Solar Grand Plan
Ken Zweibel, James Mason & Vasilis Fthenakis
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.
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.
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.
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.
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.
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.
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
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.
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.
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
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.
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.
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.
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.
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.
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.
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.
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
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.
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.
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).
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.
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.
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.
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.
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.
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
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.
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.
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.
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.
$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
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
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.
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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