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High prices for gasoline and home heating oil are here to
stay. The U.S. is at war in the Middle East at least in part to
protect its foreign oil interests. And as China, India and
other nations rapidly increase their demand for fossil fuels,
future fighting over energy looms large. In the meantime, power
plants that burn coal, oil and natural gas, as well as vehicles
everywhere, continue to pour millions of tons of pollutants and
greenhouse gases into the atmosphere annually, threatening the
planet.
Well-meaning scientists, engineers, economists and
politicians have proposed various steps that could slightly
reduce fossil-fuel use and emissions. These steps are not
enough. The U.S. needs a bold plan to free itself from fossil
fuels. Our analysis convinces us that a massive switch to solar
power is the logical answer.
Solar energy’s potential is off the chart. The energy in
sunlight striking the earth for 40 minutes is equivalent to
global energy consumption for a year. The U.S. is lucky to be
endowed with a vast resource; at least 250,000 square miles of
land in the Southwest alone are suitable for constructing solar
power plants, and that land receives more than 4,500
quadrillion British thermal units (Btu) of solar radiation a
year. Converting only 2.5 percent of that radiation into
electricity would match the nation’s total energy consumption
in 2006.
To convert the country to solar power, huge tracts of land
would have to be covered with photovoltaic panels and solar
heating troughs. A direct-current (DC) transmission backbone
would also have to be erected to send that energy efficiently
across the nation.
The technology is ready. On the following pages we present a
grand plan that could provide 69 percent of the U.S.’s
electricity and 35 percent of its total energy (which includes
transportation) with solar power by 2050. We project that this
energy could be sold to consumers at rates equivalent to
today’s rates for conventional power sources, about five cents
per kilowatt-hour (kWh). If wind, biomass and geothermal
sources were also developed, renewable energy could provide 100
percent of the nation’s electricity and 90 percent of its
energy by 2100.
The federal government would have to invest more than $400
billion over the next 40 years to complete the 2050 plan. That
investment is substantial, but the payoff is greater. Solar
plants consume little or no fuel, saving billions of dollars
year after year. The infrastructure would displace 300 large
coal-fired power plants and 300 more large natural gas plants
and all the fuels they consume. The plan would effectively
eliminate all imported oil, fundamentally cutting U.S. trade
deficits and easing political tension in the Middle East and
elsewhere. Because solar technologies are almost
pollution-free, the plan would also reduce greenhouse gas
emissions from power plants by 1.7 billion tons a year, and
another 1.9 billion tons from gasoline vehicles would be
displaced by plug-in hybrids refueled by the solar power grid.
In 2050 U.S. carbon dioxide emissions would be 62 percent below
2005 levels, putting a major brake on global warming.
 Photovoltaic Farms
In the past few years the cost to produce photovoltaic cells
and modules has dropped significantly, opening the way for
large-scale deployment. Various cell types exist, but the least
expensive modules today are thin films made of cadmium
telluride. To provide electricity at six cents per kWh by 2020,
cadmium telluride modules would have to convert electricity
with 14 percent efficiency, and systems would have to be
installed at $1.20 per watt of capacity. Current modules have
10 percent efficiency and an installed system cost of about $4
per watt. Progress is clearly needed, but the technology is
advancing quickly; commercial efficiencies have risen from 9 to
10 percent in the past 12 months. It is worth noting, too, that
as modules improve, rooftop photovoltaics will become more
cost-competitive for homeowners, reducing daytime electricity
demand.
In our plan, by 2050 photovoltaic technology would provide
almost 3,000 gigawatts (GW), or billions of watts, of power.
Some 30,000 square miles of photovoltaic arrays would have to
be erected. Although this area may sound enormous,
installations already in place indicate that the land required
for each gigawatt-hour of solar energy produced in the
Southwest is less than that needed for a coal-powered plant
when factoring in land for coal mining. Studies by the National
Renewable Energy Laboratory in Golden, Colo., show that more
than enough land in the Southwest is available without
requiring use of environmentally sensitive areas, population
centers or difficult terrain. Jack Lavelle, a spokesperson for
Arizona’s Department of Water Conservation, has noted that more
than 80 percent of his state’s land is not privately owned and
that Arizona is very interested in developing its solar
potential. The benign nature of photovoltaic plants (including
no water consumption) should keep environmental concerns to a
minimum.
The main progress required, then, is to raise module
efficiency to 14 percent. Although the efficiencies of
commercial modules will never reach those of solar cells in the
laboratory, cadmium telluride cells at the National Renewable
Energy Laboratory are now up to 16.5 percent and rising. At
least one manufacturer, First Solar in Perrysburg, Ohio,
increased module efficiency from 6 to 10 percent from 2005 to
2007 and is reaching for 11.5 percent by 2010.
