Environment Thursday, January 8, 2004. Post by apsmith
The individual chapters that make up this book have been
thoughtfully selected to cover essentially the full spectrum of
options available, and all address the same global problem on
a 50 to 100-year timescale. But the discussion is not entirely
coherent: for example energy units vary across the chapters -
total energy (for a year, or available from a given
resource), can be seen here in terawatt-hours, terawatt-years, or
exajoules, in some cases referring to thermal, in other cases
electric power requirements. At least the book has consistently
abandoned the imperial ‘btu’, still used elsewhere for example in tables
from the US Energy Information
Administration, and there’s
no reference to equivalent barrels of oil or cubic feet of
More significantly, each chapter brings the biases of the authors
to bear, which actually turns this book into an interesting debate,
with each option seen trying to put its best foot forward, backed
by real data.
The opening and closing chapters are not so much about energy,
but about CO2 – specifically (in the first chapter) the severity of
the climate change problem and projections from current trends under
a variety of economic/energy model scenarios. And (in the last chapter)
the range of “mitigation” approaches available, other than reduction of
fossil fuel use (which the middle of the book is all about). This
really is a very serious problem for this century. The last chapter
points out, however, that we may actually have some technical/engineering
tools to handle it.
In fact, we have already been inadvertently reducing the warming effects
through emission of sulfate aerosols – (from p. 428):
anthropogenic sulfate aerosols in the troposphere currently
influence the global radiation budget by around 1 W/m^2 – enough to
counter much of the effect of current anthropogenic CO2. [... on side
effects ...] one of the many interesting valuation problems posed by
geoengineering: How much is a blue sky worth?
But the middle chapters are the key to the puzzle, because whatever we
can do about the CO2 effects, we also only have finite resources of
fossil fuels available. Much of humanity suffers from lack of access
to low-cost energy already. Is there hope?
The first part of the problem, discussed in chapter 2 and repeated
with variations in some of the subsequent chapters on detailed energy
solutions, is understanding just exactly how much energy the world
will need, and under various scenarios, how much CO2 that can be
expected to produce. The Intergovernmental
Panel on Climate Change (IPCC) has one set of future
scenarios; the World Energy Council
has another from IIASA
(International Institute for Applied Systems Analysis); various
others are also cited.
The basic parameters that go into the scenarios are captured in
the so-called “Kaya identity”; the rate at which carbon is released
is the product of the following terms:
For 1990, N was 5.3 billion, GDP/N was $4100 (1990 US$) per person per year,
E’/GDP was 0.49 watt year per $US(1990), and C/E was 0.56 kg carbon per
watt year, leading to a total of 6 billion tons of carbon released.
Population growth is a factor, but the largest plausible changes in
population expected this century make little difference to the
total; we have two far more urgent problems reflected in these
In other words, the range of values for factor 1 don’t make much
difference. Factor 2 will, most scenarios expect, increase greatly
this century. The overall product
has to drop; that means the focus has to be
on factors 3 and 4: reducing
primary energy intensity (conservation and economic shifts), and
reducing carbon intensity (reduction in fossil fuel use).
The third chapter is the only one that really goes into depth on
the economic issues; this, by Robert Lempert and Michael
Schlesinger (of RAND and the University of Illinois respectively),
discusses the basic economic tradeoffs between the possible
initial strategies “do a little”, and aggressive emissions controls.
They find optimal an adaptive policy strategy that
includes both taxes (carbon taxes
or general energy taxes to promote efficiency) and “technology incentives”.
The technology incentives are targeted to bring
down the costs of emissions reductions – these would include
supporting R&D, training people, standardization and certification,
funding demonstrations and infrastructure, disseminating information,
market liberalization, and tax credits and subsidies
to encourage adoption and suitable economies of scale.
Under the adaptative scheme, tax rates and technology incentives are
adjusted in light of climate damage expectations, economic growth,
and technology adoption targets; incentives would expire after a period
of time for technologies not making sufficient progress.
