**A Road Map to the Decarbonization of the U.S. Energy Mix.**

**The Potential Impact of Solar Thermal Energy**

**Reuel Shinnar**[^1]**, Francesco Citro**

**The Clean Fuels Institute**

**City College of New York**

Presented at the AAAS Symposium on the Decarbonization of the U.S.
Energy Mix, St. Louis, February 2006

**I. Introduction**

Today, 85% of the energy used in the U.S. comes from carbon-rich fossil
fuels: oil, natural gas and coal (1). But, the demand throughout the
world is increasing and there is little doubt that proven resources of
oil and natural gas will peak in the next twenty to fifty years. It is
not surprising that many leaders in Government and technology are
calling for their replacement by alternative energy sources. Additional
motivation for the decarbonization of the U.S. energy mix is the danger
of global warming, which many attribute to the CO~2~ emissions that
accompany the use of fossil fuels.

Any switch to alternative energy to be doable and affordable has to be
done over a long period, at least 30 to 50 years. It is hardly too soon
to develop a blueprint and timetable for achieving this goal.

In this paper we present a plan for the gradual replacement of 98% of
our total fossil fuel needs with available and affordable technology
(which would also reduce 97% of present total CO~2~ emissions). We show
that the direct use of electricity produced from alternative sources can
replace 72% of the fossil fuel we consume. Another 26% can be replaced
by hydrocarbons produced from syngas, a mixture of carbon oxides
produced by gasifying biomass and hydrogen generated by electrolysis
powered by alternative energy sources. 50% of this goal could be
achieved over thirty years, and 80-90% over about 50 years. We have
limited the scope of this paper to a discussion of our technological
options. A comprehensive plan would also focus on other critical
problems such as priorities and costs, political and economic
constraints, regulatory issues and government-mandated incentives
without which the free market is not likely to reduce CO~2~ emissions or
prepare for a distant, uncertain future. However, for society the
penalty of strongly reduced oil and gas supplies would be catastrophic,
unless we prepare in advance, as the timescale for achieving a
substantial reduction is very large. Such a plan must be based on
existing technologies, or at least on technologies that are available in
a form which can be scaled up and implemented at a cost that can be
estimated reliably. While research could and should lead to better
technologies, and should be continued, we can never be sure which
research will lead to useful results. In the 1970s, a worldwide research
effort to produce H~2~ from nuclear reactors by thermochemical cycles
was terminated with no results after approximately 40 billion (2005
dollars) dollars were spent (2). Further constraint on any such a plan
is that the new technology should allow gradual phase in and preferably
should use available distribution systems, which suggests wide use of
electricity from alternative sources.

It is encouraging that proven technologies for decarbonizing our energy
mix that use existing distribution systems already exist. The approach
described in this paper is to a large part based on electricity from
alternative sources, and the prime candidate is solar thermal energy
with storage. Plants with 354 MWe installed capacity have been operating
in California since the late 1980's (3). This technology has been
overlooked until now despite the fact that it probably has a larger
potential than all other options. Our paper will compare its
capabilities and costs with other available options. Before costs are
taken into consideration, however, it must be acknowledged that
technologies that achieve decarbonization by replacing power plants and
other existing uses of fossil fuels cannot be competitive in the free
market without some form of government incentive or subsidy. The only
time when this is possible without incentives is either when the
equipment becomes obsolete or the technology is no longer competitive or
the fossil fuels costs become too expensive. We will show, however, that
for new installations with specific applications a variety of
alternative technologies are already competitive. Of these, solar
thermal energy has applications on the broadest scale.

It appears that the free market is actually moving the U.S. towards a
tolerance for increased CO~2~ emissions. Natural gas, hydrogen and
ammonia plants in the U.S. vent about 100 million tons of already
separated CO~2~ a year into the air (4). Based on ref. 5, an investment
of \$4.6 billion would be required to separate 100 million tons of CO~2~
a year in coal power plants. In recent years, a large fraction of the
natural gas-fired combined cycle power plants for generating base power
have been shut down due to high gas prices. They are being replaced by
conventional coal-fed power plants. Also, petroleum feedstocks are
becoming heavier, thus increasing CO~2~ emissions. It is urgent that we
achieve decarbonization by promoting specific applications for proven
technologies that are economically attractive. We have shown elsewhere
that some large applications of thermal solar energy are already
economically competitive (6).

II. **Available Methods for the Decarbonization of the Economy**

Today, only three options are available to help reduce the consumption
of fossil fuels:

1\. Reducing total energy demands.

2\. Switching to alternative energy sources.

3\. Converting coal feed to H~2~ (if our only aim is to reduce CO~2~
emissions) and sequestering the CO~2~ simultaneously.

As all available methods for alternative energy have limitations, a
comprehensive plan should not be based on a single option. Following is
a more detailed discussion of the options for alternative energy.

1\. Solar thermal energy with storage is a proven technology, which is
ready for implementation (6). We will show that it can supply most of
the energy needs of the U.S., which can be supplied by electricity.
Solar thermal is already competitive with most technologies currently in
use for intermediate loads, which constitute 50% of our electricity
needs. Furthermore, this technology can be designed to generate large
amounts of instantaneously dispatchable, variable electricity to
compensate for fluctuations in demand (presently 10% of our electricity
needs). In the future it could also be used to compensate for
uncontrollable inputs from other alternative energy sources, such as
wind and solar cells.

