Page 113 - Sustainable Cities and Communities Design Handbook

90 Sustainable Cities and Communities Design Handbook

that energy was supplied by fossil fuels (coal, petroleum, and natural gas).
Nuclear and renewable power sources provide the balance of the US energy
mix.
American homes and businesses consumed 3800 TWh of electricity in
2015, an average of 11,800 kWh per capita (Electric Power Annual, 2015).
Although coal provided as much as half of the United States’ electricity as
recently as 2008, it now provides the fuel for less than one-third of the total
electricity consumed. Coal’s dominance of the US electricity market has ebbed
in large part due to competition with low-cost natural gas. Between 2000 and
2010, natural gas power plants accounted for 81% of new power production
capacity, and now natural gas is the fuel for 32% of US electricity. Nuclear
power provides a further 19%, maintaining its market share for years, even
though only one new reactor unit has come online since 1996 (in large part due
to the substantially improved capacity factors for existing plants). Large-scale
hydroelectric facilities form the other major, low-carbon electricity source,
contributing about 6% of the electricity consumed. A mix of conventional
renewable energy sources like wind, sunlight, and biomass contribute roughly
7.4%.
Residential and commercial buildings are large energy consumers in the
United States, accounting for more than a quarter of end-use energy con-
sumption (Estimated U.S. Energy Consumption, 2016). Natural gas and
electricity are the primary energy sources in the built environment, with
temperature regulation, lighting, and water heating being the chief energy-
consuming activities.
The transportation sector, which comprehends personal, public, and com-
mercial ground travel as well as aircraft and marine vessels, is almost exclu-
sively powered by fossil fuels. Petroleum products account for 92% of the
primary energy input in the transportation sector in 2016, and natural gas
contributed an additional 2.7%. Biomass-derived ethanol and biodiesel are the
chief sources of renewable transportation fuel, providing 5%. At present,
electricity is a negligible component of the transportation energy system, a
mere 0.1%. Significant growth in electric vehicle use in the coming years is
forecast, however.

WIND
Wind turbines translate the kinetic energy of moving air into mechanical
energy, which in turns powers a generator that produces electrical energy.
Conventional turbines have a horizontal-axis design, in which two or three
rotor blades are mounted atop a tower and arrayed such that they resemble
airplane propellers. When oriented into the wind, the movement of air across
the blades generates lift, spinning the shaft connected to an electric generator.
Wind power output from this conventional turbine design is a function of two