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Laser SPS and the Hydrogen Economy

by R.G. Williscroft

From L5 News, October 1980

Sunlight is concentrated in geostationary orbit and beamed to Earth as concentrated laser energy. Receiving sites are marine locations where incoming energy is used to split sea water into its constituent components, hydrogen and oxygen. The hydrogen is pressurized and passed directly into a pipeline network or liquefied and loaded into tankers for shipment to other pipeline network terminals. The hydrogen would then be distributed as it is needed to energy consumers for use either as a direct heating fuel, as a raw material for various chemical processes, or a source of energy for the local production of electricity.

Hydrogen economy
Fig. 1: The Hydrogen Energy Economy

This concept differs significantly from current satellite power system (SPS) proposals. The SPS reference system was developed by the Department of Energy (DOE) and NASA from independent studies by the Johnson and Marshall Space Flight Centers. In brief, it features a satellite with a planar array of photovoltaic cells. An antenna at one end of the satellite transmits microwave energy to earth. On Earth, a rectenna converts the microwaves into direct current which is then distributed along conventional grids. (Table 1).

Table 1: Reference Characteristics for the SPS

Satellite
SPS generation capability with utility interface: 5GW
Overall dimensions (km) 5.3 x 10.4 x .5
Power conversion - photovoltaic options: GaAIAs, silicon
Satellite mass (kg): 34 x 106, 51 x 106
Structure material: Graphite composite
Construction location: Geosynchronous Earth Orbit at 35 900 km,
     with staging base in low earth orbit at 450 km

Transportation
Earth to LEO:
     Cargo, payload:
     Vertical-takeoff, winged two-stage transport,
     424 ton payload
     Personnel, number:
     Modified shuttle, with capacity for 75 persons
LEO to GEO:
     Cargo: Electric space tug
     Personnel, number:
     Two-stage LOX/LH2 orbit transfer vehicle, with capacity for 160 persons

Microwave power transmission
No. of antennas: 1
dc-RF converter: klystron
Frequency, GHz: 2.45
Receiving antenna dimensions, km: 10 x 13
Power density at receiving antenna, mW/cm2:
     Center: 23
     Edge: 1

Source: U.S. DOE

The concept proposed in this article differs from the SPS Reference System in three fundamental ways: a) Energy is transmitted to Earth as a concentrated laser instead of microwave energy; b) The rectenna is marine-based rather than shore-based; c) Received power is converted into hydrogen for pipeline distribution rather than direct current for grid distribution.

Socio-Economics

In a recent study done by Nansen and Johnson [2], the total cost per kWh for projected 1,000 mW coal and nuclear plants going on line in the year 2000 is 5.1 cents, whereas that for a 5,000 mW SPS is only 3.3 cents (Table 2). The major differences lie in cost escalation, which is less for SPS primarily because it can be built faster than the other plants, and in fuel, operation and maintenance costs, since SPS has no fuel costs and the system is essentially maintenance-free.

Table 2: Power System Economics
 
 
1,000 mW
Coal Plant
1,000 mW
Nuclear Plant
5,000 mW
SPS
40 Year Basis      
Current cost/kW
$1,000
$1,300
$2,340
Cost escalation (%/yr)
0.5%
0.7%
0.3%
Plant factor
0.72
0.76
0.92
Cost to acquire (Yr. 2000)
$8.7 x 109
$13.4 x 109
$14.1 x 109
Avg. capitalized cost/kWh
2.0¢
3.1¢
3.2¢
Fuel cost/kWh
2.4¢
1.8¢
0
O&M cost/kWh
0.7¢
0.2¢
0.1¢
Total cost/kWh
5.1¢
5.1¢
3.3¢
100 year basis
Capitalized cost/kWh
2.4¢
4.1¢
2.4¢
Fuel cost/kWh
3.6¢
2.6¢
0
O&M cost/kWh
1.3¢
0.3¢
0.2¢
Total cost/kWh
7.3¢
9.0¢
2.6¢

 Source: Nansen and Johnson [2]

Many experts on SPS are convinced that the satellite may last for 75 to 150 years. So assuming a 100-year basis instead of 40, Nansen and Johnson arrive at about 7 cents per kWh for coal and nuclear plants and only 2.6 cents for SPS. The primary reasons for this increasing difference is the amortization of two-and-one-half plants compared to the nominal 100-year lifetime and zero fuel costs for the SPS. Annual plant revenue requirements and the effects of inflation make up the other major factors influencing the cost of power during the lifetime of a plant. When Nansen and Johnson assumed a modest three-percent inflation rate and estimated that a coal plant would require over 10 times the annual revenue of an SPS after 30 years, they arrived at the startling result that for plants going on line in the year 2000, the cost per kWh for power would rise to 70 cents for coal and would drop to well below 3 cents for SPS by the year 2040. When looked at over a 100-year period, the SPS costs far less than comparable coal plants, decreasing to less than five percent of the coal plant costs by the 80th year and continuing lower. The long-term cost for nuclear generation would be even higher than for coal, because like SPS, it has a very high construction cost, but like coal it also has an increasingly more expensive fuel cost.

