Seven Elements That Have Changed the World (29 page)

Silicon opened the heavens beyond the natural limitations of the eye. The further we saw, the further we wanted to see. Galileo’s invention started a drive to build ever more powerful telescopes. By the middle of the seventeenth century, wealthy astronomers were building telescopes up to 50 metres in length, requiring a system of masts and pulleys for operation. The greater length of telescopes was one way of overcoming the blurring of the image which resulted from the curvature of the lens.
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In these ‘refracting telescopes’, different colours of light were bent by a different amount as they passed through the lens, producing an unclear image. Isaac Newton overcame this problem by inventing a ‘reflecting telescope’ that used mirrors rather than lenses. The mirrors reflected each part of the incoming light in the same way, regardless of its colour, so that a clear image was produced. To Newton, his telescope was further proof that white light is composed of a spectrum of colours.

Even when very large mirrors were used, the image produced remained clear. And the bigger the mirror, the further the telescope could see. Eighteenth-century astronomer William Herschel took this principle to
extreme lengths.
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He did more than any astronomer to improve the power of reflecting telescopes, extending our view of the Universe far outside the Solar System. ‘The great end in view,’ he wrote to Sir Joseph Banks, President of the Royal Society, ‘is to increase what I have called “The Power of Extending into Space … ”’
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By grinding and polishing larger and larger mirrors, Herschel was eventually able to resolve starry pinpricks of light into diffuse objects.
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Some of these ‘nebulae’ were later shown to be galaxies akin to the Milky Way. Reflecting telescopes have grown in size ever since: from the two-and-a-half-metre circumference mirror in the Hooker telescope on Mount Wilson in 1917, to the five-metre Hale telescope on Palomar Mountain in 1948. Today, telescopes, with mirrors of more than 10 metres, sit high on mountains in the Canaries and Hawaiian islands, recording the night sky around us with unprecedented accuracy.

Photons not only carry information about the stars from which they originated, they also carry energy. Long before the invention of the telescope, mirrors were used to capture and concentrate the light energy emitted from our own star, the Sun.

