The Next Frontier?

Space Solar Power: The Next Frontier?

1. Search for Solutions: Why Space?

Outer space captures the imagination of all human beings. Outer space’s sheer immensity and vastness, fraught with many dangers, has the potential to resolve most terrestrial energy constraints that limit enterprise and slow the advance of human progress. At every impasse, human beings have strived to conquer their surroundings and solve the most complex and seemingly insurmountable dilemmas which they encounter. Revolutions have come, and advancements have been made, all in the name of progress. Understanding the effects of human activity on the planet’s many ecological systems as well as the unending desire to improve our way of life has made Homo sapiens not only the dominant lifeform on the planet, but a prosperous species. Advancements of human understanding have led to a dramatic if not perilous conclusion: fossil fuel consumption is creating widespread greenhouse gas emissions, which are insulating the Earth’s atmosphere, dubbed simply “global warming”.

The lion’s share of energy produced and consumed on the earth comes from fossil fuels. Coal, natural gas, and other petroleum products dominate the energy marketplace due to their extensive availability. Infrastructure necessary for the transportation of fuel products spans nearly the entire modern world. In the developing world political power trades hands in areas where petroleum is accessible, creating intense power struggles arbitrated by those who have stakes in the uninterrupted flow of fossil fuels to both the east and west. The United States celebrates recently overcoming its catastrophic dependence on foreign petroleum and seeks to usher in a new period of economic prosperity based on freshly discovered resources like the Marcellus shale. The vice-like grip that has developed over the energy market by big oil corporations has slowed the growth of viable solutions to the Earth’s climate change crisis. The people of the Earth rely so heavily on the flow of petroleum products to sustain their way of life that a comprehensive solution or cure-all cannot and will not suffice. The United States government is attempting to negate and slow the effects of climate change by moving the country toward a more diverse energy portfolio incorporating clean renewable energies like wind, solar, geothermal, and others. The solution to the growing demand for substantial amounts of energy for electricity on earth could be found in outer space. In order to successfully provide useful power to Earth from outer space, a few capabilities are necessary. The foremost requirement is a means of conveyance for the people, parts, and equipment into outer space. The next pivotal pieces of this project are solar panels capable of withstanding long periods in the vacuum without costly repairs and maintenance. The final major capability that must be realized is a method of delivery for the collected energy to be effectively delivered to the surface; microwave power transmission via transmitter to rectenna is the primary method discussed in this paper. Other methods for wireless power transmission are being analyzed, specifically the use of laser technology.

1. Means of Conveyance: Achieving Geo-synchronous Earth Orbit

            The largest obstacle facing SBSP is the tremendous cost and complexity of achieving geo-synchronous orbit around the Earth. Geo-synchronous orbit (GSO) is necessary due to the period of coverage over a given area by a satellite per day. GSO is different from low Earth orbit (LEO) and Geo-stationary orbit because it provides nearly continuous coverage; LEOs provide only few minutes of coverage in their approximately 90 minute revolutions around the globe. Geo-stationary satellites will simply not work for SBSP because their stationary position will not provide the requisite coverage for SBSP to work at the scale of the demand for power. GSO is the most viable option regarding the effectiveness of SBSP satellites to supply power to the surface. There are a number of issues with placing satellites into GSO that make accomplishing this objective (placing large solar panel carrying satellites in orbit) increasingly complicated. The altitude required to achieve GSO is around 22,000 feet; the same altitude currently used for most of the world’s communications satellites. The vastness of outer space is therefore not as it would seem. Solutions to the problem of over-crowding in GSO are being researched. One study from the University of Rome proposes alterations in orbital trajectories which would help deconflict the crowded airspace for future communications satellites (Circi et al. 2015).

