Wind, water and solar technologies can provide 100 percent of the world’s energy, eliminating all fossil fuels. HERE’S HOW
In December leaders from around the world
will meet in Copenhagen to try to agree on
cutting back greenhouse gas emissions for
decades to come. The most effective step to implement
that goal would be a massive shift away
from fossil fuels to clean, renewable energy
sources. If leaders can have confidence that such
a transformation is possible, they might commit
to an historic agreement. We think they can.
A year ago former vice president Al Gore
threw down a gauntlet: to repower America
with 100 percent carbon-free electricity within
10 years. As the two of us started to evaluate the
feasibility of such a change, we took on an even
larger challenge: to determine how 100 percent
of the world’s energy, for all purposes, could be
supplied by wind, water and solar resources, by
as early as 2030. Our plan is presented here.
Scientists have been building to this moment
for at least a decade, analyzing various pieces of
the challenge. Most recently, a 2009 Stanford
University study ranked energy systems according
to their impacts on global warming, pollution,
water supply, land use, wildlife and other
concerns. The very best options were wind, solar,
geothermal, tidal and hydroelectric power—
all of which are driven by wind, water or
sunlight (referred to as WWS). Nuclear power,
coal with carbon capture, and ethanol were all
poorer options, as were oil and natural gas. The
study also found that battery-electric vehicles
and hydrogen fuel-cell vehicles recharged by
WWS options would largely eliminate pollution
from the transportation sector.
Our plan calls for millions of wind turbines,
water machines and solar installations. The
numbers are large, but the scale is not an insurmountable
hurdle; society has achieved massive
transformations before. During World War II,
the U.S. retooled automobile factories to produce
300,000 aircraft, and other countries produced
486,000 more. In 1956 the U.S. began
building the Interstate Highway System, which
after 35 years extended for 47,000 miles, changing
commerce and society.
Is it feasible to transform the world’s energy
systems? Could it be accomplished in two decades?
The answers depend on the technologies
chosen, the availability of critical materials, and
economic and political factors.
Clean Technologies Only
Renewable energy comes from enticing sources:
wind, which also produces waves; water, which
includes hydroelectric, tidal and geothermal energy
(water heated by hot underground rock); and
sun, which includes photovoltaics and solar power
plants that focus sunlight to heat a fluid that
drives a turbine to generate electricity. Our plan
includes only technologies that work or are close
to working today on a large scale, rather than
those that may exist 20 or 30 years from now.
To ensure that our system remains clean, we
consider only technologies that have near-zero
emissions of greenhouse gases and air pollutants
over their entire life cycle, including construction,
operation and decommissioning. For example,
when burned in vehicles, even the most
ecologically acceptable sources of ethanol create
air pollution that will cause the same mortality
level as when gasoline is burned. Nuclear power
results in up to 25 times more carbon emissions
than wind energy, when reactor construction
and uranium refining and transport are considered.
Carbon capture and sequestration technology
can reduce carbon dioxide emissions from
coal-fired power plants but will increase air pollutants
and will extend all the other deleterious
effects of coal mining, transport and processing,
because more coal must be burned to power the
capture and storage steps. Similarly, we consider
only technologies that do not present significant
waste disposal or terrorism risks.
In our plan, WWS will supply electric power
for heating and transportation—industries that
will have to revamp if the world has any hope of
slowing climate change. We have assumed that
most fossil-fuel heating (as well as ovens and
stoves) can be replaced by electric systems and
that most fossil-fuel transportation can be replaced
by battery and fuel-cell vehicles. Hydrogen,
produced by using WWS electricity to split
water (electrolysis), would power fuel cells and
be burned in airplanes and by industry.
Plenty of Supply
Today the maximum power consumed worldwide
at any given moment is about 12.5 trillion
watts (terawatts, or TW), according to the U.S.
Energy Information Administration. The agency
projects that in 2030 the world will require
16.9 TW of power as global population and living
standards rise, with about 2.8 TW in the
U.S. The mix of sources is similar to today’s,
heavily dependent on fossil fuels. If, however,
the planet were powered entirely by WWS, with
no fossil-fuel or biomass combustion, an intriguing
savings would occur. Global power demand
would be only 11.5 TW, and U.S. demand would
be 1.8 TW. That decline occurs because, in most
cases, electrification is a more efficient way to
use energy. For example, only 17 to 20 percent
of the energy in gasoline is used to move a vehicle
(the rest is wasted as heat), whereas 75 to 86
percent of the electricity delivered to an electric
vehicle goes into motion.