If the authors of the various chapters disagree on anything, they
clearly disagree on the degree to which we can expect improvements in the
third factor: energy intensity. Clearly, there have been tremendous
improvements in energy intensity in the past century, and before.
But how much further can it go? Most experts (according to Watts, chapter 2)
see continued improvements between 0.8 and 1.4% per year; some argue
(in particular Hassol, Strachan, and Dowlatabadi in chapter 4)
that the numbers could be considerably higher; however in practice
efficiency improvements often go to increased capability
rather than reduced energy use – for example, average house size
has increased significantly in the US, and new houses are loaded
with many more devices and appliances.
Including efficiency/intensity improvements then,
the first three factors in the Kaya identity determine a target total
energy requirement for the world. Given
the need for significant reduction in CO2 output (and the fact
that fossil fuels will eventually run out), that leaves a target
number for non-fossil energy that the various alternatives
must meet over the next 100 years. In every scenario this means a dramatic
increase in non-fossil energy production, so no matter what else
happens, we clearly need these technologies.
First a note on forms of energy. Actually useful energy (work) usually
is applied to our devices in a mechanical or electrical form; some
industrial processes depend on energy in a chemical form as well.
The one major exception is heating, which requires just low
quality thermal energy (although heating can be done with greater than
one-to-one conversion through use of heat pumps). Wind and
hydro plants use mechanical energy; solar photovoltaics generate
electrical energy from light which is itself electromagnetic.
Interconversion between mechanical and electrical energy through
motors and generators is very efficient (90% or more), so they can
be viewed as pretty much interchangeable forms. But going from heat
to electrical or mechanical energy involves considerable losses;
typical steam turbine generators run at about 33% conversion
efficiency – i.e. only 1/3 of the thermal energy gets converted
to electricity. This factor of 3 between thermal and electrical energy
is used quite routinely in the literature; in fact hydroelectric production
is typically multiplied by a factor of 3 to give a thermal energy equivalent.
The rough rule of thumb then is that an equivalent electrical energy
requirement is 1/3 of the thermal requirement.
Interconversion between electrical and chemical energy is intermediate
in efficiency – for rechargeable batteries typically about 70-80% (round
trip), for fuel cells it can range from 40% to 90% or so. Burning chemicals
typically generates just thermal energy, although in a vehicle internal
combustion engine or in a gas turbine generator the combustion gases
produce mechanical energy directly with (for combined cycle gas
turbines) efficiencies of 50% or more. Generally we want to minimize
the number of these interconversions between primary energy supply
and the final use; for example, burning coal to produce electricity
to electrolyze hydrogen to be used in fuel cells to produce electricity
to power a vehicle is not likely to be a good use of the primary coal energy.
The actual world energy requirement numbers that come out,
finally, both in terms of energy capacity, and capital investment,
are enormous. Current (2003) total production of thermal energy worldwide
is about 14,000 GW (14 terawatts). With the factor of three rule
of thumb, that’s equivalent to just under 5000 GW electric. That’s
14 TW for a year, every year right now – in energy quantities
(multiplying by the number of hours or seconds in a year) that comes to about
120,000 TWh (thermal) which is equivalent to 450 x10^18 joules,
or 450 exajoules (EJ) of thermal energy. With the 1/3 rule of thumb,
that translates to 40,000 TWh or 150 EJ of electrical energy, every
year. Actual world electricity consumption is about 1/3 of that again,
or 13,000 TWh per year, right now (the remaining energy consumption is
primarily transportation and home and industrial direct use of fossil
The picture for 2050, then, is an increase in total energy use
of between 33% and 140%; 19 to 33 TW (thermal) total. Criswell’s
scenario (chapter 9; more below) sees a need for up to 60 TW (thermal)
by 2050, to address world poverty in an adequate fashion. 60 TW (thermal)
was seen as a likely requirement by 2100, under the high growth
IIASA scenarios. The main point here is non-fossil fuels have to comprise
at least 9 to 10 TW (thermal) of supply by 2050, under any of the
scenarios. That’s well over half of current energy usage. So
the question for the remainder of the book: what (if any) of
the nuclear or renewable options available can actually meet this
enormous requirement, in a sustainable fashion and at a cost that
won’t cripple global growth?
