Co2

Notes:

Column descriptions (same for Tables 9.2-9.6)

#1. Name of the large scale power system and primary energy source.

#2. Total quantity of energy that can be reasonably extracted over the life of the energy source. Terawatt-year of thermal energy (TWt-y) is used unless noted otherwise in the text.

#3. Annual power rate, in terawatts of thermal power (TWt), at which the source of energy is renewed. Other power units may be noted in the text.

#4. Lists the major non-technical factors limiting 20 terawatts (TWe) of electrical power.

#5. Lists the major technical factors that limit production of 20 TWe of electric power.

#6. Estimates the lifetime of each energy source, in years, at 20 TWe of electric output.

#7. Lists the major pollution products of each power system.

#8. Indicates the long-term trend in cost for producing 20 TWe of power.

#9. Estimates the maximum power production, in TWe, for each power system.

Table 9.3 Renewable terrestrial systems in 2050

Power System

Maximum energy inventory on Earth (TWt-y)

3. Key non- Limiting Deplete or Long-term Feasible

Annual technical technol. exhaust 7. trend of total electric output renewal rate issues @ <20 factors (Y) @ 20 TWe Pollution costs by 2050 in

6. Hydro

<14

<5

• Costs

•Sites

<1

•Sediment

•NA

<1.6

electric

• Multi-use

•Rainfall

•Flue water

-Site

*NSA (Not

•Dam failure

- Fresh water

stand-alone)

6.1 Salinity-

1700 to

0.5

• Blocking

• Conversion

0.02 (rivers)

• Restrict river

•NA

<0.3

gradient to

seawater

to

hydrologie

means

to

flows

- seawater

24000

7

cycles

• Brine

700 (polar

• Membranes,

- brine

to brine

• Brine pond area

production

caps)

brine

7. Tides

0

<0.07 (tech.

• Costs

• Sites

<0.01

• Change local

•NA

<0.02

feasible)

• Shoreline

• Input

tides

effects

• NSA

• Fish kills?

8. Waves

0

1 to 10 (global

• Costs

• NSA

<0.1

• Transfer

•NA

<0.1

deep waters)

• Shore

• Good sites

- Gases

or much less

processes

- Nutrients

• Navigation

- Heat

- Biota

9. Ocean

-2X105

-2100

• Costs

• Sites

<800

• #8 above

•NA

<0.1

thermal

but perhaps

but

• Ocean local

• Low effic.

@ 7% conv.

• OTEC

<100

<0.04% is

and global

• Bio-fowling

effic.

- mass

affordable to

likely useful

circulation

• Transmission

But locally

- rusts

access

• Cooling

to shore

perhaps

- fouling

surface

<1

• La Nina

waters

effects

10. Geo- S9X106 <30 global thermal (global in top Mostly low

7 km) grade

• Geologic risks

• Reinjection effects?

• Intrusiveness

• Biota hazards

depletion @10%effic. -heat on continents

Flow -minerals @10%effic. resistance Efficiency

irregular • Noise down

MWe/km2 - local transmiss.

Storage - global

Table 9.4 Terrestrial solar power systems

Maximum

4.

5.

6.

8.

9.

energy

3.

Key non

Limiting

Deplete or

Long-term

Feasible

inventory on

Annual

technical

technol.

exhaust

7.

trend of total

electric output

1.

Earth

renewal rate

issues @ <20

factors

(Y) @ 20 TWe

Pollution

costs

by 2050 in

Power System

(TWt-y)

(TWt)

TWe

@ 20 TWe

or 60 TWt

products

@ 20 TWe

TWe

12. Terrestrial

0

<1 to 20

• Very high

• Irregular flux

>109

• Waste heat

• Possibly

<3.3

solar power

MWe/km2

systems cost

• NSA

• Induced

down

• Sum of 12

(thermal)

output of regional

• Local climate change

climates • Production

• Slow learning

and 13

system

• Weather

wastes

• Land use

13. Terrestrial

0

Above

Above

Above

Above

Above

Above

• Above

solar power (#12)

(photovoltaic)

solar power (#12)

(photovoltaic)

Power System

Maximum energy inventory on Earth (TWt-y)

3. Key non- Limiting Deplete or Long-term Feasible

Annual technical technol. exhaust 7. trend of total electric output renewal rate issues @ <20 factors (Y) @ 20 TWe Pollution costs by 2050 in

14. Nuclear fission (No breeder)

15. Nuclear breeder (238U/Th)

16. Nuclear breeder

17. Nuclear fusion-fission or accelerator (D-T with

238U-Th)

18. Nuclear Fusion (D-T)

<430

=33000

238U

>1X109

19. Nuclear <100 to Fusion (D-3He lxlO5 lunar)

• Full life cycle costs

• Political acceptance

• Health and safety

• Proliferation

• Wastes control

• Reactor life time

=550

=300000

• Rate of fuel production per unit of power

• Practical fusion

• Reactor life time

• 3He inventory

■ Radioactive

- fuels

- parts

- wastes

• Weapons grade materials

• Radioactivity (much lower)

• Perhaps constant or decreasing

■ Possibly decreasing

Table 9.6 Space and lunar power systems

Maximum

4.

5.

6.

8.

9.

energy

3.

Key non

Limiting

Deplete or

Long-term

Feasible

inventory on

Annual

technical

technol.

exhaust

7.

trend of total

electric output

1.