In the middle of the seventeenth century, Father Athanasius Kircher, a Jesuit scholar, positioned five mirrors so as to direct sunlight on to a target 30 metres away. The heat produced was so intense that his assistant could not comfortably stand at the target. ‘What terrible phenomena might be produced,’ Kircher wondered, ‘if a thousand mirrors were so employed!’
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Kircher would probably have been familiar with the legend of Archimedes’ burning mirrors. At the start of the third century
BC,
as the Roman ships of General Marcellus advanced towards Syracuse, Archimedes directed his soldiers to raise and tilt their reflective shields towards the armada. The result was dramatic; the concentration of heat was so intense that the ships were set alight. Burning mirrors were among a large armoury of imaginative inventions that Archimedes deployed to defend Syracuse against the Romans. With his knowledge of geometry, Archimedes could calculate how to focus light rays and also aim projectiles to destroy the enemy’s ships before they could get close enough to land to do damage.
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In his sixteenth-century book
Pirotechnia
, Vannoccio Biringuccio recalls a conversation with a friend who had created a mirror almost 70 centimetres across. One day, while watching an army review in the German city of Ulm, the man entertained himself by using his mirror to direct sunlight on to the shoulder armour of one soldier, creating so much heat that ‘it became almost unbearable to the soldier … so that it kindled his jacket underneath and burned it for him, cooking his flesh to his very great torment’.
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In the sixteenth century, Leonardo da Vinci designed some novel peacetime applications for the sun’s rays. Ambitious as always, Leonardo planned to build a six-kilometre-wide concave mirror that would focus sunlight on to a central pole to heat water or melt metals.
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As with so many of his inventions, this particular monstrous device never made it beyond his sketchbook. It was not until the Industrial Revolution in Great Britain that glass and mirror constructions were possible on a bigger, but not quite Leonardo, scale. In his later years, Henry Bessemer built a solar furnace for the smelting of metals. Inside a 10-metre-high tower, a reflector directed sunlight on to a four-square-metre concave mirror in the roof. This focused the light through a lens at the bottom of a tower and into a crucible. He managed to melt copper and vaporise zinc in this furnace, but it was not very efficient and cost a great deal to build. After some years, even Bessemer ‘became disheartened, and abandoned the solar furnace’.
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Across the Atlantic in Philadelphia, an American inventor, Frank Shuman, turned his attention to the problem of concentrating solar power. At the turn of the twentieth century, using the heat-trapping properties of glass, he raised the temperature of water in something he called his solar hot box to just below boiling point, even when there was snow on the ground.
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‘I am sure it will be an entire success in all dry tropical countries,’ he wrote. ‘It would be a success here on any sunshiny day; but you know how the weather has been.’
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In Egypt, where the weather was rather more reliable, his solar hot boxes powered steam engines used to pump water for irrigation. Another inventor, Aubrey Eneas, built a series of giant cone reflectors, some over 65 square metres in area, to collect solar radiation in the intensely sunny states of California and Arizona. Eneas was also inspired by the parabolic trough reflectors invented by John Ericsson,
the Swedish-American engineer who built the
Monitor
ironclad during the American Civil War, but who also devoted the last twenty years of his life to building solar machines. Both Bessemer and Ericsson, pioneers in the production and use of iron, were concerned that the coal supplies they used to smelt iron ore and power steam engines would run out, and so they sought alternative sources of energy. Eneas’s plan was to provide a cheap energy source for those living in the desert, far from traditional coal supplies. By increasing the scale of their systems, both inventors had hoped to produce cheaper solar power; but even at scale, these concentrated solar power systems could not provide electricity which was competitive with that generated from conventional sources. And that remains the case today. On the arid plains near Fuentes de Andalucía, Spain, there are more than 2,500 mirrors, each with an area of 120 square metres, directing sunlight towards a tower placed at their centre. In the tower, molten salt is heated to almost 600 degrees centigrade. The molten salt can be stored in tanks until it is needed, when it can be used to drive steam turbines and generate electricity. But without very large subsidies, even this modern plant is uncompetitive.

Solar power was forgotten until shortly after the Second World War, when scientists at Bell Laboratories in New York began to investigate some unusual electrical properties of silicon. The research of Gerald Pearson, Daryl Chapin and Calvin Fuller led, in 1954, to the creation of the first silicon photovoltaic cell.

Daryl Chapin had been tasked by Bell Laboratories with developing a new portable power source which would power their telephone systems in tropical climates, where traditional dry-cell batteries degraded quickly. He began to investigate wind machines, steam engines and solar energy as possibilities. Rather than trying to capture the Sun’s energy using mirrors and heat boxes, Chapin decided to investigate another medium for harnessing solar energy, known as the photovoltaic effect.

Alexandre-Edmond Becquerel, the father of Henri Becquerel (of radiation fame) discovered the photovoltaic effect in 1839.
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Becquerel placed
two brass plates in a conductive liquid and shone a light on them. He noticed that the light caused an electric current to flow in the solution. If this current could be used, the energy of the Sun could be harnessed.

Over a hundred years later, scientists had still only succeeded in harnessing one two-hundredths of incoming sunlight using photovoltaic cells. This did not make enough power for Chapin’s needs and so he began to search for alternatives. Word of Chapin’s work reached Gerald Pearson and Calvin Fuller, two other scientists working at Bell Labs, who were experimenting with the unusual electrical properties of silicon semiconductors. They thought the materials they had been developing could be used to create a photovoltaic cell. To their surprise, their idea not only worked but also created a photovoltaic cell that was five times better than anything else available.
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In April 1954, they announced the invention of the Bell Solar Battery, demonstrating to journalists how it would be used to power a radio transmitter. It quickly began to prove its value in providing energy to Bell’s developing markets in the tropics. Solar cells got their first big break, though, when they were used in the American Vanguard space programme in 1958. While the vehicle’s chemical batteries were rapidly depleted, the solar unit continued to function years after the launch. In satellites, solar cells had found their first major market.
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Even today, solar cells are often the most cost-effective way of generating energy for remote regions, avoiding the costly infrastructure of setting up power lines and transporting fuel. Their versatility allows them to be installed as single units in remote, energy-poor regions. In 2001, I visited Indonesia to see BP’s solar rural electrification project, at the time the fifth largest of its kind in the world. Small-scale silicon solar cell arrays were used to generate electricity for almost 40,000 homes in village communities. Electric water pumps can be used to irrigate crops and electric lighting has been brought into homes, schools and medical centres. Solar cells have also indirectly improved education and learning. As I saw, children could study not only during the day but also at night.

