Posts Tagged ‘community wind’

For those interested in wind, we are pleased to announce the public release of the Distributed Wind Site Analysis Tool (DSAT).  Built with funding from US DOE’s Wind Powering America Program and other sources, DSAT is a powerful new online tool for making accurate performance predictions for distributed wind energy projects.  Combining proven calculation techniques, computer modeling, and real-world performance data, DSAT is a valuable resource for landowners and communities considering wind power projects.

Please visit http://dsat.cadmusgroup.com to see DSAT for yourself.

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Community wind projects often face opposition on a range of issues. Concerns about potential noise and visual impact, avian (bird) mortality, and impact on residential property values are the most common. While the permitting process includes components that provide stakeholders with more information and prompts mitigation measure development, community wind project teams do best by proactively hearing and responding to their community’s concerns.

Impact on residential property values is one of the most polarizing issues facing community wind projects. While introducing community members to research on property value impacts and other issues is just one aspect of easing their concerns, it can be important to building project support.

One potentially valuable resource is “Wind Energy Facilities and Residential Properties: The Effect of Proximity and View on Sales Prices” –a Lawrence Berkeley National Laboratory-authored study on the relationship between wind projects and property values (Journal of Real Estate Research, 2011). This article is based on one of the most comprehensive studies to date on this issue, and it is one of only three peer-reviewed studies on the topic. The study looked at 7,459 homes within 10 miles of 24 wind projects across the country, and field visits were made to each home.

This article may be particularly helpful, as it examines three different (and common) perceived impacts of wind projects, all of which were found to have no statistically significant impact on the sale of homes in the study sample:

  • Scenic vista: A perception that a home may be devalued because of the view of a wind energy facility, and the potential impact of that view on an otherwise scenic vista.
  • Area stigma: A perception that the area surrounding a wind energy facility will appear more developed, which may adversely affect home values in the local community regardless of whether any individual home has a view of the wind turbines.
  • Nuisance Stigma: A perception that factors that may occur in close proximity to wind turbines, such as sound and shadow flicker, will have an adverse influence on home values.

By engaging community members in conversations about their concerns early and often, project teams can better understand prevailing attitudes about the issues and design an appropriate outreach effort tailored to the residents and other stakeholders.  Outreach efforts might include sponsored “fieldtrips” to other wind turbines in the region or inviting representatives from regions with completed wind projects to present. Alternatively, neighborhoods can host coffee nights at a local library or other community gathering point for open discussions. Ideally, such events would be hosted by a neutral third-party wind expert, such as an academic, representative from the state’s energy department, or consultant or developer not attached to the project.

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Wind projects can offer positive economic and environmental benefits for communities and project owners but need to be sited carefully and with sensitivity to the surrounding landscape.  One of the concerns frequently voiced over wind power projects is shadow flicker.

What is Shadow Flicker?

Shadow flicker is a term used to describe the shadows cast by moving wind turbine blades in direct sunlight.  Depending on the sun’s position, the weather, the turbine rotor orientation, and other factors, this flickering shadow can sometimes fall upon an occupied structure or other sensitive area.  Shadow flicker is usually of concern only for larger wind turbines, such as the multi-megawatt turbines used in community and commercial scale projects.  Smaller wind turbines, such as those used for residential applications, generally do not create noticeable shadow flicker impacts.

Is Shadow Flicker Dangerous?

There is no evidence that shadow flicker causes any harmful health effects.  In everyday life, such as driving a car, most people experience flickering shadows.  Shadow flicker is problematic because it may be considered an annoyance by the occupants or users of an area where it occurs.

How is Shadow Flicker Assessed?

Shadow flicker is typically expressed in terms of duration, usually in terms of hours of impact per year.  Calculating this impact involves a number of factors:

  • Sun position
  • Wind direction/rotor orientation
  • Cloudiness and weather
  • Location of sensitive receptors
  • Elevation
  • Terrain/obstructions
  • Turbine/tower specifications

Industry software packages such as WindPro, when used properly, are able to make these calculations and generate predictions of the shadow flicker impacts for the area surrounding the proposed turbine.  An example graphic generated by this kind of analysis is shown in the figure below.

This shadow flicker analysis reveals the anticipated impact on the area surrounding a proposed turbine.

The butterfly-like shape is made up by lines of shadow flicker impact, similar to the lines on a topographic map.  For example, a house with windows facing the proposed turbine located along the blue line could expect about 30 hours of shadow flicker in a typical year.

Are There Standards for Shadow Flicker Impacts?

Unfortunately, most zoning and other regulations related to wind power only refer to shadow flicker in a general sense, using language such as “shall generate no significant impact.”  Some statewide and international standards define “significant impact” as 30 hours or more of shadow flicker per year.

Can Shadow Flicker be Mitigated?

There are several ways to address potential shadow flicker impacts.  The best method is to have a shadow buffer zone between the proposed turbine and any residences or other sensitive receptors.  If that is not possible, shadow flicker can be mitigated by planting trees or other visual screens between the affected receptor and the turbine.  Finally, the project owner can program the turbine to shut down during certain times of day, or under certain conditions, to reduce shadow flicker impacts.

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