Earth

renewal rate

issues @ <20

factors

(Y) @ 20 TWe

Pollution

costs

by 2050 in

Power System

(TWt-y)

(TWt)

TWe

@ 20 TWe

or 60 TWt

products

@ 20 TWe

TWe

20. Geo-space

• 0 with power

20 to 250

• Life cycle

• Geo-arc

>10"

• Microwave

•NA

<1

solar power

relay

We/m2

costs

length

noise

• Down from

Even with

sats (from

satellites

times rectenna

• Fleet

• Managing

• Transport

very high

— 100 decrease

Earth)

• -0.01 with

area

- visible

- satellites

-noise

initial cost

in Earth-to-

storage

- variable

- shadows

- exhaust

orbit transport

-life

• Load

• New sky

costs

• System likely

following

objects

NSA

• Spectrum

• Orbital

availability

debris

• Shadowing

Earth

21.

• 0 with sat to

<250xD

• Above (#20)

• Managing

>10"

• Above (#20)

Up

<0.1

LEO/MEO -

satellite re-

We/m2 times

•NSA

- satellites

• Earth

Due to

Even with

solar power

beaming

rectenna area

- shadows

illumination

maintenance

— 100 decrease

sats

• 0.01-0.05

• D = Duty

- debris

for debris

in Earth-to-

with storage

cycle

• Load

orbit transport

0.01<D<0.3

following

costs

• Spectrum

availability

• Duty cycle

22. Space

•0 to 0.01

20 to 250 X D

• Above (#20)

• Very large

>10"

• Microwave

Down

<1

solar power

with excess

We/m2 times

•NSA

deep space

noise

sats in deep

capacity in

rectenna area

industry

• New sky

space

space

0.3<D<1

• Power use on

objects

Earth

23. Lunar

• 0 with EO

20 to 250 X D

• Life cycle

• Power use on

>10"

• Microwave

Potentially

>20

solar power

beam

We/m2 times

costs

Earth

noise

-0.1 ii/kWe-h

to -1000 in

system

redirectors

rectenna area

• Area of

• Debris of

22nd century

• 0.01 Moon

0.3<D<1

Moon

redirectors

eclipse

• EO beam

• 0.04 with no

redirector

EOs

satellites

diffuse, degraded in intensity, interrupted by the day-night cycle and the atmosphere, and <25% intersects the populated continents. Systems to gather solar power on Earth and transfer it to diverse final users are very expensive. Thus, commercial solar power is limited to niche markets. An earlier version of Tables 9.2-9.6 was first published by Criswell and Waldron (1991) and slightly revised by Criswell (1998b). Hoffert and Potter (1997) have also explored these topics.

9.2.1 Mixed and carbon systems extrapolated from current practice

Mixed systems

The 14.2 TWt global power system of the year 2000 is a mixed system (Nakicenovic et al., 1998). It is fueled primarily by carbon (fossil coal and renewable wood) and hydrocarbons (fossil oils and gases). Nuclear and hydroelectric contribute ~10% of the primary energy. Mixed global power systems can consist of enormously different combinations of primary energy sources and options for conversion, storage, and distribution of the commercial energy. There are strong motivations to extend the use of existing power systems and practices. This extension minimizes needed investments for increased capacity, takes advantage of locally attractive "gifts of nature", such as hydropower or biomass in Developing Nations, can stretch the lifetime of non-renewable sources, utilizes current business practices and labor skills, and can be pursued by existing businesses.

Case A2 of Nakicenovic et al. (1998: p. 69-71, p. 118-124, p.134) projects the highest level of world economic growth. Table 9.1 summarizes the growing power use projected by Case A2 from 2000 to 2100. Global power production is 33 TWt in 2050. In 2050, coal produces 10.6 TWt. At this rate coal reserves are projected to last ~ 170 years. Oils and gases produce 13.6 TWt and they are projected to last for ~ 100 years. Conventional nuclear provides 1.3 TWt and reserves are adequate for ~280 years.

Total power increases to 64 TWt by 2100. Between 2000 and 2100 this mixed system consumes 3600 TWt-y of primary energy, mostly fossil and nuclear. By 2100, the fossil fuels and biomass provide 65% of primary energy. Projected lifetime of coal reserves at 2100 is ~50 years. Gas and oil use is dropping rapidly as they approach exhaustion. Consumption of coal and biomass is rising along with that of nuclear. Carbon dioxide and other emission of fossil fuels rise at a rapid rate throughout the 21st century. Carbon dioxide production reaches 20 GtC/y in 2100 and cumulative emissions from 1990 are ~ 1500 GtC. Atmospheric CO2 approaches 750 ppmv, or 2.8 times the pre-industrial value, and global warming the order of 3 to 4.5°C is projected. There is increasing confidence that greenhouse warming is occurring (Kerr, 2000a).

Investment in this mixed system is 0.2 T$/y in 1990. It is projected to be 1.2 T$/y by 2050 and assumed, for this illustration, to rise to 2.3 T$/y by 2100 in order to install 64 TWt of capacity. Total investment from 2000 to 2100 is ~ 120 T$. See Table 9.1.