Even if demand did rise to 16.9 TW, WWS
sources could provide far more power. Detailed
studies by us and others indicate that energy
from the wind, worldwide, is about 1,700 TW.
Solar, alone, offers 6,500 TW. Of course, wind
and sun out in the open seas, over high mountains
and across protected regions would not be
available. If we subtract these and low-wind areas
not likely to be developed, we are still left
with 40 to 85 TW for wind and 580 TW for solar,
each far beyond future human demand. Yet
currently we generate only 0.02 TW of wind
power and 0.008 TW of solar. These sources hold
an incredible amount of untapped potential.
The other WWS technologies will help create
a flexible range of options. Although all the
sources can expand greatly, for practical reasons,
wave power can be extracted only near
coastal areas. Many geothermal sources are too
deep to be tapped economically. And even though
hydroelectric power now exceeds all other WWS
sources, most of the suitable large reservoirs are
already in use.
The Plan: Power Plants Required
Clearly, enough renewable energy exists. How,
then, would we transition to a new infrastructure
to provide the world with 11.5 TW? We
have chosen a mix of technologies emphasizing
wind and solar, with about 9 percent of demand
met by mature water-related methods. (Other
combinations of wind and solar could be as successful.)
Wind supplies 51 percent of the demand, provided
by 3.8 million large wind turbines (each
rated at five megawatts) worldwide. Although
that quantity may sound enormous, it is interesting
to note that the world manufactures 73 million
cars and light trucks every year. Another
40 percent of the power comes from photovoltaics
and concentrated solar plants, with about
30 percent of the photovoltaic output from rooftop
panels on homes and commercial buildings.
About 89,000 photovoltaic and concentrated
solar power plants, averaging 300 megawatts
apiece, would be needed. Our mix also includes
900 hydroelectric stations worldwide, 70 percent
of which are already in place.
Only about 0.8 percent of the wind base is installed
today. The worldwide footprint of the
3.8 million turbines would be less than 50 square
kilometers (smaller than Manhattan). When the
needed spacing between them is figured, they
would occupy about 1 percent of the earth’s
land, but the empty space among turbines could
be used for agriculture or ranching or as open
land or ocean. The nonrooftop photovoltaics
and concentrated solar plants would occupy
about 0.33 percent of the planet’s land. Building
such an extensive infrastructure will take time.
But so did the current power plant network. And
remember that if we stick with fossil fuels, demand
by 2030 will rise to 16.9 TW, requiring
about 13,000 large new coal plants, which themselves
would occupy a lot more land, as would
the mining to supply them.
The Materials Hurdle
The scale of the WWS infrastructure is not a barrier.
But a few materials needed to build it could
be scarce or subject to price manipulation.
Enough concrete and steel exist for the millions
of wind turbines, and both those commodities
are fully recyclable. The most problematic
materials may be rare-earth metals such as neodymium
used in turbine gearboxes. Although the
metals are not in short supply, the low-cost sources
are concentrated in China, so countries such
as the U.S. could be trading dependence on Middle
Eastern oil for dependence on Far Eastern
metals. Manufacturers are moving toward gearless
turbines, however, so that limitation may become
Photovoltaic cells rely on amorphous or crystalline
silicon, cadmium telluride, or copper indium
selenide and sulfide. Limited supplies of
tellurium and indium could reduce the prospects
for some types of thin-film solar cells, though
not for all; the other types might be able to take
up the slack. Large-scale production could be restricted
by the silver that cells require, but finding
ways to reduce the silver content could tackle
that hurdle. Recycling parts from old cells could
ameliorate material difficulties as well.
