Energy Solutions to Air Pollution and Global Warming - Air Pollution and Global Warming: History, Science, and Solutions - page 321

Athird type of CSP technology is a parabolic dish
(e.g., satellite dish) reflector that rotates to track the
sun and reflects light onto a receiver, which transfers
the energy to hydrogen in a closed loop. The expan-
sion of hydrogen against a piston or turbine produces
mechanical power used to run a generator or alterna-
tor to produce electricity. The power conversion unit is
air cooled; thus, water cooling is not needed. Parabolic
dish CSP is not coupled with thermal storage.
CSP plants require either air or water cooling. The use
of air cooling, which is desirable in water-constrained
locations, reduces overall CSP plant water requirements
by 90 percent, with a cost of only about 5 percent less
electric power produced (USDOE, 2008).

13.2.8. Use of Wind, Water, and Sunlight
Power for Transportation
The cleanest and most efficient transportation technolo-
gies proposed for use on a large scale with WWS
electricity include battery electric vehicles (BEVs)
(Figure 13.10), hydrogen fuel cell vehicles (HFCVs) ,
and hybrid BEV-HFCVs. For ships, a WWS option is
ahybrid hydrogen fuel cell-battery system, and for air-
craft, liquefied hydrogen combustion.
BEVs store electricity in and draw power from bat-
teries to run an electric motor that drives the vehicle.
Because BEVs have zero tailpipe emissions, their only
possible emissions beyond production and decommis-
sioning of the vehicle are associated with the elec-
tricity they use. As long as the electricity they use
is from a WWS source, the air pollution and global

Figure 13.9. Reflectors focusing solar energy onto a
10-megawatt receiver power tower at Solar One, a
concentrated solar power plant in Barstow, California.
Photo by Sandia National Laboratory Staff, available
from the National Renewable Energy Laboratory,
U.S. Department of Energy, www.nrel.gov.

reflective lenses to heat a fluid in a collector at high
temperature. The heated fluid (e.g., pressurized steam,
synthetic oil, molten salt) flows from the collector to a
heat engine where a portion of the heat (up to 30 percent)
is converted to electricity. Some types of CSP allow the
heat to be stored for many hours so that electricity can
be produced at night.
One type of collector is a set of parabolic trough
(long U-shaped) mirror reflectors that focus light onto
apipe containing oil that flows to a chamber to heat
water for a steam generator that produces electricity.
Asecond type is a central tower receiver with a field
of mirrors surrounding it (Figure 13.9). The focused
light heats a circulating thermal storage medium, such
as molten sodium nitrate or potassium nitrate salts ,
within an insulated reservoir to more than 500 ◦ C. The
heat is then used to evaporate water flowing adjacent
to the reservoir to produce steam for a steam turbine,
which generates electricity. By storing heat in an insu-
lated thermal storage media, the parabolic trough and
central tower CSP plants can delay the heating of water,
and thus electricity production, until nighttime. In fact,
the heat can be stored for up to 15 hours before it is
completely used, allowing for 24 hours of electricity
production during and following a sunny day, as demon-
strated by the Gemasolar CSP plant in Seville, Spain, in
July 2011. During cloudy and winter days, electricity is
also produced at night, but for fewer hours.

Figure 13.10. Battery electric 2010 Tesla Roadster,
which uses thousands of lithium ion laptop batteries.
The vehicle can travel 244 miles (395 km) on one
charge and requires 3.5 hours for a full charge. Photo
by Mark Z. Jacobson.