Both the fuel users and producers must deal with externality cost created by the use of these non-renewable fuels. Externality cost arises from the greenhouse effects of carbon dioxide, neutralizing acids and ash, suppressing dust, and the effects of uncertainties in energy supplies. Other factors such as the costs to human health of mining and emissions and defense of primary energy sources must be included. For discussion, assume the externality cost equals the price of the primary fuels. Total externality cost is then ~800 T$. Total cost of this Case A2 global power system, from 2000 to 2100, is ~ 1800 T$. Thus, total cost of energy to users is projected to be ~ 13% of integral GDP. The oil supply disruptions of the 1970s, which increased oil prices by a factor of two to three, slowed global per-capita growth for a decade. If externality cost was ~ 15 times the price of the fuels, all economic gains over the 21st century would be wiped out.

There is a long standing debate about whether or not the use of a depletable resource (fossil and nuclear fuels) in a core economic activity (production of commercial power) leads to the creation of "net new wealth" for the human economy inside the biosphere. Solar energy from facilities beyond Earth offers a clear alternative to depletable fossil and nuclear fuels. The solar energy for facilities in space definitely provide "net new energy" to Earth. It is arguable that space and lunar solar power systems offer expedient means to supply dependable and clean renewable power at attractive commercial rates.

Tables 9.2-9.6 characterize the options for a global power system (column #1) that might be utilized to achieve 60 TWt by 2050 and maintain that level thereafter. This scenario requires a more aggressive development of commercial energy than is projected in Case A2 of the WEC study and delivers ~600 TWt-y more thermal-equivalent energy over the 21st century. Refer to Row 1 of Table 9.2 and column 2. For Case A2, ~3200 TWt-y of non-renewable fuels are available in 2050. Case A2 analyses project that renewable commercial power systems produce 7.7 TWt in 2050 (Column #3). Column #4 summarizes the key non-technical issues that will limit the production of 20 TWe, or 60 TWt, by 2050. Specifics for the mixed systems of Case A2 are deferred to the discussion of each major potential element of the mixed power system (rows #2-#19). The same is true for columns #5 and #7. Column #6 provides an estimate of the lifetime of the fuel resources at the year 2050 for Case A2 at their burn rate in 2050 of 24 TWt. Non-renewable fuels will be exhausted by ~2180. Case A2 projects 64 TWt by 2100. Thus by 2120 the fossil fuels will be depleted.

The cost of energy from the mixed system is likely to tend upward. Rather than focusing capital on the most cost-effective power systems, it will be necessary to provide R&D, construction, and maintenance funds to a wide range of systems. The costs of non-renewable fuels will increase as they are depleted, and, very likely, the cost of measures to protect the environment will also increase. Column #8 of Tables 9.2-9.6 indicates a rising cost, driven in part by the need to replace most capital equipment and systems before 2100. The total power production of Case A2 is equivalent to 33 TWt in 2050. Total electric output would be only 11 TWe (Column #9). Case A2 does not provide the 20 TWe required in 2050 for an energy-prosperous world.

Nakicenovic et al. (1998) also consider power systems that are more environmentally friendly than Case A2. Case C assumes extensive conservation of energy, greatly expanded use of renewable sources of power, and a reduced rate of growth of the world economy. In Case C global power may be as low as 19 TWt in 2100, or ~ 1.7 kWt/person. Integral GWP (2000 to 2100) is -10000 T$. Neither energy nor economic prosperity is achieved on a global scale. Case C is closer to the power and economic profiles considered by the Intergovernmental Panels on Climate Change.

Carbon-basedpower systems

The mixed-power system in row #1 uses contributions from each of the next 18 types of power sources. Each of these is examined in terms of its ability to provide 60 TWt or 20 TWe by 2050 and indefinitely thereafter.

Bioresources (#2)

Bioresources is used to provide more detail as to the analysis approach. In Column #2 the energy inventory available on Earth, for this and all following power options, is described in terms of terawatt-years of total thermal power, whether the primary energy source provides thermal, nuclear, or electric energy. To a first approximation, 1 TWt of thermal power yields approximately 0.33 TWe of electric power. Most useful biomass is available on land in the form of trees, with a total thermal energy inventory of -230 TWt-y. Primary estimates for biofuels are from Trinnaman and Clarke (1998: 213, 124), Criswell (1994, 1998b), Criswell and Waldron (1991), and references therein. Ten billion people will ingest -0.003 TWt, or 3 GWt, of power in their food.

Column #3 provides an estimate of the rate at which the primary energy resource is renewed within the biosphere of Earth (TWt-y/y or TWt). Annual production of dry biomass is approximately equally divided between the oceans and land. However, the primary ocean biomass is immediately lost to the ocean depths or consumed in the food cycle. New tree growth provides most of the new useful biomass each year. The renewal rate is approximately 50 TWt-y/y or 50 TWt of power.

Columns #4 and #5 identify the major non-technical and technical issues relevant to the energy source providing 20 terawatts of electric power (20 TWe) by 2050. For bioresources, costs will be high because of gathering, transportation, and drying of biomass that has a relatively low fuel density per unit of mass. The continents will be stripped of trees, grasses, and fuel crops, biodiversity will be sharply reduced, and great political conflicts will ensue. New nutrients will be required as most biomass is removed from fuel farms. Massive irrigation will be required and land use will be dominated by growth of fuel-wood. Agriculture will compete with fuel production for land, water, nutrients, labor, and energy for the production processes.