Three components could pose challenges for
building millions of electric vehicles: rare-earth
metals for electric motors, lithium for lithiumion
batteries and platinum for fuel cells. More
than half the world’s lithium reserves lie in Bolivia
and Chile. That concentration, combined
with rapidly growing demand, could raise prices
significantly. More problematic is the claim by
Meridian International Research that not enough
economically recoverable lithium exists to build
anywhere near the number of batteries needed in
a global electric-vehicle economy. Recycling
could change the equation, but the economics of
recycling depend in part on whether batteries are
made with easy recyclability in mind, an issue the
industry is aware of. The long-term use of platinum
also depends on recycling; current available
reserves would sustain annual production of 20
million fuel-cell vehicles, along with existing industrial
uses, for fewer than 100 years.
Smart Mix for Reliability
A new infrastructure must provide energy on
demand at least as reliably as the existing infrastructure.
WWS technologies generally suffer
less downtime than traditional sources. The
average U.S. coal plant is offline 12.5 percent of
the year for scheduled and unscheduled maintenance.
Modern wind turbines have a down time
of less than 2 percent on land and less than 5 percent
at sea. Photovoltaic systems are also at less
than 2 percent. Moreover, when an individual
wind, solar or wave device is down, only a small
fraction of production is affected; when a coal,
nuclear or natural gas plant goes offline, a large
chunk of generation is lost.
The main WWS challenge is that the wind
does not always blow and the sun does not always
shine in a given location. Intermittency
problems can be mitigated by a smart balance of
sources, such as generating a base supply from
steady geothermal or tidal power, relying on
wind at night when it is often plentiful, using solar
by day and turning to a reliable source such
as hydroelectric that can be turned on and off
quickly to smooth out supply or meet peak demand.
For example, interconnecting wind farms
that are only 100 to 200 miles apart can compensate
for hours of zero power at any one farm
should the wind not be blowing there. Also helpful
is interconnecting geographically dispersed
sources so they can back up one another, installing
smart electric meters in homes that automatically
recharge electric vehicles when demand is
low and building facilities that store power for
Because the wind often blows during stormy
conditions when the sun does not shine and the
sun often shines on calm days with little wind,
combining wind and solar can go a long way toward
meeting demand, especially when geothermal
provides a steady base and hydroelectric can
be called on to fill in the gaps.
As Cheap as Coal
The mix of WWS sources in our plan can reliably
supply the residential, commercial, industrial
and transportation sectors. The logical next
question is whether the power would be affordable.
For each technology, we calculated how
much it would cost a producer to generate power
and transmit it across the grid. We included
the annualized cost of capital, land, operations,
maintenance, energy storage to help offset intermittent
supply, and transmission. Today the cost
of wind, geothermal and hydroelectric are all
less than seven cents a kilowatt-hour (¢/kWh);
wave and solar are higher. But by 2020 and
beyond wind, wave and hydro are expected to
be 4¢/kWh or less.
For comparison, the average cost in the U.S.
in 2007 of conventional power generation and
transmission was about 7¢/kWh, and it is projected
to be 8¢/kWh in 2020. Power from wind
turbines, for example, already costs about the
same or less than it does from a new coal or natural
gas plant, and in the future wind power is
expected to be the least costly of all options. The
competitive cost of wind has made it the second-
largest source of new electric power generation
in the U.S. for the past three years, behind natural
gas and ahead of coal.
Solar power is relatively expensive now but
should be competitive as early as 2020. A careful
analysis by Vasilis Fthenakis of Brookhaven
National Laboratory indicates that within 10
years, photovoltaic system costs could drop to
about 10¢/kWh, including long-distance transmission
and the cost of compressed-air storage
of power for use at night. The same analysis estimates
that concentrated solar power systems
with enough thermal storage to generate electricity
24 hours a day in spring, summer and fall
could deliver electricity at 10¢/kWh or less.
Transportation in a WWS world will be driven
by batteries or fuel cells, so we should compare
the economics of these electric vehicles with
that of internal-combustion-engine vehicles. Detailed
analyses by one of us (Delucchi) and Tim
Lipman of the University of California, Berkeley,
have indicated that mass-produced electric vehicles
with advanced lithium-ion or nickel metalhydride
batteries could have a full lifetime cost
per mile (including battery replacements) that is
comparable with that of a gasoline vehicle, when
gasoline sells for more than $2 a gallon.
When the so-called externality costs (the
monetary value of damages to human health,
the environment and climate) of fossil-fuel generation
are taken into account, WWS technologies
become even more cost-competitive.
