When we think of wind energy, most of us conjure up images of towering turbines on massive wind farms. But this is not always the case. Methods for harvesting wind energy can vary significantly, both in project size and type. Generally, there are three different scales of wind projects: distributed, land-based utility-scale, and offshore utility-scale. Size within these different scales also can vary greatly.
Distributed wind projects are defined by their proximity to the end-user. They are installed at or near the point of end-use and generally do not need to be distributed through a public utility via transmission and distribution lines. These systems usually are installed on residential, agricultural, commercial, and industrial sites. According to the Department of Energy (DoE), approximately 44% of all buildings in the United States have the technical capability to install and utilize distributed wind systems.
Residential systems can be as small as 400 watts to power a home and be as sizable as 100 kW for a much larger home. A typical home will utilize an average of 897 kWh per
month of energy, which could be significantly curtailed by a 5 to 15 kW wind turbine. Turbines, however, can get even smaller. Micro-turbines, such as the one pictured to the right, can be as small as 20 watts and used to charge batteries. These have been used when there is no access to electricity, for instance, on a boat.
Utility-scale wind generally is defined as turbines that are more than 100 kW in size. These include multi-turbine wind farms that have connectivity to the electric transmission system and distribution of energy to the end-user through the utility. Generally, utility-scale projects are either land-based or offshore. According to the DoE, there are more than 52,000 land-based wind turbines currently operational in 41 states.
By contrast, there is only one operational offshore wind project in the United States. This is the Block Island Wind Farm off the coast of Rhode Island, which has a capacity of 30 MW. Offshore wind projects are constructed in bodies of water, generally in the ocean on the continental shelf. These projects bring the benefit of higher wind speeds than their land-based counterparts and do not have the same land-use implications. If you’d like to get a look at the Department of Energy’s “Wind Vision” through the year 2050, click here.
Types of Turbines:
One type of turbine available for wind energy is a horizontal axis (HAWT), which is most common. The blades, shaft, and generator sit on top of the tower and face towards the wind. The blades turn the shaft. If the wind becomes too strong, the shaft is able to slow the speed. The height of the tower allows the turbine to reach the strongest sites for wind power. It also allows the turbines to have a variety of placements, such as offshore, on uneven lands, and in forested areas. One disadvantage of these turbines is that they are difficult to transport and install.
A second type of turbine is a vertical axis (VAWT), which has all of the important components close to the ground. These types of turbines are easy to maintain and have lower construction and transportation costs than HAWT turbines. VAWT turbines are most effective when placed at hilltops, ridgelines, and passes. Unfortunately, these turbines are not very efficient, because the blades spin into the wind, which causes drag.
A third type of turbine is the ducted wind turbines, also known as Honeywell wind turbines, which can sit at the edge of a roof and utilize the wind at a building’s side. Wind will flow up the side of the building and feed directly into the turbine. These devices usually are very small. The blades are approximately 24 inches in length, which allows for little change in building aesthetics. They also occupy unused space on rooftops. One of the major advantages to these types of turbines is that they allow for on-site generation and there is no need for transmission lines.
There is a tremendous amount of complexity to the different types and sizes of wind projects, further complicated by rapidly improving and evolving technology. It offers immense flexibility, however, as wind energy can charge your cell phone on your yacht while you’re at sea, or an entire city, using a sizable offshore installation, and everything in between.