"Advanced Technology Paths to Global Climate
Stability: Energy for a Greenhouse Planet."
"Stabilizing the carbon dioxide-induced climate
change is an energy problem. Stabilization requires energy sources that do not
emit carbon dioxide to the atmosphere.
Mid-century primary power requirements will be three
times what we now derive from fossil fuels even with improvements in energy
efficiency. We must triple available power while reducing carbon dioxide
emission to one third.
A broad range of intensive research and development is
urgently needed to allow both climate stabilization and economic development.
Atmospheric carbon dioxide stabilization as low as 450
ppm could be needed to forestall coral reef bleaching, thermohaline, circulation
shutdown, and a sea level rise of three to five feet.
Kyoto Protocol scenarios to stabilize atmospheric carbon
dioxide minimize early emission controls by initially following a
business-as-usual scenario that combines economic growth of 2 to 3% year with a
sustained decline of 1% for year 1 in energy intensity or energy use per gross
domestic product.
Much larger cuts than those called for in the Kyoto
Protocol are needed. The level at which carbon dioxide stabilizes depends on
total emissions. Holding where we are today at 350 ppm, will require Herculean
effort. Even holding at 550 ppm is a major challenge.
Primary power consumption today is 12 Terawatts, of
which 85% is fossil-fueled. Stabilization at 350 ppm requires emission-free
power by mid-century of 30 Terawatts.
The Kyoto Protocol calls for greenhouse gas emission
reductions by developed nations that are 5% below 1990 levels by 2008 to 2012.
The United States withdrew from the accord for the stated reason that these
cuts are an economic burden. But much greater emission reductions will be
needed, and we lack the technology to make them. The developing nations are now
reneging on Kyoto because they feel that if the leading nations cannot accept
the economic burden, neither can they. They will be accelerating their energy
use the only way they can, by burning fossile fuels.The only way to reduce
emissions with equitable economic growth is to develop revolutionary changes in
the technology of energy production, distribution, storage, and conversion. But
Present U.S. policy emphasizes domestic oil production, not technology
research.
There are no known technological options that exist
today. Energy sources that can produce 100 to 300 per cent of present world
power without greenhouse emissions do not exist; either operationally or as
pilot plants. New technologies will require drastic technological
breakthroughs.
Carbon dioxide is a combustion product vital to how
civilization is powered; it cannot be regulated away. But carbon dioxide
stabilization would prevent developing nations from basing their energy supply
on fossil fuels.
Primary energy sources include terrestrial solar and
wind energy, solar power satellites, biomass, nuclear fission, nuclear fusion,
fission-fusion hybrids, and fossil fuels from which carbon has been
sequestered.
Non-primary power technologies that could contribute to
climate stabilization include efficiency improvements, hydrogen production,
storage and transport, superconducting global electric grids, and
geoengineering. All of these approaches currently have severe deficiencies that
limit their ability to stabilize global climate.
Improving Efficiency
Primary energy in metastable chemical and nuclear bonds
includes fossil fuels, fission fuels, and fusion fuels. "Renewables"
are primary energy in natural fluxes; solar photons, wind, water, and heat
flows. Energy conversion always involves dissipative losses. Efficiency can be
improved in power generation and end-use sectors: transportation,
manufacturing, electricity and indoor climate conditioning.
Mature technologies are most efficient. Large electric
generators are 98 to 99% efficient and electric motors are 90 to 97%. Rotating
heat engines are limited by the second law of thermodynamics: gas and steam
turbines to 35 to 50%, diesel to30 to 35% and internal combustion at 15 to 25%
efficiency. Electrolyte and electrode materials and catalysts limit
electrochemical fuel cells from 50 to 55% now; to 70% eventually. Fuel cells
may replace heat engines but will likely run on hydrogen. A seamless transition
would use H2 extracted from gasoline or methanol in reformers at 75 to 80%.
Renewable energy converters include photovoltaic cells at 15 to 24%; and wind
turbines at 30 to 40%; Biomass schemes are limited. Photosynthesis has a very
low sunlight-to-chemical energy efficiency, limited by chlorophyll absorption
bands with the most productive ecosystems at about 1 to 2% efficient; with a
theoretical peak of 8%. In a given technology class, efficiency starts low,
grows for decades, then levels off at some fraction of its theoretical peak
It took 300 years to develop fuel cells from
1%-efficient steam engines. The earliest gas turbines could barely turn their
compressors. The development of fusion could be similar: The best experiments
are close to balancing power to ignite the plasma; power is carried off by
fusion-generated neutrons, but no net power output has occurred yet.
Fossil and nuclear fuels are much closer to their limits
with steam-cycle efficiencies of 39 to 50%, including cogeneration and overall
primary energy-to-electricity efficiency of 30 to 36%. Impressive reductions in
waste heat have been accomplished with compact fluorescents, low emissivity
windows, and cogeneration .
