Have you ever wondered how sunlight can travel 93 million miles from the Sun to the Earth, and still have enough oomph in reserve to burn your light bulbs? That, in a nutshell, is the miracle of solar energy. As for how solar panels work, that’s a little harder to fit in a nutshell but if you think of yourself as a kind of walking, talking vessel for solar energy, it’s a little easier to understand the science behind the miracle.
Solar Energy For People In A Hurry
To begin at the beginning, energy refers to the ability to do work. In other words, energy is not a person, place, or thing. Energy is the state of being at work.
Loosely speaking, “work” consists of movement, or at least the potential for movement. So, the thing at work — aka an energy carrier — can be anything at all — a star, or an elephant, or a rock, or you lying in bed at night and dreaming of solar energy.
At the other end of the size scale, the thing at work can be as small as a subatomic particle.
That brings us to the “solar” part of the solar energy equation.
Light is a unique phenomenon because it behaves like both a wave and a particle. Its wavelike behavior includes the ability to travel through space (at the speed of light, of course). The particle behavior — first described by Albert Einstein in 1905 — includes the ability to interact with another material — in other words, to work.
That’s common knowledge now but Einstein broke with generations of settled science when he proposed that electromagnetic waves (including visible light) consist of discrete units or “packets” of energy.
Btw, coinage of the word “photon” is credited to the physical chemist Gilbert Lewis, who first used it in 1926 to describe those packets of energy.
So, How Do Solar Panels Work?
If you caught that thing about light being able to interact with other materials, you’re on to something.
Think about the last time you got a sunburn, and it’s pretty clear that photons interact with material on earth.
Sunlight can also touch off a chain reaction deep within your body — for example, by setting Vitamin D production in motion.
So, yes, you are living proof that solar energy still packs a punch after its 93 million mile journey to Earth.
That brings us to solar panels.
In 1839, teenage French scientist Edmond Becquerel got the credit for being the first researcher to document that sunlight can interact with certain metals to generate an electrical charge.
That’s the essence of photovoltaic technology, aka solar cells and solar panels.
The first functioning solar collector on record was built by an employee of the Carnegie Steel Company, William J. Bailey. In 1908 Bailey developed a solar energy harvesting device consisting of copper coils and an insulated box.
That’s more or less the idea behind today’s generation of solar panels. The rest is basically a matter of finding the most efficient materials for converting sunlight to electricity.
In the 1940s, Russell Shoemaker Ohl of Bell Laboratories accidentally stumbled on the basic element of modern solar cells when he observed the effect of sunlight on a defective sample of silicon.
It took a while after that but Bell Labs is widely credited with introducing the first working silicon-based “solar battery” in 1954.
No, Really, How Do Solar Panels Work?
For light dinner conversation, that’s about all you need to know. Sunlight creates an electrical charge in certain materials, back in the middle of the last century researchers discovered that silicon does the trick, now pass the potatoes.
If you’re interested in the meat of the muscle, NASA offers this explanation:
“Photovoltaics is the direct conversion of light into electricity at the atomic level. Some materials exhibit a property known as the photoelectric effect that causes them to absorb photons of light and release electrons. When these free electrons are captured, an electric current results that can be used as electricity.”
Now go back to Ohl’s discovery, and you can see where things get a little more complicated.
The American Physical Society has a handy rundown of Ohl’s observation. Check it out for more detail, but for those of you on the go, it all boils down to the defect in the silicon sample.
The defect was a crack, which in effect formed a visible boundary. The boundary marked the difference between invisible (aka atomic level) properties on either side:
“This crack, which had probably formed when the sample was made, actually marked the boundary between regions containing different levels of impurities, so one side was positively doped and the other side negatively doped.”
When Ohl exposed the silicon to sunlight, a positive charge built up on one side of the crack, and a negative charge built up on the other. In other words, he accidentally created a solar cell with a basic p-n (positive-negative) junction.
The buildup of charges is what makes an electric field, and then it’s just a matter of getting that one last connection in place:
“When the cell is hooked up in a circuit, an incoming photon that hits the cell can then give an electron a kick and start current flowing.”
According to APS, the Ohl’s solar cell had a conversion efficiency of 1%.
If that doesn’t sound too impressive, it’s not — at least by today’s standards.
Conversion efficiency refers to the portion of sunlight that can be converted to electricity, and the latest crop of silicon solar cells tops 25% in the lab.
Onwards & Upwards For Solar Energy
For those of you interested in more history, the US Department of Energy has assembled a handy timeline that traces all the major steps that took us from 7th century BC ant-burners (no, really!) on up to silicon and other high-efficiency materials for solar panels.
Aside from carbon nanotubes, one of the most exciting developments in recent years is graphene, a form of carbon that comes in atom-thin sheets. Graphene was discovered by a pair of researchers in 2004 and it quickly became the “it” material of solar cell research.
Graphene developments of recent note include the use of bacteria to fabricate graphene sheets with desirable “wrinkles” to enhance efficiency, and a graphene-silicon “all-weather” hybrid cell capable of harvesting energy from rainwater as well as the sun.
Another promising photovoltaic material is perovskite, which refers to a class of synthetic crystalline materials based on the naturally occurring mineral perovskite.
Belgium’s IMEC, for example, just reported a conversion efficiency of 23.9% for a silicon-perovskite cell.
Thin film technology has also had an impact on the solar field in recent years.
“Thin film” refers to solar cells that are made by depositing layers of a solution containing microscopic particles of photovoltaic material.
Though generally not as efficient as their silicon cousins, thin-film solar cells have the advantage in other ways.
The layers can be coated on practically anything — glass, for example — so thin-film solar cells can be integrated with windows and other building elements.
They are also lightweight and flexible when layered on thin sheets of plastic and other materials, lending themselves to a range of applications unavailable to conventional solar cells.
That’s just a taste. We haven’t even gotten to the inverter thing or why tracking systems are a good idea, or other solar-related fields like passive solar and solar thermal — which includes devices that can range in size from the rooftop hot water heaters on up to massive concentrating solar power plants.
Researchers are also tinkering around with artificial systems that mimic the chemical reactions involved in photosynthesis, in order to pump out hydrogen fuel and other fuel products.
To catch up on all the latest solar news — solar energy, solar panels, and much more — take a scroll through the CleanTechnica solar archives.
Photo via National Renewable Energy Laboratory
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