As society continues to expand at an increasing pace and technology becomes more pervasive, the usage of resources has begun to have an even larger impact on the planet. In recent history more focus has been placed on resource depletion and the long term affects of human consumption. Both governments and private industry understand that energy consumption must be carefully monitored and regulated to avoid resource depletion. Sustainable development has received renewed focus now that society can quantify and analyze the destructive nature of human consumption. The Brundtland Report of 1987 defined sustainable development as "Development that meets the needs of the present without compromising the ability of future generations to meet their own needs" (Brundtland, 1987). This concept can be applied to all ecological and resource systems on the planet. Any resource that is consumed by humans can benefit from sustainable development.
In efforts to promote sustainable development specifically towards environmental issues, the UN introduced the Agenda 21 program. The Agenda 21 program provided UN organizations with a plan of action to be taken internationally in every area where humans directly impact the environment. Agenda 21 highlights the fact that current levels of energy consumption and production are not sustainable, especially if demands continue to increase. The report stresses the importance of using energy resources, in a way that is consistent with the aims: of protecting human health, the atmosphere, and the natural environment (Report of the United Nations Conference on the Human Environment, 5-16 June 1972).
In 2001 the International Energy Association concluded that approximately 80% of the world's energy supply comes from fossil fuels such as oil, natural gas and coal. The total percentage of world energy supply that is derived from fossil fuels; this usage is increasing at a rate of 1.5% per annum. Humanity's rising dependence on fossil fuels and other non-renewable resources will ultimately cause catastrophic impacts on the environment including anthropogenic climate change, stratospheric ozone depletion, air/water pollution, deforestation and drastic reductions in wildlife habitat. On a societal level, continuous growth in a world where non-renewable resources are finite is unsustainable. This behavior would eventually cause an economic collapse, as the scarcity of resources would eventually inhibit current patterns of human behavior.
Many efforts have been undertaken to supplement and eventually replace fossil fuels with renewable resources such as solar, hydropower, wind and geothermal power. None of these alternative energy sources have yet to match fossil fuels in terms of availability, ease of processing and low cost per unit of energy output. During the last 40 years, both NASA and NASDA have been researching Space Based Solar Power as a permanent replacement for fossil fuels for the coming generations: (ADD STATS). This report will outline the engineering details and impressive advantages of this new technology and how it is the closest engineers have gotten to true sustainable development.
Introduction
Power from the sun is not a new concept, however the practicality of generating electrical power from solar energy has always been questioned because of the absorption of energy by unchangeable and uncontrollable environmental buffers caused by the atmosphere, obscuration by clouds, dust deposition, wind effects and limited availability of the sun's radiation at certain times of the day (low sun angle, night).
In 1968, Dr. Peter Glaser - an American scientist and aerospace engineer - invented the concept of solar power satellites in his journal which was published on November 22, 1968 for Science titled: "Power from the Sun: It's Future". Three years after his publication, Dr. Peter Glazer went on to Patent his invention titled "METHOD AND APPARATUS FOR CONVERTING SOLAR RADIATION TO ELECTRICAL POWER". In this Patent, Dr. Peter Glaser identifies the primary objectives of his invention as follows (Glaser, 1973):
SBSP technology allows the conversion of energy derived from the sun to microwave or laser beam energy through equipment maintained in geosynchronous orbit, which is then transmitted as microwave energy to appropriate collectors on earth. If executed correctly, the problems of absorption can almost completely be eliminated since microwaves/ laser beams can safely pass through the atmosphere with minimum absorption and scattering. In addition, geostationary satellites allow for continuous collection and transmission of solar energy that can be transmitted to earth regardless of the relative position of the collectors on earth (areas exposed to minimal sunlight, locations of large-scale power consumption, locations with limited availability to conventional electricity). As a result, the major drawbacks associated with direct terrestrial collection of solar energy are substantially minimized.
In brief, SBSP technology is a combination of three independent systems and they can be classified as follows in proceeding order:
SBSP Technologies: Systems Integration
The continuing role of systems integration within the space based solar power program has been to contribute to the development of new satellite and system architecture concepts through a strictly analytical process that is used to asses the value and requirements of new and advanced technologies. The process also examines the satellite concepts themselves in terms of their estimated mass, cost to implement and the ultimate cost the consumer would have to pay for electricity delivered by these satellites.