2\. Nuclear energy. New, safer designs have been developed, but they are
unproven as none have yet been built on a commercial scale. Furthermore,
the disposal of nuclear waste is a problem that is yet to be solved. To
become the major alternative energy source, 1000 GWe nuclear energy
plants would have to be built. The implementation of this large nuclear
capacity would require further study as to the long-range availability
of nuclear fuel and the disposal of accumulated waste on a global scale.
As other countries may follow our lead, our nuclear energy capacity must
be expanded with caution because of its potential for global impact,
increasing the danger of nuclear weapons proliferation.

3\. Geothermal and hydroelectric plants. Excellent energy sources, but
with limited total output.

4\. Wind is already a competitive energy source that is growing
steadily. Its limitation is that wind can vary strongly, and that the
amount of uncontrollable energy input that the national electricity grid
can accept, without compensation for variations, is limited. Solar
thermal energy, as mentioned before, could provide the compensation and
stabilization that the large-scale use of wind energy would require.

5\. Solar cells. At present, solar cells are too expensive for
large-scale implementation but this should change with further research.
Like wind, solar cells lack storage. Unlike wind, however, sunlight is
available for only part of the day. The advantage of solar cells over
thermal solar technology is that they can be placed throughout the
country. If solar cells could be produced cheaply, they could become
part of an advanced grid, stabilized by thermal solar plants with large
storage capacity. Until further research leads to the removal of these
limitations, their total contribution will be very limited.

6\. Biomass. Biomass is the only source of alternative energy that can
create liquid fuels for aviation and petrochemical feedstocks for
industry. But, biomass will not be able to provide more than about 10%
of the total energy we use at present. However, by gasifying biomass and
combining it with H~2~ from alternative sources to form syngas, triple
this amount could be produced to supply the many types of hydrocarbons
that cannot be replaced by electricity (see section VI).

III. **Quantitative Estimates for the Potential of Decarbonization by
     Electricity from Alternative Energy Sources**

Before we estimate the full potential impact of solar thermal energy on
the decarbonization of the U.S. energy mix we must first determine the
fraction of our fossil fuel use that can be replaced by electricity
generated from the alternative sources currently available. Table 1 and
Figure 1 summarize our total energy consumption and provides a detailed
breakdown of our current use of fossil fuels (1). CO~2~ emissions caused
by the various uses of fossil fuels are shown in Table 2 and Figure 2
(1).

From Table 1 we note that coal-fired power plants contribute to 25% of
total fossil fuels consumption (which cause 33% of total CO~2~
emissions, Table 2), while power plants using natural gas and oil
represent 7% of total fossil fuels use (6% of total CO~2~ emissions,
Table 2). All these power plants fueled by fossil fuels could be
replaced by electricity from alternative sources.

As natural gas and oil emit much less CO~2~ per kWh, the most cost
efficient way to reduce CO~2~ would be to replace all existing
coal-powered plants by building 300 GWe (based on ref. 1) of alternative
energy power plants such as solar thermal plants or coal power plants
with sequestration of CO~2~. As replacing all power plants is very
expensive, if the only goal is CO~2~ sequestration, CO~2~ scrubbers for
existing power plants merit a second look. Present plans for CO~2~
sequestration are based on building totally new power plants as well as
pipelines for the CO~2.~ We show later that solar thermal plants with
storage cost slightly less to build per kW capacity than coal-fired
plants with CO~2~ sequestration. Both technologies should be considered,
however, for the significant potential advantages of each.

# If reducing CO~2~ emissions is a serious national priority, this would be the most effective way to achieve it. Replacing electricity generated from oil and gas would require another 120 GWe of electricity from alternative sources (based on ref. 1).

# Other uses for fossil fuels that are relatively easy to replace with electricity include all residential and commercial non-electric energy use, 13% of the total use for fossil fuels (Table 1) which generate 11% of all CO~2~ emissions at present (Table 2). The distribution system and the technology needed for the implementation of this changeover are already available. Most uses of fossil fuels for these applications can be met much more efficiently by using electricity directly. For example, in many situations heat pumps are more efficient than conventional heating systems. 

Petroleum constitutes 40% of our energy mix (1). The petroleum we use
for commercial, residential, and power (9% of total petroleum, already
counted above) would be easy to replace by using electricity from
alternative sources directly (Table 1).

Petroleum\'s main use -almost 70% of the total is for transportation,
Table 1- can be shifted in part to alternative fuels. 80% of the
gasoline now used for private cars and light trucks (60% of oil used for
transportation, ref. 7), can be replaced by hybrid cars with plug-in
batteries. This replacement of gasoline with electricity is probably the
cheapest and most politically attractive way to reduce oil consumption
and is competitive today with \$40 a barrel of crude oil. Additionally,
railroads driven by electricity can take on much of the hauling now
handled by heavy trucks; we can probably shift 60% of the oil used for
big trucks (29% of oil used for transportation, ref. 7), but this
requires more studies as to the costs involved. Both contributions could
save 20% of total fossil fuels (Table 1), which is 44% of our total
petroleum consumption or 65% of the oil used for transportation (6).

Shifting from hydrocarbon fuels to electricity would provide an
attractive solution that would be easier to achieve than replacing coal
power plants. Unlike coal power plants, which last about 50 years, cars
are replaced much more frequently. Secondly, our dependence on imported
fossil fuels would be reduced substantially. Reducing oil consumption
has attracted much wider support than CO~2~ reduction, because
dependence on imported oil, whose prices can fluctuate very widely, has
strongly negative political and economical implications. Furthermore,
fossil-fuels resources are being depleted at an increasing rate
worldwide, and it would be wise to prepare for a non-fossil energy mix
long before peaking occurs. By replacing 65% of the oil used for
transportation with electricity from alternative sources would also
decrease CO~2~ emissions by 21% (Table 2).

