Solar - Energy Policy Analysis: A Conceptual Framework - page 107

Figure 5.2 The Solar Fuel Cycle

Materials
acquisition

Manufacturing Installation

Waste disposal Decommissioning Operation

erected to send that energy efficiently across the nation” (Zweibel, Mason, and Fthenakis 2008).
Another study suggests it would take about 10 million acres, or only about 0.4 percent of the area
of the United States, to supply all of the nation's electricity using photovoltaic collectors (USDOE
2004). However, perhaps due to a bias in favor of utility-scale energy solutions, these studies have
not given adequate consideration to the substantial areas of existing underutilized flat or slightly
tilted surfaces—building roofs, uncovered parking lots, highway walls, the sides of buildings—on
which photovoltaic collectors might be mounted.
Impervious surfaces such as roads, parking lots, and rooftops cover 43,000 square miles of the
contiguous United States, according to research published in 2004 in Eos , the newsletter of the
American Geophysical Union (Frazer 2005). That is an area about the size of Ohio. About one-
third of it, 14,333 square miles, is building roofs. Continuing development adds another quarter
of a million acres per year (Schueler 2000). Thus, there were nearly 400 billion square feet of
underutilized rooftop space already in existence in the United States in 2004 that might be us-
able for placement of solar photovoltaic or flat-plate thermal collectors. In the United States, one
square yard receives on average about five kilowatt-hours of solar energy per day. The average
efficiency of commercially available solar photovoltaic panels is about 15 percent (some claim
20 percent), so a square yard of solar photovoltaic cells will produce about 0.75 kilowatt-hours of
electric energy per day (AmericanEnergyIndependence.com 2011). Using commercially available
solar photovoltaic panels, it is estimated that the underutilized rooftop space already in existence
in the United States in 2004 would be capable of generating almost 33.3 billion kilowatt-hours
of electric energy per day. That is a little over three times the average amount of electricity con-
sumption per day in the United States in 2010 (calculated from USEIA 2011a, Table 8.9). Thus,
if only one-third of the existing underutilized rooftop space was used for photovoltaic collectors,
it would be enough to generate all of the electricity consumed in the United States today. These
calculations do not take into consideration additional capacity needed to meet demand during
peak consumption periods, but they do call into serious question the need to build new electric
generating stations of any kind, solar or otherwise, on undeveloped land such as public lands in
the desert southwest. Better utilization of existing developed building sites would make such
environmentally disruptive construction unnecessary.
Utilizing existing roof space for location of solar facilities would greatly mitigate the potential
impacts on existing land uses, archeological resources, wildlife habitat and ecosystems, perhaps
reducing the need for changing land uses to zero for photovoltaic collectors and nonconcentrating
thermal collectors (U.S. Department of Energy 2004). Solar power towers remain the single solar
technology having potential for large-scale land use impacts. Proper site selection can minimize