Background of setback for industrial wind turbines from California

There is no documented substantiation for the setback distances when calculated as (X) x (turbine_height).

Scott Larwood of CA Wind Energy Collaborative and I had several conversations on this topic leading up to the release in Nov'06 of his white paper entitled PERMITTING SETBACK REQUIREMENTS FOR WIND TURBINES IN CALIFORNIA prepared for the CA Energy Commission.
(see: http://www.energy.ca.gov/2005publications/CEC-500-2005-184/CEC-500-2005-184.PDF) (This is an updated paper from his original work from 2004)

In the report, he examines the history of setbacks in CA, the probabilities of rotor and blade failures, etc. He states "The purpose of this report is to summarize wind turbine setbacks in California and to describe any connection between rotor failure and windplant setback requirements."

He makes several statements in the Executive Summary including:

1) From this data the authors developed a picture of how the turbine setbacks were established. The majority of the ordinances were developed by ad hoc groups of local interests and the fledgling wind energy industry.

2) There is no evidence that setbacks were based on formal analysis of the rotor fragment hazard.

3) The authors recommend that a comprehensive model of the rotor fragment hazard be developed based on the results of the literature review. This tool would then be used with a variety of turbine sizes with the objective to develop risk‐based setback standards.

It's a safe bet to assume the setbacks being pushed today evolved from California ordinances. But a word of warning: the intent of Scott's report was to a) determine the reasons behind existing setback values, b) evaluate the extent to which these setbacks are barriers to building taller turbines, and c) determine if the setbacks can be REDUCED.

--Lisa

Executive Director
Industrial Wind Action Group
www.windaction.org