A question often asked about solar power is, “how does it all work?”
Here, we hope to provide a brief (just a little nerdy) overview of what happens, step by effulgent step, from the beginning of a journey of over one hundred million miles to the flicking of a switch to light a room.
We’ll cover a brief bit of solar cell history, physics, chemistry and some technical aspects of solar panel installations, answering this question in just a little over the time it takes light from the sun to reach Mars – so, about 12-13 minutes.
Chapter One: Journey from the Sun
Believe it or not, it takes tens of thousands of years for one small particle of light from the sun to hit your solar panel; and it takes a damn sight more than one particle to produce enough energy to create an electrical current.
The epic story of the photon (from Greek phōs, phōt – meaning light and styled on the word ‘electron’), our radiant, little bundle of energy begins at the very center of our sun, where the process of nuclear fusion caused by intense pressure, releases staggering amounts of energy as two atoms merge.
Like a bumblebee after too much honey wine, our little photon pings its way from atom to atom, being absorbed and emitted time and time again, over an estimated forty thousand years to reach the surface of the sun finally.
After such a long and arduous pilgrimage, the photon is flung into the void at such speed it only takes 500 seconds (8 minutes and 20 seconds) to travel 1 AU (Astronomical Unit); the from the sun to Earth – an impressive 92,955,807.3 miles.
I don’t want to get all ‘George R. R. Martin’ on you, but I’m afraid we’re close to the part where the little photon gets killed off, and we introduce a new character; the negative force in the story – the electron.
When the photon has traveled all that way, to put it in the simplest terms, it is absorbed by an atom or molecule and passes its energy to the electron, which becomes very excited.
Enough of this excitement can cause the electron to escape its atomic bonds, but this depends on the frequency of the light; for the most part, it’s a quid pro quo exchange, one high-frequency photon for one electron.
This is one of the conundrums physicists and chemists are working hard to overcome by experimenting with different materials such as Perovskite and light-absorbing dyes.
A photon with a low energy frequency is less able to excite the electron enough to dislodge it from the atom, yet multiple low-frequency photons with an accumulative sum of energy are still unable to perform the task of a singular high-frequency photon.
That said, innumerable photons are being cast in Earth’s direction, and similarly unfathomable numbers of electrons are thus being stimulated (in conductive material), and we get the movement of energized negative particles we know as electricity.
It was French physicist, Alexandre Edmond Becquerel, who at the age of 19 (in 1839), discovered that “shining light on an electrode submerged in a conductive solution would create an electrical current”.
This effect was initially called the Becquerel Effect and is what we now know as the Photoelectric or Photovoltaic Effect; this field of study was further advanced in a 1905 paper written by Albert Einstein (“On a Heuristic Viewpoint Concerning the Production and Transformation of Light“), in which he described the linear relationship between the frequency of light and the energy of dislodged electrons.
Einstein’s paper was at first received with a lot of skepticism because it undermined established understandings of light; he introduced the concept of a particle of light called a ‘Quanta’, defying the widely accepted theory that light was only a wave – which was also supported by Einstein’s thesis.
Light is made of these particles, the quantum (today’s photons), and it moves in an oscillating wave formation.
It wasn’t until in 1914, Robert Andrews Millikan proved in an experiment that Einstein’s theory was correct, paving the way for quantum physics, and resulting in Einstein receiving the Nobel Prize for Physics in 1921.
Einstein’s fresh look at the behavior of light carried over to the concept of the photoelectric effect, hypothesizing that a photon transferred its energy to an electron, broadening the comprehension of how and why light was able to create and sustain an electrical current.
The first solar cell was created by Russian physicist Aleksandr Stoletov in 1888, but it was American Russel Ohl who patented the true forebear of today’s solar cell.
It was at Bell Laboratories, however, that inventors Fuller, Chapin and Pearson demonstrated the first practical example of a Photovoltaic (PV) Cell, which is still largely used today.
