The industry needs to standardize tracker bankability reports to reduce investment risk

By Colleen O’Brien, principal engineer for DNV GL

Before investing in a solar tracking system to harness sunlight effectively, buyers customarily require an objective analysis to assess the product’s risk factors and quality. Today, there are no unified or universally recognized standards for tracker technical assessments. It is imperative for comprehensive, independent bankability studies to fill this gap in the industry.

However, the inconsistency of bankability reports often yields incomplete, inconsistent or even misleading information, leading to the inability of stakeholders to properly assess project risk.

To help solar investors tackle this challenge, DNV GL conducted a thorough gap-analysis of tracker bankability reports from various third parties. The full results and recommended practices are reported in the paper “Tracker Bankability Reviews: Guidelines for Stakeholders.” The set of guidelines aims to help standardize a methodology of solar PV tracking systems, helping stakeholders assess the performance risk of financial investments.

A key takeaway is simply that the analysis should be thorough. It must cover a review of the tracker’s structural, electrical and mechanical systems, risk of stow failure, manufacturer quality, installation and operations and maintenance (O&M) procedures and PV module compatibility. A full 15 areas are vital to a comprehensive and accurate study.

What follows is a brief summary of these guidelines along with DNV GL’s view on the recommended level of diligence that is appropriate during the technical review process.

15 tracker bankability report ground rules

  1. Company history: Summarize the supplier’s tracker manufacturing or other manufacturing experience and manufacturing locations. Also include services offered by the tracker supplier.
  2. Product description and history: Describe the field history of the specific tracker model and provide a description of the product, as well as the status of product development.
  3. Date and applicability: Clearly describe the tracker make and model and include a parts list (bill of materials, or BOM). The report should include any limitations in applicability to specific projects and design aspects varying from one project to the next. DNV GL recommends refreshing a bankability study at least every one to two years to address more recent field history.
  4. Manufacturing and quality management: Provide the manufacturer’s most current ISO status and certification, and ensure the ISO is applicable to the manufacturing locations used for production. Critically review manufacturing and quality procedures to confirm an appropriate level of detail. Inspect the manufacturing facility and confirm adherence to written procedures.
    Inspect and confirm that the packaging, labeling and bundling of components for delivery to the project site are appropriate to facilitate material storage and construction activities at typical project sites. Take into consideration the climate and weather patterns at various sites.
  5. Installation manual: Critically review the suppliers’ installation manual and confirm that the manual has an appropriate level of detail to allow typical installers to construct the system and meet the manufacturer’s stated tolerances.
  6. Regulatory requirements: Provide the status of the tracker’s certification to regulatory standards. These industry-standard tests are reasonable stress tests of some components and assemblies. For example, the Underwriters Laboratories (UL) and the International Electrotechnical Committee (IEC) typically update standards in three- to six-year cycles to address key performance or safety risk areas as issues surface in the field.
  7. Module compatibility: Confirm the tracking system does not subject modules to excessive vibration, twisting or unbalanced loading, unless modules were tested and demonstrated to withstand these loads. Modules should be mounted and bonded to ground according to the manufacturer’s installation manual and be certified for use with the tracking system to UL 3703 or other applicable test standards.
  8. Structural validation: The licensed civil and structural designer should address project-specific factors such as wind and snow loads, soil type and corrosivity in project-specific drawings and calculations. Critically assess the structural capacity of all major components and assemblies.
    As best practice, IE’s structural design should review and verify completeness of component and assembly drawings, including part numbers and revision control data, mapped in the parts list under “product applicability.”
    • Wind tunnel testing: Perform a detailed review of the wind tunnel report, including the full range of tilt angles and wind directions tested in the wind tunnel. Ensure the report aligns with wind tunnel testing methodology and complies with ASCE 7 and ASCE 49 (or other accepted international standards), as well as an analysis of:
      • Static wind loads
      • Dynamic amplification
      • Aeroelastic deflection
      • Instability: torsional galloping (stall flutter)
      • Instability: vortex lock-in
      • Flutter and divergence
  9. Mechanical and control system validation: Summarize the completeness of component and assembly drawings and provide a critical review of the suitability of the components, system validation test methodology and results. Also provide a summary of findings and review of mechanical failure modes and effects analysis.
  10. Electrical validation: If applicable, confirm electrical diagrams of the control system wiring and electrical power supply for the drive system contain an appropriate level of detail and follow good industry practices. Battery systems require additional review to assess the battery management system controls, sizing, reliability and life expectancy.
    Summarize the control system design and comment on the soundness of the design and expected reliability. To fully understand the risk assumed by the purchaser, evaluate lightning and electrical surge protection.
  11. Reliability validation: Laboratory and field test reports should indicate that a tracker reliably performs as intended. The IE should summarize the manufacturer’s extent of the reliability testing and offer an opinion regarding any gaps in materials or components that may not have been addressed.
  12. Field history: Summarize any field failures, warranty claims and corrective actions reported by the manufacturer. Analyze field performance data with conclusions presented on tracking accuracy and tracker availability.
  13. Tracking algorithm and stow: A bankability study should verify tracker can be expected to operate in most field conditions with a minimum amount of lost energy generation when not tracking, best conducted through physical testing and field trials.
    If used, the optimum position for stowing requires complex testing and analyses, which is design-specific. Describe the tracker’s wind and weather mitigation strategy and evaluate risk if the protection system fails to engage before damaging wind speeds occur.
  14. Warranty: Provide a description of warranty coverage. While it is typical for the warranty to cover equipment replacement during a five- to 10-year warranty period, the independent engineer should note any other warranty coverage provisions such as reimbursement costs for labor, shipping or lost energy.
  15. Operations and maintenance: Perform a detailed review of the manufacturer’s O&M manuals, spare parts list and cost estimate for scheduled and unscheduled maintenance and comment on whether the data is from actual field data or engineering estimates.

As a relatively young technology, most solar tracker manufacturers maintain a limited field history, contributing to the increase in risks as new participants enter the market. DNV GL’s guidelines serve to educate and help independent engineers improve independent technical evaluations of single-axis PV tracker systems. Knowledge of technology risk and cost of ownership can empower a buyer to make more informed product decisions. With a comprehensive set of guidelines, bankability reports have the power to strengthen the solar industry’s overall growth and credibility.

Colleen O’Brien is a principal engineer at DNV GL, where she performs technical due diligence reviews of commercial and utility-scale photovoltaic systems including solar resource analysis, energy forecasting, electrical and structural code compliance and construction monitoring. She graduated from University of New Hampshire, where she studied Mechanical Engineering and is a registered Professional Mechanical Engineer in California.

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