The societal impact of SPS deployment focuses on institutional, international and societal issues. With the growing US trend towards a decentralized energy policy, the ability of these institutions to deal with the centralized nature of SPS will need to be addressed. There will have to be some form of regional coordination of power plant regulation.

The financial attractiveness of SPS will depend upon its reward-to-expected risk ratio. Risks for SPS include disasters, international repercussions and technological costs. Each of these presents a large unknown. This coupled with the high implementation cost discussed earlier tends to discourage unilateral private sector financing. Two basic approaches appear possible. The first involves a joint-venture partnership between government and the private sector with resultant government regulation of prices and profits, and government license of technology. The second involves government financing of research and development phase through the issue of "Space Bonds" and thereafter is patterned like a staging company, supported by stock sales, investment income, patents, etc., or like an employee stock ownership plan which is not restricted to employees.

Development and commercialization of SPS will ultimately require some form of international organization which will require extensive treaty provisions. Treaties applicable to SPS are: a) 1967 Treaty on Principles Governing the Activities of States in the Exploration and Use of Outer Space, Including the Moon and Other Celestial Bodies (UN); b) 1972 Convention on International Liability and Damage Caused by Space Objects (UN); c) 1973 Telecommunications Convention and Final Protocol Treaty; d) Agreement Governing the Activities of States on the Moon and Other Celestial Bodies (UN) (pending ratification).

The 1967 Principles Treaty considers the space environment open to all who can use it. Since the radio frequency spectrum and geostationary orbit are considered to fall within the "province of mankind," and since space and its environs are considered part of the "common heritage of mankind," the question is raised about who should benefit from SPS.

International law has not yet established microwave exposure standards; however, the 1972 Liability Convention clearly holds a launching state liable for harm produced by microwave radiation emanating from a space object in geostationary orbit. International law also prohibits generating adverse changes in the environment.

The International Telecommunications Union (ITU) is governed by the 1973 Convention and Final Protocol. Under this and previous conventions, radio and microwave frequencies are allocated by ITU and ITU is also responsible for preventing broadcast interference. Since the SPS has a power transmission function, the question of ITU jurisdiction must be settled internationally.

The agreement currently before UN member states, known as the "Moon Treaty," may have far-reaching consequences with respect to SPS. In an attempt to put teeth into arms-control agreements, it would allow search without warrant of any structure in space or on any celestial body other than Earth. In an attempt to protect developing nations' share of space resources, it would set up an international regime empowered to create an OPEC-like monopoly over space resources, permanently removing them from private sector exploitation. This would drastically reduce the options available for SPS implementation, and would delay that implementation for years.

Military considerations will also require review. Although SPS does not serve a direct military function, there are potential weapons capabilities. The SPS could also be used to relay power to military installations, or it could function as an observation post for surveillance or some other military purpose. Even if it did not serve in such capacity, it would make an attractive target and might require some defensive capability. Therefore, international agreements will be needed to minimize SPS vulnerability and to ensure its non-militarization.

Public acceptance will be crucial to SPS implementation. The public issues revolve around microwave radiation effects, cost, land use and siting considerations inherent in the SPS Reference System. The anti-nuclear bias of the international environmentalist movement may work to the advantage of SPS deployment; however, land-use concerns may work against it, and it is also possible that the environmental impact of microwave radiation may catch the adverse attention of the international environmentalist movement.

Environmental Issues

The effects of microwaves on health and ecology have been looked at in detail by B.D. Newsom [3]. His fundamental conclusion is that what we know is much less than what we do not know about the subject. The most critical area requiring research is the effect of continuous, low-level exposure on humans and short-term, high-level exposure on airborne biota.

Deployment of an SPS will also generate other health and safety effects. These result from mining of raw materials, construction of terrestrial facilities, processing and fabrication of finished materials, transport of materials and equipment, ground station operation, space vehicle launch and recovery, orbital transfer of material and personnel, construction of SPS arrays, and operation of arrays. Many of the indicated activities are quite conventional, and the impacts they produce are common to any use of those processes. An evaluation of these impacts with respect to the SPS is only significant insofar as SPS deployment results in a substantial increase in a particular activity and its accompanying effects.

