ixEXECUTIVE SUMMARY
World demand for energy is projected to more than double by 2050 and to more than triple by
the end of the century. Incremental improvements in existing energy networks will not be
adequate to supply this demand in a sustainable way. Finding sufficient supplies of clean energy
for the future is one of society’s most daunting challenges.
Sunlight provides by far the largest of all carbon-neutral energy sources. More energy from
sunlight strikes the Earth in one hour (4.3 × 10^20 J) than all the energy consumed on the planet in
a year (4.1 × 10^20 J). We currently exploit this solar resource through solar electricity — a
$7.5 billion industry growing at a rate of 35–40% per annum — and solar-derived fuel from
biomass, which provides the primary energy source for over a billion people.
Yet solar electricity currently provides only approximately 1 millionth of the total electricity
supply, and renewable biomass provides less than 0.1% of total energy consumed. The huge gap
between our present use of solar energy and its enormous undeveloped potential defines a grand
challenge in energy research. Sunlight is a compelling solution to our need for clean, abundant
sources of energy in the future. It is readily available, secure from geopolitical tension, and poses
no threat to our environment through pollution or to our climate through greenhouse gases.
This report of the Basic Energy Sciences Workshop on Solar Energy Utilization identifies the
key scientific challenges and research directions that will enable efficient and economic use of
the solar resource to provide a significant fraction of global primary energy by the mid
21st century. The report reflects the collective output of the workshop attendees, which included
200 scientists representing academia, national laboratories, and industry in the United States and
abroad, and the U.S. Department of Energy’s Office of Basic Energy Sciences and Office of
Energy Efficiency and Renewable Energy.
Solar energy conversion systems fall into three categories according to their primary energy
product: solar electricity, solar fuels, and solar thermal systems. Each of the three generic
approaches to exploiting the solar resource has untapped capability well beyond its present
usage. Workshop participants considered the potential of all three approaches, as well as the
potential of hybrid systems that integrate key components of individual technologies into novel
cross-disciplinary paradigms.
SOLAR ELECTRICITY
The challenge in converting sunlight to electricity via photovoltaic solar cells is dramatically
reducing the cost/watt of delivered solar electricity — by approximately a factor of 5–10 to
compete with fossil and nuclear electricity and by a factor of 25–50 to compete with primary
fossil energy. New materials to efficiently absorb sunlight, new techniques to harness the full
spectrum of wavelengths in solar radiation, and new approaches based on nanostructured
architectures can revolutionize the technology used to produce solar electricity. The
technological development and successful commercialization of single-crystal solar cells
demonstrates the promise and practicality of photovoltaics, while novel approaches exploiting