Recently a colleague met Dr. Richard Swanson at a social occasion at Stanford and mentioned the StratoSolar concept to him. Dr. Swanson told him it was an old idea that had been described in a paper written by William R. Cherry in 1970. Dr. Swanson kindly forwarded a copy of the paper. Lo and behold the paper describes a concept remarkably like StratoSolar that discusses the major engineering challenges in detail. A pdf file of the paper is attached to this post.
I think that Dr. Swanson is probably the only person on the planet who remembers this paper which stems from the very early years of PV. William R. Cherry was a distinguished pioneer of PV and the prestigious Cherry award is named after him. Dr. Swanson himself is a world-renowned figure in the PV arena and the source of the famous “Swanson’s Law”.
To me, this nearly fifty-year-old paper is a validation of the StratoSolar concept from a well-respected source. I only wish we had found it sooner, though I have still not found the paper online, only the copy sent to me by Dr. Swanson. Human nature is naturally distrustful of ideas with no apparent historical precedent which goes some way to explaining the unwillingness to evaluate StratoSolar.
In 1970 PV was only used in space applications. It cost hundreds of dollars per watt compared to today’s cost of about $0.35/W. William Cherry was a visionary who contemplated the future of PV and examined space based, stratosphere, and terrestrial concepts as this later 1971 paper shows.
The Cherry paper from the 1970 Proceedings of the 8th IEEE Photovoltaics Specialists Conference describes a “floating mattress” system that is 1 mile by 1 mile and 100 ft deep floating at 50,000ft and higher in the stratosphere. Its cross braced rigid cubic structure is remarkably like StratoSolar. Its gas bags are polyethylene which was and still is the standard gas bag material, though better materials are now available. The tethers described use steel and taper from 3/8in diameter at the bottom to 3/4in. at the top. This would still be practical, but Kevlar and UHMWPE are better choices today. There are references to Goodyear for the tether and buoyancy calculations. The overall system plus tethers weighed around 10,000 tons, which is not far from what a similar sized StratoSolar system weighs. PV efficiencies have improved from the 7% in 1970 to over 20% today, so a same sized StratoSolar array would now generate three times the power.
The system could have been constructed in 1970 but the PV technology was then hundreds of times too expensive. The concept was too far ahead of its time and was forgotten. William Cherry died in 1980.
Today’s improved technologies make the concept viable and its inherent advantages of no long duration intermittency from weather and dramatically increased energy over PV on the ground make it potentially the cheapest source of energy on the planet, far cheaper than fossil fuels and available to all regardless of geographic location.
By Edmund Kelly