Another category results from activities unique to SPS deployment such as the handling of large quantities of gallium arsenide for solar cells and exposure of construction workers to extended periods in the space environment. Also to be considered are the unconventional effects caused by the potentially large-scale use of toxic materials, by the possibility of transport accidents involving the use of rocket propellants, and by launch and recovery activities resulting in air pollution, water quality impacts, noise and accidents.

The DOE has already defined environmental loadings which result from material requirements brought about by increased conventional activity. It has addressed the concentration limits for propellants in water and for air pollutants peculiar to SPS deployment, and has also addressed the impacts of acoustic noise resulting from launch activities. It has completed a preliminary occupational health and safety analysis for terrestrial workers, and has defined the areas of potential impact on space workers. For terrestrial workers, the major area of impact seems to be material acquisition. For space workers, the major areas under investigation are weightlessness and radiation.

The effects of SPS deployment on the atmosphere can be broken down into two areas, those relating to microwave and rectenna activities, and those relating to launch and transport operations. Analysis by the DOE shows that rectenna waste heat will produce about the same atmospheric effect as a suburban area and that atmospheric attenuation of the microwave beam will be too small to produce significant meteorological disturbances. However loss of beam control could have consequences which require further study.

The effects on the atmosphere of launch and reentry of transport vehicles, as well as of electric and magnetic field effects generated by an orbiting SPS are not well understood and require further study.

The harmonics and noise sidebands produced by microwave power transmission have the potential for interfering with SATCOM, microwave links, radar and radio astronomy. It is possible that a permanent degradation in one or more of these areas will be an inevitable consequence of SPS deployment.

The Laser Energy Vector

Lasers involve electromagnetic radiation whose wavelength is some 10,000 times shorter than microwaves. Because of this, transmitting and receiving components can be 10,000 times smaller. A transmitter ten meters in diameter in geosynchronous orbit can potentially send laser power at two micrometers wavelength to an earthside collector 40 meters in diameter with better than 90% efficiency averaged over time. J.D.G. Rather [4] estimates that such a transmitter would weigh 10 tons instead of 30 to 50 kilotons estimated for the equivalent SPS Reference System.

C.N. Bain [4] analyzed the effect of laser power transmission from an economic, societal and environmental viewpoint. Tables 3, 4 and 5 summarize his study and include the impact of deep ocean rectennas and use of the hydrogen as a planetside energy vector.

Key:
- Adverse impact
0 Little or no impact
+ Positive impact


Table 3: Comparison of Economic Effects

Elements
Laser
Microwave
Development
0
0
Production
+
0
Real Estate requirements
+
-
Energy payback
+
-

Table 4: Comparison of Societal Effects
 
Elements
Laser
Microwave
Land use area
0
-
Land availability
0
-
Ease of O&M
0
0
Worker health and safety
0
-
Displacement of people
0
-
Public acceptance
0
-
Aesthetics: Visible beam
0
 
Aesthetics: Infrared beam
0
 
Aesthetics: Site
0
-
Security
+
0
Weapons aspect
-
0
Frequency assignment
+
-

Table 5: Comparison of Environmental Effects
 
Elements
Laser
Microwave
Ionosphere (RFI/EMI)
0
-
Long-range communications
0
-
Ozone layer
0
0
Local climate modification
0
Global climate modification
0
0
Atmospheric photochemistry
-
0
Light scattering
0
0
Continuous insolation
0
0
Albedo
-
0
Health
0
-
Safety
-
-
Ecosystems: Biota
-
-
Ecosystems: Habitat modification
0
-
FR!/EMI
0
-
Air Pollution
0
0
Water Pollution
0
0

 Source: Bain [4]

The use of laser instead of microwaves for power transmission has a dramatic impact on the overall acceptability of the SPS. The economic advantages are tied to the very much smaller satellite required for the laser option and to the correspondingly small rectenna. In Nansen's and Johnson's economic analysis, nearly 40% of the total cost was absorbed by the in-space and rectenna structure. This portion of the total cost would be substantially reduced by the laser option. In addition, the smaller production effort should result in less energy being invested, and therefore, in a shorter energy payback time. This could result in an overall savings of one quarter to one-third of the projected per kilowatt cost.

The laser power transmission option also provides a significant reduction in the societal impact of the SPS. Forty-meter receiving sites appropriately protected by buffer zones can be located almost anywhere within range of the SPS, and practical offshore sites take on real significance. All of the environmental and communication problems identified as resulting from the microwave transmission of power go away.