Regarding the use of natural gas we noted before that all residential,
commercial and power generation uses can be replaced by electricity. 37%
of the natural gas (10% of total fossil fuels used) is used by industry,
we have no break down of the specific uses, but based on one of the
authors' experience (R.S.) at least 70% is for internal power and steam
generation, furnaces (such as in distillation) and H~2~ production. All
these uses, 7% of total fossil fuels (which generates 5% CO~2~
emissions) are switchable to electricity from alternative sources. The
only use that is not switchable is for chemical feedstocks,
approximately 30% of industrial gas use, or 3% of total fossil fuels.

Another 2% of total fossil fuels that cannot be switched at all is
direct industrial use of coal.

In summary it is feasible with existing technologies to replace 72% of
the fossil fuels now used with electricity from alternative sources
(Table 3a, and Figure 3). This shift would also reduce CO~2~ emissions
by 76% (Table 3a).

In section VI we will discuss how to replace the other 26% (2% coal in
industry is not replaceable), also shown in Figure 3.

**IV. Solar Thermal Energy with Storage**

A more detailed technical discussion of solar thermal energy with
storage can be found in the authors' recent paper, which is in
publication (available electronically), and is cited below as a
reference (6). As the main objective undertaken here is to assess the
potential of solar thermal technology for decarbonizing our energy mix,
only the relevant points of the previous work will be summarized.

Solar thermal technology utilizes solar collectors of the trough type to
concentrate solar rays on a flowing liquid that is able to sustain very
high temperatures (= 800 ºF). The heat thus collected can then be used
directly to raise steam for driving the turbines of
electricity-generating plants. Alternatively, the energy can be
harvested and stored as sensible heat in large underground ponds. Later,
the stored energy can be fed to the steam plant instantaneously to meet
variable power needs. This technology has been amply demonstrated in a
354 MWe modular plant (consisting of 9 solar thermal units) that has
been running in the Mojave Desert for the past 20 years (see Appendix A
in ref. 6).

Solar thermal energy has been evaluated in two reports by the National
Research Council (NRC, refs. 8 and 9). Both concluded that it is
unlikely to become competitive with conventional coal power. While this
conclusion may be correct, the reports missed two important points:

1.  Solar thermal energy with storage is the only alternative energy
    source -other than nuclear energy- that can supply all our energy
    needs (6). All other alternative energies have severe inherent
    limitations.

2.  Given the capital costs projected currently, solar thermal energy
    may not be competitive with coal or nuclear energy for base power
    (6). As will be explained in the next section, however, it can
    become competitive with all other conventional sources because of
    its capacity for storing heat (6). Indeed, it can supply 60% of the
    requirements of our electric grid, intermediate and peak load, at an
    acceptable cost.

**IV.1 The Importance and the Cost of Variable Loads in the Generation
of Electricity**

Most cost comparisons for alternative energy, including the two
evaluations of thermal solar by NRC (8, 9), compare the cost of base
loads (40% of our total electricity consumption, 10). But at present,
solar thermal for base load in more expensive than conventional coal
power plants and nuclear power plants. However, when we consider the
other 60% of the load, intermediate and peak electricity, the comparison
changes completely and, as shown below, solar thermal energy becomes
attractive even at present prices. Similarly, gas turbines are only
competitive for peak loads (400 hours a year).

The effect of operating power plants for only a fraction of the time
adds to capital-related costs. Capital costs are a large fraction of the
total cost of electricity from nuclear and coal power plants. Although
the penalty for natural gas plants would be smaller, they are not
included in our comparison as the cost of natural gas has increased
five-fold in the last ten years and the current shortage of gas does not
allow for a large expansion.

For a solar thermal power plant, one can consider the solar collectors
and the storage facilities for the heat transfer fluid as a plant
producing storable heat for feeding the steam power plant. In the design
of a solar thermal plant, the collectors and the heat storage (90% of
the capital cost, ref. 6) are designed to supply the total expected
electricity/day. Only the steam power plant is designed to the maximum
expected load. For nuclear and coal power plants with load-following
capability, the entire plant must be designed for maximum load. The
steam power plant of a solar thermal plant is cheaper by a factor of
four than a coal power plant and by a factor of seven than a nuclear
power plant. For intermediate loads (13 hours/day) the capital cost of
solar thermal energy increases by only 10% vs. 85% for nuclear and coal
power plants. Despite the fact that initially the capital investment for
solar thermal plants is double that of coal and nuclear plants, their
cost-effective design for intermediate and peak loads plus their lower
maintenance costs and "zero" fuel costs make them competitive even today
(6).

Furthermore, solar thermal technology could be integrated with wind and
solar cells to provide an output for the electric grid that is reliable
and controllable in order to offset strong variations in demand and
fluctuations in input from environmental sources. Thus, solar thermal
plants are the energy sources of choice whenever large instantaneous
control capabilities are required, an essential need in a decarbonized
economy. For example, solar thermal energy can provide the equivalent of
a 4 GWe power plant for 6 hours a day, at a 30% increased capital cost
compared to a 1 GWe power plant designed for base load vs. 300% for
nuclear or coal technology.

