a century later by one of the leading technologists in the industry today.
“Einstein,” he said, “explained it all.”3
SOLAR CELLS
Today, while wind has captured much more investment, no part of the renewable industry is attracting as much research focus as the quest to directly harness the power of the sun—especially photovoltaic cells, or PV, otherwise known as solar cells.
In many ways solar cells represent the purest ideal for renewable technologies. Sunlight is an abundant resource in almost all corners of the earth. Once the cells are made, there are no complex industrial facilities to operate. Cells—a basic system that can go on the roof of a house—can be installed in a matter of hours. They don’t necessarily even need any transmission lines. Just the direct conversion of sunlight into electricity.
This transformation may sound like the type of feat that alchemists in the Middle Ages claimed to accomplish—the “great work” of transmuting base metals into gold. But unlike the magic of the Middle Age wizards, this modern alchemy is real: light penetrates a surface and emerges as electricity. It is fundamental physics. That was Einstein’s great insight.
Though the market for PV has seen enormous growth since the mid-2000s, it is still much smaller than that of wind. Yet nothing else across the renewables spectrum generates such high expectations as the potential of directly harnessing the power of the sun—especially for PV. And with good reason. It saves hundreds of millions of years—about the time it can take for organic matter to be transformed into fossil fuels. There is conviction that, in the words of MIT physicist Ernest Moniz, solar energy will eventually be the “tallest pole in the tent”—the ultimate source of electric power. But when? And will photovoltaics fundamentally transform our entire electric power system? Will this system shift from a network of generating stations and wires to one where every house and office building is a mini–power plant, generating its own electricity, without coal, natural gas, nuclear power, or even wind? Or will, instead, a new kind of power plant become commonplace, where the dispatched electricity is generated from solar panels ?4
FROM LIGHT TO ELECTRICITY
Generalized diagram of a solar photovoltaic cell
Source: U.S. Department of Energy
Whatever the path, one obstacle that stands in the way is scale. To get to scale—to proliferate across the rooftops of the world—requires the conquest of costs. And that depends upon further innovation. Costs may be coming down, but they are still higher than competitive sources of generation. Mass production has not yet brought costs down to what is required for true scale.
Where PV are competitive is where there is no established infrastructure of wires delivering electricity, such as in outer space or remote jungle villages, and they may also be competitive when power prices are high and the solar resources are strong. Otherwise they need significant government support and subsidies. In Germany, the country that did much to transform solar cells from a small niche into a substantial business, those price supports have been at levels as much as five times the cost of conventional electricity. But the whole weight of the industry is concentrated on that single goal—bringing costs down further.
“THOROUGH INVESTIGATION”
Well before Einstein had put pen to paper in 1905, earlier scientists and engineers had already observed the photoelectric effect—that in some circumstances light could produce an electric charge—but they just could not explain it. A few scientists and engineers worked with the element selenium, producing electric current by exposure to sunlight, and even candlelight. Werner Siemens, the founder of the Siemens engineering company, proclaimed that “the direct conversion” of the “energy of light into electrical energy was an entirely new physical phenomenon” that required “thorough investigation.” It was left to Einstein to explain the why.5
Until that time, physicists insisted that light was a wave moving through the ether—an invisible substance that supposedly suffused the universe. Einstein thought otherwise. Light, he said in his paper on the photovoltaic effect, was made up of tiny particles called quanta, also known as photons, that moved at 186,000 miles per second and were indivisible.
It was this paper that established the science that explained photovoltaic reactions. When sunlight descends on solar photovoltaic cells, the photons are absorbed. They dislodge and displace electrons within the semiconductor. These loose electrons flow out of the silicon along minute channels—almost like water flowing through a canal—as electric current. The photons are one form of energy, and the elections another form.
Einstein received the Nobel Prize in 1922 not for the paper that