More efficient automotive power conversion is possible .
Emissions depend on vehicle mass, driving patterns, and aerodynamic drag, as
well as well-to-wheels efficiency. Power trains are 18 to 23% efficient for
internal combustion, 21 to 27% for battery-electric; 35 to 40%, 30 to 35% for
IC-electric hybrid and 30 to 37% for fuel cell-electric .
Ultra fuel-efficient cars are available today but
consumer demand for sport utility vehicles has driven the fuel economy of the
U.S. car and light truck fleet to a 21-year low of 20 mpg on the highway. Even
doubling efficiency we will be overwhelmed if China and India follow the U.S.
path from bicycles and mass transit to cars. Asia already accounts for 80% of
petroleum consumption growth.
Advances in efficiency and conservation by themselves
cannot solve the problem. Carbon-neutral fuels are necessary.
Decarbonization and Sequestration
Reducing the amount of carbon emitted per unit of
primary energy is called decarbonization. The long-term trend has been from
coal to oil to gas, with each fuel emitting progressively less carbon dioxide
per joule of heat. Continuation of the trend would lead to use of H2, a
carbon-neutral fuel, but H2 does not exist in geological reservoirs. Processes
requiring energy are needed for its synthesis. The energy can come from fossil
fuel feedstocks. Per unit of heat generated, more carbon dioxide is produced by
making H2 from fossil fuel than by burning the fossil fuel directly.
Emission-free H2 manufactured by water electrolysis powered by renewable or
nuclear sources is not yet cost effective.
But the decarbonization of fuels alone will not mitigate
global warming. The problem is providing 30 Terawatts emission-free in 50
years. High-carbon fossil resources such as coal are most abundant, followed by
oil and gas. Lower emissions requires disposing of excess carbon.
One vision of "clean" coal incorporates carbon
dioxide capture and sequestration: Coal, biomass and waste materials are
gasified, cleaned of sulfur and reacted with steam to form H2 and carbon
dioxide. .After heat extraction, the carbon dioxide is sequestered and the H2
used for transportation or electricity generation. Decarbonization is thus
linked to sequestration. Sequestration reservoirs include oceans, trees, soils,
depleted natural gas and oil fields, deep saline aquifers, coal seams, and solid
mineral carbonates.
Sequestration uses existing fossil fuel infrastructures,
including carbon dioxide injections for enhanced recovery from existing oil and
gas fields and the capture of carbon dioxide from power plant flue gases.
The simplest air capture is forestation. Tree and soil
sequestration does not require combustion product separation or more fuel, but
the capacity to absorb carbon dioxide is limited. Uptake occurs during growth
of organic matter.Historical data and models imply a temperate forest carbon
sink today of 1 to 3 billion tons of carbon per year but some models show
forests reversing from sinks to sources later this century as global warming
increases soil respiration and as the trees decay.
The exchange time of carbon dioxide with trees is ~7
years. On the oceans fertilization-enhanced plankton carbon uptake can be as
fast if organic detritus oxidizes near the surface. Biological sequestration
approaches to longer term storage include sealing undecayed trees underground
and sinking agricultural residues to the deep ocean, but this is not
efficient..
Air capture by aqueous calcium hydroxide in shallow
pools, with carbon dioxide recovery by heating, has also been proposed , but
breaking the Ca-carbon dioxide bond requires substantial energy.
Ocean injections can substantially decrease peak
atmospheric carbon dioxide levels, although all cases eventually diffuse some
carbon dioxide back to the atmosphere. Back-diffusion and pH impacts of ocean
carbon dioxide disposal could be diminished by accelerating carbonate mineral
weathering that would otherwise slowly neutralize the oceanic acidity produced
by fossil fuel carbon dioxide .
A far-reaching removal scheme is reacting carbon dioxide
with the mineral serpentine to sequester carbon as a solid in magnesium
carbonate "bricks" by vastly accelerating silicate rock weathering
reactions, which remove atmospheric carbon dioxide over geologic time scales
Thus, carbon sequestration could be a valuable bridge to renewable and/or nuclear
energy. However, if other emission-free power are unavailable by mid-century,
enormous sequestration rates could be needed to stabilize atmospheric carbon
dioxide . Substantial research investments are needed now to make this
technology available in time.
Renewables
Renewable energy technologies include biomass, solar
thermal and photovoltaic, wind, hydropower, ocean thermal, geothermal, and
tidal. With the exception of firewood and hydroelectricity (close to
saturation), these are collectively <1% of global power.
All renewables suffer from low areal power densities.
They arent't where you need them in concentration.