**IV.2 Estimated Costs for Solar Thermal Energy**

The cost estimates for solar thermal energy were taken from the recent
Sargent and Lundy report (11) commissioned by the U.S. DOE and reviewed
by the NRC (9) as discussed in detail in reference 6. In our earlier
discussion of these estimates we compared published data for solar
thermal plants with both nuclear and various coal technologies (6). At
this point, it is important to emphasize that although the estimate for
solar thermal technology by Sargent and Lundy is based on available
technology and a conventional approach to building power plants, it
misses two critical factors:

a\. With a much larger market and increased competition, costs should be
reduced significantly. For example, LNG plants and combined-cycle power
plants leveled out at half the initial predicted cost.

b\. Additionally, they did not take into account that, with a large
market, solar collectors (70% of cost, ref. 11) could be designed for
mass production so that costs could be reduced by a factor of three.

It is fortunate that solar power is already sufficiently competitive for
many existing large-scale needs to initiate the creation of this market.
Ultimately, solar thermal plants could become the cheapest source of
alternative energy and of electric power in general.

A comparison of the costs of base power appears in Table 4, while Table
5 compares the costs of intermediate power for the technologies
discussed above. From Table 4 we note that for base power, solar thermal
is competitive only with future coal power plants with sequestered
CO~2~. We discuss this later. For variable loads (60% of our electricity
demand), however, solar thermal is already competitive (Table 5). With
increased large-scale use, it should also become competitive for base
loads.

As most deserts in the U.S. are in the Southwest, we will need to
connect the Pacific grid to the National grid so that solar thermal
power could serve the whole nation. Fortunately, the distances which
must be spanned are not large but planning on a national scale will be
required.

**IV.3 Compensation for Variable Power Inputs and Fluctuations in Demand
on the Grid**

Variable power requirements were a problem for the grid until recently
only because of variations in consumer demand. When switching to a
non-fossil energy economy, wind and solar cells will become a large
source of fluctuations in power generation as they have a strongly
variable output and lack a capacity for storage. Solar thermal plants,
however, are uniquely suited for large-scale load following. Such plants
could make it possible to create an advanced grid that integrates
nuclear, wind and solar cell technologies because solar thermal energy
can compensate for variations in demand and fluctuations in power inputs
into the grid.

The actual composition of the advanced grid and the fraction of the grid
generating capacity solar thermal electricity should contribute require
further studies. It is encouraging to realize, however, that the
available U.S. desert area is sufficient to generate several times our
current energy needs (the control of such a grid will be different from
the present one but the theoretical tools for designing such a grid are
available). Thus, we have the technology to supply all our future
electricity needs from alternative sources at a reasonable cost.
Moreover, the switch to electricity from alternative sources can be done
gradually.

**V.** **The Potential Contributions of Solar Thermal Energy and
Electricity from Alternative Sources**

In the preceding section we tried to show that solar thermal energy can
serve as a viable source of electricity. It is also the only source of
alternative electricity that, like nuclear energy, can support a major
share of our electric energy needs. Although we advocate a more
diversified approach, the fact is that there is sufficient sunlit area
in the U.S. for supplying all our energy needs. The total power that
could be generated from all other proven alternative energy sources,
such as hydroelectric, geothermal, wind, and solar cells, is severely
limited. Furthermore, solar thermal can become the mainstay of an
advanced grid. Solar thermal technology merits a more thorough
reevaluation. Several large demonstration plants (250-400 MWe) with
adequate storage capacity should be subsidized by Government support -as
was provided to launch nuclear power- to help prove that solar thermal
power can be useful to industry at acceptable cost.

This paper focuses on an existing version of solar thermal energy (3).
Other designs that have been proposed should also be evaluated, but only
those with sufficient storage can have a large impact.

Full decarbonization of the U.S. economy can take from 30 to 50 years;
so, implementation cannot wait until either global warming has an
unacceptable impact or oil and natural gas supplies have peaked, as then
it will be too late. The cheapest way to initiate decarbonization is by
building new power plants and enlarging our National grid with
alternative energy slowly until we double or triple our total
electricity generating capacity. We must start now.

We showed in Section III that on a BTU basis, 72% of the decarbonization
of the energy mix could be achieved by available, affordable technology.
The fact that alternative technologies are already available does not
mean the U.S. should stop research for new and better ideas. To the
contrary, a detailed plan for the development of available technologies
as outlined above could serve as a yardstick in the evaluation of new
research proposals and achievements.

Our discussion of the advanced grid did not include coal power plants
with CO~2~ sequestration because they are designed to produce base
power, not intermediate or variable power, and therefore are not
suitable for stabilizing the grid. Additionally, such plants have a
higher electricity cost than any other power source. Although they may
create no CO~2~ emissions, new coal plants do not address the need to
decarbonize our energy mix. Furthermore, coal reserves are finite and
should be preserved as a chemical resource for the long range. For the
near term, however, coal plants with CO~2~ sequestration could be used
for generating H~2~ to stretch crude oil reserves and upgrade heavy oil
and tar sands. H~2~ from coal gasifiers with CO~2~ sequestration is at
present much cheaper than H~2~ from electrolysis (based on Table 4,
\$11-12 per MMBtu for the gasifier vs. close to \$30 for electrolysis,
12).

In Section III we discussed how 72% of the energy we derive from fossil
fuels could be shifted gradually to electricity from alternative
sources. In the section which follows we consider how we can develop
decarbonized energy to meet the balance of our needs.

