A. Permitted Locations And Number: A small wind energy system that complies with the provisions of this section is permitted only as described in this title.
B. Minimum Lot Size: A horizontal axis small wind energy system may only be erected on a lot that is capable of meeting the setback requirements of this section. A vertical axis small wind energy system, whether mounted vertically or horizontally, may be erected on a lot that is capable of meeting the setback requirements of this section. The fall zone limits the lot size requirement so the tower will not cross the property line of the property in which it is erected in the event the tower falls or collapses.
C. Design Standards:
1. Pole Or Tower Design: The design of the small wind energy system may include a monopole/freestanding design, or a guywired tower, whether mounted on the ground or on a building.
2. Total Extended Height: The total extended height of the small wind energy system shall not exceed thirty five feet (35'). Otherwise, exceptions to the height limitations are subject to approval by the land use authority as a conditional use permit pursuant to chapter 20 of this title. Sufficient clearance to lower and raise the tower and turbine is to be provided and maintained.
3. Safety:
a. The minimum height of the lowest extent of a turbine blade/rotor shall be twenty feet (20') above the ground, if on a horizontal axis turbine. There is no minimum rotor height for a vertical axis turbine, provided the blades/rotor must be located or isolated (e.g., fenced) such that they are not easily accessible to anyone but maintenance personnel.
b. No tower shall have an external climbing apparatus within twelve feet (12') of the ground. All access doors or accessways to towers and electrical equipment shall be locked when not in use.
c. Appropriate warning signage/marking is to be placed on towers, guywires and electrical equipment.
d. All small wind energy systems must have a manufacturer's maximum RPM (revolutions per minute) rating of less than five hundred (500).
e. Small wind turbines that are operating erratically shall be shut down and/or lowered to the ground. Examples of erratic operation include, but are not limited to, the following:
(1) Unusual noises such as those indicating failure of bearings.
(2) Unusual vibrations such as those indicating that the rotor is out of balance.
(3) Falling or loosely hanging parts, such as tail vanes.
4. Setbacks:
a. In determining the required separation of a small wind energy system from the uses listed, all applicable setbacks are to be followed. Where multiple setbacks are applicable, the most restrictive applies.
b. For safety purposes, a small wind energy system shall be set back from the nearest property line, public road right of way, tanks containing combustible/flammable liquids, and aboveground communication or electrical lines not less than 1.1 times its total extended height if located on a freestanding tower or pole, or if mounted on a building, the distance of the likely fall zone.
c. Additional setbacks from neighboring residences and residentially zoned lots are set forth in subsection C5 of this section.
5. Noise Limitations And Additional Setbacks: To reduce noise impacts to neighboring residential properties, no small wind energy system or combination of small wind energy systems shall produce noise that exceeds fifty (50) dBA, as measured at the property line of any neighboring residentially zoned lot not owned by the small wind energy system developer. (Note: Public road right of way counts toward the setback.)
a. Separation Of Multiple Systems: If more than one small wind energy system is proposed and the setback from a neighboring residence or residential property line is applicable, professional documentation (e.g., a noise study) shall be submitted indicating that the above noise limitations will be met. A situation with multiple small wind energy systems must consider the effects of combined noise levels (may add up to 3 dB) and the appropriate sound propagation calculations (whether line source properties apply to the situation).
b. Single Systems: To establish the minimum setback necessary to comply with the above noise limitations in situations of single wind energy systems, the applicant shall provide from a reliable source the noise emission level (a.k.a., noise rating) of the system, as measured at a specified distance from the rotor or tower and at a given wind speed (e.g., 52 decibels at 100 feet from the tower, 30 miles per hour wind). Any noise rating must be based on at least a ten (10) m/s (22.3 miles per hour) wind speed to qualify for use. If the proposed setback is at least as far as the distance used for the noise rating, and the noise rating is less than the above noise limits, then no further calculations are necessary. Otherwise, the following calculations can be utilized to determine if the proposed setback is sufficient to comply with the above noise limits:
Step 1: Calculate the difference in decibels (dB) that would occur at the neighboring residential property line and/or residence, as applicable, versus the noise level at the distance used for the noise rating statement.
Equation: dB difference = 20 x logic, of (distance A / distance B)
Where "distance A" is the distance from the system used to establish the noise rating, and "distance B" is the proposed distance between the wind energy system and the neighboring residential property line and/or residence. Logic stands for logarithm to the base-10. (Note: Simplified calculators are available on the internet. The above equation is based on the general rule that sound in the clearly audible frequency range will reduce 6 dB for every doubling of distance from the source, assuming a single source of sound.)
Step 2: The result of the above equation is a negative number, which represents the reduction in decibels from distance A to distance B. Subtract the absolute value (positive equivalent) of that number from the noise rating of the system and compare the answer to the applicable maximum allowable noise level (50 dBA). If the result is less than the maximum allowable noise level, the proposed location is acceptable, provided all other applicable setbacks are met.
In situations where a noise rating is not available on a specific model, the city may either require a noise study to be performed by a qualified professional, or make a conservative estimate based on a wind energy system of similar characteristics (blade type and size, RPM speed, rated output, rotor diameter, startup speed, etc.) plus a safety factor of three (3) dB to establish the required setback.