The second largest obstacle facing SBSP is the tremendous fuel costs of achieving the altitude of 22,000 feet. The cost of launching and maintaining a satellite in GSO is so extraordinarily high, that major advancements in industrializing outer space cannot be made. The National Aeronautics and Space Administration (NASA) place the cost of a space launch at around $450 million (NASA, 2015). The average space shuttle is adjudged to have a “total weight… [Of] 1,607,185 pounds” (NASA, 2015). A total launch cost of $450 million with a total weight of 1,607,185 pounds equates to $280 per pound. This already staggering figure is only increased when one takes into account that the cost of the shuttle required to carry the materials to construct the satellite. These high costs can be attributed to the lack of infrastructure supporting private space flight. Recently however, efforts have being made by private corporations like SpaceX, led by entrepreneur Elon Musk, to produce space craft capable of achieving the required altitude at considerably less cost. SpaceX has developed both the Falcon 9 and Falcon Heavy rockets which are capable of carrying materials to LEO and can be reused in the future, and can further decrease future shuttle construction costs. Another alternative to conventional shuttle launches is the Skylon rocket, or spaceplane, currently under development by Reaction Engines limited, which uses a single stage to orbit design to cut fuel costs. Both the Falcon rockets and the Skylon space plane are designed to be reused in order to cut launch costs.

Table1. Possible Launch Vehicle Comparison

 

Rocket:	Skylon	Falcon 9	Falcon Heavy
Stage	Developmental	In Production	In Production
Launch cost(USD)	450M	450M	450M
Shuttle Cost(USD)	45M*	61M	90M
Payload to LEO(lbs)	24,000	28,991	116,845

*Target Price for developmental technology (Amos, 2014)

 

Source: (SpaceX, 2015) & (Reaction Engines, 2008)

 

            A combination of technologies will likely be the solution to overcoming the cost of space craft and launches. Engineer Keith Henson describes a unique and entirely possible solution to the cost of space launch by recommending the inclusion of laser stages in rocket propulsion into GSO. As he states in his article Beamed Energy and the Economics of Space Based Solar Power, the “combination of Skylon and large propulsion lasers should reduce the cost to lift one million tons of power satellite parts per year to GEO to less than $100 per kg[$220 per lb.]. This permits electrical power cost of 2 cents per kWh or less with good prospects for reduction (over a decade) to one cent per kWh or even less” (Henson, 2010). Henson’s projections are dubious because they are largely dependent on developmental technologies which are not truly established, do not account for the cost of developing said technology, and would still rely heavily on considerable initial capital investment. The possibility of technology alleviating the extraordinary cost of space flight exists however, and while Henson’s ideas are only preliminary and theoretical, they are demonstrative of man’s innovative guile in overcoming obstacles.

III. Powering the Future: Solar Panels in Outer Space

                Photovoltaic solar panels are the most essential and critical difference maker in the effectiveness of a SBSP system. Currently solar panels are not a very efficient energy producer due to their low output of electricity compared to their cost and maintenance.  The amount of electricity a solar panel can produce depends on several key factors like the panel’s surface area, the technology of the panel employed, and the duration of exposure to sunlight. Photovoltaic solar panel’s energy efficiency ranges on average from 10 to 40% (Martin et al, 2010). Recent research into graphene based solar panels has proven potential efficiency ratings of approximately 60% (Bilal, 2015). While graphene based solar panels are not a proven technology and are still developmental, this example illustrates the inventive nature of scientists researching photovoltaics. Graphene solar panels may not be the future of solar cell technology, but due to the large scale employment of solar arrays on the ground, we can expect solar panel efficiencies to only improve with time, proportionate with their utility. For the purposes of this paper, a minimum of 30% efficiency is assumed.

Weight is a critical factor regardless of the solar panel used. Panels weigh on average anywhere from 15kg to 30kg, or roughly 30 to 60 lbs. depending on size (ENF, 2015). For the purposes of this paper a solar panel of median weight of 45lbs. is used. A theoretical solar panel with the dimensions depicted in Figure 2 has a total surface area of 40.9ft², or 3.8m². Assuming ideal exposure, depicted in figure 3, a single panel of the aforementioned dimensions with a 30% efficiency rating is capable of producing 1558.3 watts of electricity (Figure 3.). The total amount of received solar radiation to such a panel equates to 5194.6 watts. 30% efficiency results in a loss of 3636.3 watts, leaving markedly high margin for improvement in this area. A theoretical graphene solar panel, providing the overcoming of its many design hurdles and cost, with the previously mentioned 60% efficiency rating, would be capable of producing 3116.76 watts.