Biomass plantations can produce carbon-neutral fuels for
power plants or transportation, but photosynthesis has too low a power density
for biofuels to contribute significantly to climate stabilization. Obtaining 10
Terawatts from biomass would requires 10% of Earth's land surface, comparable
to all of human agriculture.
PV and wind energy need less land, but other materials
can be limiting.
For solar energy, U.S. energy consumption may require a
PhotoVoltaici array covering a square ~160 kilometers on each side; a total of
of 26,000 square kilometers.
The electrical equivalent of 10 TW would require a
surface array of 470 km on a side for 220,000 square kilometers. However, all
the PV cells shipped from 1982 to 1998 would only cover ~3 square kilometers. A
massive scale-up is required to get to 30 Terawatts. More cost-effective Photo
Voltaic panels and wind turbines are expected as mass production drives
economies of scale. But Earth-based renewables are intermittent, dispersed
sources unsuited to baseload without transmission, storage, and power
conditioning.
Wind power is often available only from remote or
offshore locations. Meeting local demand with PV arrays today requires
pumped-storage or battery-electric backup systems of comparable or greater
capacity. "Balance-of-system" infrastructures could evolve from
natural gas fuel cells if reformer H2 is replaced by H2 from PV or wind
electrolysis. Reversible electrolyzer and fuel cells offer higher current (and
power) per electrode area than batteries, ~20 kWe m 2 for proton exchange
membrane (PEM) cells. PEM cells need platinum catalysts, a 10-TW hydrogen flow
rate could require 30 times as much as today's annual world platinum
production). Advanced electrical grids would also foster renewables. Even if PV
and wind turbine manufacturing rates increased as required, existing grids
could not manage the loads. Present hub-and-spoke networks were designed for
central power plants, ones that are close to users. Such networks need to be
reengineered. Spanning the world electrically evokes Buckminster Fuller's
global grid.
With high-temperature superconductivity, electricity can
be trasferred between day and night hemispheres and pole-to-pole. Worldwide
deregulation and the free trade of electricity could have buyers and sellers
establishing a supply-demand equilibrium to yield a worldwide market price for
grid-provided electricity. Mass-produced widely distributed PV arrays and wind
turbines making electrolytic H2 or electricity may eventually generate 30 TW
emission-free.
The global grid proposed by Buckminster Fuller with
modern computerized load management and high-temperature superconducting cables
could transmit electricity from day to night locations and foster low-loss
distribution from remote, episodic, or dangerous power sources.
Space solar power exploits the unique attributes of
space to power Earth. The Solar flux is 8 times higher in space than the
surface average on the spinning, cloudy Earth. If theoretical microwave
transmission efficiencies of 50 to 60% can be realized, 75 to 100 We could be
available at Earth's surface per square meter of PV array in space, One fourth
the area of earth surface PV arrays of comparable power.
In the 1970s, the National Aeronautics and Space
Administration and the U.S. Department of Energy studied a SPACE SOLAR POWER
design with a PV array the size of Manhattan in geostationary orbit (GEO) 35,800
km above the equator that beamed power to a 10-km by 13-km surface rectenna
with 5 GWe output.
10 TW equivalent requires 660 of these SPACE SOLAR POWER
units.
Alternative locations are 200- to 10,000-km altitude
satellite constellations, the Moon, and the Earth-Sun L2 Lagrange exterior
point. Japan's Institute of Space and Aeronautical Science will attempt to beam
solar energy to developing nations a few degrees from the equator from a
satellite in low equatorial orbit. Papua New Guinea, Indonesia, Ecuador, and
Colombia on the Pacific Rim, and Malaysia, Brazil, Tanzania, and the Maldives
have agreed to participate in such experiments).
A major challenge is reducing or externalizing high
launch costs. With adequate research investments, SPACE SOLAR POWER could
deliver electricity to global markets.
Capturing and controlling sun power in space.
(A) The power relay satellite, solar power satellite
(SPS), and lunar power system all exploit unique attributes of space of high
solar flux, lines of sight, lunar materials and the shallow gravitational well
of the Moon.
(B) An SPS in a low Earth orbit can be smaller and
cheaper than one in geostationary orbit because it does not spread its beam as
much; but it does not appear fixed in the sky and has a shorter duty cycle ;the
fraction of time power is received at a given surface site.
Fission and Fusion
Nuclear electricity today is fueled by Uranium 235.
Bombarding natural Uranium with neutrons of a few eV splits the nucleus,
releasing energy. The 235U isotope, is often enriched to 2 to 3% to make
reactor fuel rods.
The existing 500 nuclear power plants are variants of
water-cooled submarine reactors. Loss-of-coolant accidents such as Three Mile
Island and Chernobyl may be avoidable in the future with "passively
safe" reactors. Available reactor technology can provide carbon dioxide
emission-free electric power, though it poses well-known problems of waste
disposal and weapons proliferation.