Column #6 estimates the time in years that a particular energy source will be depleted if it provides 20 TWe or ~ 60 TWt. In the case of biomass, the global inventory of biofuels will be depleted in less than three years. Because the net-energy content of dried biomass is low, it is assumed that 90 TWt of biomass fuel enables only 20 TWe. The renewal rate and energy content of biofuels are so low that they cannot provide 60 TWt or 20 TWe on a sustainable basis.

The primary pollution products of biomass are summarized in Column #7. For biofuels these include obvious products such as smoke. However, methane and CO2 will be released from decaying biomass and disturbed soils. Recycling of CO2 to oxygen will be reduced by at least a factor of two until forests recover. Erosion will be increased. Diseases will be liberated as animals are driven from protected areas.

Column #8 indicates the long-term trend in cost if the final electric power is provided exclusively by the given source of energy. Bioresources are unable to provide the 20 TWe, or 60 TWt, on a sustainable basis. Thus, Bioresources are NOT APPLICABLE (NA). Column 9 estimates the feasible electric output of each energy source by 2050. Sustainable power output can be limited by the size of the resources base (biofuels, oils and natural gas, coal), pollution products (coal), the cost that society can afford, availability of technology (controlled nuclear fusion), or other factors. Case A2 projects <0.2 TWt as the limit on power production from biomass.

Peat (#3), coal (#4), oils, gas (#5), and natural gas hydrates (5.1) The 60 TWt system requires 4500 TWt-y of input energy through the year 2100, and 6000 TWt-y through the 22nd century. If only peat, oil, and natural gas are used, they will be exhausted well before the end of the 21st century (columns #2, #3, #6). Coal would be exhausted early in the 22nd century. See Trinnaman and Clarke (1998, p. 205, peat). For coal (#4) and oil and gas (#5) see Nakicenovic et al. (1998, p. 69 - Cases A1, A2, and C). The thermal-to-electric conversion efficiencies are assumed to be 33.3% for coal and 45% for oil and gas. Column #9 uses the output of power systems of Case A2 to estimate the feasible electric output by 2050 of coal and oil/gas (Nakicenovic et al., 1998).

Natural gas hydrates were discovered in marine sediments in the 1970s and are considered to represent an immense but largely unmapped source of fuels (Haq, 1999). Global marine deposits of the frozen methane hydrates may exceed 10000 gigatons in carbon content. Assuming 45 GJ of net thermal energy per ton of natural gas liquids, this corresponds to 14000 TWt-y of energy or more than twice the estimated stores of coal, oils, and natural gas. However, the marine deposits are present in relatively thin and discontinuous layers at greater than 500 meters depth. There is little commercial interest at this time because cost-effective recovery may not be possible.

There is growing evidence that enormous quantities of methane can be released to the atmosphere as the hydrates in the deep ocean unfreeze due to undersea avalanches and increasing deep sea temperature (Blunier, 2000; Kennett et al., 2000; Stevens, 1999; Dickens, 1999; Norris and Röhl, 1999). Such releases are associated with sudden shifts from glacial to interglacial climate. Large-scale hydrate mining and warming of the deep waters by OTEC systems (next section) could release large quantities of methane.

9.2.2 Renewable terrestrial systems

Renewable terrestrial power systems, except for Tidal (#7) and Geothermal (#10), are driven indirectly as the Sun heats the oceans and land. Conventional hydroelectric dams can provide only 1.6 TWe by 2050 because of a lack of suitable sites. See Trinnaman and Clarke (1998, p. 167) and Criswell (1994,1998b). Tides (#7) and Waves (#8) are very small power sources (Trinnaman and Clarke, 1998).

Hydroelectric (#6) and not stand-alone (NSA) Hydroelectric facilities are generally considered to be dependable sources of power for local or regional users. They are considered "stand-alone". However, even major facilities can decrease in output. In the case of the Grand Coulee Dam this is occasionally caused by lack of regional rainfall and insufficient stream flow through the Columbia River Basin of Washington State. Under these conditions even major hydroelectric dams can become not stand-alone (NSA). Their power output must be augmented by fossil fuel or nuclear power plants attached to the same power grid. As regional and global power needs increase, hydroelectric systems are less able to provide dependable power on demand. Backup systems, such as fossil fuel power plants, must be provided. At this time, the electric grids of conventional power systems can support ~20% of their capacity in the form of NSA power sources such as hydro and the more quickly varying wind and solar.

Alternatively, NSA systems could be distributed across large regions, even on different continents, to average out variations in power supplied to the system. Massive systems must be established to transmit power over long distances, possibly worldwide. Power storage must be provided close to major users. Unfortunately, it is impossible to predict the longest time required for adequate power storage. Such ancillary systems, especially when employed at a low duty cycle, greatly increase the cost of a unit of electric energy. Unit cost of power will undoubtedly be higher than for a more cost-effective stand-alone system. For these reasons, the "feasible" power capacity of renewable systems tends to be substantially less than the potentially available power.

Salinity-gradients (#6.1). Isaacs and Schmitt (1980) provided one of the first comprehensive reviews of potentially useful power sources. They noted that energy can be recovered, in principle, from the salinity-gradient between fresh or brackish water and seawater. They note that fresh river water flowing into the sea has an energy density equivalent to the flow of water through a 240 meter high dam or ~2.3 MW/(ton/second). They mention five conversion techniques and note also that any reversible desalination technique can be considered. They caution that none are likely economically feasible. Laboratory experiments in the 1970s demonstrated the generation of 7 We/m2 across copper heat exchange surfaces at 60% conversion efficiency. Using the above engineering numbers, the capture of all accessible fresh water run-off from the continents, ~6.8 X 1013 tons/y (Postel et al., 1996), is projected to yield ~0.3 TWe. The fresh and salt waters must pass through ~4 X 105 km2 of copper heat exchangers. The polar ice caps and glaciers, 2.4 X 1016 tons, are the major stores of fresh water. Polar ice melt worked against seawater can release ~ 1700 TW-y of total energy, or, using the above numbers —1000 TWe-y.