**VI. The Role of H~2~ and Biomass in the Decarbonization of Our Energy
Mix**

Many resources have recently been placed behind programs that aim to
develop H~2~ as a main energy source. But H~2~ is an energy carrier not
an energy source, because energy is required to generate it. H~2~ can be
produced from natural gas, which is already in short supply. Were we to
generate sufficient H~2~ to fuel our cars, we would double our total
natural gas consumption. Producing H~2~ from coal would introduce a
difficult switching problem, as H~2~ cannot be produced at a gas station
and so, an extensive transport system would be required. The only
available way to produce H~2~ from alternative sources is by
electrolysis, an expensive process. Other ways to produce H~2~ from
alternative sources, e.g., the photoelectrochemical and photochemical
decomposition of water, have not yet been developed, but, merit
research. A recent NRC report concluded that the H~2~ economy requires
further research and is not ready for implementation (13). This places
H~2~ beyond the scope of our discussion.

As long as H~2~ must be made by electrolysis, it is clearly preferable
to use electricity directly whenever possible. As electricity costs are
comparable to many uses of oil and gas, the direct use of electricity
from alternative sources should be maximized in the near future. As
noted above, however, about 28% of our use of fossil fuels cannot be
replaced with the direct use of electricity nor can they be replaced by
direct use of H~2~; e.g., we cannot substitute electricity or H~2~ for
petrochemical feedstocks or airplane fuel. As will be discussed below,
H~2~ can play a different important role in the development of
alternative fuels.

We have the technology to synthesize almost any known hydrocarbon from
syngas (a mixture of H~2~, CO and CO~2~) either via methanol or from
Fischer-Tropsch intermediates (14, 15), which can be made to react by
using shape-selective catalysts (16, 17). The H~2~ needed for both these
processes can be obtained from electrolysis. The source of the carbon
oxides is less obvious. If they are generated by combusting fossil
fuels, we continue to create the same CO~2~ emissions as before. It has
been suggested that CO~2~ can also be separated from air, but this is
not practical as 20 lbmol of CO~2~ would be required per equivalent
barrel of crude produced (at a theoretical 100% efficiency). Since the
concentration of CO~2~ in the air is only 0.03%, it would require 65,000
lbmol of air (or 21 million SCF) to produce one barrel of oil. The non
feasibility of such an approach becomes obvious if we consider that for
a 50,000 barrel/day plant, the volume of air that would have to pass
through the CO~2~ scrubber (or extractor) is equal the volume that would
be required to combust enough coal to fuel 600 GWe coal-powered plants
(twice the total capacity of all coal power plants installed today in
the U.S.).

The only way available to obtain carbon oxides from renewable sources is
from the gasification or combustion of biomass with oxygen. The
technology for the gasification of biomass is available as gasifying
biomass is very similar to the gasification of peat or lignite (for
example, in the Winkler or the DOW gasifier, ref. 18).

The role of H~2~ in biomass utilization is based on the underlying
chemistry. The production of all hydrocarbons, including fuels from
syngas is based on the overall reactions:

n CO + 2n H~2~ → (CH~2~)n + n H~2~O (1)

n CO~2~ + 3n H~2~ → (CH~2~)n + 2n H~2~O (2)

Reactions (1) and (2) occur during the Fischer-Tropsch process which is
preferable for producing diesel and jet fuel. Each of the two overall
reactions above can also occur in two steps with methanol as an
intermediate. This is the preferred route for producing gasoline and
most chemicals (16, 17).

Most biomass has a chemical composition Cn(H~2~O)m and contains H~2~
only in the form of water. Just as in coal liquefaction, the H~2~ for
the syngas is formed from CO by the shift reaction:

CO + H~2~O → CO~2~ + H~2~ (3)

which can occur either in the gasifier or in a separate shift reactor.
As reaction (1) requires two moles H~2~ per mole CO, we have to shift at
least two moles of CO (reaction 3) for each mole of CH~2~, ending up
with one-third of the carbon in the product and the rest as CO~2~. If we
add H~2~ from alternative sources we can convert all the CO and CO~2~
formed during the gasification to CH~2~ thus tripling the useful
product. In addition, we save the shift reactor and the CO~2~ removal.

We estimate that biomass could provide 10% of our total energy needs. By
adding H~2~, the yield could be tripled to 30%, enough to meet our
energy for which electricity cannot be substituted directly (26% of
total fossil fuels used, as estimated in Section III, which also reduce
CO~2~ emissions by another 21%, breakdowns are given in Table 3b). If we
could generate H~2~ by electrolysis on site, the oxygen could be used
for gasification. Producing the methanol intermediate without H~2~
addition is so similar to producing methanol from a sub-bituminous coal
that it should cost no more. Adding H~2~ would half the cost of the
production process, though the H~2~ itself is more expensive.

At present, H~2~ can be produced by electrolysis at a cost of \$30/MMBtu
(12) or about \$150 a barrel gasoline (a barrel of gasoline is
approximately 5 MMBtu). An important research project would be to reduce
the cost of H~2~ produced from alternative energy sources, which is
recommended in ref. 13.

VII. **Summary.**

In this paper we try to show that with the technologies currently
available, 98% (72% by electricity from alternative sources and 26% by
syngas processes, the carbon oxides for the syngas being produced by the
gasification of biomass and the H~2~ by electricity from alternative
sources) of our economy could be decarbonized at an affordable cost,
albeit this is more expensive than cheap oil or coal without pollution
control (replacing 98% of fossil fuels would also reduce 97% of CO~2~
emissions, 76% by using electricity from alternative sources and 21% by
syngas processes).

We focused here on what could be done with existing technology, and
showed that we do have the technology to create a viable economy that
does not depend on fossil fuels. In no way we want to imply that total
replacement of all fossil fuel energy is required in 50 years time span.
50% decarbonization in thirty years and 80-90% in fifty years is
probably a more reasonable goal, which would stretch our oil and gas
reserves and reduce CO~2~ emissions.