There are a few options for collecting solar power from orbit, all of which heavily depend on the advancement of wireless power transmission (WPT) technologies. The progress of WPT technology will greatly influence the design of a SBSP station. The design of a SBSP station would likely have the WPT system as its central architectural feature with solar panels built around the WPT device. Several smaller satellites, each containing an onboard WPT system could be utilized; alternatively a single WPT device could be employed with several appendages housing an array of solar panels. The former places an emphasis on WPT technology, and the ability to control a large group of GSO power satellites and maintain signal strength to a terrestrial receiver. The latter would require a large WPT device and result in a massive orbital structure more exposed to the dangers of outer space such as micrometeoroids and space debris.  Regardless of the method employed the effectiveness of a SBSP system will be heavily dependent on the method of WPT employed.

1. Method of Delivery: Microwave Power Transmission

The great Nikola Tesla, partial father of man’s mastery of electrical generation, celebrated inventor, engineer, and thinker envisioned a future where humankind would fulfill all of its energy needs by drawing power wirelessly from source to receiver (Lumpkins, 2013). Tesla was among the first to pursue the study of wireless power transmission, and in the early 1900s designed and built Wardenclyffe Tower, a powerful radio tower that was designed to be capable of energy transmission. Though Wardenclyffe Tower was ultimately abandoned due to “financial panic” it is an early example of Tesla’s experimentation with WPT (Roguin, 2004).  It wasn’t until 1968 that the next major breakthrough would be made by electrical engineer William C. Brown. Brown received a patent for the “microwave to DC converter” in 1969 (Brown et al, 1969). Brown’s original microwave power converter works by converting microwaves into a direct current electrical charge via a rectifying antenna, or rectenna, and is credited with developing the first WPT system (Brown et al, 1969).

SBSP would require the electromagnetic energy from the sun to be first converted into direct current electrical energy by photovoltaic solar panels, and then transmitted from geosynchronous orbit through the use of microwaves to a rectenna on the Earth’s surface, where it is then converted from direct to alternating current for use. The major problem with this model in regards to achievability is the amount of transmission loss the signal is subjected to throughout the process. When William C. Brown developed his WPT system it operated with 26% efficiency (Brown, 1984). The prototype system Brown produced in 1968 has been improved upon recently by researchers in Japan. As reported by Evan Ackerman of the Institute of Electrical and Electronic Engineers (IEEE), in March of 2015:

JAXA was able to deliver 1.8 kilowatts ‘with pinpoint accuracy’ to a receiving antenna (rectenna) 55            meters away using …microwaves. According to JAXA, this is the first time that anyone’s been able to             send such a high power output with this level of direction control. Also on Thursday, Mitsubishi (in      partnership with JAXA) managed to send 10 kilowatts of power over a distance of 500 meters, using larger      antennas with …an emphasis on power over precision (Ackerman, 2015).

The efficiency of that transmission was not reported; however, Japanese researchers associated with JAXA are on record in another publication from the IEEE stating that “power loss during the microwave power transmission [and] reception is expected to be less than 50%” and further “conversion efficiency from microwave to dc is expected to exceed 80% in the near future” (Sasaki, S., Tanaka, K., & Maki, K., 2013).

1. Predictions and Potential Outcomes

                 Determining an optimistic value for the cost of achieving GSO, and providing for further decreases in cost proportionate with the growth of the private space flight industry presents a challenging dilemma. Corporations such as SpaceX, and future technologies, like the Skylon Rocket from Reaction Engines Ltd., discussed in section II of this paper may improve the tremendous cost long term. In an ideal scenario, 20 to 30 years hence, space flight will be common and industrialized. Reduction in costs associated with space flight is essential to the progress of SBSP systems. The cost of space flight today is put plainly: prohibitive. Solar panels are widely available and research into their improvement is ongoing. Solar panel technology, as a feature of a SBSP system, is an area where optimism is warranted as these technologies are being continuously refined. The examples provided in section III of this paper place average energy efficiency at or near 30% with room for improvement. Microwave power transmission technology is being researched and, as discussed in section IV, currently is adjudged to be at or near 50% efficiency, with an expectant outlook of that figure reaching 80% in the near future.

