Minimizing Wind Project Geohazard Risks
Impact Opportunity and Cost of Change as a Function of Wind Project Advancement
Introduction
Wind projects are not born overnight. Before we see wind turbine generators (WTGs) spinning and generating clean energy, many years are are required in development, design and construction. These distinct but often overlapping phases come with their own sets of tasks, timelines and narrowing opportunities for reducing risks stemming from geotechnical hazards.
As in all large expenditure projects, early decisions have the greatest impact on project financial performance while the cost of making design changes increases as a function of project advancement. Therefore, it makes sense to “front-load” the geotechnical risk assessment effort to avoid cost overruns due to missed geohazards or inadequate early project estimates. By the same token, it would not make sense to employ detailed design site characterization methods during the development phase when the project is lacking definition.
At Civil renewables, we have the expertise necessary to recommend rational and balanced distributions of the geotechnical investigation effort and methods that are suitable for each phase of project execution irrespective of when or how we are retained on the project. In this blog article, we go over typical industry practices and some common-sense recommendations mostly extracted from this 2013 ISSMGE paper titled “Geotechnical Explorations for Wind Energy Projects.”
Phase 1 - Development (by Developer)
The initial phase involves site selection, landowner agreements and wind data collection, which can take anywhere from two to many years. During this period, developers identify suitable locations, evaluate wind resources, and conduct environmental impact assessments to ensure the project's viability. This development phase would ideally conclude with a Power Purchase Agreement (PPA). Typically, little to no attention is given to geohazards and feasibility of foundation systems during this phase. The developer typically engages third parties for environmental impact assessments. For geohazards, we recommend that the developer engage a geotechnical engineer to perform, at a minimum, a desktop study based on published public domain information and possibly some site visits and excavation pits. The investment in a desktop study is very little money that is well spent because it can reveal potential geohazards to guide project area selection or to look out for during the subsequent phases of the project.
Some developers go a little further than a desktop study by commissioning a preliminary geotechnical investigation. This is even better but, depending on project timelines, we still recommend a desktop study be commissioned prior to the preliminary geotechnical investigation to inform the projects layouts under consideration and the exploration locations for such an investigation. The desktop study will increase the chances of retaining, as part of the final layout, the WTG locations explored during the preliminary investigation.
Phase 2 - Design (by Developer & EPC Firm)
Following successful financial and environmental feasibility studies, the design phase kicks in, lasting approximately one to two years. This stage involves the selection of wind turbines and evaluation of different layout configurations. Simultaneously, developers navigate the complex regulatory landscape to obtain necessary permits and approvals. This stage is typically divided into two phases:
Phase 2a - Preliminary Design (by Developer or EPC Firm)
The preliminary design phase is commonly performed by the developer as part of early pricing exercises that are useful in informing the project award to the EPC contractor. Sometimes, the preliminary investigation is also left for the EPC firm, with increased uncertainty both for the developer and EPC firm. Regardless of whose scope the preliminary investigation is under, it should benefit from a prior desktop study or a desktop study that integrated with the preliminary investigation. The preliminary investigation would typically consist of:
Exploratory borings at a subset of WTG locations selected to provide coverage of different geotechnical settings anticipated across the project area, as well as at Operations and Maintenance (O&M) building and Substation (SS) areas.
Geophysical surveys using seismic methods such as Multi-Analysis of Surface Waves (MASW) at a subset of WTG locations.
Laboratory testing, as appropriate.
Electrical and thermal resistivity field and laboratory testing.
The preliminary investigation should be sufficient to provide a design basis that is adequate for preliminary design quantities. If performed under the developer scope, this information should prove beneficial to both developer and EPC firm in their contract negotiations.
Phase 2b - Detailed Design (Typically by EPC Firm)
The detailed design phase is commonly performed by the EPC contractor to produce site specific foundations designed for project-specific wind turbine loads. The geotechnical design parameters would be based on a full geotechnical investigation where:
Each WTG location is explored using at least one boring.
Geophysical surveys using seismic methods such as Multi-Analysis of Surface Waves (MASW) at a subset of WTG locations.
Laboratory testing, as appropriate.
Electrical and thermal resistivity field and laboratory testing.
The development and design phases are iterative, with adjustments made based on ongoing assessments and feedback from various collaborating experts, including wind energy specialists, engineers, environmental scientists, and regulatory professionals, to ensure a comprehensive and sustainable wind energy project. However, the development and design phases are typically undertaken separately by the developer (development scope) and then EPC firm (detailed design scope). This process breaks the required iterative feedback loop when the developer hands off the project to the EPC contractor for the detailed design phase. For this reason, some developers keep at least some portions of the preliminary design scope before awarding the project to an EPC firm with the intent that the preliminary work would be adopted and used by the EPC firm to take the project to the detailed design stage.
Phase 3 - Construction (by EPC Firm)
Construction is the subsequent phase, typically lasting up to one year, where turbines, electrical infrastructure, and transmission lines are installed. Not much room is left at this stage for design changes. With some luck, there may be an opportunity for value engineering but changes at this stage are mostly on the negative end of the spectrum where they are very costly for the project.