Pressurized Caverns
The great limiting factor of solar power, of course, is that
it generates little electricity when skies are cloudy and none
at night. Excess power must therefore be produced during sunny
hours and stored for use during dark hours. Most energy storage
systems such as batteries are expensive or inefficient.
Compressed-air energy storage has emerged as a successful
alternative. Electricity from photovoltaic plants compresses
air and pumps it into vacant underground caverns, abandoned
mines, aquifers and depleted natural gas wells. The pressurized
air is released on demand to turn a turbine that generates
electricity, aided by burning small amounts of natural gas.
Compressed-air energy storage plants have been operating
reliably in Huntorf, Germany, since 1978 and in McIntosh, Ala.,
since 1991. The turbines burn only 40 percent of the natural
gas they would if they were fueled by natural gas alone, and
better heat recovery technology would lower that figure to 30
percent.
Studies by the Electric Power Research Institute in Palo
Alto, Calif., indicate that the cost of compressed-air energy
storage today is about half that of lead-acid batteries. The
research indicates that these facilities would add three or
four cents per kWh to photovoltaic generation, bringing the
total 2020 cost to eight or nine cents per kWh.
Electricity from photovoltaic farms in the Southwest would
be sent over high-voltage DC transmission lines to
compressed-air storage facilities throughout the country, where
turbines would generate electricity year-round. The key is to
find adequate sites. Mapping by the natural gas industry and
the Electric Power Research Institute shows that suitable
geologic formations exist in 75 percent of the country, often
close to metropolitan areas. Indeed, a compressed-air energy
storage system would look similar to the U.S. natural gas
storage system. The industry stores eight trillion cubic feet
of gas in 400 underground reservoirs. By 2050 our plan would
require 535 billion cubic feet of storage, with air pressurized
at 1,100 pounds per square inch. Although development will be a
challenge, plenty of reservoirs are available, and it would be
reasonable for the natural gas industry to invest in such a
network.
Hot Salt
Another technology that would supply perhaps one fifth of
the solar energy in our vision is known as concentrated solar
power. In this design, long, metallic mirrors focus sunlight
onto a pipe filled with fluid, heating the fluid like a huge
magnifying glass might. The hot fluid runs through a heat
exchanger, producing steam that turns a turbine.
For energy storage, the pipes run into a large, insulated
tank filled with molten salt, which retains heat efficiently.
Heat is extracted at night, creating steam. The molten salt
does slowly cool, however, so the energy stored must be tapped
within a day.
Nine concentrated solar power plants with a total capacity
of 354 megawatts (MW) have been generating electricity reliably
for years in the U.S. A new 64-MW plant in Nevada came online
in March 2007. These plants, however, do not have heat storage.
The first commercial installation to incorporate it—a 50-MW
plant with seven hours of molten salt storage—is being
constructed in Spain, and others are being designed around the
world. For our plan, 16 hours of storage would be needed so
that electricity could be generated 24 hours a day.
Existing plants prove that concentrated solar power is
practical, but costs must decrease. Economies of scale and
continued research would help. In 2006 a report by the Solar
Task Force of the Western Governors’ Association concluded that
concentrated solar power could provide electricity at 10 cents
per kWh or less by 2015 if 4 GW of plants were constructed.
Finding ways to boost the temperature of heat exchanger fluids
would raise operating efficiency, too. Engineers are also
investigating how to use molten salt itself as the
heat-transfer fluid, reducing heat losses as well as capital
costs. Salt is corrosive, however, so more resilient piping
systems are needed.
Concentrated solar power and photovoltaics represent two
different technology paths. Neither is fully developed, so our
plan brings them both to large-scale deployment by 2020, giving
them time to mature. Various combinations of solar technologies
might also evolve to meet demand economically. As installations
expand, engineers and accountants can evaluate the pros and
cons, and investors may decide to support one technology more
than another.
Direct Current, Too
The geography of solar power is obviously different from the
nation’s current supply scheme. Today coal, oil, natural gas
and nuclear power plants dot the landscape, built relatively
close to where power is needed. Most of the country’s solar
generation would stand in the Southwest. The existing system of
alternating-current (AC) power lines is not robust enough to
carry power from these centers to consumers everywhere and
would lose too much energy over long hauls. A new high-voltage,
direct-current (HVDC) power transmission backbone would have to
be built.
Studies by Oak Ridge National Laboratory indicate that
long-distance HVDC lines lose far less energy than AC lines do
over equivalent spans. The backbone would radiate from the
Southwest toward the nation’s borders. The lines would
terminate at converter stations where the power would be
switched to AC and sent along existing regional transmission
lines that supply customers.