Fresh and ocean water mixing into a coastal brine pond can potentially be the power equivalent to a dam 3500 meters high. Given solar-powered brine ponds of sufficient total area, the above power and energy inventories could be increased by a factor of 14. Maintaining 20 TWe output requires the production of ~3.3 X 1013 tons/y of brine. The evaporation and transpiration of water from all land is ~7 X 1013 tons/year. This implies that 50% of all land, or 100% of lower latitude land, would be given over to brine production. It is worth reading Isaacs and Schmitt (1980) to expand one's mind to possible energy sources such as volcanic detonations, brine in salt domes, tabular-iceberg thermal sinks, tornadoes and thunderstorms, and other smaller sources of averaged power.

Ocean thermal energy conversion (#9)

"The oceans are the world's largest solar collector" (Twidell and Weir, 1986). The top 100 meters of tropical waters are 20-24°C warmer than waters ~ 1km to >7km below the surface (~5 to 4°C). Approximately 25% of the mass of tropical ocean waters has a difference of ~24°C between the surface and deep waters. Approximately 1% has a temperature difference of ~28°C. Thermal energy of the surface waters is renewed daily by sunlight. Cold water renewal is primarily through the sinking of waters in the high latitude oceans, primarily in the southern hemisphere, and the release of ~ 1600 TWt through evaporation of water to the atmosphere (Hoffert and Potter, 1997). Secondary cooling of waters in the North Atlantic releases ~500 TWt of power that heats the air that streams eastward and heats northern and Western Europe (Broecker, 1997). Thousands of years are required to produce ~1 X 1018 tons of deep cold ocean waters.

Ocean Thermal Energy Conversion (OTEC) systems mine the energy of the temperature difference between the cold waters of the deep tropical oceans, and the warm surface waters. The cold waters are pumped upward 1 to 6 kilometers and are used to condense the working fluids of engines driven by the hot waters above. Engineering models indicate ~7%> efficiency is possible in the conversion of thermal to electric power (Avery and Wu, 1994). Prototype OTEC plants demonstrate an efficiency of 3%. Small demonstration plants have demonstrated net electric power outputs of 15 kWe and 31.5 kWe. This net output is slightly more than 30% of the gross electric output of each plant, respectively 31.5 kWe and 52 kWe. Twidell and Weir (1986) note that pumping of cold sea-water from and to depth will likely absorb ~50%> of the gross electric output of a large OTEC plant.

An upward flow of 2 X 1015 tons/y of deep water is required to produce 20 TWe of net electric output over a temperature difference of 20 °C. This implies that a maximum of ~2 X 105 TWt-y, or ~2 X 104 TWe-y, of energy can be extracted over a "short" time from the ocean. However, when 20 TWe of commercial power is considered, several factors combine to significantly decrease the extractable energy.

OTEC systems are projected to have high capital costs. A current challenge is to reduce the cost of just the heat exchangers to less than 1500 $/kWe capacity. Offshore installations will be far more expensive than onshore installations. Offshore installations require platforms, means of transmitting energy or power to shore, and more expensive support operations. Producing intermediate products such as hydrogen decreases overall efficiency and increases costs. Trinnaman and Clarke (1998: p. 332-334) suggest an OTEC potential <0.02 TWe by 2010. To grow significantly by 2050 the costs of OTEC plants must be minimized. This requires onshore construction. Thus, only a fraction, possibly <1%, of the coldest deep waters and warmest surface waters can be economically accessed.

The warmest tropical waters extend ~ 100 meters in depth from the surface. A 20 TWe OTEC system processes this mass of water in ~ 1 year. La Nina-like events might be enhanced or created by the outflow of cold, deep waters from a fleet of OTEC installations located in the equatorial waters of the eastern Pacific. Levitus et al. (2000) have discovered that the heat content of the oceans has increased by ~2 X 1023 J, or 6300 TWt-y, from 1948 to 1998. This corresponds to a warming rate of 0.3 W/m2 as averaged over the surface of the Earth and likely accounts for most of the "missing" energy expected to be associated with greenhouse heating since the 1940s (Kerr, 2000). Note that the change in ocean heat content since the 1940s is of the same magnitude as associated with extracting 20 TWe of electric energy from the oceans over a 50 year period. See Watts (1985) for a discussion of the potential effects of small natural variations in deep-water formation on global climate.

The major ocean currents convey enormous quantities of water and thermal power from low to high latitudes. Production of cold and higher density and salinity water in the North Atlantic plays a key enabling role in the present general circulation. However, the relative roles of salinity differences, wind, and tides as the driving forces of the circulation have not been clear. New data indicates that winds and lunar tides transfer ~2 TWm of mechanical power to the oceans to drive the large scale ocean currents and the associated transfer of ocean thermal energy between the cold waters of the high latitudes and the warm waters of the low latitudes. The estimate of lunar tidal power is based on recent analyses of seven years of data on the height of the ocean, obtained by means of an altimeter onboard the TOPEX/POSEIDON satellite. According to Egbert and Ray (2000) and Wunsch (2000), the winds across the ocean provide ~60% of the power that drives ocean circulation. The dissipation of lunar tidal forces in selected portions of the deep ocean provides ~40% of the driving power. Wunsch maintains that the ocean would fill to near the top with cold water and the conveyor would shut down without the ~ 1 TWm of lunar tidal power to drive the circulation of the ocean (Kerr, 2000b).