9 to 30 TW (thermal), translates to 26,000 – 87,000 TWh/yr
or 95 – 320 EJ/yr (electric) of non-fossil energy
by 2050. Chapter 5 (Short and Keegan) summarizes the potential from various
renewable sources in a table on p. 145: current global renewable use
is about 8,000 TWh (electric)/yr – mostly from biomass burning in developing
countries, the remainder from hydro power. Long-term
“technical potential” for pure solar power is over 280,000 TWh/yr (electric),
for biomass over 140,000 TWh/yr, for hydro and wind perhaps
14,000 TWh/yr each, and for geothermal and ocean energy perhaps 2000 TWh/yr.
The potential they see economically exploitable by 2025 is primarily
in biomass (8-15,000 TWh/yr) and hydro (4-6000 TWh/yr); solar and wind could
contribute 1000 to 2000 TWh/yr each. In other words, these
renewable sources may be barely sufficient to meet the 2050 demand,
but biomass and hydro would continue to be the primary contributions.
For solar and wind we have a serious problem, discussed in chapters 5 and 6
- the intermittency issue. A utility can’t rely on the
power to be there, and so has to build in (and order ahead of time)
sufficient capacity to meet peak needs without taking them into account.
Similar issues apply with transmission of power; solar and wind generators
would have to pay the capital costs of power lines without being able
to make full 24×7 use of them. This currently limits these to well under
20% of supply in most utility systems. The main way to mitigate all this
is with power storage: pumped hydro or compressed air are traditional
methods, but are very location dependent, among other failings.
Other proposed storage methods (flywheels, batteries, electrolysis
and fuel cells with hydrogen storage) are relatively costly. Something
like 5 TWh of overnight storage would be needed for a system with just
3000 TWh/yr (electric) of solar/wind; at current prices of $100/kWh or
more, that amounts to at least $500 billion worth of batteries, which
would need replacing every 5 years or so.
Intermittency can also be mitigated by spreading the load
across many different supply locations; doing so would require
much longer-distance power transmission – a worldwide
superconducting grid for example. But capital costs for that also
could easily be multiple trillions of dollars, without significant
Two other problems remain with solar and wind – capital cost of
the photovoltaics and turbines themselves, and
land usage. Actually, land usage for solar may not be worse than
for coal, when the area destroyed by coal mining is counted; of course
existing coal mines are one of the “lock-in” features of our
current fossil fuel dependency, so it’s still a problem. But capital
costs are the real show-stoppers: for photovoltaics, at $3/peak watt
current prices (solar thermal systems are roughly the same),
even in an ideal location, 2000 TWh/yr requires about 1 TW peak
capacity, or $3 trillion capital investment. For wind, prices are
now about $1/peak watt, and capacity factors somewhat better, so
the 1000 TWh/yr for wind may require “only” $300 billion
investment (but addresses only about 4% of the minimal
renewable requirement). Continued cost improvements as
manufacturing scales up should cut these costs somewhat.
Annual expenditures on energy systems are already close to
$1 trillion/yr, however, so these numbers, while immense, shouldn’t
be impossible. Doubling or tripling world hydro capacity, as
this scenario calls for, would also involve trillions of dollars of
But there are three other major energy options that need to be considered
to help fill this need for non-fossil energy by 2050, one or all
of which may end up being more cost effective and thus less harmful to
global economic growth: nuclear fission (chapter 7), fusion
(chapter 8), and solar power collected in space rather than
on Earth’s surface (chapter 9).
