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March 27, 2017



Q&A with John Perlin


UCSB physicist John Perlin’s Let it Shine: The 6,000 Year Story of Solar Energy, (New World Library, 2013) is a comprehensive look at the evolution of solar energy as a viable energy resource. Originally published in 1980 as A Golden Thread: 2,500 Years of Solar Architecture and Technology, the book has been updated in the present version. Perlin’s work offers a unique element of focus on solar energy technology.


LAW: The subtitle of Let It Shine highlights your book as a 6,000-year story of solar energy. Subtitles are important to attracting potential viewer interest, so why that particular subtitle?

JP: The subtitle was not some arbitrary date. It marks the time when the first human structures were designed and constructed according to the changing position of the sun in relationship to the earth so that the buildings maximized solar heat gain in winter and minimized it during the hotter months. Builders did this by providing the openings with an unobstructed exposure to the south and a roof extending beyond the building to keep the rays of the high summer sun from striking the building, while allowing sunlight from the low winter sun to flow underneath the overhangs and into the interior.


Climax Solar water heater ad, 1892


LAW: Why is your first lesson of solar, about knowing where the sun is, so critical to effective solar installation? It seems a no-brainer but what are the consequences of ignoring the common-sense logic of taking advantage of the sun’s flight across the horizon?

JP: Every place I do a lecture I always ask, “Where does the sun rise and set?” and always get the same unanimous reply, “The sun rises in the east and sets in the west.” In fact, as the Chinese discovered more than 5,000 years ago, the sun’s position in the relationship to the earth changes daily throughout the year. Only during the two equinoxes does the sun rise due east and sets due west. During the winter solstice the sun rises in the southeast, by noon it is directly south, and sets in the southwest. In the summer just the opposite occurs with the sun rising in the northeast and setting in the northwest. The consequences of not knowing this information can be catastrophic for living comfort in a building. If a house or building opens to the east or west it turns into an inferno in summer that can only be ameliorated by air-conditioning while becoming a refrigerator in winter necessitating a reliance on a large heating system. Building with a knowledge of where the sun actually is throughout the year, greatly reduces the need for outside heating and cooling, significantly lowering the consumption of electricity and natural gas which can be both costly and polluting.


Solar water heater in an Israeli kibbutz


LAW: You state that if a solar device is successfully designed, there is no need for any other energy source.  Please elaborate.

Rather than use the word, successfully, let us say instead, properly, and then add to designed, operated, and constructed. For example, in a properly designed solar house – built to maximize solar heat in winter and avoid in summer, if its occupants do not operate it correctly – for instance, fail to cover the windows at night with some type of insulated material, the house will not benefit as much as it could from the design. Or, for that matter, if constructed without the necessary thermal mass, a properly designed solar house will not optimally perform. The same rules apply to solar water heating; concentrators; and photovoltaics.


LAW: You note that Albert Einstein is the father of modern photovoltaic technology. Tell us about the evolution of modern photovoltaic technology.

JP: Millennia passed before it became known what light is. The greatest scientist of the nineteenth century, James Clerk Maxell, proved that light is electromagnetic radiation. Einstein, in 1905, correctly described electromagnetic radiation as a flow of discrete packets of energy he called quanta which are now known as photons, whose energy varies inversely by wavelength – that is, the shorter the wavelength the more energy the photon packs. Einstein came to this conclusion by examining the results of multiple experiments conducted during the late nineteenth and early twentieth centuries that could not be accounted for by the then-current notion that light consisted of heat and light rays bundled together.

For example, two British scientists, William Grylls Adams and Richard Evans Day, in 1875 lit a candle an inch away from several bars of selenium connected to an electrical measuring device called a galvanometer. The needle of the device reacted immediately, showing that an electrical current had been generated. Screening the flame from the selenium bars caused the needle to immediately drop to zero. These rapid responses ruled out the possibility that the heat from the candlelight had produced the current, because in such cases the needle would have risen and fallen gradually. The scientists were jubilant, assured they had discovered something never seen before, that in their words, “a current could be started [in the selenium] by the action of light alone.” Adams and Day called the new phenomenon “photoelectric.” Today it is called “photovoltaic.”

Contemporaries believed that the discovery would lead to a “scientific revolution of the first importance,” resulting in “the total extinction” of electrical power plants and “the utter repression of smoke.” Squeezing enough electricity out of selenium when exposed to sunlight for generating useful amounts of power though proved illusory. Scientists despaired. The authors of the authoritative work on the subject, Photoelectricity and Its Applications, reflected this pessimism, when writing in 1948, “It must be left to the future whether the discovery of materially more efficient cells will reopen the possibility of harnessing solar energy for useful purposes”.


Nebuhl, Switzerland, solar-powered community


LAW: Do you think that the 21st Century will see near-total, widespread adoption and further evolution of practical, user-friendly photovoltaic technology? What are triggers, what are barriers?

JP: Energy transformations take time. A little less than 200 years ago, common knowledge believed that without Nantucket whale oil, all of the world’s lights would go out and its industries would cease to function. The first petroleum discovery occurred in 1839. Yet it did become king until after the First Wold War. In 1954, less than a watt of solar cells had been installed. Today, about 200 billion watts exist worldwide. The triggers to this phenomenal growth story include the German Renewable Energy Act, the Chinese subsidizing photovoltaic manufacturing, American corporate solar electricity purchases, and so much more. Futue triggers such as inexpensive storage and mass use of electric vehicles will overwhelm any artificial barriers to pv imposed by utility companies, fossil fuel and nuclear companies and their allies in government. The photovoltaic tide, I believe, is unstoppable.


Solar-powered space satellite


LAW: What other solar-related technologies do you value?

JP: Combining solar architecture and photovoltaics really excites me. Photovoltaic overhangs protecting south-facing solarized windows would let the overhangs reduce the need for air conditioning in summer and also power whatever cooling needs remained while the south-facing solarized windows would let sunlight pour into the building in winter providing heat and supplying electricity to heating equipment to cover the remaining load. Another possible combo – photovoltaic and solar hot water panels in the same install. The pv supplements the solar hot water supply by powering heat pumps and the heat removed by the solar hot water panels cools the pv panels down so they generate more electricity.

 John Perlin can be reached at: johnperlin@physics.ucsb.edu // ‪(805) 453-8814.