Compliance with the setbacks established through the above equation shall be deemed sufficient to comply with the noise limitations of this subsection for permitting and enforcement purposes; provided, failure of the system to operate at or below the rated noise emission level due to worn, damaged or broken parts, shall constitute noncompliance and the system shall be shut down until repairs are made to bring the system back into compliance. High wind occurrences may result in noise levels above that calculated, as the noise ratings are based on high, but not extreme wind speeds. Noise resulting from such high wind occurrences does not constitute noncompliance with this section. (Ord. 2012.04, 1-18-2012)
If the noise rating is based on one hundred feet (100') from the source, the following table may be used for quick reference. If the noise rating is based on fifty feet (50') from the source, simply subtract six (6) dB from the noise rating and follow the row across to find the setback equivalents. If the noise rating is based on some other distance, use the equation above. (Note: The following table is not applicable to situations with multiple small wind energy systems or to large wind energy systems.)
dB Rating At 100' From Source | Setback Equivalent Of 50 dB, In Feet |
dB Rating At 100' From Source | Setback Equivalent Of 50 dB, In Feet |
65 | 563 |
64 | 501 |
63 | 447 |
62 | 398 |
61 | 355 |
60 | 317 |
59 | 282 |
58 | 242 |
57 | 224 |
56 | 200 |
55 | 178 |
54 | 159 |
53 | 142 |
52 | 130 |
51 | 113 |
50 | 100 |
49 | 89 |
48 | 79 |
47 | 71 |
46 | 63 |
45 | 56 |
44 | 50 |
43 | 45 |
42 | 40 |
41 | 35 |
40 | 31 |
39 | 28 |
38 | 25 |
37 | 22 |
36 | 20 |
35 | 18 |
(Ord. 2012.04, 1-18-2012; amd. 2014 Code)
6. Visual Standards:
a. Small wind energy systems are to be finished and maintained as manufactured.
b. No small wind energy system shall be lighted unless required by the federal aviation administration (FAA). When lighting is required by the FAA, it shall be the red, intermittent, glowing style, rather than the white, strobe style, unless disclosed and justified through the application review process.
c. No advertising signs of any kind or nature whatsoever shall be permitted on any small wind energy system.
d. The design of any accessory buildings or related structures shall, to the extent reasonably possible, use materials, colors, textures, screening and landscaping that will blend the facility into the natural setting and existing environment.
e. The property owner shall reasonably attempt to site the system at a location that minimizes the potential for shadow flicker impacts to their own and neighboring residences.
7. Electrical Interconnections: All electrical interconnection or distribution lines shall be underground and comply with all applicable codes and public utility requirements.
8. Signal Interference: Efforts shall be made to site small wind energy systems to reduce the likelihood of blocking or reflecting television and other communication signals. If signal interference occurs, both the small wind energy system owner and individual receiving interference shall make reasonable efforts to resolve the problem. No small wind energy system shall cause permanent and material interference with television or other communication signals.
9. Overspeed Controls: Every small wind energy system is to be equipped with an automatic overspeed control, braking system or feathering system.
a. Small wind turbines must have some positive means of shutdown. Examples of acceptable means for shutting the turbine down include, but are not limited to, dynamic braking (usually accomplished by shorting the alternator phases together); mechanical brakes that slow and then lock the rotor.
b. Small wind turbines must have some means of controlling the rotational speed of the turbine rotor in high winds. Examples of acceptable means of control include, but are not limited to, furling mechanically forced yawing, and blade pitch control. VAWT type small wind turbines, which cannot use the above controls, must still incorporate some other means, such as braking.
10. Fire Protection: All small wind energy systems are to be provided with a defensible space for fire protection, in accordance with the city building codes.
D. Permit Applications: A building permit is required for a small wind energy system. The application is to include the following information:
1. Site Plan: A site plan, drawn to scale, showing the location of the proposed small wind energy system; the locations of all existing buildings and structures, dimensioned to the property lines; the location of any septic system, well, utility line or easement, access easement, or any tank containing flammable materials on the property; the area required for raising and lowering the tower; the defensible space area required by the international building code; and the applicable setbacks for the small wind energy system.
2. Noise Compliance Documentation: Provide the information necessary to demonstrate that the applicable noise requirements of subsection C5 of this section will be met.
3. Standard Drawings: Engineered plans and calculations shall be required to obtain a building permit for a small wind energy system. Plans and calculations shall be stamped, dated and signed in accordance with state codes, ordinances and laws governing such actions, by an engineer licensed and in good standing with the state. Plans and calculations must verify that the structure is designed and capable of withstanding the conditions of the site, including, but not limited to, wind load, snow load, seismic conditions, and soil conditions, as required by the building department. Soils testing by a qualified soils engineer that is licensed by, and in good standing with, the state may be required.
4. Specifications: Specific information on the type, model, size, rotor material, rated power output, rated rotor speed, overspeed safety features and survival wind speed, as well as the name and address of the manufacturer, is to be provided. These items are typically included in a specification sheet available from the manufacturer.
5. Electrical Components: A line drawing of the electrical components of the system in sufficient detail to establish that the installation conforms to all applicable electrical codes.
6. Net Metering Agreement: If the system will be connected to the electricity grid, the applicant must provide documentation with the building permit that the required net metering agreement is being considered by the utility company (e.g., work order number status). The fully executed net metering agreement must be provided to the building inspector prior to operation of a system that will be connected to the grid. (Ord. 2012.04, 1-18-2012)