV manufacturers are doing little to address the issue-it is a Florida issue. As a result of the limited structural capacity of PV Modules, code officials are today requiring Signed & Sealed drawings for new solar electric installations to verify the capacity of the installation. It may well be that more than drawings should be reviewed- it may be that the inherent capacity of the equipment should be verified. While this is not a significant issue on the economics of C&I installations, it is a serious impact for homeowners interested in "going solar" with PV. This issue needs to be addressed if Florida is to utilize solar energy, it's most abundant resource!

Florida, the sunshine state, has abundant sunshine 12 months of the year, unfortunately it also has some of the highest wind loads in the country. Metro Dade established the requirements and test procedures years ago that have been integrated into the FBC and can be used to improve the inherent ability of solar collectors and modules to meet today's wind load requirements. Hopefully these issues and the limited structural capacity of Photovoltaic Modules will be addressed so that PV can be installed throughout the State. Healey & Associates has been involved in testing of solar equipment, providing structural installation information to assist the industry and the Florida Solar Energy Center in addressing the structural issue and the need for collector testing to the levels required in Florida for years. We believe the time has come to face the issue and address it.