My attention was caught by a recent news story about the Space Island Group, which intends to build commercial space stations for a multitude of purposes, including the manufacture of solar power satellites (SPS). The article credited SIG with the intent to supply half the world’s energy needs by capturing the sun’s power in space and beaming it to the Earths’ surface using microwaves. The article inferred that the Group believes it can capture a $1 trillion share (in today’s terms) for an initial development and launch investment of $10 billion. Given that energy demand is forecast to increase by perhaps 60% by 2030, this is not only an extremely ambitious technical target and an incredible commercial ambition. Just how realistic is the ambition and how likely are they to succeed?

First a little background on SPS, which is really necessary if we are to put the goals in context:

• An SPS installation would consist of a huge PV array in geostationary orbit linked to a microwave transmitter assembly aimed at a large area receiving antenna on Earth.

• The attractions of such an arrangement include the fact that the array would be in sunlight over 99% of the time. The SPS would be in Earth’s shadow on only a few days at the spring and fall equinoxes and, even then, for a maximum of an hour and a half late at night when power demands are at their lowest.

• The idea of beaming energy to Earth via satellite was first proposed by Peter Glaser in 1968 who was later awarded a patent. The idea itself makes sense!

• There have been investigations of the concept almost continually since then by almost every respectable authority, including the US DOE, NASA, NRC as well as the European and Japanese and these are ongoing.

So, if it has technical merit, what are the problems?

• The PV array would be much larger than any assembled yet on Earth. A 5GW array is often discussed. I we could buy this for $3/watt – which is well below current factory gate module prices – this would imply a current cost of $15 billion for the modules alone in this array. Granted mass production on this scale will make costs much lower and some thin film companies are predicting eventual system costs of $1/watt.

• Several factors may mitigate against this though:

o There are two extreme manufacturing options: manufacture the panels one Earth and ransport them into space: manufacture the systems in space from materials either obtained in space or transported from Earth.

o Current space launch rates (Shuttle) run between $3,000 and $5,000 per pound ($6,600/kg and $11,000/kg).

o To give an idea of the scale of the problem, assuming a typical solar panel mass of 20 kg per kilowatt, and without considering the mass of the support structure, antenna or significant mass reduction of focusing mirrors, a 5 GW power station would weigh about 100,000 metric tons.

o This is excessive though, as a space solar-panel would not need to support its own weight, and would not be subject to earth’s corrosive atmosphere. Very lightweight designs might achieve 1 kg/kW, or 5000 metric tons for a 5 GW station.

o This would be the equivalent of between 50 and 1000 launches to send the material to low earth orbit, where it would be turned into subassembly solar arrays, which then use ion-engine style rockets to move to geostationary orbit. With an estimated serial shuttle-based launch cost of $500 million to $800 million, total launch costs would range between $22 billion and $400 billion On top of this, would be the cost of large assembly areas in low Earth orbit and in geostationary orbit.

o Not all PV modules are suitable for space use and those most extensively tested – based on triple junction gallium arsenide cells – are much more expensive than silicon or CIGS thin film.

o The cost of the transmitter and receiving antennae will be additional to the array cost. For 5GW system using 2.45GHz radiation, a transmitter might have a diameter of 1km – in this case the receiving antennae would need to have a diameter of over 10km. Although these might be simple structures they will not be cheap!

o But let’s be optimistic – unreasonably so! Let’s assume that the panels and electronics can be manufactured for $1/watt, that transportation costs are at the low end of the estimates ($22 billion), and the antennas add only $1/watt

o This would give a total cost for a single 5GW array of $32 billion – roughly $6.40/watt, which I less than the current cost of terrestrial systems

• This 5 GW system would generate almost 40TWh/year, worth almost $2 billion at 5 cents per watt. A long payback!

• The current World electricity demand is about 1500 TWh/year and may grow to 20,000TWh/yr in 2010 and 30,000 TWh/yr in 2030. This single 5GW installation would contribute less than less than 2% of the world’s needs in 2010

I have not even tried to address seriously the problems of satisfying governments and the populace that they are not about to be “microwaved” should such a project go ahead. In truth, my perception is that there is little or no evidence that the systems as envisaged would posed any hazard to man or animal and launch costs will depend dramatically on the designed structures and the manufacturing methods. However, I see these are refinements that are not needed to decide it the postulate makes sense: to quote from the article which originally intrigues me:

“SIG is currently pursuing a $200 billion, 20-year energy purchase contract from India and/or China this year, 5% of which will cover all of SIG’s development and early launch costs. SIG’s target is to supply half the world’s electricity generation and distribution, currently a $2 trillion annual market.”

Now I have no idea what SIG envisage their “development and early launch costs “ to include, but I am forced to conclude that, realistically, $10 billion will not even cover the cost of deploying one 5GW system and see little chance that they will capture 50% of the demand in any realistic timeframe.

This all sounds as if I am completely turned off by the idea, but the opposite is true! It would need only 50 of these “power stations” to satisfy global demand in 2010 and the concept of producing vast amounts of energy in space and “beaming” the power, safely and economically, to where it is needed, is a dream worth aspiring to. I just don’t think we are going to get there in my lifetime!