The AC system is also simply out of capacity, leading to
noted shortages in California and other regions; DC lines are
cheaper to build and require less land area than equivalent AC
lines. About 500 miles of HVDC lines operate in the U.S. today
and have proved reliable and efficient. No major technical
advances seem to be needed, but more experience would help
refine operations. The Southwest Power Pool of Texas is
designing an integrated system of DC and AC transmission to
enable development of 10 GW of wind power in western Texas. And
TransCanada, Inc., is proposing 2,200 miles of HVDC lines to
carry wind energy from Montana and Wyoming south to Las Vegas
and beyond.
Stage One: Present to 2020
We have given considerable thought to how the solar grand
plan can be deployed. We foresee two distinct stages. The
first, from now until 2020, must make solar competitive at the
mass-production level. This stage will require the government
to guarantee 30-year loans, agree to purchase power and provide
price-support subsidies. The annual aid package would rise
steadily from 2011 to 2020. At that time, the solar
technologies would compete on their own merits. The cumulative
subsidy would total $420 billion (we will explain later how to
pay this bill).
About 84 GW of photovoltaics and concentrated solar power
plants would be built by 2020. In parallel, the DC transmission
system would be laid. It would expand via existing
rights-of-way along interstate highway corridors, minimizing
land-acquisition and regulatory hurdles. This backbone would
reach major markets in Phoenix, Las Vegas, Los Angeles and San
Diego to the west and San Antonio, Dallas, Houston, New
Orleans, Birmingham, Ala., Tampa, Fla., and Atlanta to the
east.
Building 1.5 GW of photovoltaics and 1.5 GW of concentrated
solar power annually in the first five years would stimulate
many manufacturers to scale up. In the next five years, annual
construction would rise to 5 GW apiece, helping firms optimize
production lines. As a result, solar electricity would fall
toward six cents per kWh. This implementation schedule is
realistic; more than 5 GW of nuclear power plants were built in
the U.S. each year from 1972 to 1987. What is more, solar
systems can be manufactured and installed at much faster rates
than conventional power plants because of their straightforward
design and relative lack of environmental and safety
complications.
Stage Two: 2020 to 2050
It is paramount that major market incentives remain in
effect through 2020, to set the stage for self-sustained growth
thereafter. In extending our model to 2050, we have been
conservative. We do not include any technological or cost
improvements beyond 2020. We also assume that energy demand
will grow nationally by 1 percent a year. In this scenario, by
2050 solar power plants will supply 69 percent of U.S.
electricity and 35 percent of total U.S. energy. This quantity
includes enough to supply all the electricity consumed by 344
million plug-in hybrid vehicles, which would displace their
gasoline counterparts, key to reducing dependence on foreign
oil and to mitigating greenhouse gas emissions. Some three
million new domestic jobs—notably in manufacturing solar
components—would be created, which is several times the number
of U.S. jobs that would be lost in the then dwindling
fossil-fuel industries.
The huge reduction in imported oil would lower trade balance
payments by $300 billion a year, assuming a crude oil price of
$60 a barrel (average prices were higher in 2007). Once solar
power plants are installed, they must be maintained and
repaired, but the price of sunlight is forever free,
duplicating those fuel savings year after year. Moreover, the
solar investment would enhance national energy security, reduce
financial burdens on the military, and greatly decrease the
societal costs of pollution and global warming, from human
health problems to the ruining of coastlines and farmlands.
Ironically, the solar grand plan would lower energy
consumption. Even with 1 percent annual growth in demand, the
100 quadrillion Btu consumed in 2006 would fall to 93
quadrillion Btu by 2050. This unusual offset arises because a
good deal of energy is consumed to extract and process fossil
fuels, and more is wasted in burning them and controlling their
emissions.
To meet the 2050 projection, 46,000 square miles of land
would be needed for photovoltaic and concentrated solar power
installations. That area is large, and yet it covers just 19
percent of the suitable Southwest land. Most of that land is
barren; there is no competing use value. And the land will not
be polluted. We have assumed that only 10 percent of the solar
capacity in 2050 will come from distributed photovoltaic
installations—those on rooftops or commercial lots throughout
the country. But as prices drop, these applications could play
a bigger role.
2050 and Beyond
Although it is not possible to project with any exactitude
50 or more years into the future, as an exercise to demonstrate
the full potential of solar energy we constructed a scenario
for 2100. By that time, based on our plan, total energy demand
(including transportation) is projected to be 140 quadrillion
Btu, with seven times today’s electric generating capacity.