What fission, fusion, and space solar all have in common is their
ability to directly replace base power supply currently provided
by coal (fission already supplies about 0.5 TW of base power worldwide).
These are not intermittent, as are wind and terrestrial solar. Even hydro and
biomass have seasonal supply variations. Coal has the highest carbon
intensity of any fossil fuel; replacement of utility base power
generation should be the top priority to combat global warming.
Krakowski and Wilson (chapter 7) give an amazingly thorough review
of the situation for nuclear fission energy. The first concern is
fuel supply itself. Fission, like fossil
energy, relies on a fuel material whose supply may be somewhat
limited. Known reserves of uranium (other than low concentrations
in granite and seawater) are actually roughly equivalent
in energy content to estimated fossil fuel reserves. However, on
the fossil fuel side, that equivalence is dominated by
oil shale and sub-sea “clathrates”, which may not be physically
(or environmentally soundly) recoverable. Total fossil fuel
is close to a million EJ or about 500 years of the long-run
thermal energy requirement in the high-growth scenario (at 60 TW(thermal)
by 2100), but not including clathrates and oil shale, that
is reduced to about 50 years of reserves at the 2100 rate (i.e.
we’re not even going to make it to 2100).
But the uranium number also depends on use of breeder reactors
and fuel reprocessing to make use of the full energy content
of the U-238, as well as the initial U-235 that supplies
energy the first time through. Krakowski and Wilson go into
a lot of details on proposals to make that as safe as possible
and reduce the threat of terrorists or rogue states
getting hold of the intermediate plutonium. They wrote, however,
before September 11, 2001; even these proposals may not be
viable any longer. With just once-through processing, the
high-grade uranium known would only last us about 5 years
if it were to supply the world’s energy at 2100 levels. They
speculate that there is a lot of uranium ore still waiting to
be discovered, however, if prices were to rise. Reprocessing,
use of thorium, and extraction from low concentrations in rock
or seawater would increase the supply to thousands of years worth.
Whatever the solution it is clera that fission energy, to meet world
energy needs, would have a much bigger impact on the world than
it has up to now.
Aside from fuel supply, four cardinal issues for expansion of nuclear
energy are of concern:
1. Safety – North American reactors have a good safety record; nevertheless
the Chernobyl accident demonstrated the devastation that is potentially
there. Systems are designed to have a probability of less than one
in ten thousand for a core meltdown in any given year; but that could
mean one every 5 years if nuclear supplied 2 TW of power, or one per year
at the 10 TW or higher level (with roughly 10,000 nuclear plants worldwide).
Most scenarios for future fission have kept total supply below 1.5 TW
through 2050 for this and other reasons.
2. Waste disposal – there are actually some solutions to this. Sweden
apparently has settled on a publicly agreeable disposal solution for their
reactors. Fuel reprocessing can extract the worst isotopes and send
them back into the fuel cycle to have their energy actually do some good.
The remaining fuel could potentially be less hazardous than the original
uranium ore. The current situation in the US with once-through fuel
cycles and hundreds of supposedly temporary waste storage sites
is not reassuring to anybody, though.
3. Proliferation of nuclear weapons – basically eternal vigilence
is the key. Will that be possible? Particularly as the industry has
to cut costs to be competitive? Proliferation is less of an issue with
the once-through cycles, however, since the resultant plutonium
stays embedded with other highly radioactive wastes.
4. Costs. In the 1970′s-1980′s, primarily due to burdensome
safety reviews and what the authors term “over-regulation”, nuclear
power plants in the US came in with costs on the order
of $4000/kW or more. Those costs may not be really representative;
a new reactor in Taiwan is being built for about $1690 per kW (electric).
