Gable wind turbines, beware!

Professional installers are intended to "Advise against installations on unproductive sites that are too turbulent, on gables or roofs," and must now inform on the subject, in order to promote the development of quality small wind turbines in France.

The malfunctions are of three types:

• the electrical production of these installations is generally much lower than the figures announced during the project setup phase,
• damage can occur to the gables or roofs to which the support masts are attached,
• the operation of small wind turbines can create noise disturbances in the home as well as neighborhood issues due to proximity.

This is the consequence of the fact that almost all small wind turbine installations in built-up areas have
not taken into account the physical reality of the wind domain in this type of environment:

• low wind speeds,
• high turbulence

Professional installers are intended to "Discourage installations on unproductive sites that are too turbulent, on gables or roofs," and must now inform on the subject to promote the development of quality small wind turbines in France.

Why do individuals turn to the installation of a gable wind turbine?

• Due to constraints of available horizontal space (urban and peri-urban).
• To comply with regulations (minimum distance between a building and the plot boundary must be greater than or equal to 3m).
• For price reasons, as these machines are often sold in "kits" at seemingly attractive prices (using tax credits and integrated loan offers as sales arguments).
• Due to overly optimistic promises regarding the project's profitability.

Why is a gable wind turbine rarely effective?

• To produce well without the mechanics suffering, a wind turbine must find a strong and steady wind. This wind is only available in open areas, far from the ground and any obstacles. However, mounted on a gable, these conditions are not met: the same machine mounted on a mast twenty meters high will produce much more electricity.
• The urban or peri-urban environment is also not suitable: winds are often turbulent, causing the wind turbine to act like a weather vane, resulting in reduced energy production.
• The productions announced by installers are often fanciful. Wind power does not perform miracles: to produce a lot, a large surface area blade swept by a strong and steady wind is needed. A small discreet wind turbine will generate discreet production.

Warning: a spinning wind turbine does not necessarily produce.

Why is the attachment of a wind turbine to the building strongly discouraged?

Under the effect of the wind, the wind turbine undergoes stresses transmitted to its frame and then to the supporting wall. These stresses must be considered over a projected lifespan of 20 years. Both regular mechanical forces and vibrations make this type of installation dangerous for a dwelling. Added to this are noise nuisances.
Finally, maintenance operations are easier if the machine is installed on a tilting mast fixed to the ground.

Fragility of this type of installation

Mechanical forces

The supporting mast is fixed to the gable wall, often with two brackets. The seals in the wall are subject to
two types of stresses:

• Vertical shear stresses, due to the weight of the aerogenerator and the mast.
• Horizontal stresses, due to the drag of the aerogenerator on the mast head, especially during strong gusts of wind.

Brick, stone, or cinder block masonry composing gable walls resist vertical forces well. But masonry joints do not support horizontal forces for very long, hence a risk of cracking.

Vibrations and resonance

The vibrations caused by the operation of the wind turbine amplify the effect of mechanical forces. Over time, the vibrations can cause cracks and then infiltrations, leading to structural degradation. The propagation of acoustic waves through construction materials should not be overlooked.

Reminder of the regulations

The installation of a wind turbine on a gable altering the exterior appearance of the house requires at least a prior declaration to the Town Hall. Some Local Urban Plans or subdivision regulations prohibit the installation of wind turbines.

If the house to be equipped is within the 500 m protection perimeter around a listed monument, the opinion of the Architect responsible for the Buildings of France is required.

Small wind turbines are often connected to the customers' electrical panel. They are therefore indirectly connected to the distribution network. This connection must be subject to an operating agreement request with the network manager Enedis (formerly ERDF), to ensure the safety of network operators, if the equipment used meets the current VDE standards this will not be necessary.

Noise regulations impose thresholds not to be exceeded for the neighborhood. If the wind turbine is placed near a neighboring property, the sound impact must be considered to avoid a complaint that would lead to an obligation to dismantle the machine.

Insurance

Insuring a wind turbine is essential: the owner of the wind turbine must request an extension of their civil liability insurance to cover the risk related to the electrical connection and material damage in case of an accident. This extension generates little or no additional cost. Home insurance will cover vandalism and lightning.

The wind

For reference, wind energy increases with the cube of the wind speed.
For example, with the same swept area, doubling the wind speed results in eight times higher power.
Two important elements to understand are the roughness coefficient and the wind's energy potential.

The roughness coefficient

The roughness coefficient varies significantly depending on land use.
A high roughness coefficient implies very weak winds at low altitudes.

Atmospheric photograph: Andreas Maier / Pexels

Wind speed

Wind speed varies depending on land use.
According to European EC1 rules, to find the wind energy density observed at a height of 10 meters in open country, one must be at 45 m in the suburbs and 72 m in the city.

Order of magnitude of production:

The production of wind turbines depends on the wind resource available at the specific location of installation and the technical characteristics of the installed equipment.
The number of equivalent full power hours is calculated from the announced annual production (E) and the nominal power of the wind turbine (P):

Number of equivalent full power hours: HEPP = E/P

For example, a wind turbine with a nominal power of 2 kW producing 4,000 kWh per year delivers 2,000 equivalent full power hours. The order of magnitude of the number of equivalent full power hours measured on small wind turbines installed in France is commonly between 500 h and 2,000 h.

Given the unfavorable nature of gable-mounted wind turbine installations, it is unlikely that their annual production will exceed 1,000 equivalent full power hours!

Conclusion

This type of installation is not recommended as it is unproductive and dangerous for the building.
Install a meter measuring the energy produced by the wind turbine.

Reminder:

To counteract abusive commercial practices, individuals have a 14-day withdrawal period from the signing of the order contract or purchase commitment. No payment can be demanded during this period. The detachable form, which must be attached to the contract, must be returned within the required time frame by registered mail with acknowledgment of receipt.