Ever since the idea of space based solar power was introduced in the late 1960's, engineers and architects from NASA, NASDA and private organizations have proposed many solar satellite concepts. These designs range from small 50-100 kW systems placed in lower orbit, to massive multi giga-watt systems in geosynchronous orbit (Figure __). Some designs incorporate microwave power transmission energy (Figure __), while others transmit their power to the ground via a laser beam (Figure __).
One of the earliest concepts proposed was a sun-tower satellite (Figure __). The architecture of this concept involves a long tower-like configuration with circular concentrated solar collectors spread symmetrically along the length of the tower, and at the bottom of the sun tower, a large microwave transmitter that always faces the earth along the satellites path of orbit. This design was especially attractive since the construction of the tower was relatively simple and assembly was easily achievable in space. However, this particular design did have some major drawbacks. Due to the sun-towers orientation in orbit, throughout the day the solar arrays (collectors) would be exposed to full or partial shadowing caused either by the earth, or the solar arrays themselves. Furthermore, its unique configuration would require the sun tower to be many tens of kilometers in length, in order to deliver the desired amounts of energy.
Throughout the iteration process, it was later determined that in order to avoid the varying illumination problem, the satellites are to be employed in an orbital configuration such that the solar arrays on the satellites are constantly being illuminated by the sun while letting the transmitter slowly rotate so that the energy can always be redirected and transmitted to the earth. This was an early approach that was taken on by the DOE/NASA Power Satellite Study in late 1970's (Figure __). More recent concepts, suggested using 2D arrayed large rotating reflectors to redirect the microwave energy to earth (Figure _). While the added array dimension reduces the electrical cable length requirements over those in the sun-tower design, the weight of these cables along with power management equipment still form the majority of the total satellite mass. With this in mind, another concept was proposed that substantially reduced added mass caused by cable and power management/distribution equipment. This concept called the integrated symmetrical concentrator or ISC (Figure __) redirects the suns energy by reflection, rather than first converting to electricity then distributing over long cable lines.
All of these concepts have one thing in common. They are all too large to be brought to orbit and deployed in a single launch. For this reason, NASA is currently investigating small laser based systems that can be launched and deployed as independent spacecraft's without further assembly. These spacecrafts would become part of larger constellations of other laser-based systems operating in geosynchronous orbits. Such units could presumable start delivering power as soon as they are in place and the delivered power could be increased as new satellites join the constellation.
SBSP Technologies: Innovative Solar Energy Collection Technologies
The efficiency of energy collection in an SBSP satellite depends highly on the type of photovoltaic technology being used to convert solar radiation into direct current electricity. Furthermore power generation in space for an SBSP system poses multiple challenges. First, an extraordinarily large area of PV arrays will be required for large-scale power generation. In addition, to hold down SBSP system weight, solar PV voltages much higher than ever before may be needed. NASA, NASDA and other private institutions have done extensive research on several innovative technologies that can reduce the surface area needed for PV arrays, reduce overall system weight and increase solar energy to DC energy efficiencies. The details of each researched innovative technology can be found below. Some of these technologies have the added advantage that they may be combined with one another.
Thinner and lighter than traditional silicon solar cells, thin film solar cells (TFSC's) require less material as well as a lower grade material therefore making them less expensive to manufacture. NASA in collaboration with universities across the United States have engineered a series of what is called single source precursor molecules. A single source precursor molecule is a single molecule that contains all of the individual elements (Copper, Indium and Sulfur or Selenium) that are deposited on the final solar cell material. The precursor molecule is then grown on to the final lightweight space qualified material through a process called low-temperature chemical vapor deposition.
Conventional solar cells have the potential to be 12-30% efficient in converting light to electricity depending on the type of cell. However when the new technology of utilizing quantum dots is incorporated into a solar cell structure, the cells potential for converting light can increase dramatically. Quantum dots are essentially an extra layer of material comprised of small atoms within the solar structure that absorb sunlight. They have the potentially to triple solar cell efficiencies.