Unlike fossil fuels, which occur in pockets dotted about the Earth, the Sun shines everywhere. In one year, more energy reaches the Earth’s surface from the Sun than will ever be extracted from all sources of coal, oil,
natural gas and uranium. In one day, the Earth’s surface receives 130,000 times the total world demand for electricity. Despite this, solar energy still accounts for only a thousandth of total global electricity production. Part of the reason is that harnessing the energy of the Sun is notoriously inefficient. A small electric current is produced each time a photon of light is absorbed by a silicon solar cell. This is because the photon’s energy is transferred to an electron and its positive counterpart, called a ‘hole’, in the cell.
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However, while all the energy of a photon is transferred when it is absorbed, not many photons are absorbed in the first place. The photon must have just the right amount of energy for this to happen, and only a fraction of photons do. As a result, even the very best laboratory-based solar cells capture and convert only 40 per cent of the light that falls on them into electricity. The cells used in normal commercial applications convert between 10 and 20 per cent. That still makes them several times more efficient than the first solar cells, created at Bell Labs in 1954. That improvement, in the space of only sixty years, is remarkable; after billions of years of evolution, plants, which convert light into stored energy through photosynthesis, have only developed an efficiency of 3 per cent.

The greatest barrier to the success of the solar cell, however, has not been technical, but economic: solar cells have produced costly electricity because they have been expensive to manufacture. This is beginning to change as new technologies, such as using cheaper offcuts from the silicon used in chip manufacture, begin to mature. The cost of manufacturing, too, has fallen rapidly, in large part because of the economies of scale obtained by Chinese producers in China’s growing market. Nonetheless, electricity generated from solar cells has not yet reached grid parity, the point at which cells would be economically competitive with traditional non-renewable fuel sources. That point, though, is getting closer. As more solar cells are made they generally become cheaper; in 2011, manufacturing capacity increased by almost 75 per cent on top of an average annual growth rate of 45 per cent over the past decade. This continued growth will be vital in the transition to a low-carbon energy economy.
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When they announced the invention of the silicon solar cell by Bell Labs in 1954, the
New York Times
wrote that it marked ‘the beginning of a new era, leading eventually to the realization of one of mankind’s most
cherished dreams, the harnessing of the almost limitless energy of the sun for the uses of civilization’.
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That dream may become a reality, and it will be one free of emissions of greenhouse gases. There is still a long way to go before the scale of solar energy comes close to that of fossil fuels or nuclear energy, but, of all renewable energy sources, solar has so far proved itself to be the most promising.

Anchorage, Alaska, 1970: red lights were flashing wildly on the control panel. The core memory of the computer had just crashed. Back then a computer crash was literally a crash, the spinning mechanical disks grinding together to a halt. The constant restarts made running even the simplest program extremely arduous. It would be a long night. I was working as a petroleum engineer in my first real job. Because of my experiences at Cambridge University I was, in those days, one of a handful of people who knew how to make the solution of engineering problems easier by using a computer. I was working to an extreme deadline. My boss was about to go to a meeting with some very powerful men from some even more powerful US oil companies. They were to discuss how much of the giant Prudhoe Bay field each of the participating companies owned. He wanted me to find an answer and to make sure that he, from a then small company, impressed the other bigger companies with his technical prowess.