The primary challenge for space solar power towers is economics. Over half the cost of current SBSP systems is associated with launch costs. To reduce launch costs the size of the SBSP system must be reduced. In order for SBSP concepts to become an economically viable source of clean energy, it is necessary to lower the SPS satellite’s mass and size to the point that it can be launched into working orbit with currently available commercial launch vehicles – and without requiring any on-orbit astronaut assembly or unnecessary infrastructure. This is only possible by designing a smaller, yet more efficient, SPS system that would operate in an orbit closer to Earth.

Looking at the NASA 1980s SBSP reference models, there are actually two, the first NASA base line model uses silicon photovoltaic cells at 16.5 percent efficiency and has a mass of 51,000,000kg and the second model uses higher efficiency gallium aluminum arsenide photovoltaic cells at 20 percent efficiency and 2x solar concentration and has a mass of mass 34,000,000kg. The second model is has only 66.6 percent the mass of the first model. Both models provide 5gw of power and the transmitter is the same size on both models because the amount of power being transmitted is the same and the satellite location in GEO is the same. The second model is clearly more efficient in power production and has less mass to orbit which means lower launch cost so let’s use it for comparison.

Improvements in photovoltaic (PV) technology can reduce the mass to orbit needed to construct SBSP satellites. The NASA 1980 reference model had a mass of 34,000,000kg. Of this 20,618,000kg was for the photovoltaic cells and supporting structure and 13,382,000kg were for the transmitter. With improved PV cells operating at 40 percent efficiency the power production component of the satellite can be reduced by 50 percent, which would reduce the satellites mass by 10,309,000kg. This would be a reduction in satellite mass of 30.2 percent.

There have been a number of studies on the economics of based space solar power; however, these studies have always focused on locating the solar power satellite in GEO. Medium Earth Orbits and Low Earth Orbits are sometimes mentioned in these studies but the discussion always focuses on GEO. This is interesting because the limitation on successful deployment of SBSP systems has always been limited by the mass to orbit problem, a problem which can be solved by MEO and LEO satellite positioning. It has been known since at least 1980 (J. Drummond, 1980) that positioning the power satellite in a lower orbit would reduce the mass of the satellite transmitter by an “order of magnitude”. Since the transmitter makes up a large part of SBSP satellite mass a 90 percent reduction in transmitter mass would seem to be very beneficial.

We see that the transmitter in these models is 1 km in diameter and its mass is estimated at 13,382,000kg. If we reduce this by “an order of magnitude” or 90% by moving the SBSP satellite into LEO, as suggested by Drummond in 1980, the mass savings would be 12,043,800kg. This is 12 million kilograms you don’t have to launch into space and a 35.4 percent reduction in Solar Satellite mass. If the satellite where to use 40 percent efficient PV cells, which reduced the mass to 23,691,000kg and we moved the satellite into low Earth orbit (LEO), which would reduce the mass even more to 11,647,200kg, the amount of mass launched into orbit would be reduced by 22,352,800kg or 65.7 percent.

Molly Macauley states “To the surprise of many naysayers, there is evidence of positive value of SSP but the savings do not appear large enough for it to be competitive” (Macauley, 2009) and this is referring to GEO SBSP. What if the mass of SBSP systems could be substantially reduced by 90 percent? It has be shown that the transmitter mass can be reduced by an “order of magnitude” by moving the satellite to a lower orbit, but what about the power production part of the system?

If the SBSP Satellite uses solar concentration at 2,000 suns we can also reduce the power system component by an order of magnitude or 90% (IBM, 2008). The satellite mass is 34,000,000kg less transmitter mass of 13,382,000kg giving a power component mass of 20,618,000kg multiplied by .1 for an order of magnitude reduction gives 2,061,800kg. Adding the power component at 2,061,800kg to the reduced mass transmitter at 1,338,200 gives a total of 3,400,000kg for a 5gw SBSP Satellite verse 34,000,000kg for the NASA GEO model at x2 concentration. We have now reduced the total mass to orbit for an SBSP Satellite by 90%. Note that moving the transmitter closer also reduces the ground receiver (rectenna) by 90%.

A 3.4 million kg satellite is still very large so let’s break it up into smaller pieces. There are five existing or very near term launch vehicles that can lift 20,000kg into orbit. These are the Delta IV Heavy, Atlas V Heavy, Ariane 5, Proton and the Falcon IX Heavy. So, let’s break the satellite into smaller 20,000kg satellites. Taking the 5gw Satellite with a mass of 3,400,000kg and breaking it into smaller 20,000kg Satellites would give us 170 small satellites that can be launched on existing or very near term launch vehicles. Each satellite would produce 29,411,764mw of energy (5gw / 170).

The cost to launch these 170 satellites using the lowest cost launch available today, which would be the Proton, is estimated at $100,000,000 each for a total of $17,000,000,000. We can see that SBSP is a major enabling technology for launch vehicles.