Solar array technology has made tremendous advances from the 10% efficient single crystal silicon solar cell to the 27% triple junction solar cell; however many future space applications (include SBSP) will require power systems that must perform in harsh environments at increased power densities. The rainbow photovoltaic concentrator concept offers the combination of high solar energy concentration and high efficiency energy output. The rainbow concentrator uses prisms oriented on a cylindrical parabolic curve to spectrally split the incoming light and direct it onto an array of different band gapped solar cells that match the energy of the incident light. The efficiency of rainbow photovoltaic concentrators is expected to reach 40%.
Power Tile technology (Figure __) introduces several new technologies including ultra high efficient solar cells, thin film thermoelectric devices and inorganic solid state lithium batteries. Power tiles utilize thin film thermoelectric that create electrical current anywhere a significant difference in temperature is found. The greater the temperature difference, the more energy can be derived. The power tile is assembled first with highly efficient PV cells that use either the rainbow of multi-junction technology. A thin film thermoelectric devices is then integrated on the backside of the PV cells and on top of the multi layer solid-state battery. Finally, thermal management structures are used to provide the greatest temperature differential possible across the thermoelectric device. Preliminary testing concluded that power tiles can double the power to mass ratio.
SBSP Technologies: Wireless Power Transmission
In 1864, James C. Maxwell derived the famous "Maxwell Equation" which related electric and magnetic fields to their sources, charge and current density. Twenty-four years after the discovery of this phenomenon, German physicist Heinrich Hertz succeeded in showing experimental evidence of radio waves through his spark-gap radio transmitter experiment. This remarkable discovery led to the start of wireless power transmission (WPT). Microwave and Electromagnetic Radiation (EMR or Laser beam) Transmission technology are currently the two most researched methods for wireless power transmission for SBSP systems. Both methods require antennas, transmitters (generators, amplifiers) and rectennas (receiving antennas).
Microwave Power Transmission (MPT) requires the use of phased array antennas from/to the moving transmitter/receiver. A phased array antenna is an antenna that can control the direction and speed of a microwave beam accurately - biggest advantage being the ability to steer the direction of the microwave beam. The antenna elements might be dipoles [1], slot, parabolic, or any other type of antenna. MPT also requires innovative technology for the generation and transmission of microwave radiation. To obtain efficient wireless power transmission over long distances, higher efficient generator/amplifiers for the MPT system are needed than those currently being used in wireless communication systems. MPT generators/amplifiers can either be classified as being vacuum or solid-state devices. Different technologies within each category offer different average output power at different radio frequencies and that can be seen in Figure __.
An alternative to MPT is electromagnetic radiation (EMR or Laser) power transmission. In the case of EMR closer to the visible spectrum, semiconductors used in laser diodes can convert energy into concentrated high intensity radiation that can be beamed to appropriate receivers hundreds of kilometers away. Similar to MPT, EMR technology allows power to be wirelessly transmitted from satellite in geosynchronous orbit to virtually any receiver in line of site. Unlike MPT however where power is transmitted via large radial microwave signals, laser fronts propagate with narrow cross-sectional areas, which improve energy confinement. In addition, because EMR technology only requires a controlled system of laser semiconductor diodes, it is considerably more compact and lightweight than MPT technology (which require large transmitting antennas). Also, the risk of interference with existing radio waves in the earth's atmosphere is eliminated as laser waves travel with smaller wavelengths. However laser power transmission does also have its drawbacks. The electrical potential conversion processes both before and after transmission have been proven to be only 40 to 50% efficient. In addition, laser electromagnetic radiation can be susceptible to losses caused by atmospheric absorption.
SBSP Technologies: Environmental Impact
For most large-scale energy related projects being implemented today, an Environmental Impact Analysis (EIA) is conducted in direct correlation with the cost-benefit analysis. Like all emerging technologies, the environmental impact analysis of SBSP technologies reveals both positive and negative outcomes. However when conducting EIA, it is also important to judge SBSP technology in retrospect to its alternatives and it's compared advantages. Much like terrestrial solar power technology, SBSP does not involve the combustion of environmentally harmful fuels. As a result, solar power provides clean carbon-free energy during its operational stages.
