“The supply of coal and oil, [Frank Shuman] opined, would eventually be depleted. ‘One thing I feel sure of,’ he wrote prophetically in a 1914 Scientific American article, ‘is that the human race must finally utilize direct sun power or revert to barbarism.’”
Energy history brings perspective and caution to the real-world prospects of dilute, intermittent energies becoming 21st century mainstays. The wisdom of history also checks the notion that solar (and wind) are infant industries in need of ‘temporary’ government subsidies. 
I recently encountered a history piece about an early solar entrepreneur, Frank Shuman, written by Christopher Dougherty nine years ago for a Philadelphia magazine. Excerpts from Frank Shuman: Finding The Future In Tacony, A Century Ago follow.
Nearly a century ago, Philadelphia solar energy pioneer Frank Shuman toiled in obscurity, dreaming–and building–a solar powered device he felt would change the way the world made energy and did work…. Shuman’s “Sun Engine” is a poignant reminder that while humanity has been slow to reduce our greenhouse gas emissions, we have certainly not lacked the technology, or foresight, to do so. On the expansive lawn between an ivy-covered house and workshop at Disston and Ditman Streets, Shuman integrated his deep knowledge of glass, optics, and convection heating to create a powerful array capable of doing actual work.
Shuman, a consummate inventor with 64 patents to his name, closely followed international developments in solar power. In 1906, he set the controls for the heat of the sun … he insulated boxes, built semi-convex reflectors around them to concentrate the sun’s rays, put them on swivels to follow the sun’s track, placed his water in a vacuum to lower its boiling point and—in a major breakthrough—attached a low pressure steam engine to the array.
In the early 20th Century, Philadelphia was an unlikely seat of solar technology; arguably for most of the 19th Century, the city was an R&D hub for fossil fuel utilization as well as a primary consumer of coal and producer of refined oil products. Beginning in the early part of the 19th Century the two seats of scientific wisdom, the American Philosophical Society and Franklin Institute popularized new techniques and methods of burning the ever-abundant anthracite coal….
For Shuman, to fail to embrace solar power was to invite social calamity. The problem was simply mathematical: there are finite resources like coal and oil whereas the sun’s power was infinite. The supply of coal and oil, he opined, would eventually be depleted. “One thing I feel sure of,” he wrote prophetically in a 1914 Scientific American article, “is that the human race must finally utilize direct sun power or revert to barbarism.”
Based on the output of his device, he reasoned that an array covering 20,250 square miles in an unpopulated portion of Africa’s Sahara Desert would produce the same amount of energy as all of the coal mined in 1909. Displaying an understanding of the social value of solar, he urged “…all far-sighted engineers and inventors to work in this direction” not only for their own profit but “the eternal welfare of the human race’.”
Frederick Blount Warren, writing for Technical World Magazine in 1907 after a visit to Tacony, was more expansive in tabulating the benefits of solar:
And now, suppose a moment is given to contemplation of the changes that will have been wrought when solar-power has been developed as fully as the steam engine is at the present time… Mankind might then begin to receive its birthright of an uncontaminated atmosphere, health and purity would once more find a foothold in the constitutions of future generations….
Engineering News profiled Shuman in 1909, Nature magazine did so in 1912, and in a 1911 feature, the New York Times proclaimed [a] “Method to Harness the Sun is Found; Engineer says that Frank Shuman of Philadelphia has solved the problem.” ….
Hope springs eternal. The notion that the sun’s energy can be converted into electricity because it is just there to be concentrated is naivete. There is such a thing as physics to explain how the sun’s work over the ages has created a dense, reliable stock of potential energy versus a dilute, intermittent flow from the sun.
 As Milton and Rose Friedman warned: “The infant industry argument is a smoke screen. The so-called infants never grow up.” Free to Choose (1979), pp. 5–6.