So what does that break down into in the grand scheme? This paper will use the energy demand of the residential sector of the United States of America and furthermore only contributions made by fossil fuels. The United States Energy Information Administration reported residential sector energy consumption from fossil fuels to be 6.227 trillion BTU in 2014 (EIA, 2015). Broken down into a per hour figure, the result is over in 710 million BTU per hour of energy consumption; 710,844,748 BTU to be exact. 710 million BTU converts to a total demand in wattage of about 208,320,000 watts per hour.

Table 2. Surface Area required accounting for photovoltaic panel efficiency.

Efficiency:	E1: 100% (Solar Constant)	E2: 60% (Forecast)	E3: 30% (Current)
Required Panel Surface Area:	152,392 m² (1367w/m²)	254,048 m² (820.2w/m²)	508,097 m² (410.1w/m²)

 

Table 3. Surface Area required accounting for both panel efficiency and WPT System losses.

Panel Efficiency	E1	E2	E3
With 50% Transmission Loss	304,784.2 m² (683.5w/m²)	508,097 m² (410.0w/m²)	1,015,947 m² (205.05w/m²)
With 20% Transmission Loss	190,490 m² (1093.6w/m²)	317,483.5 m² (656.16w/m²)	634,967 m² (328.08w/m²)

 

The example solar panel, discussed in section III of this paper, has a surface area of 3.8m² and a total weight of 45lbs. The resulting arithmetic’s outcome is approximately 11.85 lb. per m².  Now, to calculate the cost of conveying those materials to LEO on the three launch platforms discussed in section II, using the best case scenario (E2) of 60% efficient solar panels and an 80% efficient WPT system, and worst case scenario (E3) of 30% efficient solar panels and a 50% efficient WPT system. Panel weight is a measure of the weight of the panels required for each scenario depicted in tables 2 and 3. Total represents the costs of the launch vehicle and the launch itself and does not account for the cost of the materials being transported.

Table 4. Best case: associated material transportation costs.

Launch Platform:	Skylon	Falcon 9	Falcon Heavy
Panel Weight (lbs)	3,746,305.3	3,746,305.3	3,746,305.3
Payload to LEO (lbs)	24,000	28,000	116,845
Launch Cost (USD)	$495,000,000	$511,000,000	$540,000,000
Launches Required	156	133	32
Total	$77,220,000,000	$67,963,000,000	$17,280,000,000

 

Table 4. Worst case: associated material transportation costs.

Launch Platform:	Skylon	Falcon 9	Falcon Heavy
Panel Weight (lbs)	11,988,174.6	11,988,174.6	11,988,174.6
Payload to LEO (lbs)	24,000	28,000	116,845
Launch Cost (USD)	$495,000,000	$511,000,000	$540,000,000
Launches required	499	428	102
Total	$247,005,000,000	$218,708,000,000	$55,080,000,000

 

Launch costs dramatically affect the overall cost of transportation. Until such a time when the cost of conveyance to LEO is reduced significantly, costs are extremely prohibitive. These calculations do not take into account the total weight of the remainder of the satellite required to house solar panels, or the weight of a WPT system, or the significant overhead or recurring costs to man launches and launch facilities.

Conclusion

Using an average cost of electricity of 12.5 cents per kilowatt hour, and a total energy production of 208,320 kilowatts per hour, the proprietors of this technology would stand to make around $26,000 an hour. To recoup the cost of even the best case scenario, it would take 76 years of continuous operation. This leads to the conclusion that even though we have the potential to achieve SBSP, the cost of space travel is ultimately too high to provide any reasonable return on investment. The outlook for the future of this technology is bright however, because scientists all around the globe are working to improve nearly every component of the design, and private industry is also progressing, leading to reduced costs of space flight.  A SBSP system may not exist for decades, but the pursuit of improvement and the search for clean renewable energy will ultimately lead to its success. As infrastructural hurdles are overcome, new challenges will take their place, but if humans seek to master a future absent of the effects of climate change and mass pollution these monumental endeavors must be seen to fruition. Fossil fuels are a finite resource where Sol is by contrast almost infinite. Time and innovation may author this concept born of science-fiction into humanity’s reality.

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