However because the manufacturing of PV cells involves electrically demanding processes, a life-cycle analysis may prove solar technology as being harmful in indirect ways. In efforts to quantitatively analyze the potential environmental impacts of the PV manufacturing industry, the Electrical Power Research Institute (EPRI) conducted a projected titled " Potential Health and Environmental Impacts Associated with the Manufacture and Use of Photovoltaic Cells". The report concluded "the estimated carbon dioxide emissions are nearly all released during the manufacturing of the PV cells and components, and thus the emission are determined by the source of the electricity used". Hill and Baumann did a quantitative comparison of CO2 emissions between coal plants generating the same amount of electricity as the completed PV modules over their useful life. In a journal titled "environmental costs of photo-voltaics", it was estimated that during PV cell manufacturing in Western Europe, approximately 50-60 g/kWh of carbon were emitted (Hill & Baumann, 1993). When compared to the average carbon emission from conventional energy systems of about 570g/kWh (Alsema and Nieuwlaar, 2000), the PV manufacturing industry only contribute a fraction of the carbon emitted by conventional energy production methods. Alsema and Nievwlaar (2000) also showed that PV systems had potential energy payback times of 2-3.2 year for systems implemented in areas of high insolation[1].
Launch missions for the employment of SBSP satellites also have a detrimental impact on the environment. In 2008, NASA conducted a report titled "Record of Decision: Constellation Programmatic Environmental Impact Statement" which outlines the environmental impacts of newly designed launch vehicles (Ares) that will eventually replace the traditional space shuttle. Research for this report concluded that combustion products from burning solid propellant would release hydrogen chloride (HCl), aluminum oxide (Al2O3), oxides of nitrogen and particulate matter. Similar to a traditional space shuttle launch, the deposition of these pollutants would undoubtedly contribute to acidic deposition, air and water contamination resulting from the exhaust cloud. In the case of a launch accident, heat, fire, flying debris and HCl deposition could damage the immediate surroundings. However, as experienced in the past, damaged vegetation is expected to re-grow within the same growing season. With respect to Ozone Depleting Substances (ODS) and global warming, the report concluded: "It is estimated that the annual emissions of HCl and Al2O3 from Constellation launch vehicles would induce less than 0.0012 percent of the estimated annual global average ozone reduction for corresponding years". Similar to the environmental impacts of PV cells, it was concluded that the majority of GHG emission would come from NASA's energy use for the manufacturing and implementation of new launch vehicles.
NASA and the DOE also conducted a study that among other initiatives, looked into the environmental impacts of microwave and laser radiation. The study titled "Space-Based Solar Power as an Opportunity for Strategic Security" concluded that "the peak density of the transmission beam is significantly less than noon sunlight, and at the edge of the rectenna equivalent to the leakage allowed and accepted by millions in their microwave ovens". The likelihood of the beam wandering over a city was predicted to be extremely low, and if occurring would be extremely anti-climactic
SBSP Technologies: Socio-Economic Impacts
Space Based Solar Power (SBSP) provides a clean and abundant source of cheap energy after high initial costs. Alternative sources of power generation have a substantial impact on the environment, require extensive government regulation and incur hidden costs during their lifespan. SBSP has proven to offer a decisive advantage over other forms of energy production. SBSP also has positive affects on technology advancement, international relations, employment in advanced technology-related industries and power generation. SBSP can provide clean energy in virtually limitless supply. SBSP will have a minimal physical impact on our surroundings due to the primary installations' location in space.
Several socioeconomic benefits are immediately apparent. Currently there is a distinct lack of high-tech development in North America. With the rising power of international corporations, projects and the jobs they create are moved to other countries where there are more economic incentives such as competitive wages and reduced government regulation. SBSP would require government funding and development initially. Once government has set the precedent, private enterprise will have an incentive to participate in SBSP development. This will result in the creation of a significant number of high-tech, high skill jobs during the development phase alone. Once project construction is implemented, more jobs will be created, as there will be a need for significant manufacturing capacity and transportation of the required components.
International cooperation is another direct benefit of SBSP. The sheer magnitude of research and development required alone cannot be handled by a single country or private corporation, never mind the construction and logistics required to implement SBSP on a scale that would provide significant energy output. By distributing the workload over several participating countries it can be possible to increase the pace of development and implementation. A perfect example of international cooperation in practice is the International Space Station project (ISS). ISS required several modules to serve different functions on the space station. Components from countries all over the world are used to assemble the ISS and this collaboration has resulted in new technologies and increased employment in all countries that have participated in the ISS project. Another added benefit of international collaboration is that a peaceful and productive tone for international relations will be set. The largest current international collaborative project is the United Nations, an organization beset with differing opinions and conflicts of interest. Inaction, nonparticipation and alternate agendas of member countries have significantly reduced the effectiveness of the United Nations. SBSP focuses on the common goal of cheap and efficient means of energy production in order to help reduce environmental impact and create development and technological advancement in third-world countries. A simple common goal is required for international cooperation to be effective.