“The technological hurdles remain large as well. For example, in order to collect enough solar energy so as to have a large amount after beaming it the huge distance from the sun to earth (depending on the efficiency of solar cells and transmission frequencies,  energy is lost en route), the transmitting antennas have to be truly enormous. Their size requires multiple rocket launches and an as-yet fully developed ability to robotically assemble the array of antennas in space. The receiving antennas on the ground must also be large, covering hundreds of acres, and are likely to encounter not-in-my-backyard concerns.” (Macauley, 2009) I have proven that this need not be the case and that by using the latest available technology and locating the SBSP Satellite in LEO you remove the need for all the unnecessary supporting infrastructure of past SBSP concepts. The mass of the transmitter is reduced by an order of magnitude as was pointed out by Drummond way back in 1980 and the satellites can be launched on existing launch vehicles.

“What did our findings suggest?  SSP could be competitive under the very stringent assumptions we have described, but is not likely to be the most cost-effective source of green power.” (Macauley, 2009) This is an interesting assumption since it is clearly not true. But this is what happens when you analyze the wrong strategy. It is further stated “The possible cost advantages of SSP range from $27 million to $100 million, assuming that there are penalties for the externalities of competing technologies and rapid adoption of fully reliable SSP. In all locations, however, and even with the cards stacked for SSP, its mean estimated benefits are on average an order of magnitude less than other types of renewable energy, particularly wind and biomass.” (Macauley, 2009) When you consider the incentives and infrastructure cost to develop other renewable energy sources, such as wind and biomass, SBSP can actually beat them hands down if the right strategy is used. For example in Texas wind energy is produced at approximately 5 cents per kwh, but this is a subsidized cost. Without the taxpayer subsidy the cost would be 7 cents per kwh. We also find that there is a new infrastructure cost to move this power to major markets in Dallas and Houston. This cost is estimated to $5 billion and is funded in the form of a tax at $4 per month on everyone’s electric bill. Additionally we find that in Texas all power producers are guaranteed the highest price so if a gas-fired plant comes on line at 20 cents per kwh the wind producer gets that price as well and this is where the real wind profits come from. So, what is the true price for wind energy in Texas? This is not an argument about wind power good, bad or otherwise, it is just pointing out that wind powers true costs and those of other forms of energy both conventional and alternative need to be real cost estimates. Those estimates when put head to head with SBSP in LEO will place SBSP out in front of the pack.

When you consider that all of the alternative energy sources combined including wind, biomass, ground solar, etc., together cannot meet current energy demand and certainly not future energy demand what other “green” option is there? SBSP has the potential to supply sufficient clean and zero emission power not only for Earth but for off Earth colonies as well. No other near term power source has that potential. The US Department of Energy invested zero funds into this potential energy source but approved over $4.6 billion for “clean coal”. (Feldman, 2009) The European Union is spending some $140 annually on alternative energy via cap and trade and in 2010 spent zero on SBSP development. (Kanter, 2010)

The chicken and egg problem often discussed when considering space development can be solved by simply investing in some chickens (space assets). The idea that we could produce eggs (cheaper launch vehicles) without them was always flawed, because there are no existing markets for such vehicles. The focus of space development should be on finding the lowest cost of entry into sustainable and profitable space markets and let that drive launch vehicle development. NASA has long sought taxpayer funding to build hen houses (space infrastructure) but has not invested in any hens (space markets) and this is why it could never justify hen house development and has had its programs cancelled one after the other (Ares 1, Ares 5, OSP, SLI, etc., etc.). It is also the reason we will see thousands of NASA workers being laid off and some $12 billion in launch vehicle infrastructure that will rust away at the Cape because NASA cannot justify the investment in new Heavy Lift Launch Vehicle (HLLV). In 2010 NASA invested zero funds into SBSP. It may be time for NASA to realize that space exploration alone is no longer enough to justify massive launch vehicle investment and that it needs new space markets to help carry some of the burden. This is also true for the “New Space” companies such as SpaceX wanting to build new rockets. They need new space markets like SBSP more than NASA does. My point is that a targeted investment in SBSP technology could get us a lot of chickens.

References:

Molly Macauley and Jhih-Shyang Shih, The Economics of New Green Technology Investment:  The Case of Satellite Solar Power, February 23, 2009

J. Drummon, Power Conversion Technology, Inc.,Comparison of Low Earth Orbit and Geosynchronous Earth Orbit, 1980 part of the Satellite Power System Concept Development and Evaluation Program. DOE and NASA from 1977 to 1981.

KANTER, JAMES, The New York Times, In Europe, Companies Work the Angles on the Carbon Trade, Published: October 10, 2010

IBM, 2008, Research Unveils Breakthrough In Solar Farm Technology “Liquid Metal” at the Center of IBM Innovation to Significantly Reduce Cost of Concentrator Photovoltaic Cells, http://www-03.ibm.com/press/us/en/pressrelease/24203.wss

Feldman, Stacy. Solve Climate News, Canada Dumps Vital Renewable Energy Incentives for “Clean” Coal, Feb 3, 2009