A massive switch from coal, oil, natural gas and nuclear power plants
to solar power plants could supply 69 percent of the U.S.’s electricity
and 35 percent of its total energy by 2050.
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.