That still means 1.5 TW of nuclear power (supplying roughly 12,000 TWh
(electric) per year of energy) would have a capital cost of $2.5 trillion
Fusion – the picture painted here is one of long-term promise,
but probably not helpful by 2050. Two major fusion research
reactors are being built over the next decade – the international
ITER magnetic confinement reactor (for $5 to 10 billion) and
the US National Ignition Facility (NIF – $2 to 5 billion) to
study “inertial confinement”. Both projects are suitable for
scientific and engineering discovery of extreme properties,
but disturbingly, neither turns out to be close to a good
design for a commercial reactor. Supply of fuel, however,
is not a problem: it seems that water by weight contains roughly
100 to 300 times as much energy as gasoline, for the various
fusion reactions that may be feasible “early in the
third millenium”, as the authors phrase it.
So – short story – fusion will likely not be helping much,
if at all, by 2050.
Chapter 9 is David Criswell’s take on space solar power,
in particular heavily promoting his
Lunar Solar Power proposal.
I’m most familiar with the situation here, and find I have
to quibble with some of the numbers he uses; on the other
hand, he makes a very persuasive case.
Unlike all the other strategies outlined in the book, Criswell’s
lunar solar power is (at least according to him) scalable and
affordable enough to not only meet all world energy needs as
currently projected, but to allow for significant expansion in
global world product without environmental harm.
Now, like all the others, Criswell’s scheme is a trillion-dollar
scale proposal. Unfortunately, unlike the others, it’s hard to do
it in small steps; this is one giant project. While it seems likely
it could be the most economically efficient of all of them, working
towards it in smaller chunks seems the only way to make it actually
happen. What would those smaller chunks be? Criswell discusses more
traditional solar power satellites (in geosynchronous orbit); he
dismisses them on a number of grounds (for example, their large
size would make the number required for his 20 TW electric rather
excessive – however, at a smaller scale they make a lot of sense)
and I believe we can now do better than some of his numbers for
regular satellites. But he makes a lot of good points.
I actually met Criswell last May – I had invited him as our Saturday
keynote speaker at the National Space Society
annual meeting in San Jose. His
testimony from last fall is an eloquent
summary of his position. Of course he’s been talking about this
for nearly 20 years; what’s different now seems to be (1) we need
the energy now more than ever, and (2) the space program is really
looking for a new goal. Is there any chance something will come of this?
Finally, to sum it all up:
(1) Human-generated CO2 and the associated global warming is a big
problem for the coming century, although there are some engineering
strategies that could (with other side-effects) mitigate it.
(2) We’re going to be running out of fossil fuels anyway in the
next few centuries; without alternatives, global economic prosperity
will be endangered much sooner than that.
(3) Depending on how far efficiency improvements can get us, the
mid-century energy requirement from non-fossil sources is between
9 and 30 TW(thermal), or 3 – 10 TW (electric), year-round.
(4) No current renewable technology can provide that power level
for less than about $10 trillion in capital investment.
(5) The best plan seems to be an adaptive one: introduce a carbon
tax and technology incentives of all sorts for the renewable options,
and then adjust both taxes and incentives in response to changing
assessments of CO2 damage and non-fossil technological promise.
(6) Wind may be ready for large scale installation; however
investments are needed in energy storage and transmission technologies
to make it really practical. Biofuels are already in large-scale
use: R&D investments to improve their efficiencies, perhaps including
genetically engineered crops, should be supported. Solar is a little
further away, but R&D there should be strengthened because of the
(7) Nuclear fission will be around – we need to decide whether to
try to make it a big part, or a small part, of our energy future
(i.e. choosing between once-through and breeder fuel cycles).
(8) Fusion likely won’t help by mid-century. But the long-term
payoff may be large; we should continue to invest moderately in
(9) Space solar power, whether or not on the Moon, has enormous
theoretical potential. Technology incentives to prove its capabilities
seem warranted – investments and demonstration projects at least
for photovoltaic capabilities, light-weight
space construction, space launch, and wireless power transmission.
all seem well justified by this and spinoff applications.
SciScoop Science is owned and operated by David Bradley Science Writer.