The 2017 hurricane season demonstrated that many solar projects in the Caribbean are not engineered and constructed with sufficient survivability. Forensic investigations have shown that even basic wind codes were not observed in many cases, resulting in widespread failures.
In 2018, we co-authored a hurricane survivability study with the Rocky Mountain Institute, and since then we have consulted to the National Renewable Energy Laboratory and Aon Insurance on regional survivability measures.
This article highlights some important and basic measures to ensure PV Systems in the Caribbean are built to survive Category 5 storms and deliver clean energy for many years.
These are our top considerations for engineering and building resilient and survivable solar-energy systems in the Caribbean. The primary considerations that make a Caribbean project different are wind resistance and corrosion.
The intent of this information is to ensure the highest survivability and reliability of Caribbean solar-energy systems. These measures are intended to ensure the wind and corrosion on their own do not disable the system. It is difficult to control for flying debris, however, at least twice a year, inspect the array surroundings and remove loose debris that can become projectiles during a hurricane.
The first step is to define a rigorous quality assurance (QA) and quality control (QC) process. Include the QC inspection checklist in the contract documents to ensure compliance with no changes to cost or schedule. The following specifics can be included in the specification and inspection protocol.
- Determine the Wind Exposure and Risk Category for the project site. Confirm if any topographic factor or other aggravating factors are necessary.
- Engineer to the local wind-speed code. If the code is silent on wind speed, refer to ASCE 7-10 or OECS code for minimum wind speeds. If an OECS location, include the regional “climate change” adder to the wind speed. Accept an owner preference if higher than code, but never if lower than code.
- Commission a structural sufficiency study for all projects: structural analysis of existing roofing, attachments, and structural members for roof mounted; geotechnical analysis for ground mounted systems with foundations.
- Ensure the racking system and foundations (or attachments) are engineered and sealed to the calculated reaction forces using the structural/geotechnical data. This includes uplift, torqueing, and lateral forces.
- Mechanical Strength. Generally speaking, 2400 Pa uplift-rated modules usually are not sufficient for the Caribbean, unless the project is Risk Category I. Confirm the structural positive and negative loading based on the above criteria. Confirm the selected solar module (panel) meets that load specification.
- Confirm whether the module rating is certified to UL-1703 or IEC-61215. We recommend only 61215-rated modules for the Caribbean due to the cyclical loading test protocol.
- The IEC test uses the “LRFD” rating (Load and Resistance Factor Design, with no safety factor), and the UL test uses “ASD” rating (Allowable Strength Design, and includes safety factor). Confirm the testing in the Installation Manual and compare to the environmental requirements. This will help ensure compliance with insurance and underwriting certification.
- Tighten all mechanical and electrical attachment hardware to specified torque settings, mark hardware, and check markings as part of ongoing preventative maintenance.
- Specify through-bolting or individual clamping of modules. Do not use multi-module midclamps due to the susceptibility to sequential failures.
- Lay out rooftop arrays so that the modules stay in Wind Zone 1. If necessary, use Zone 2, but at all costs, avoid Zone 3 and never let modules overlap or extent beyond the edge of the roof face.
- Select modules certified to IEC-61701 for the appropriate salt-mist corrosion exposure.
- Power electronics and inverters should not be exposed to outside conditions unless they are NEMA-6 (or better) sealed electronics enclosures. Ventilation fans and cooling fins can be exposed to ambient air if inspection and replacement is possible and part of the preventative maintenance program.
- Racking foundations that are below ground shall be aluminum or hot-dip galvanized steel with a coating at least 3.5 mils (G350) and ideally 4 mils (G400).
- All hardware should be stainless steel, ideally grade 316. Do not use galvanized “tek screws”.
- Provide galvanic isolation between dissimilar metals.
- Specify stainless steel NEMA-4X enclosures (transformers, disconnects, switches), rather than ordinary painted steel. Use Aqueous Guard coating.
- Apply appropriate corrosion control and anti-seize coating to module plugs, DC and AC terminations, and hardware.
WIRE MANAGEMENT & ELECTRICAL
- Zipties cannot be used in any location that receives direct sunlight any time during the day or year. In those locations, use stainless steel zipties with PVC coating, stainless steel wire clips, or stainless steel band clamps.
- When used, zipties shall be UL-listed, rated UV-resistant, have a steel tooth (not plastic), and at least 40 lb breaking strength.
- Wire nuts shall not be used for DC conductors. Instead, use Ilsco terminal blocks, Ideal-22 clamps, or other UL-Listed mechanical means.
- Install Transient Voltage Surge Suppression (TVSS) on all DC Combiners, AC Combiner panels, and switchboards.
- Provide a manual DC disconnect for any DC conductors that run underground or inside a building. Consider compliance with NEC-2017 regarding rapid shutdown even if not part of local code.