Page 114 - Sustainable Cities and Communities Design Handbook

Renewable Energy: Scaling Deployment in the United States Chapter j 5 91

factors: swept area and wind speed. As the rotor area (determined by the blade
length) of the turbine doubles, the power output quadruples. A doubling of
incoming wind speed translates to an eightfold increase in power output.
Since 1998, the size of wind turbines has substantially increased, with rotor
diameter more than doubling and tower height increasing by nearly 50%
(Wind Technologies Market Report, 2015). This has contributed to a 180%
increase in power output and has contributed to the price of wind-generated
electricity dropping from about 40 cents/kWh in the early 1980s to around an
average of 2e5 cents/kWh for newly built projects today (Wind Technologies
Market Report, 2015; Cost of Wind Energy Review, 2015). Modern turbines
can reach peak power outputs in the megawatt range, meaning that utility-scale
aggregations of turbines (i.e., wind farms) can readily scale up to several
gigawatts in size. Although arraying turbines in wind farms can help achieve
economies of scale (particularly with respect to transmission costs), the use of
stand-alone turbines can be an economically viable means of providing power
to systems in remote locations, such as communications towers or rural irri-
gation networks.
Also in operation are various vertical-axis designs, which have a vertically
oriented main rotor shaft and are usually situated on the ground or rooftops.
Because wind speeds tend to be lower closer to the ground and these vertical-
axis systems tend to be small in size, the power output from this category or
turbines is usually low (in the watt or kilowatt range). Vertical-axis turbines
represent about 2% of the generation capacity of small wind systems but are
increasingly popular installations for distributed, renewable energy generation
(Distributed Wind Market Report, 2015).
Although wind power has been employed in the United States since the
mid-19th century, the US modern wind industry did not develop until the
1970s, when it was launched in response to the increasing cost of oil-based
electricity generation. By the mid-1980s, California had 1.2 GW of installed
wind capacity, which accounted for more than 90% of the global total.
California’s dominance in this area is commonly attributed to the federal and
state investment tax credits that were in place, as well as state-mandated utility
contracts for wind power. After the expiration of state and federal investment
incentives, the US wind industry stagnated until the late 1990s, at which time
the first in a series of production tax credits (giving renewable power producers
a rebate for each kWh generated) sparked renewed growth in domestic
installations. In recent years, wind power has been a major component of
nationwide generation capacity addition, growing from 10% of new capacity
additions in 2005 to more than 40% of new additions in 2015 (Wind Technologies
Market Report, 2015).
In 2015, nearly 8600 MW of new wind generation capacity was brought
online in the United States, bringing the cumulative installed capacity to nearly
74,000 MW. At 17,700 MW, Texas leads the country in terms of total wind