TODAY’S STUDY: A ROADMAP TO BRING WIND HOME
Built-Environment Wind Turbine Roadmap
J. Smith, T. Forsyth, K. Sinclair, and F. Oteri, November 2012 (NREL)
For the United States to generate 20% of its electricity requirements from wind technology by 2030, strong support from the general public will be needed. The majority of this production will come from large commercial wind projects installed throughout the United States, both land-based and offshore. To date, many of the easily developable sites have already been utilized, and future sites could face a range of potential barriers, including resistance from the general public.
Although only a small contributor to total electricity production needs, built-environment wind turbines (BWTs) nonetheless have the potential to influence the public’s perception of renewable energy, and wind energy in particular. Higher population concentrations in urban environments offer greater opportunities for project visibility and an opportunity to acquaint large numbers of people to the advantages of wind projects. However, turbine failures will be equally visible. High-profile installations, many of which have failed to produce electricity as advertised, could have a negative effect on public safety and perception of wind technology because the general public cannot differentiate between emerging technology and proven technology used in the commercial wind industry.
The market currently encourages BWT deployment before the technology is ready for full-scale commercialization. To address this issue, industry stakeholders convened a Rooftop and Built-Environment Wind Turbine Workshop on August 11 - 12, 2010, at the National Wind Technology Center, located at the U.S. Department of Energy’s National Renewable Energy Laboratory in Boulder, Colorado. Workshop attendees adopted the following vision statement:
“To provide current, state-of-the-science recommendations for optimization (reliable and safe) of wind turbine design and placement in the built environment, assessment of potential challenges unique to the built environment, a list of barriers, and priorities for addressing those knowledge gaps with data/observations and modeling tools.”
Workshop attendees identified barriers to BWT deployment in five key areas.
• Safety is considered the most critical issue for BWTs. Sub-areas include fatigue resistance, braking redundancy, fail-safe mechanisms, and ice- and part-shedding containment.
• Understanding the wind resource (including annual averages, turbulence, and extremes) and developing better wind resource maps are also considered high priorities to support BWTs.
• Improvements to the turbine technology, such as using control strategies to reduce vibration and noise, understanding loads measurements and yaw rates, and developing design and testing standards, will move the BWT industry toward stronger customer acceptance.
• At the same time, in terms of building-mounted systems, understanding building interactions will be pivotal. Concerns exist regarding resonance frequencies, and an understanding of how the building-turbine vibrations are coupled is needed. BWT system designs must comply with building codes as well as integrate with the building’s mechanical and electrical systems.
• Non-technical obstacles, such as concerns regarding safety hazards during installation, operations and maintenance, and inspections must be understood. Consumer outreach and education, along with overcoming economic barriers, must also be addressed. The BWT roadmap also outlines stakeholder actions to overcome the barriers identified. The actions are categorized as near-term (0 - 3 years), medium-term (4 - 7 years), and both near- and medium-term. The BWT industry is evolving rapidly, so long-term actions cannot be projected.
Workshop attendees developed a strategic approach to accomplish these actions that identifies two focus areas: understanding the built-environment wind resource and developing testing and design standards. In this report, the authors summarize the expertise and resources needed in these areas. A wide variety of domestic and international stakeholders are currently engaged with BWTs. Existing wind tunnels, wind measurement data, and models could be utilized and enhanced to expedite the development and deployment of BWTs.
This roadmap identifies key barriers to the development and deployment of BWTs and outlines a strategic approach to addressing these barriers.
What are built-environment wind turbines (BWTs)? In this roadmap, BWTs are defined as wind turbines located in an urban or suburban environment (built environment). Most BWTs are also classified as small wind turbines (SWTs), which are 100 kilowatts (kW) or less.
While the terms “BWT” and “SWT” are interchangeable in many cases, this roadmap uses the term “SWT” when referring to turbines 100 kilowatts and less and the term “BWT” when referring to SWTs in the built environment. “SWT” refers to a category of turbines, and “BWT” refers to a specific application or market niche. See Appendix I for a detailed description of BWTs.
