Background[edit | edit source]
As costs of PV decrease at a disproportionate rate to the related racking, an alternative approach relaying on lightweight reusable plastic to develop a self-ballasted PV rack is being investigated. Such a racking approach would eliminate the need for roof penetrations or structural modifications, and would reduce production costs by eliminating necessary ballasts and material sourcing. Current flat-roof racking alternatives rely on aerodynamic wind deflection methods, modular designs to improve load sharing and stiffness, roofing adhesives, to reduce the required ballast weight, but still rely on some form of ballast integration within the array.
Search Terms[edit | edit source]
"Ballast less" Solar Racking"
"Solar Racking" & "Ballast"
"Solar Racking" & "Non-penetrating"
"Ballast less PV Racking"
Market Analysis[edit | edit source]
Ballast-less Systems[edit | edit source]
- no roof penetration or ballasts unless located less than 9ft from edge of building
- concrete slabs (ballast) required for corner and edge lines of panels, center of array is free from all additional ballast
- withstand 120 MPH winds
- material: polypropylene UV stabilized
- complete wedge unit, fully enclosed, and interlocking
- non-ballasted solution relies on hot air welding to secure racking
- Individual panel "feet" affixed to roof using a penetrating coating
- Offer ballasted and ballast less mounting options
- ballast less mounting options are dependent on non-penetrating adhesive mounting to a bitumen roof (not acceptable on all roof materials)
Ballasted Systems[edit | edit source]
- Ballasted modules relying on cinderblock ballasts and metal framing
- Modular design connects adjacent rows of panels to the same rack
General Summary[edit | edit source]
“What’s up with solar ballast?,” Solar Power World, Apr. 07, 2016. https://www.solarpowerworldonline.com/2016/04/whats-solar-ballast/ (accessed Oct. 14, 2021).
- General overview on projected use of ballasts in PV racking and
- pros/cons of ballasted and ballast-less approaches versus market availability
- anticipated movement for nonpenetrating solution, but minimal ballast-less design approaches currently
References[edit | edit source]
Zero-Penetration PV Racking[edit | edit source]
M. Browne, S. Gamble, and M. Gibbons, “Wind Turbulence and Load Sharing Effects on Ballasted Roof-Top Solar Arrays,” in Advances in Hurricane Engineering, Miami, Florida, United States, Nov. 2012, pp. 448–459. doi: 10.1061/9780784412626.039.
- Discussion based on current ballasted racking systems installed on commercial buildings
- Breakdown of incentives and challenges for ballasted and (target) self-ballasted approaches
- local loading and deflection
- lifting and dragging effects of wind
- existing rooves and water proofing
- Design methodology for reducing ballast weight while maintaining reliability (fully self-ballasted solution not investigated)
- Largest target for reducing cost without structural upgrades: aerodynamic wind load reduction
- load sharing through system stiffness to strengthen lifting regions (Distribution of stiffness decreases as edge of array is reached)
- Calculating required ballast
- Complete wind tunnel testing validating load reduction approaches
- recommended to reduce conservative wind loading coefficient estimates using "scale modeling in boundary layer wind tunnel and wall of wind testing"
- peak uplift and downforce distribution depending on wind direction modeled
Peek, Richard T. 2014. "Innovative Ballasted Flat Roof Solar PV Racking System". United States. https://doi.org/10.2172/1167673. https://www.osti.gov/servlets/purl/1167673.
- injection molding approach
- vacuum forming and thermoforming
- only 1.3 lbs/ft^2 weighted array
- methodology in transitioning from metal to plastic products and selection
- Optimal reduction of weight associated with low tilt angle, optimal energy generation demands high tilt angle
- superiority of curved wind deflector proven in wind tunnel studies
- no patent commercial variant by partner https://cascadese.com/post-modern/
The role of corner vortices in dictating peak wind loads on tilted flat solar panels mounted on large, flat roofs[edit | edit source]
D. Banks, “The role of corner vortices in dictating peak wind loads on tilted flat solar panels mounted on large, flat roofs,” Journal of Wind Engineering and Industrial Aerodynamics, vol. 123, pp. 192–201, Dec. 2013, doi: 10.1016/j.jweia.2013.08.015.
- experimental approach and test procedure to determining required ballast using scaled wind tunnel tests
- array to building generated wind field discussion and test design
- Interesting result regarding minimal dependency of uplift force on panel array distance from roof edge outside of winds acting on the "sunny-side"
- roof-edge zone not necessary on all sides
- detailed wind behavior across specific angular contact range of panels and for varying building heights
Mechanical Characteristics and Failure Mode of Asphalt Concrete for Ballastless Track Substructure Based on In Situ Tests[edit | edit source]
F. Qinghong, X. Chen, D. Cai, and L. Lou, “Mechanical Characteristics and Failure Mode of Asphalt Concrete for Ballastless Track Substructure Based on In Situ Tests,” Applied Sciences, vol. 10, p. 3547, May 2020, doi: 10.3390/app10103547.
- pros and cons for asphalt adhesion method to ballast less and non-penetrating roof mounting
Testing Method and Existing Results[edit | edit source]
Wind Field Measurements around Photovoltaic Panel Arrays mounted on large flat Roofs[edit | edit source]
Pratt, R Nicolas, "Wind field measurements around photovoltaic panel arrays mounted on large flat-roofs" (2012). Electronic Thesis and Dissertation Repository. 986.
Relevance: paper investigates wind loads and their correlation to design variables. A better understanding of aerodynamic variables translates to design for minimized loading and thus minimized ballast weight
- Relationship between panel installation and resulting uplift forces
- increasing tilt angle = transition form vortex induced suction to local flow around the panels
- small tilt angles governed by large scale building vortices
- flow separation at building edges result in vortices: largest mean and peak suction forces occur when wind approaches and is split along the building's corner
- peak roof suction position varies depending on the oncoming flow and boundary layer depth. As the boundary layer depth increases, peak suction occurs closer to the leading edge of the building
- separating and reattaching shear layer (separation bubble) varies the pressure field close to the roofs surface
- reducing the turbulence scale reduces the magnitude of peak suctions
- smaller scale turbulence vortices are shed before they can mature
Design and testing Considerations
- Splitter plates can be used to remove and control the boundary layer and directly influence the variables described above
- CFD results can deviate by up to 35% and suggest the preferred need for wind tunnel testing
- Positive effects of pressure equalization by strategic use of openings between two surface
- internal AND external surfaces optimized to reduce the net load
- peak uplifts on panels are LOWER than those on buildings without panels installed suggesting promising results from panel design to neutralize loads
- utilizing shielding effects of surrounding panels
- Tests must be conducted at 0 (north), 30-60 (corner vortex), and 180 degrees relative to the building
- Pressure taps must be used to measure pressure on the upper and lower surface of the PV panels - a total of 3 were used per panel along the panel centerline
Abiola-Ogedengbe, Ayodeji, "Experimental investigation of wind effect on solar panels" (2013). Electronic Thesis and Dissertation Repository. 1177.
3D Printing and PV Racking Integration[edit | edit source]
3-D printing solar photovoltaic racking in developing world. Energy for Sustainable Development[edit | edit source]
Ben Wittbrodt, Joshua Pearce. 3-D printing solar photovoltaic racking in developing world. Energy for Sustainable Development, Elsevier, 2017, 36, pp.1-5. ff10.1016/j.esd.2016.08.001ff. ffhal-02113479f
- cost benefit analysis of using recycled plastic (0.10 USD per kg)
- Tested using PLA and HDPE
- 3D printed method allows for quick and easy repairs
- Risk: transition to brittle material is common in polymer with prolonged exposure to UV light