Improved technology is a significant benefit of SBSP. The technologies required in several areas of science can only help further advance our level of technological development and application. Manufacturing processes must be improved in order to provide kilometers of photovoltaic cells. New construction methods are needed for lightweight support structures so they can easily transported and maneuvered into position. An efficient transportation method is required for getting completed components into space in vast quantities quickly and cheaply. Microwave technology will require development for SBSP's required applications. Resulting improvements can help increase the efficiency of current communications technology. Computer aided development has improved by leaps and bounds, allowing for far shorter development cycles compared to before. This new "problem" will require revisiting computer-aided development in order to model an environment that has yet to be fully understood. Finally, the resulting need for increased space activity can only provide more
advancement in the field of manned space exploration. The problems faced by astronauts regarding exposure to solar radiation and extreme temperatures must be solved in order for personnel to work in such conditions on such a massive project. Spacewalks on a massive scale will be required to complete phases of construction in a reasonable timeframe and within budgetary constraints. The technological advancement in all of these areas will help stimulate the improvement of technology throughout our world.
The primary drawback of SBSP is the high initial investment required not only for a full-scale plant but a demonstration plant as well. An initial SBSP plant capable of producing approximately 10 MWe would cost an estimated $8-9 billion USD according to the report Space-Based Solar Power as an Opportunity for Strategic Security. By comparison, a conventional nuclear plant would provide 1 GWe of energy for approximately the same price. This demonstration SBSP plant can transmit power to any place on the planet but the energy output is significantly lower than other means. A full-scale implementation of SBSP would require investment of upwards of $100 billion USD. By comparison, the cost to transport a payload to outer space by current available means costs over $600/lb. The report Space-Based Solar Power as an Opportunity for Strategic Security suggests that SBSP on a large scale would only be feasible if transportation costs approach $200/lb, a significant reduction in cost that is not yet possible. Costs affecting the production of photovoltaic cells are also a significant issue. Currently there is neither the means of production nor is there an acceptable economy of scale to support the production of large batches of photovoltaic cells for SBSP applications. The transportation and support of personnel and equipment in earth orbit is also currently cost prohibitive.
Barriers to the development and construction of SBSP plants are numerous. Restrictive government legislation that keeps intellectual property related to space development and possible military applications prevent cooperation with international parties. Aside from legislation, different political opinions will drastically inhibit the development of SBSP technology, as politicians will be divided in support. Private party lobbyists hold significant power over elected officials and have much to loose to SBSP. OPEC and private energy corporations stand to see their primary form of economic activity rendered obsolete by SBSP. International cooperation will be difficult to stimulate as different countries have different and conflicting agendas. As explained earlier, the United Nations is an excellent example of how international relations are difficult to broker and require extensive negotiation. Issues over sovereignty is space are another concern as this collective project will have contributions from many participants, all of whom will want to be rewarded for their contributions. The potential for political deadlock is great when dealing with a project of such large scope.
SBSP Technologies: Conclusion
Space Based Solar Power is an alternative energy source that has been researched for over 40 years. During this time society has focused research and development towards other forms of energy such as nuclear power, hydroelectric generation, renewable sources such as wind and solar power and experimental technologies such as nuclear fusion. As time has passed, our dependence on fossil fuels and polluting methods of power generation has only increased. Now, at the dawn of the 21st century, mankind has reached a critical point where the resources we rely on to fuel our society are starting to deplete. SBSP has the potential to provide abundant clean energy for all of mankind throughout the world.
Clean energy is a problem mankind must finally address. The effects of global warming, pollution and excessive consumption are beginning to have a detrimental impact to our environment. The changing climate, the unpredictable weather patterns, the destruction of natural habitats and the negative health impact of our addiction to fossil fuels will not decrease until a significant portion of the energy we consume is derived from renewable, non-polluting sources. A substantial paradigm shift is needed before we can even begin to comprehend the depth of our consumption problem. In order for future generations to be able to evolve and prosper as we do a significant change must occur.