Overall construction cost for a WWS system
might be on the order of $100 trillion worldwide,
over 20 years, not including transmission. But
this is not money handed out by governments or
consumers. It is investment that is paid back
through the sale of electricity and energy. And
again, relying on traditional sources would raise
output from 12.5 to 16.9 TW, requiring thousands
more of those plants, costing roughly $10
trillion, not to mention tens of trillions of dollars
more in health, environmental and security costs.
The WWS plan gives the world a new, clean, efficient
energy system rather than an old, dirty, inefficient one.
Our analyses strongly suggest that the costs of
WWS will become competitive with traditional
sources. In the interim, however, certain forms
of WWS power will be significantly more costly
than fossil power. Some combination of WWS
subsidies and carbon taxes would thus be needed
for a time. A feed-in tariff (FIT) program to
cover the difference between generation cost and
wholesale electricity prices is especially effective
at scaling-up new technologies. Combining FITs
with a so-called declining clock auction, in
which the right to sell power to the grid goes to
the lowest bidders, provides continuing incentive
for WWS developers to lower costs. As that
happens, FITs can be phased out. FITs have been
implemented in a number of European countries
and a few U.S. states and have been quite successful
in stimulating solar power in Germany.
Taxing fossil fuels or their use to reflect their
environmental damages also makes sense. But at
a minimum, existing subsidies for fossil energy,
such as tax benefits for exploration and extraction,
should be eliminated to level the playing
field. Misguided promotion of alternatives that
are less desirable than WWS power, such as farm
and production subsidies for biofuels, should
also be ended, because it delays deployment of
cleaner systems. For their part, legislators crafting
policy must find ways to resist lobbying by
the entrenched energy industries.
Finally, each nation needs to be willing
to invest in a robust, long-distance
transmission system that can carry
large quantities of WWS power from
remote regions where it is often greatest—
such as the Great Plains for wind
and the desert Southwest for solar in
the U.S.—to centers of consumption, typically
cities. Reducing consumer demand during peak
usage periods also requires a smart grid that
gives generators and consumers much more control
over electricity usage hour by hour.
A large-scale wind, water and solar energy
system can reliably supply the world’s needs,
significantly benefiting climate, air quality, water
quality, ecology and energy security. As we have
shown, the obstacles are primarily political, not
technical. A combination of feed-in tariffs plus
incentives for providers to reduce costs, elimination
of fossil subsidies and an intelligently expanded
grid could be enough to ensure rapid deployment.
Of course, changes in the real-world
power and transportation industries will have to
overcome sunk investments in existing infrastructure.
But with sensible policies, nations
could set a goal of generating 25 percent of their
new energy supply with WWS sources in 10 to
15 years and almost 100 percent of new supply
in 20 to 30 years. With extremely aggressive policies,
all existing fossil-fuel capacity could theoretically
be retired and replaced in the same period,
but with more modest and likely policies
full replacement may take 40 to 50 years. Either
way, clear leadership is needed, or else nations
will keep trying technologies promoted by industries
rather than vetted by scientists.
A decade ago it was not clear that a global
WWS system would be technically or
economically feasible. Having shown that it
is, we hope global leaders can figure out
how to make WWS power politically
feasible as well. They can start by committing
to meaningful climate and renewable
energy goals now.
MORE TO EXPLORE
Stabilization Wedges: Solving the
Climate Problem for the Next 50
Years with Current Technologies.
S. Pacala and R. Socolow in Science,
Vol. 305, pages 968–972; 2004.
Evaluation of Global Wind Power.
Cristina L. Archer and Mark Z.
Jacobson in Journal of Geophysical
Research—Atmospheres, Vol. 110,
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Going Completely Renewable:
Is It Possible (Let Alone Desirable)?
B. K. Sovacool and C. Watts in
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pages 95–111; 2009.
Review of Solutions to Global
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Energy Security. M. Z. Jacobson in
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The Technical, Geographical, and
Economic Feasibility for Solar
Energy to Supply the Energy Needs
of the U.S. V. Fthenakis, J. E. Mason
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Reprinted with permission. Copyright © 2009 Scientific American,
a division of Nature America, Inc. All rights reserved.