An OTEC system with a net output of 20 TWe, using the demonstration data and calculations mentioned above, will require a gross electrical output of approximately 60 TWe. Twenty terawatts of the additional 40 TWe is directed into the operation of the plant and approximately 20 TWe into the pumping of cold waters from great depth and returning the heated water to depth. The 20 TWe of pumping power is ~20 times the tidal power the Moon places into the general circulation of the deep waters. Given the complexity of real, versus averaged, ocean currents it seems inevitable that the OTEC pumping power will modify the circulation of the ocean. Highly accurate and trustworthy models of ocean circulation must be demonstrated and the effects of large scale OTEC systems included before major commitments are made to large OTEC systems. What is large for OTEC? A first estimate can be made by assuming that the pumping power of an OTEC system is restricted to <10% of the lunar tidal power. This implies a gross OTEC electric output of <0.1 TWe or 100 GWe. Using the above engineering estimates for OTEC implies a maximum net electric output of 30 GWe or less than the electric power capacity of California. This is far smaller than the 10 TWe output suggested by some OTEC advocates (see www.seasolarpower.com/).

The massive up-flow of cold, deep waters for a 20 TWe OTEC system will change the nutrients, gas content, and biota of the surface and deep waters. There is ~50 times more CO2 in the ocean than the atmosphere (Herzog et al., 2000). The ocean/atmospheric exchange of CO varies over a six year interval (Battle et al., 2000). The effects of changing ocean circulation must be understood. It is not unreasonable to anticipate restricting the flow of cold, deep waters to the surface tropical waters to perhaps 20% of full potential flow. At 20 TWe, most of the mined waters will likely be pumped back to the depths. The pumping energy will reduce the OTEC's efficiency and warm the local deep waters. Over time the depth-to-surface temperature difference decreases. This reduces to — 1/5th the useful local inventory. The factors of 1%, 4/20ths, and 20% multiply to 0.04%. Thus, the ultimate inventory of energy may be reduced to the order of 0.04% of ultimately extractable energy at high pumping rates. This implies a useful inventory of —90 TWt-y (or <6 TWe-y) that might be extracted from favorable locations. These crude estimates must be revised using detailed models of the ocean circulation through and about the most favorable sites. The United States National Renewable Energy Laboratories provides an extensive web site on OTEC and references (www.nrel.gov/otec/).

Geothermal (#10)

The thermal energy of the Earth is enormous but non-renewable. It originates from the in-fall energy of the materials that form the Earth and the ongoing decay of radioactive elements. This geothermal power flows from Earth at the rate of 0.06 W/ m2 (Twidell and Weir, 1986: p. 378). Thus, Earth releases only 30 TWt or less than half that required for a 60 TWt global power system. Approximately 9 X 106 TWt-y of high temperature rock exists 1 to 7 km beneath the surface of the Earth. Only a tiny fraction of the energy is currently accessible at high temperatures at continental sites close to volcanic areas, hot springs, and geysers. However, in principle, these rocks can be drilled, water circulated between the rocks and turbines on the surface, and energy extracted. However, the costs are high (Nakicenovic et al., 1998: 56). There is considerable uncertainty in maintaining re-circulating flow of water between hot deep rocks and the surface (Trinnaman and Clarke, 1998: 279). The useful global potential is likely less than 0.5 TWe.

Wind turbines (#11)

Winds near the surface of Earth transport ~300 TWm of mechanical power (Isaacs and Schmitt, 1980). The order of 100 TWm is potentially accessible over the continents, especially in coastal regions. Trinnaman and Clarke (1998: pp. 299-300) report the continental wind power resource to be ~ 100 times that of the hydro power resource, or approximately 160 TWm. Wind turbines (#11) are efficient and offer access to a major source of renewable power. Approximately 3 to 10 MWe (average) can be generated by a wind farm that occupies 1 square kilometer of favorable terrain. If wind farms occupy 2.4% to 7% of the continents then averaged output can be ~ 20 TWe. However, at the level of a commercial power system wind farms demonstrate a major limitation of all terrestrial renewable power sources.

Wind farms are NOT STAND-ALONE (NSA) power systems. For example, wind farms are now connected to power grids that take over power production when the wind is not adequate. Wind farms in California have supplied as much as 8% of system demand during off-peak hours. Research indicates that 50% penetration is feasible (Wan and Parsons, 1993). For these reasons the "feasible" power level is taken to be less than 6 TWe. This is consistent with Case A2 of Nakicenovic et al. (1998: p. 69) in which wind farms supply all the renewable commercial power, or 23% of global power. Refer to Strickland (1996) for a less hopeful discussion of continental-scale use of wind power and other renewable systems that provide intermittent power.