We also showed that solar thermal energy could play a significant role
in such a program and could anchor an advanced grid, which integrates a
variety of alternative energy sources. The U.S. is fortunate to have the
resources and desert area needed for supply all its energy needs.
Further development of these technologies and their introduction on a
large scale would provide a model for the world, especially for
developing nations. As the problems inherent in such a plan are not
solely technical, the free market cannot be expected to invest in CO~2~
reduction or to fund an uncertain future. It is clear that Government
planning and support will be needed before we can achieve these goals.
It is encouraging to know, however, that the tools for decarbonizing our
economy are available to us if we have the will to use them. The first
step would be a wide discussion and formulation of a detailed plan and
timetable for implementation. This plan should also include more
detailed evaluation of the different technologies, including approximate
cost estimates, not only for the technologies, but also the cost of the
implementation (enlargement of the grid, replacement of equipment,
etc.). The starting point should be applications that are competitive or
nearly competitive today.

In ref. 6 we gave a ballpark estimate as to how much alternative
electric generation capacity would be needed, we came up with 1500-2000
GWe, somewhere in the 5-6 trillion dollar range. Over 30 years this is
170-200 billion dollars a year, definitely an affordable cost if society
wants to do it. It would also stimulate the American economy.

The plan should also be coordinated closely with another critically
urgent need, which would share many elements: how to deal with the
coming peaking of oil reserves.

# **Acknowledgements** 

The authors want to express their sincere appreciation to Dr. Mildred
Green Shinnar for editing, and in part rewriting, the paper. The authors
also want to thank Dr. Robert L. Hirsch, Dr. John J. Wise, and David
Gushee for reviewing the paper and providing valuable comments.

+-------------+--------+---------+-------+-----------+--------+-----+
|             | **R    | **Comme | **In  | **Transpo | **E    | **T |
|             | esiden | rcial** | dustr | rtation** | lectri | ota |
|             | tial** |         | ial** |           | city** | l** |
+-------------+--------+---------+-------+-----------+--------+-----+
| # **Pe      | **1    | **      | **9.  | *         | **1    | *   |
| troleum\*** | .546** | 0.753** | 436** | *26.131** | .207** | *39 |
|             |        |         |       |           |        | .07 |
|             |        |         |       |           |        | 3** |
+-------------+--------+---------+-------+-----------+--------+-----+
| **Natural   | **5    | **      | **8.  | **0.668** | **5    | *   |
| Gas\***     | .244** | 3.217** | 317** |           | .062** | *22 |
|             |        |         |       |           |        | .50 |
|             |        |         |       |           |        | 8** |
+-------------+--------+---------+-------+-----------+--------+-----+
| **Coal\***  | **0    | **      | **1.  | **0**     | **20   | *   |
|             | .010** | 0.083** | 776** |           | .888** | *22 |
|             |        |         |       |           |        | .75 |
|             |        |         |       |           |        | 7** |
+-------------+--------+---------+-------+-----------+--------+-----+
| ##### R     | **0    | **      | **1.  | **0.239** | **3    | **6 |
| enewable {# | .435** | 0.106** | 751** |           | .619** | .15 |
| renewable . |        |         |       |           |        | 0** |
| unnumbered} |        |         |       |           |        |     |
|             |        |         |       |           |        |     |
| **Energy**  |        |         |       |           |        |     |
+-------------+--------+---------+-------+-----------+--------+-----+
| #####       | **0**  | **0**   | **0** | **0**     | **7    | **7 |
| Nuclear Ene |        |         |       |           | .973** | .97 |
| rgy {#nucle |        |         |       |           |        | 3** |
| ar-energy . |        |         |       |           |        |     |
| unnumbered} |        |         |       |           |        |     |
+-------------+--------+---------+-------+-----------+--------+-----+
| ##### Tota  |        |         |       |           |        | *   |
| l {#total . |        |         |       |           |        | *98 |
| unnumbered} |        |         |       |           |        | .46 |
|             |        |         |       |           |        | 1** |
+-------------+--------+---------+-------+-----------+--------+-----+
|             |        |         |       |           |        |     |
+-------------+--------+---------+-------+-----------+--------+-----+
| #####       |        |         |       |           |        | *   |
| \*: Total F |        |         |       |           |        | *84 |
| ossil {#tot |        |         |       |           |        | .33 |
| al-fossil . |        |         |       |           |        | 8** |
| unnumbered} |        |         |       |           |        |     |
|             |        |         |       |           |        |     |
| #           |        |         |       |           |        |     |
| #### Fuels  |        |         |       |           |        |     |
| Consumption |        |         |       |           |        |     |
|  {#fuels-co |        |         |       |           |        |     |
| nsumption . |        |         |       |           |        |     |
| unnumbered} |        |         |       |           |        |     |
+-------------+--------+---------+-------+-----------+--------+-----+

Table 1. U.S. Energy Consumption by Sector and Source (Quadrillion Btu),
Year 2003.