To date, most wind turbines installed in the built environment have been sited with limited understanding of or regard for the unique challenges of BWTs (Encraft 2009). Most SWTs were designed for rural areas, not the built environment with its high turbulence, lower average wind speed, more frequent wind direction changes, and potentially higher vertical inflow. Nor were turbines designed to be in close proximity to people, businesses, and other property. Poor siting and improper use of BWTs could lead to turbine failure, possibly resulting in injury, property damage, and potential liabilities. These liabilities extend to not only BWT owners but also to the industry, which would suffer from general negative perceptions of wind technology.
Recent research on wind energy in urban areas demonstrates that there are promising opportunities to extend the use of wind energy in the built environment. However, developers must pay careful attention to the micro or local wind conditions produced by the stochastic wind interactions with localized structures. Turbine efficiency is highly sensitive to the rapid variations in wind conditions that prevail in the built environments (Kooiman and Tullis 2010). Other difficulties include transfer of vibration and loads to a building structure, potentially causing noise and structural failures (Encraft 2009).
Understanding the loads, dynamics, yaw rate, and other technical specifications is critical in designing or modifying existing commercial products.
The number of BWT installations is increasing as consumers have easier access to relatively inexpensive SWTs (James et al. 2010). In 2010, BWT units experienced substantial sales growth to more than 1,700 kW, or 7% of 2010 U.S. SWT capacity sales.
This represents a remarkable 430% growth from 2009. In terms of units, 1,074 roof-top units were sold (American Wind Energy Association 2011). Many people are motivated by a desire to be environmentally responsible, and they want clean, renewable energy to help power their homes or businesses. While the increased visibility of a BWT can be used to enhance a “green” image, a poorly sited turbine will not produce much electricity and may not even spin, which implies that “turbines don’t work.” Moreover, poor siting will likely increase fatigue issues and may drastically shorten a turbine’s life span. This perception of BWT underperformance introduces a risk that the public will become disillusioned with the greater wind energy industry (Encraft 2009).
By developing the “Built-Environment Wind Turbine Roadmap,” representatives from industry, government, academics, and those with an interest in BWTs have produced a document that addresses the critical needs of safety, technology, and non-technical obstacles in the built environment. Although this is a U.S.-centric document, it includes contributions from international stakeholders. Further, this work will be coordinated through the International Energy Agency (IEA) so that a variety of international entities can pursue this research area. This work is intended to aid in the crafting of public and business BWT policy by providing current, state-of-the-science recommendations.
This roadmap delves into the background of BWTs, including the current state of the BWT industry and the current state of BWT technology. Furthermore, this document describes the five categories of BWT industry barriers: safety, wind resource, turbine technology, building interactions, and non-technical obstacles. An action section addresses these barriers. One action may address more than one barrier, so these actions are grouped into three categories defined by their urgency: near-term (0-3 years), medium-term (4-7 years), and both. Because BWTs are a new wind technology and are evolving rapidly, long-term actions cannot be projected for the current BWT industry. The document concludes with a strategy section that identifies resources to help carry out the actions and provides a plan to remove BWT barriers.
This document is based on presentations and the ensuing discussions from the Rooftop and Built-Environment Wind Turbine Workshop hosted at the National Wind Technology Center (NWTC) at the U.S. Department of Energy’s National Renewable Energy Laboratory (NREL) on August 11-12, 2010. Workshop participants are experienced in SWT modeling and data collection.
Some of the key points from the workshop include:
• Approximate correlations exist between wind tunnel measurements and computational fluid dynamics (CFD) models for specific sites.
• More sophisticated CFD wind resource modeling tools exist, and there is a substantial body of existing work pertaining to other wind propagation models.
• Countries of focus on the topic of built-environment wind turbines (see www.urbanwind.net) exist, and the International Energy Agency Task 27 recently proposed new work.
• As a result, novel approaches to wind energy harvesting may emerge as important players in the effort to increase wind energy use in urban areas. During the workshop, the participants agreed to the following vision statement:
“To provide current, state-of-the-science recommendations for optimization (reliable and safe) of wind turbine design and placement in the built environment, assessment of potential challenges unique to the built environment, a list of barriers, and priorities for addressing those knowledge gaps both with data/observations and modeling tools.”
This roadmap is a step toward that vision.