It is necessary to examine the effect of large scale wind farms on the coupling of the Earth and the atmosphere. Such studies have not been done. A 20 TWe system of wind farms would extract approximately one-tenth of the global wind power. Climate changes comparable to mountain ranges might be induced by wind farming operating at a global level. It is known that winds and the rotation of the Earth couple through the friction of the winds moving over the land and oceans to produce a seismic hum within the free-oscillation of the Earth (Nishida et al., 2000). What happens when larger coupling between the specific areas on Earth and the global winds is established?

9.2.3 Terrestrial solar power systems

The continents and the atmosphere above them intercept —50000 TWs of solar power with a free-space intensity of 1.35 GWs/km2 ("s" denotes solar power in space). However, due to the intermittent nature of solar power at the surface of the Earth, it is very difficult for a dedicated terrestrial solar power system, complete with power storage and regional power distribution, to output more than 1 to 3 MWe/km2 when averaged over a year. Even very advanced technology will be unlikely to provide more than 20 MWe/km2 (Criswell and Thompson, 1996; Hoffert and Potter, 1997). Terrestrial solar power systems (TSPS) are NOT STAND-ALONE sources of commercial solar power. For dependable system power, the solar installations, either thermal or photovoltaic, must be integrated into other dependable systems such as fossil fuel systems. Terrestrial solar photovoltaic systems have been growing in capacity at 15%/y. A doubling of integral world capacity is associated with a factor of 1.25 decrease in the cost of output energy. At this rate of growth and rate of cost decrease, TSPS energy may not be competitive commercially for another 50 years (Trinnaman and Clarke, 1998: p. 265).

Strickland (1996; in Glaser et al., 1998: Ch. 2.5) examined both a regional TSPS and much larger systems distributed across the United States. Costs and the scale of engineering are very large compared to hydroelectric installations of similar capacity. Intercontinental solar power systems have been proposed. Klimke (1997) modeled a global system of photovoltaic arrays and intercontinental power grids scaled to provide Europe with —0.5 TWe of averaged power. Capital costs for a larger 20 TWe global photovoltaic system that delivers 1000 TWe-y might exceed 10000 trillion dollars, = 1 X 1016 dollars, and provide electric energy at a cost of — 600/kWe-h (Criswell, 1999). The system could be shut down by bad weather over key arrays.

Even an intercontinental distribution of arrays does not eliminate the problems of clouds, smoke from large regional fires, or dust and gases from major volcanoes or small asteroids (<100 meters in diameter). Changes in regional and global climate could significantly degrade the output of regional arrays installed at enormous expense. It is impossible to predict the longest period of bad weather. Thus, it is impossible to engineer ancillary systems for the distribution of power and the storage of energy during the worst-case interruptions of solar power at the surface of Earth. In addition, large arrays are likely to be expensive to maintain and may induce changes in their local microclimates. In Table 9.4, the total power from both options #12 and #13 is taken to be <3.3 TWe or the equivalent of 10 TWt. This is 30% of the total global power, 33.3 TWt in 2050, for Case A3 of Nakicenovic et al. (1998: p. 98).

9.2.4 Nuclear power systems

At the beginning of the 21st century, nuclear reactors output —0.3 TWe and provide 17% of the world's electric power. By 1996 the world had accumulated —8400 reactor-years of operating experience from 439 reactors. By 2010 nuclear operating capacity may be —0.4 TWe. Adequate economically recoverable uranium and thorium exist on the continents to yield 270-430 TWt-y of energy, depending of the efficiency of fuel consumption. This corresponds to 4 to 7 years of production at 20 TWe. Nakicenovic et al. (1998: p. 52, p. 69 Case A1) estimate that nuclear systems may provide as much as 1.6 TWe by 2050. Krakowski and Wilson (2002) estimate that conventional nuclear plants may provide as much as 5 TWe by 2100. A major increase in commercial nuclear power requires the introduction of breeder reactors.

Breeder reactors potentially increase the energy output of burning a unit of uranium fuel by a factor of —60 (Trinnaman and Clarke, 1998: Chaps. 5 & 6, back cover). Continental fuels could supply 20 TWe for —500 years. The oceans contain 3.3 parts per billion by weight of uranium, primarily 238U, for a total of 1.4 X 109 tons (see www.shef.ac.uk/chemistry/web-elements/fr-geol/U.html). Burned in breeder reactors this uranium can supply 20 TWe for — 300000 years. There are wide-spread concerns and opposition to the development and use of breeder reactors. Concerns focus on proliferation of weapons-grade materials, "drastically improving operating and safety" features of reactors, and the disposal of spent fuels and components.

Wood et al. (1998) propose sealed reactors that utilize a "propagation and breeding" burning of as-mined actinide fuels and the depleted uranium already accumulated worldwide in the storage yards of uranium isotopic enrichments plants. These known fuels can provide —1000 TWe-y and enable the transition to lower-grade resources. To provide —1 kWe/person, this scheme requires — 10000 operating reactors of —2 GWt capacity each. Each sealed reactor would be buried hundreds of meters below the surface of the Earth and connected via a high pressure and high temperature helium gas loop to gas turbines and cooling systems at the surface. At the end of a reactor's operating life, ~30 years, the fuel/ash core would be extracted, reprocessed, and sealed into another new reactor. The used reactors, without cores, would remain buried. A 20 TWe world requires the construction and emplacement of ~2 reactors a day. Spent reactors accumulate at the rate of 20000 per century. A major increase in research, development, and demonstration activities is required to enable this option by 2050. Krakowski and Wilson (2002) do not envision breeder reactors as providing significant commercial power until the 22nd century. Perhaps electrodynamically accelerated nuclei can enable commercial fission with sub-critical masses of uranium, thorium, deuterium, and tritium. This could reduce proliferation problems and reduce the inventory of radioactive fuels within reactors (#17).