+---------+--------+---------+-------+-----------+--------+-----+-----+
|         | **R    | **Comme | **In  | **Transpo | **E    | **T | #   |
|         | esiden | rcial** | dustr | rtation** | lectri | ota | ### |
|         | tial** |         | ial** |           | city** | l** | # T |
|         |        |         |       |           |        |     | ota |
|         |        |         |       |           |        |     | l { |
|         |        |         |       |           |        |     | #to |
|         |        |         |       |           |        |     | tal |
|         |        |         |       |           |        |     | -1  |
|         |        |         |       |           |        |     | .un |
|         |        |         |       |           |        |     | num |
|         |        |         |       |           |        |     | ber |
|         |        |         |       |           |        |     | ed} |
|         |        |         |       |           |        |     |     |
|         |        |         |       |           |        |     | *   |
|         |        |         |       |           |        |     | *(% |
|         |        |         |       |           |        |     | )** |
+---------+--------+---------+-------+-----------+--------+-----+-----+
| #       | *      | **54**  | **    | **1822**  | **96** | **  | **  |
|  **Petr | *106** |         | 422** |           |        | 250 | 43. |
| oleum** |        |         |       |           |        | 0** | 3** |
+---------+--------+---------+-------+-----------+--------+-----+-----+
| **      | *      | **171** | **    | **35**    | *      | **  | **  |
| Natural | *277** |         | 420** |           | *267** | 117 | 20. |
| Gas**   |        |         |       |           |        | 0** | 3** |
+---------+--------+---------+-------+-----------+--------+-----+-----+
| *       | **1**  | **9**   | **    | **0**     | **     | **  | **  |
| *Coal** |        |         | 186** |           | 1906** | 210 | 36. |
|         |        |         |       |           |        | 2** | 4** |
+---------+--------+---------+-------+-----------+--------+-----+-----+
| **      |        |         |       |           |        | **  | *   |
| Total** |        |         |       |           |        | 577 | *10 |
|         |        |         |       |           |        | 2** | 0** |
+---------+--------+---------+-------+-----------+--------+-----+-----+

Table 2. U.S. CO~2~ Emissions by Sector and Source (Million Metric
Tons), Year 2003.

+---------------------------+--------------------+--------------------+
| **Fossil Fuel Use**       | # **Foss           | **CO~2~ Emissions  |
|                           | il Fuel Replaced** | Reduction**        |
|                           |                    |                    |
|                           | **(%)**            | **(%)**            |
+---------------------------+--------------------+--------------------+
| **All Coal for            | **25**             | **33**             |
| Electricity**             |                    |                    |
+---------------------------+--------------------+--------------------+
| # **All Natural Gas and** | **7**              | **6**              |
|                           |                    |                    |
| **Petroleum for           |                    |                    |
| Electricity**             |                    |                    |
+---------------------------+--------------------+--------------------+
| **All Natural Gas + Coal  | **13**             | **11**             |
| +**                       |                    |                    |
|                           |                    |                    |
| **Petroleum for           |                    |                    |
| Residential**             |                    |                    |
|                           |                    |                    |
| **and Commercial**        |                    |                    |
+---------------------------+--------------------+--------------------+
| **65% of Petroleum**      | **20**             | **21**             |
|                           |                    |                    |
| **used in                 |                    |                    |
| Transportation**          |                    |                    |
+---------------------------+--------------------+--------------------+
| **70% of Industrial       | **7**              | **5**              |
| Natural Gas**             |                    |                    |
|                           |                    |                    |
| (used for power and steam |                    |                    |
| generation,               |                    |                    |
|                           |                    |                    |
| furnaces and H~2~         |                    |                    |
| production)               |                    |                    |
+---------------------------+--------------------+--------------------+
| **Total**                 | **72**             | **76**             |
+---------------------------+--------------------+--------------------+

**Table 3a. Potential for Fossil Fuels Replacement and CO~2~ Reduction
by Electricity from Alternative Sources.**

+---------------------------+--------------------+--------------------+
| **Fossil Fuel Use**       | # **Foss           | **CO~2~ Emissions  |
|                           | il Fuel Replaced** | Reduction**        |
|                           |                    |                    |
|                           | **(%)**            | **(%)**            |
+---------------------------+--------------------+--------------------+
| **All Petroleum in        | **11**             | **7**              |
| Industry**                |                    |                    |
+---------------------------+--------------------+--------------------+
| **35% of Petroleum**      | **11**             | **11**             |
|                           |                    |                    |
| **used in                 |                    |                    |
| Transportation**          |                    |                    |
+---------------------------+--------------------+--------------------+
| **30% of Industrial       | **3**              | **2**              |
| Natural Gas**             |                    |                    |
|                           |                    |                    |
| (used for chemical        |                    |                    |
| feedstocks)               |                    |                    |
+---------------------------+--------------------+--------------------+
| **All Natural Gas**       | **1**              | **1**              |
|                           |                    |                    |
| **used in                 |                    |                    |
| Transportation**          |                    |                    |
+---------------------------+--------------------+--------------------+
| **Total**                 | **26**             | **21**             |
+---------------------------+--------------------+--------------------+

**Table 3b. Potential for Fossil Fuels Replacement and CO~2~ Reduction
by Syngas Processes (carbon oxides produced by biomass gasification with
H~2~ by electricity from alternative sources).**