To be conservative, again, we estimated how much solar plant
capacity would be needed under the historical worst-case solar
radiation conditions for the Southwest, which occurred during
the winter of 1982–1983 and in 1992 and 1993 following the
Mount Pinatubo eruption, according to National Solar Radiation
Data Base records from 1961 to 2005. And again, we did not
assume any further technological and cost improvements beyond
2020, even though it is nearly certain that in 80 years ongoing
research would improve solar efficiency, cost and storage.
Under these assumptions, U.S. energy demand could be
fulfilled with the following capacities: 2.9 terawatts (TW) of
photovoltaic power going directly to the grid and another 7.5
TW dedicated to compressed-air storage; 2.3 TW of concentrated
solar power plants; and 1.3 TW of distributed photovoltaic
installations. Supply would be rounded out with 1 TW of wind
farms, 0.2 TW of geothermal power plants and 0.25 TW of
biomass-based production for fuels. The model includes 0.5 TW
of geothermal heat pumps for direct building heating and
cooling. The solar systems would require 165,000 square miles
of land, still less than the suitable available area in the
Southwest.
In 2100 this renewable portfolio could generate 100 percent
of all U.S. electricity and more than 90 percent of total U.S.
energy. In the spring and summer, the solar infrastructure
would produce enough hydrogen to meet more than 90 percent of
all transportation fuel demand and would replace the small
natural gas supply used to aid compressed-air turbines. Adding
48 billion gallons of biofuel would cover the rest of
transportation energy. Energy-related carbon dioxide emissions
would be reduced 92 percent below 2005 levels.
Who Pays?
Our model is not an austerity plan, because it includes a 1
percent annual increase in demand, which would sustain
lifestyles similar to those today with expected efficiency
improvements in energy generation and use. Perhaps the biggest
question is how to pay for a $420-billion overhaul of the
nation’s energy infrastructure. One of the most common ideas is
a carbon tax. The International Energy Agency suggests that a
carbon tax of $40 to $90 per ton of coal will be required to
induce electricity generators to adopt carbon capture and
storage systems to reduce carbon dioxide emissions. This tax is
equivalent to raising the price of electricity by one to two
cents per kWh. But our plan is less expensive. The $420 billion
could be generated with a carbon tax of 0.5 cent per kWh. Given
that electricity today generally sells for six to 10 cents per
kWh, adding 0.5 cent per kWh seems reasonable.
Congress could establish the financial incentives by
adopting a national renewable energy plan. Consider the U.S.
Farm Price Support program, which has been justified in terms
of national security. A solar price support program would
secure the nation’s energy future, vital to the country’s
long-term health. Subsidies would be gradually deployed from
2011 to 2020. With a standard 30-year payoff interval, the
subsidies would end from 2041 to 2050. The HVDC transmission
companies would not have to be subsidized, because they would
finance construction of lines and converter stations just as
they now finance AC lines, earning revenues by delivering
electricity.
Although $420 billion is substantial, the annual expense
would be less than the current U.S. Farm Price Support program.
It is also less than the tax subsidies that have been levied to
build the country’s high-speed telecommunications
infrastructure over the past 35 years. And it frees the U.S.
from policy and budget issues driven by international energy
conflicts.
Without subsidies, the solar grand plan is impossible. Other
countries have reached similar conclusions: Japan is already
building a large, subsidized solar infrastructure, and Germany
has embarked on a nationwide program. Although the investment
is high, it is important to remember that the energy source,
sunlight, is free. There are no annual fuel or
pollution-control costs like those for coal, oil or nuclear
power, and only a slight cost for natural gas in compressed-air
systems, although hydrogen or biofuels could displace that,
too. When fuel savings are factored in, the cost of solar would
be a bargain in coming decades. But we cannot wait until then
to begin scaling up.
Critics have raised other concerns, such as whether material
constraints could stifle large-scale installation. With rapid
deployment, temporary shortages are possible. But several types
of cells exist that use different material combinations. Better
processing and recycling are also reducing the amount of
materials that cells require. And in the long term, old solar
cells can largely be recycled into new solar cells, changing
our energy supply picture from depletable fuels to recyclable
materials.
The greatest obstacle to implementing a renewable U.S.
energy system is not technology or money, however. It is the
lack of public awareness that solar power is a practical
alternative—and one that can fuel transportation as well.
Forward-looking thinkers should try to inspire U.S. citizens,
and their political and scientific leaders, about solar power’s
incredible potential. Once Americans realize that potential, we
believe the desire for energy self-sufficiency and the need to
reduce carbon dioxide emissions will prompt them to adopt a
national solar plan.
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