The nuclear power industry achieved ~2.4 TWe-y of output per major accident through the Chernobyl event. Shlyakhter et al. (1995) note that the current goal in the United States is to provide nuclear plants in which the probability of core melt-down is less than one per 10 TWe-y of power output. This corresponds to 10 TWe-y per core melt-down. Suppose a 20 TWe world is supplied exclusively by nuclear fission and the objective is to have no more than one major accident per Century. This implies 2000 TWe-y per major accident or a factor of ~200 increase in industry-wide safety over the minimum current safety standard for only core melt-downs. A 20 TWe nuclear industry would provide many other opportunities for serious health and economic accidents. Less severe accidents have destroyed the economic utility of more commercial reactors than have reactor failures. Many utilities are unwilling to order new nuclear plants due to financial risks. Also, political concerns have slowed down the use of nuclear power through the regulatory processes in several nations (Nakicenovic et al., 1998: p. 84-87).

Nuclear fusion (#18, 19)

Practical power from controlled fusion installations for the industrial-scale burning of deuterium and tritium is still a distant goal. Europe, Japan, Russia, and the United States have decreased their funding for fusion research (Browne, 1999). It is highly unlikely that fusion systems will supply significant commercial power by 2050. Large-scale power output, >20 TWe, is further away. At this time the economics of commercial fusion power is unknown and in all probability cannot be modeled in a reasonable manner.

The fuel combination of deuterium and helium-3 (3He) produces significantly fewer neutrons that damage the inner walls of a reactor chamber and make reactor components radioactive. However, this fusion process requires ten times higher energy to ignite than deuterium and tritium. Unfortunately helium-3 is not available on the Earth in significant quantities. Helium-3 is present at ~10 parts per billion by mass in lunar surface samples obtained during the Apollo missions. Kulcinski (NASA, 1988, 1989) first proposed mining 3He and returning it to Earth for use in advanced fusion reactors. It is reasonable to anticipate that 3He is present on most, if not all, of the surface lunar soils. The distribution of 3He with depth is not known. The ultimately recoverable tonnage is not known. It is estimated that lunar 3He might potentially provide between 100 and 1 X 105 TWt-y of fusion energy (Criswell and Waldron, 1990). Far larger resources of 3He exist in the atmospheres of the outer planets and some of their moons (Lewis, 1991). Given the lack of deute-rium-3He reactors, and experience with massive mining operations on the Moon, it is unlikely that lunar 3He fusion will be operating at a commercial level by 2050.

Three essential factors limit the large-scale development of nuclear power, fission and fusion, within the biosphere of Earth.

• The first factor is physical. To produce useful net energy the nuclear fuels must be concentrated within engineered structures (power plant and associated structures) by the order of 106 to 108 times their background in the natural environment of the continents, oceans, and ocean floor. A fundamental rule for safe systems is to minimize the stored energy (thermal, mechanical, electrical, etc.) that might drive an accident or be released in the event of an accident. Nuclear fission plants store the equivalent of several years of energy output within the reactor zone. In addition, the reactors become highly radioactive. Loss of control of the enormous stored energy can disrupt the reactor and distribute the radioactive materials to local regions of the biosphere, and even distant regions, at concentrations well above normal background. A 20 TWe fission world will possess ~ 60 to 600 TWt-y of fissionable materials in reactors and reprocessing units. Fusion may present relatively fewer problems than fission. However, even 3He fusion will induce significant radioactivity in the reactor vessels.

• The concentration of fuels from the environment, maintenance of concentrated nuclear fuels and components, and long-term return of the concentrated radioactive materials to an acceptable background level present extremely difficult combinations of physical, technical, operational, economic, and human challenges. Nuclear materials and radioactive components of commercial operations must be isolated from the biosphere at levels now associated with separation procedures of an analytical chemistry laboratory (parts per billion or better). These levels of isolation must be maintained over 500 to 300 000 years by an essential industry that operates globally on an enormous scale. Such isolation requires enormous and focused human skill, intelligence, and unstinting dedication. Research scientists, such as analytic chemists, temporarily focused on particular cutting-edge, research projects sometimes display this level of intelligence and dedication.

The energy output must be affordable. Thus, total costs must be contained. How can such human talent be kept focused on industrial commodity operations? Can automated control of the nuclear industry be extended from the microscopic details of mining operations to the level of international needs? Ironically, if this level of isolation can be achieved the nuclear fission industries will gradually reduce the level of natural background radiation from continental deposits of uranium and thorium. • The last factor is more far ranging. Given the existence of the Sun and its contained fusion reactions, is it necessary to develop commercial nuclear power for operation within the biosphere of Earth? Are the nuclear materials of Earth and the solar system of much higher value in support of the future migration of human beings beyond the solar system? Once large human populations operate beyond the range of commercial solar power, it becomes imperative to have at least two sources of independent power (fission and fusion). Such mobile societies will likely require massive levels of power. Terrestrial and solar system nuclear fuels are best reserved for these longer-range uses.

Solar Power

Solar Power

Start Saving On Your Electricity Bills Using The Power of the Sun And Other Natural Resources!

Get My Free Ebook


Post a comment