### 

+------------------------------+--------------+----------+-------------+
|                              | #####        | **Hours  | ##          |
|                              | Investment { | per      | ### Cost pe |
|                              | #investment  | Year**   | r kWh {#cos |
|                              | .unnumbered} |          | t-per-kwh . |
|                              |              |          | unnumbered} |
|                              | **(\$/kW     |          |             |
|                              | installed)** |          | **(cents)** |
+------------------------------+--------------+----------+-------------+
| **Solar Thermal -- Near Term | **4000\***   | **4900** | **8.0**     |
| \[11\]**                     |              |          |             |
+------------------------------+--------------+----------+-------------+
| **Solar Thermal -- Future    | **3220**     | **4900** | **6.2**     |
| \[11\]**                     |              |          |             |
+------------------------------+--------------+----------+-------------+
| ##### Conventional Coal      | **1200**     | **6500** | **4.5**     |
| Power Plant {#conventional-c |              |          |             |
| oal-power-plant .unnumbered} |              |          |             |
|                              |              |          |             |
| **(with Scrubbers) \[5,      |              |          |             |
| 19\]**                       |              |          |             |
+------------------------------+--------------+----------+-------------+
| **Clean Coal \[5\]**         | **1550**     | **6500** | **5.6**     |
+------------------------------+--------------+----------+-------------+
| **Clean Coal \[19\]**        | **2000**     | **6500** | **7.0**     |
|                              |              |          |             |
| ######### **(                |              |          | **2-3**     |
| with CO~2~ separation in the |              |          |             |
|  plant** {#with-co2-separati |              |          |             |
| on-in-the-plant .unnumbered} |              |          |             |
|                              |              |          |             |
| **--no counting cost of      |              |          |             |
| sequestration)**             |              |          |             |
|                              |              |          |             |
| **Estimated Cost of          |              |          |             |
| Sequestration**              |              |          |             |
+------------------------------+--------------+----------+-------------+
| **Nuclear \[19\]**           | **2200**     | **6500** | **6.0**     |
+------------------------------+--------------+----------+-------------+

###### Table 4. Electricity Costs for Solar Thermal Compared to Coal and Nuclear (6) {#table-4.-electricity-costs-for-solar-thermal-compared-to-coal-and-nuclear-6 .unnumbered}

\*: the estimate was obtained as follows:

near term estimate in ref. 4: 4,816 \$/kW installed

20% scalable with exponential scale-up factor of 0.6 saves 540 \$/kW
installed

> 8 parallel trains built simultaneously should save 10-20% of the
> non-scalable part of the plant, for a saving of 380-760 \$/kW
> installed.

### 

+------------------------------------------------+---------------------+
|                                                | ##### In            |
|                                                | termediate {#interm |
|                                                | ediate .unnumbered} |
|                                                |                     |
|                                                | **(cents/kWh)**     |
+------------------------------------------------+---------------------+
| **Solar Thermal -- Near Term**                 | **8.0**             |
+------------------------------------------------+---------------------+
| **Solar Thermal -- Future**                    | **6.2**             |
+------------------------------------------------+---------------------+
| ##### Conventional Coal Power Plant            | **8.0**             |
| {#conventional-coal-power-plant-1 .unnumbered} |                     |
|                                                |                     |
| **(with Scrubbers)**                           |                     |
+------------------------------------------------+---------------------+
| **Clean Coal**                                 | **10-11**           |
+------------------------------------------------+---------------------+
| **Clean Coal**                                 | **12-13**           |
|                                                |                     |
| ######### *                                    | **2-3**             |
| *(with CO~2~ sequestration in the plant** {#wi |                     |
| th-co2-sequestration-in-the-plant .unnumbered} |                     |
|                                                |                     |
| **--no counting cost of disposal)**            |                     |
|                                                |                     |
| **Estimated Cost of Sequestration**            |                     |
+------------------------------------------------+---------------------+
| **Nuclear**                                    | **10-11**           |
+------------------------------------------------+---------------------+

**Table 5. Cost per kWh of Energy During Intermediate Loading (6)**

![](media/image1.wmf)**Figure 1. U.S. Energy Consumption by Source (Year
2003)**

![](media/image2.wmf)**Figure 2. U.S. CO~2~ Emissions By Sources (Year
2003)**

![](media/image3.wmf)

**Figure 3. Potential Replacement of the U.S. Fossil Fuels By
Alternative Energy**

1: Petroleum used in Residential + Commercial + Power Generation

2: Gasoline

3: Diesel

4: Jet Fuel

5: Petroleum used in Industry

6: Natural Gas used in Residential + Commercial + Power Generation

7: Natural Gas used in Industry

8: Natural Gas used in Transportation

9: Coal

**References**

1.  [http://www.eia.doe.gov](http://www.eia.doe.gov/)

2.  Shinnar, R., Shapira D., and Zakai, S., *\"Thermochemical and Hybrid
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3.  Shinnar, R., *"The Raise and Fall of Luz"*, ChemTech, 23, 50-53,
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6.  Shinnar, R.; Citro, F.; "*Solar Thermal Energy: The Forgotten Energy
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    [www1.ccny.cuny.edu/ci/cleanfuels](http://www.ccny.cuny.edu/ci/cleanfuels)).

7.  Davis, S. C., Diegel, S. W.; "*Transportation Energy Data Book*",
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10. <http://www.eas.asu.edu/~holbert/eee463/ECONOMICS.HTML>

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12. Shinnar, R.; Citro, F.; "*Evaluating Processes in the Early Research
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    [www1.ccny.cuny.edu/ci/cleanfuels](http://www.ccny.cuny.edu/ci/cleanfuels)).

13. *"The Hydrogen Economy: Opportunities, Costs, Barriers, and R&D
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14. Anderson, R. B.; *"The Fischer-Tropsch Synthesis"*, Academic Press
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15. Shinnar, R.; Haag, W. O.; Huang, T. J.; Kuo, J. W.; *"Conversion of
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16. Chang, C. D.; *"Hydrocarbons from Methanol"*, Marcel Dekker, Inc.,
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17. Chen, N. Y.; *"Shape Selective Catalysis in Industrial
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18. DOE (Department of Energy), *"Major Environmental Aspects of
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19. Private Communications with Bechtel.

[^1]: ^\*^ To whom correspondence should be addressed. Tel.:
    212-650-6679. Fax: 212-650-6686.

    E-mail: shinnar@ccny.cuny.edu.