Page 121 - Sustainable Cities and Communities Design Handbook

98 Sustainable Cities and Communities Design Handbook

Hybrid Systems
Pairing renewable energy systems has the potential to improve economics or
performance over what could be achieved by each system working in isolation.
For example, sitting solar and wind systems together can reduce the overall
transmission costs as there is a day/night complementarity in peak output that
could reduce grid congestion and allow for smaller transmission lines. Simi-
larly, combining offshore wind turbines with marine power stations has been
proposed as a means of reducing the construction and maintenance costs for
each. Hydroelectric systems can serve as energy storage units for wind farms,
making use during the day of water pumped uphill by the excess generation of
turbines at night. Such hybrid systems have yet to achieve substantial
deployment but may have promise as a means to overcome the limitations of
individual renewable systems.

SUMMARY OF SCALING RENEWABLES IN THE UNITED
STATES

Fossil fuels are the dominant energy source in the United States, providing over
four-fifths of all primary energy consumed. However, renewable energy sources
are abundant, and when harnessed they can contribute significantly to the
satisfaction of US heat and power demands. Over the past several decades,
renewable energy technologies have advanced significantly and have achieved
ever-greater levels of deployment, both by utilities and by individual consumers:

l Wind turbines currently produce electricity at costs competitive with other
fossil-fuel-based generators, leading annual capacity additions of wind
power to be among the highest in the electric power sector.
l Solar technologies can efficiently utilize sunlight to provide both heat and
electricity. PV and thermal systems both have become popular modes of
distributed energy provision, with rapidly falling prices for PV systems
making solar power particularly attractive.
l Geothermal deposits provide consistent, clean energy for both electricity
generation and heating. The number of hydrothermal power plants is
rapidly increasing, particularly in the western United States, through which
heat pumps bring geothermal energy to households in every region.
l Biomass is one of the largest sources of nonfossil power in the United
States, especially for industrial applications. The quantity and variety of
feedstocks available for combustion are substantial, providing for multiple
avenues for expanding the biopower sector.
l Marine energy resources are vast, but the technologies to exploit them are
still immature.
Owing to its size and patterns of energy consumption, the United States
presents an informative study of the obstacles and opportunities associated