The main problem with fission for climate stabilization
is fuel. Current estimates of Uranium in recoverable proven reserves are 17
million metric tons, This represents 60 to 300 Terawatt-years of primary energy
At 10 TW, this would only last 6 to 30 years--hardly a basis for energy policy.
Japanese researchers have harvested dissolved Uranium
from flowing seawater But even with 100% 235U extraction, the flow rate needed
to make reactor fuel at the 10 TW rate is five times as much as the outflow
from all the worlds's rivers. Getting 10 Terawatts primary power from 235U in crustal
ores or seawater extraction may not be impossible, but it would be a big
stretch.
Despite enormous hurdles, the most promising long-term
nuclear power source is still fusion.
Steady progress has been made toward
"breakeven" with tokamak toroidal near-vacuum chamber, magnetic
containments.The focus has been on the deuterium-tritium reaction. Deuterium in
the sea is virtually unlimited.but there is very little Tritium on earth. If
Deuterium-Tritium reactors were operational, lithium bred to Tritium could
generate 16,000 Terawatt-years, or twice the thermal energy in fossil fuels.
The Deuterium -Helium 3 (D-3He) reaction yields charged
particles that are directly convertible to electricity. Ignition of D-T-fueled
inertial targets and associated energy gains of Q 10 may be realized within the
next decade.
Experiments are under way to test a D-3He reactor
prototype. Rare on Earth, 3He may someday be cost-effective to mine from the
Moon. It is even more abundant in gas-giant planetary atmospheres. Seawater
Deuterium and outer planet 3He could power civilization longer than any source
other than the Sun.
Devices with a larger size or a larger magnetic field
strength are required for net power generation. A "burning plasma
experiment" could produce net fusion power at an affordable scale and
could allow detailed observation of confined plasma during self-heating by hot
alpha particles. The Fusion Energy Sciences Act of 2001 calls on DOE to
"develop a plan for United States construction of a magnetic fusion burning
plasma experiment for the purpose of accelerating scientific understanding of
fusion plasmas." This experiment is a critical step to the realization of
practical fusion energy. Demonstrating net electric power production from a
self-sustaining fusion reactor would be a breakthrough of overwhelming
importance but cannot be relied on to aid carbon dioxide stabilization by
mid-century.
The conclusion from our 235U fuel analysis is that
breeder reactors are needed for fission to significantly displace carbon
dioxide emissions by 2050. Breeding could be more acceptable with safer fuel
cycles and transmutation of high-level wastes to benign products.Fission is
energy rich and neutron poor, whereas fusion is energy poor and neutron rich. A
single fusion breeder could support perhaps 10 satellite burners, whereas a
fission breeder supports perhaps one. But both fission and fusion are unlikely
to play significant roles in climate stabilization without aggressive research
and, in the case of fission, without the resolution of outstanding issues of
high-level waste disposal and weapons proliferation.
Geoengineering
"Geoengineering" is planetary climate
engineering on Earth and terraforming on other planets. Geoengineering refers
mainly to altering the planetary radiation balance to affect climate and uses
technologies to compensate for the inadvertent global warming produced by
fossil fuel carbon dioxide and other greenhouse gases.
SunBlock
An early idea was to put layers of reflective sulfate
aerosol in the upper atmosphere to counteract greenhouse warming. Variations
include injecting sub-micrometer dust to the stratosphere in shells fired by
naval guns, increasing cloud cover by seeding, and shadowing Earth by objects
in space.
A proposed 2000-km-diameter mirror fabricated from lunar
materials would be placed at the L1 Lagrange point. The mirror's surface would
look like a permanent sunspot, and would deflect 2% of solar flux to compensate
for carbon dioxide heating. The deflected sunlight might be directed to the
moon to light the shadowed side.
Geoengineering research is an insurance policy should
global warming impacts prove worse than anticipated and other measures fail or
prove too costly. Large-scale geophysical interventions are inherently risky
and need to be approached with caution. Even as evidence for global warming
accumulates, the dependence of civilization on the oxidation of coal, oil, and
gas for energy makes an appropriate response difficult.
The disparity between what is needed and what can be
done without great compromise will become more acute the longer we wait. Energy
is critical to global prosperity and equity.
If Earth continues to warm, people may turn to advanced
technologies for solutions. Combating global warming by radical restructuring
of the global energy system could be the technology challenge of the century.
radical departures from our present fossil fuel system are needed. .Staying the
course will require leadership. Stabilizing the climate will not be easy. At
the very least, it requires political will, targeted research and development,
and international cooperation. Most of all, it requires the recognition that,
although regulation can play a role, the fossil fuel greenhouse effect is an
energy problem that cannot be simply regulated away."
From Science Magazine - November 2002