While it is true that certain new problems surface, mainly related to the relatively intense heat generated near the concentrated laser beam, these problems seem controllable and do not appear to have any of the potentially far-reaching consequences of those related to microwave power transmission. The one exception is the option of using the laser as a weapon, since the international community is so sensitive to the use of space for military purposes. In conjunction with this, it should be noted that any use of the laser option for weapons purposes would have to be designed into the SPS from the beginning.

The Hydrogen Energy Vector

Almost a decade ago D.P. Gregory [5] built a strong case for a complete hydrogen economy where all modes of power generation are dedicated to hydrogen production. The International Association for Hydrogen Energy has been promoting the advantages of a hydrogen economy for a number of years.

According to Gregory, the cost of energy delivery by pipeline is about one fourth the cost of electrical delivery. The reasons for this become obvious when one considers the vast land and material requirements needed to support the massive electric grid complex. But the impact of hydrogen as an energy vector goes far beyond the cost of energy delivery. Hydrogen is essentially non-polluting. When burned it becomes water vapor, therefore wherever hydrogen replaces fossil fuel, the entire set of pollutants associated with the burning of fossil fuel goes away.

Gregory envisioned nuclear and conventional solar power plants producing hydrogen at remote locations, and pipeline transportation. Local consumption would be either directly by burning or catalytic conversion, and in the production of chemicals, or indirectly by electricity production using both conventional and fuel cell technology. His concept removed the polluting or dangerous operations to remote sites and eliminated many of the more polluting aspects of current power production.

What is proposed here goes far beyond that. The primary energy source is out in space, inexhaustible and always accessible. The space-to-Earth energy vector is essentially innocuous, presenting no forseeable insurmountable problems.

The planetside energy vector allows for energy distribution without adverse environmental impact and without consumption of any Earth resource beyond that required for the initial system installation.

Ultimately an SPS is envisioned which uses a laser tuned to a resonant wavelength of the water molecule for direct production of hydrogen. In the meantime, however, the SPS must be considered basically an electricity producer. Hydrogen should be viewed as an energy carrier for SPS energy under those circumstances where delivery of the energy in electrical form may not he practical. Ideally the initial receiver sites would be so located that they would efficiently augment the local grid and could gradually take up the slack created by retiring conventional power generators, while at the same time generating hydrogen during grid off-peak periods (Fig. 2).

Grid structure
Fig. 2: Integrated grid structure

With the passage of time more and more of the grid demand will be supplied by SPS as conventional power generators are retired out of the system and new satellites are constructed. There will be a concurrent increase in hydrogen production. Moreover grid demand itself will increase. However, instead of expanding the grid, this scenario calls for meeting the increased demand with hydrogen energy. This hydrogen would be delivered by tanker and/or pipeline to the area of increased grid demand. Furthermore, where the loss of grid capability due to the aging of grid elements and their subsequent retirement from the grid is a factor, the slack can be picked up by extending the hydrogen delivery system rather than by replacing the grid elements. Equilibrium within a balanced energy budget is finally reached when the only remaining grids are those associated with local hydrogen-powered electrical generating systems.

Looking towards the future, modified LNG carriers, or perhaps specially constructed ships, will enable establishment of remotely located deep ocean rectennas which will remove almost all remaining objections to implementation of an SPS. The end result is abundant, inexpensive, non-polluting, renewable energy for all humankind.

References

1. US Department of Energy. DOE/NASA Reference System Report for Satellite Power System (SPS). US DOE, DOE/ER-0023, Oct. 1978. (All references to DOE and to NASA refer back to this multi-volume reference.)

2. Nansen, R.H., and O.E. Johnson, "Economic Aspects of Energy from Space." In Space Shuttle: Dawn of an Era; Proceedings, Annual Meeting, AAS 1979.

3. Newsom, B.D. Research Plan for Study of Biological and Ecological Effects of the Solar Power Satellite Transmission System. NASA CR-3044, 1978.

4. Rather, J.D.G. "Lasers Versus Microwaves for Solar Space Power." In Bain, C.N., Potential of Laser for SPS Power Transmission (US DOE, HCP/ R-4024-07, Oct. 19781.

5. Gregory, D.P. "The Hydrogen Economy," Scientific American, Vol. 228, No. 1, 13-21, 1973.

 

R.G. Williscroft R.G. Williscroft is currently in charge of the National Ocean Survey diving activities on the US East Coast. The opinions represented in this article are those of the author and do not represent his employer, the US Government.

L5


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