Although the power of wind is enormous, wind is inconsistent in direction, in strength and when it blows. Among the three renewable energy resources that we will explore, wind is the least consistent.

Today when we think of harnessing the wind, the wind turbine is the first image that comes to mind. In this article we will also look at passive strategies to harness the wind.

Passive Strategies:

Natural ventilation is the key passive strategy to help with energy costs in our homes. If we create homes to properly take advantage of natural ventilation, much of our current HVAC usage can be eliminated. There a two primary means to designing for natural ventilation: wind driven and stack ventilation.

The concept behind wind driven natural ventilation is something we are all familiar with. You open a window on one side of the house and another across the room and a current of wind is created, also known as cross ventilation. Most wind driven ventilation systems are a bit more complex than just opening a window. They are installed on the roof and direct the prevailing winds into the home. Most systems are composed of a single element with separate ducting for incoming cool air and exhausted warm air. The whole system is based on the displacement of the warm air by the incoming cool air.

Natural stack ventilation takes advantage of cross ventilation, the buoyancy of warm air and something known as the venturi effect. The venturi effect is caused by a wind current moving over an opening, creating suction and pulling the air on the other side of the opening out. Intakes for stack ventilation are typically placed as low as possible in the home, taking advantage of cooler air near the ground as well as low lying wind currents. This cooler air fills the spaces from below as warmer air is forced up due to the relative buoyancy of warmer air compared to denser, cool air. This warm air is then pulled from the interior of the home through a chimney that is exposed to the wind currents that are typically higher at the top of the home. This last step is caused by the venturi effect.

While most natural ventilation systems are focused on cooling our spaces, these techniques can be used in concert with other strategies such as thermal masses to aid in heating as well. Passive systems do have the capability to completely offset your mechanical HVAC systems for cooling purposes, but in many regions, homeowners will still be required to install HVAC systems per building codes.

Active Strategies:

The passive strategies that we just discussed are fairly low-tech and have been harnessed for centuries, and so too has the wind turbine or wind mill. Historically wind mills were used to convert the energy in the wind into work, in the form of grinding and processing mills. Nowadays we have all seen large wind farms with enormous wind turbines stretching into the sky, but smaller versions of these units are feasible for the home owner. There are two basic configurations for home wind turbines, horizontal and vertical axis designs.

When we think about wind turbines, most of us envision horizontal axis wind turbines (HAWTs. Large blades are joined at a central axle that rotates to power the turbine which produces electricity. The historic version of the HAWT had a fixed orientation, but today's wind turbines turn to face the proper direction to maximize benefit in ever changing wind conditions. To gain the most benefit from a HAWT, they must be mounted on tall poles to reach more consistent, higher speed winds.

Most HAWTs don't start producing power until the wind reaches certain speeds, typically around 5-10 mph, and also have a tendency to become unstable in very high winds. To solve the problem of instability, many HAWTs have breaks that will slow or even stop the blades to avoid damage. There are new products on the market such as the Windtronics turbine that we discussed in a previous article that address the stability and efficiency issues inherent in horizontal axis wind turbines. There are also some companies developing unique configurations and designs for HAWTs such as those found at the following sites.
Aerotecture (can be used as both horizontal and vertical axis unit)
Architectural Wind (these systems take advantage of wind currents caused by buildings)

Vertical axis wind turbines (VAWTs) are the new players in the wind energy market and have many and varied configurations. VAWTs don't have the large blades of their horizontal cousins and typically rely on helix spirals to harness the power of the wind. Due to the fact that VAWTs spin along around a vertically oriented axis, they are able to handle wind from any direction without the need for rotation of the assembly as a horizontal axis turbine does. VAWTs also have the ability to produce electricity at lower wind speeds, sometimes as low as 4 mph.

VAWTs don't require the same large tower or pole to reach higher winds, but at the same time lack the opportunity to harness that high velocity wind. VAWTs can be mounted to either the ground or roof and have a very small footprint. In many cases, VAWT designs are more aesthetically appealing and are less likely to draw the ire of neighbors and zoning boards.

Whichever turbine configuration you choose, adding a wind turbine to your home to reduce your draw on the electrical grid may be a wise choice. The turbine will, of course, need to be wired into an inverter and a battery storage system can be beneficial in times when the wind is not blowing hard enough to produce electricity. Wind turbines can also be paired with solar panels to create a system that produces power 24 hours a day. While the sun is a daytime resource, wind potential is often higher from dusk til dawn.

Conclusions:

Whether powered by the movement of the earth or pressure differences in the atmosphere, the wind around your home can be a powerful source of renewable energy for you home. Passive strategies will work in most any location, but should be more seriously considered in climates that primarily require cooling. Before investing in a wind turbine for your home, make sure to check on the prevailing winds and the “wind zone” that you are in. You want to be in zones 3 or above to make a wind turbine an economic option.