John Mankins - The Case for Space Solar Power

There is not the slightest indication that nuclear energywill ever be obtainable. It would mean that the atom would have to be shatteredat will.

Albert Einstein (1934)

Reliable and affordable energy is fundamental to our globalsociety. It is only through the availability of vast amounts of cheap energy largely from fossil fuels that the worlds population grew fromless than one billion in 1800 to more than seven billion in 2013. Most of thatenergy is used in the form of electricity, with most of that electricity generatedthrough the burning of coal. As the worlds economy has grown over the pastthree decades raising the quality of life in China, India, and manyother countries the need has become all the more urgent to increase theenergy available for industry, transportation, for heating and cooling, forpersonal use, and so on. Just before the beginning of the economic crisis in2008, this soaring demand resulted in drastic increases in the prices of mostconventional sources of energy. In addition, during the past several decadesconcerns have emerged that societys overwhelming dependence on fossil fuels isdriving other kinds of change: growth in atmospheric concentrations ofgreenhouse gases (such as carbon dioxide and methane) and increases in averageglobal temperatures. If left unchecked, most scientists now believe thatincreasing concentrations of greenhouse gases in the atmosphere will alter theglobal climate by the end of this century, with sweeping impacts on societiesacross the globe.

As a result, there is great interest in finding new, moresustainable alternatives to fossil fuel-based energy supplies. Of thenon-fossil fuel alternatives that exist hydroelectric power, nuclearpower, wind power, wave energy and others one of the most accessibleand intuitively attractive is solar power. However, despite significantadvances in performance, reductions in cost, and dramatic growth in the totaldeployed capacity in recent years, ground-based solar power remains largely aniche technology, providing only a small portion of societys energy needs.

Fortunately, there is a promising alternative toconventional ground-based solar power systems, albeit one that is a relativelyunknown: Space Solar Power.

The energy in the sunlight found in space near Earth is considerablygreater than that which remains in sunshine after it passes through theatmosphere, even on a clear day. In fact, the power intensity of sunlight inspace is about 1,368 watts per square meter, as compared to only about 1,000watts/m2 at noon on a clear day near the equator a drop ofabout twenty-seven percent (27%). Figure 1-1 presents thedifference between sunlight on Earth and in space, illustrating thehour-by-hour daily solar energy at geostationary Earth orbit (GEO) andcomparing it to the average solar energy at a typical location at around 30north latitude on Earth (in this case, a location such as central Texas in theU.S.) in June and in December.

This initial attenuation of sunlight is compounded byadditional factors: the day-night cycle, a reduction averaging roughly sixtypercent (60%); changes in the available sunlight due to the weather, areduction of twenty percent (20%) for light clouds, but up to seventy-to-eightypercent (70%-80%) for heavy clouds; and changes due to the seasons, of up tosixty percent (60%) or more, depending on the latitude of the site. Thecombination of these factors results in the available solar energy in space ataround GEO or above being about ten times greater than the best averageavailable at most locations on Earth.