Section IX – Space Solar Power is America’s Unavoidable Energy Future
Just as a leap forward in technology to fossil fuels prevented an energy supply crisis in the late 1800s, America must undertake a similar leap forward in technology to circumvent the upcoming end of the age of affordable fossil fuels. With no suitable terrestrial options available at this time, we must turn to the one truly sustainable energy source—our sun. However, with the impracticality of harvesting sufficient solar energy at ground level being apparent, the technological course of action to pursue is space-based solar power or, simply, space solar power. In space at Earth’s geostationary orbit, sunshine is nearly continuous.
While there are several approaches to implementing space solar power, the baseline approach is to undertake this in geostationary orbit. Geostationary orbit or GEO is, as shown in Fig. 27, a circular Earth orbit about 26,000 miles above the Earth’s equator. A satellite located in this specific orbit will circle the Earth once every day making it appear stationary in the sky. Thus, just as it is the ideal location for broadcasting television signals to Earth receivers, it is also a good location for a satellite that transmits electrical power to the surface to supply terrestrial power grids.
A. About 50,000 sq. mi. of land would enable the United States to use space solar power
Invented in 1968 and studied extensively in the 1970s and 1980s—almost two generations ago—one concept for a space solar power satellite is shown in Fig. 28. In this illustration, sunlight (yellow) is reflected by arrays of circular mirrors onto two circular arrays of photovoltaic panels. These panels generate electricity that powers a transmitter to transmit the electrical power to the receiver site on the ground. With the exception of only a few short periods each year, the sunlight is continuous, meaning that the power transmitted to the ground is continuous and suitable for baseload power much as that supplied by nuclear and coal power plants. Each solar power satellite (SPS) would transmit between 5 and 10 GW if it is based in GEO (5 GW is used in this example).
The author estimates that 1.7 sq. mi. of solar mirrors or direct collector area would be needed to yield 1 GW of power output from the ground receiver site. Recall from the nuclear power example, the U.S. 2100 energy need would be met by 6,505 GW of continuous power. Hence, at 5 GW from each solar power satellite, the United States would need about 1,301 solar power satellites operating in 2100—the rest of the world perhaps 6X more. With each satellite requiring about 8.5 sq. mi. of solar mirrors or collectors, a total of 11,059 sq. mi. of mirrors or collectors would be needed in GEO. Is there enough room in GEO? Yes. The circumference of GEO is about 165,000 miles. Nature, once again it would seem, has given humanity the source of the energy it needs just as the T needed to harness this energy becomes available.
6,505 GW needed in 2100 ÷ 5 GW per satellite = 1,301 solar power satellites
6,505 GW needed in 2100 x 1.7 sq. mi. per GW
= 11,059 sq. mi. of collector in GEO
In the baseline space solar power design studied in the 1970s and 1980s, the electrical power is transmitted to the ground receiving site as microwave energy. This means that the ground receiver is not photovoltaic arrays but radio antennas. The frequency of the microwaves is primarily governed by the transparency of the atmosphere to the microwave energy. With this fact, combined with the distance the power is transmitted and the peak power level to be permitted at the ground receiver, the size of the ground receiving antenna can be computed.
Figure 29 illustrates the size of a ground receiving site producing 5 GW of baseload power. The immediate area occupied is 37.5 sq. mi. The site produces about 0.133 GW/sq. mi. The transmitted power is at its maximum at the center of the ellipse. There the power level is about one fourth of sunlight at noon on a clear summer day. The power level tapers off to near zero at the boundary of the site, consistent with federal regulations. As with other industrial facilities, the site would be fenced off out to a distance of a mile or so to keep the public from any potential harm. That land would be suitable for farming. In sparsely populated locations, such a fence may not be needed.
The 6,505 GW of baseload electrical power needed in 2100 would require about 50,000 sq. mi. of land for the space solar power receiver sites. This is illustrated in Fig. 30 compared to the net land area estimated to be needed for ground solar and wind. The difference is striking.
6,505 GW of electrical power in 2100 x 7.5 sq. mi. per GW
= 48,788 sq. mi. of SSP receiver sites
Recall that the advanced ground solar farms would likely yield in the ballpark of 123 GWh of variable solar electricity per sq. mi. per year. Wind farms will yield about 46 GWh of variable wind electricity per sq. mi. per year. Space solar power, immune to the variability of the day-night cycle and local weather, will yield an average of about 1,100 GWh of base load electricity per sq. mi. of ground receiver per year.
0.133 GW/sq. mi. x 365 days/yr. x 24 hours/day x 0.95 = 1,107 GWh/sq. mi. per year
When looking at Fig. 30, take note of the fact that these space solar power receiving sites would be spread out across most of the lower 48 states. The western states, in particular, have a great deal of open land suitable for their placement and would likely host most of the receiving sites. However, most states would be able to host some receiver sites to provide in-state baseload electrical power production.
B. A spacefaring industrial revolution is needed to undertake space-based solar power
In 1976, Gerard K. O’Neill, a professor of physics at Princeton University, released the book The High Frontier: Human Colonies in Space. He introduced the new paradigm of transforming humanity into a true human spacefaring civilization focused primarily on the construction of space solar power platforms. This book spurred tremendous public and professional interest in space solar power and the emergence of a spacefaring civilization. The key point of Dr. O’Neill’s writing was that the magnitude of effort required—in terms of in-space industrial capacity and the use of extraterrestrial natural resources for fabrication—will invariably move humanity into the Earth-Moon system in large numbers and will do so permanently.
Some will scoff at this as being unrealistic. Yet, consider the situation with aviation only a century ago and compare its technologies at the start of World War I, when aviation was barely a decade old, with where it progressed less than three generations later at the start of the jet age. Today, as you read this, there are likely several thousand commercial aircraft and a quarter million passengers in the skies above America and we don’t give it a second thought. Unthinkable a century ago; ignored today due to its commonplace part of our culture.
The Earth-Moon system by the end of this century will witness a comparable cultural transformation as America undertakes its only real current engineering-ready replacement for fossil fuels—space solar power. Human space flight will expand beyond the current meager capabilities of infrequent access to low Earth orbit to achieve routine and safe operation throughout the Earth-Moon system. In leading this transformation, America will undergo a substantial spacefaring industrial revolution—rivaling the emergence of commercial aviation—as American industry develops the industrial mastery needed to meet the challenge of replacing fossil fuels with space solar power. It should not take a genius to understand the national potential of this coming spacefaring industrial revolution. Just as aviation defined the 20th century, the 21st century will be defined by America becoming a true commercial human spacefaring nation.