SBSP relies on concepts that have already been proven. The use of photovoltaic cells in space has occurred during the majority of man's exploration of near space. Wireless power transmission is based on principles that govern most telecommunications technology. The total systems integration that SBSP requires will need considerable testing and expensive pilot projects to not only verify the concept and evaluate efficiencies but also spur support and further innovation. The separate systems that derive SBSP are still in infancy and necessitate further advancements in the fields of energy transmission, collection and space faring logistics. These advancements can provide benefits to other technological areas that we cannot clearly identify today. While the large-scale implementation of these technologies will be challenging and requires a significant investment in research and development as well as actual construction, the concept is sound and the potential return cannot only be measured in dollars and GWe.
The socioeconomic benefits of SBSP are enormous. Besides the promise of cheap and clean energy, an abundance of energy can elevate the third world and developing countries. Many technologies that can help poverty stricken and inhospitable areas have demands for large amounts of energy from a stable source. The political climate would be considerably cooler thanks to distinct lack of competition for remaining fossil fuel reserves. A global project of this scale can only unite countries together as they put aside their differences in the pursuit of technological innovation. An economy that does not rely on the commodity prices of fossil fuels can only help a tech industry that has been plagued by high startup and resource costs. The undoubtedly clean nature of SBSP can only help reverse global warming and ensure mankind's survival in the coming centuries.
The drawbacks and barriers to SBSP are also abundant. The enormous startup cost will be difficult for nations and private enterprise to stomach. A demonstration project capable of 10 MWe will cost billions. The full-scale project is so large that it has been difficult for experts to peg the cost of large-scale SBSP applications that would supply a significant amount of energy and lower our dependence on fossil fuels. The maturity of technology required for SBSP applications will require significant investments in the areas of research and development, space faring logistics, advanced manufacturing techniques and large scale production methods. Many of the apparently simple steps required to undertake this project are in fact complex problems that mankind has not encountered before. Aside from enormous cost and technological advancement, current legislation and politicians will also be barriers against SBSP. The short-term nature of politics, versus the long-term nature of SBSP development and implementation clash, as few individuals are willing to divert resources from elsewhere. International cooperation is still a hazy concept as current international organizations such as the United Nations have a very difficult time reaching consensus, ultimately the issues these organizations face will continue unabated. The issue of orbiting assets in space also proves to worry many nations, as they fear being restricted from technology they cannot see or control. SBSP will be limited by a lack of willpower to accept the high costs (both monetary and social) and by short-term self-interest.
Ultimately Space Based Solar Power is a sound concept but one that requires considerable effort and sacrifice by all of mankind. A project of this scope has never been attempted before. By solving social, economic, technological, environmental and political problems we can ensure that mankind not only protects its habitat but also that mankind will have a potential stepping-stone towards the stars. In light of recent expenditure on other technologies that have yet to produce measurable results, perhaps we should seriously consider what Space Based Solar Power could do to help ensure not only our survival but our advancement as a race.
Report of the United Nations Conference on the Human Environment, Stockholm, 5-16 June 1972 (United Nations publication, Sales No. E.73.II.A.14 and corrigendum), chap. I
Bruntland, G (ed) (1987). Our Common Future: The World Commission on Environment and Development, Oxford: Oxford University Press.
Alsema, EA and E Nieuwlaar, 2000. Energy Viability of Photovoltaic Systems. Energy Policy, Vol. 28, pp. 999-1010.
Hill, R and AE Baumann, 1993. Environmental Costs of Photovoltaics. IEE Proceedings, Vol. 140, No. 1, pp. 76-80.
Potential Health and Environmental Impacts Associated with the Manufacture and Use of Photovoltaic Cells, EPRI, Palo Alto, CA, and California Energy Commission,
RADIATION TO ELECTRICAL POWER United States Arthur D. Little, Inc. (Cambridge, MA) http://www.freepatentsonline.com/3781647.html
Glaser, Peter. METHOD AND APPARATUS FOR CONVERTING SOLAR RADIATION TO ELECTRICAL POWER. Arthur D. Little, Inc. (Cambridge, MA), assignee. Patent 3781647. 25 Dec. 1973. Print.