Chapter Two: Inside the Panel
The Photovoltaic cell has been developed and improved upon a lot since the days of Stoletov, but the technology itself has not changed much in the last 130 years or so.
The very same principles are being used today from Arnold Schwarzenegger’s million solar rooves pledge, to Jimmy Carter’s and Barak Obama’s White House solar panel installations, to millions of home and business owners across the globe; and with good reason.
Using the knowledge that the energized electron can create a current is not enough, however.
We need an impetus; something to create Voltage (described as electric potential difference) – which is like hydraulic pressure, but with subatomic particles – to drive the electric current and direct it from point A to point B.
Enter the extrinsic semiconductor.
The solar panel consists of cells covered in a layer of glass, or other translucent material that acts both as a window for the light to pass through, and as protection for the wafers of semiconductors beneath.
The majority (over 90%) of solar cells contain layers of a crystalline lattice of silicon as the semiconductor; there are two opposing layers of silicon that have been ‘doped’ (it is the doping process that changes an intrinsic semiconductor to extrinsic) with different chemical elements to produce an n-type layer (or donor – giving, repelling), usually made with phosphorous; and a p-type layer (acceptor – receiving, attracting), made with boron.
This is called the P-N junction; P-type – Positive and N-type – negative;
There are several different materials used in solar cell production, yet silicon is unwaveringly popular due to its durability and overall efficiency compared to others, but research and development have delivered some interesting products offering unique advantages for unique applications.
The one that has really tickled the giddy spot of many eco-nerds is the evolution of Organic Photovoltaics (OPV).
Organic PV cells have so much potential, as they could, in theory, provide electricity at a much cheaper rate than silicon due to them being less expensive to manufacture on a large scale.
The cells are made from carbon-rich polymers and can be modified to amplify specific attributes within, such as sensitivity to different frequency bands in the spectrum of light.
There are several drawbacks to the OPV technology; cell lifetime is generally shorter than, and efficiency is less than half that of silicon; however, OPV cells have a much larger range of structures they can be applied to, making them a viable option for those with lofty architectural ideas.
All in all, it is still a work in progress, so who knows where the technology will be in another 5 or 10 years?
Other semiconductor materials include expensive to manufacture, or toxic chemicals such as Cadmium Telluride (CdTe), Copper Indium Gallium Selenide, Gallium Arsenide, and Perovskite; each have their pros and cons, and each still in development.
Before we digress too much from the topic at hand – back to what happens inside…
When the photon agitates an electron, and the electron disentangles itself from its chemical atomic orbital, it is the antagonistic relationship between n-type and p-type that squeezes the electrons along to create the electric current (to balance or cancel the electric potential), until it reaches an electrode.
Chapter Three: From Panel to Plugging In
The circuit is not yet complete.
Many cells are needed to make a panel, and many panels are needed to make an array or system that may be required to run a home, heat a swimming pool, or power a satellite.
Cells are linked in parallel and/or series circuits to combine DC (direct current) electrical energy toward a junction box, a small, yet vital piece to the whole solar power puzzle.
Every solar junction box is attached to the panel and its functions include heat regulation, and protection from external threats like water, dirt, and insects.
The main objective of the junction box is to pull all that electron juice into one cable and direct it toward your home.
The junction box typically contains four diodes, which are terminal electrical components with a dual purpose; ideally, the diodes should have as high as possible resistance in one direction and as low as possible resistance in the other.
Again, we come across the silicon semiconductor in crystalline form with a p-n junction (p-type and n-type asymmetry) that maintains the flow of electricity in the desired direction (away from the source) and protecting the solar panels from the feedback of energy.
The DC energy then flows to a solar inverter or power box where it is converted into useful, and safe AC (alternating current – thank you, Nicola Tesla), that we use to run our domestic appliances, warm our water, and heat our homes.
There are first, off-grid or stand-alone inverters, being disconnected from the utility grid, but connected to batteries storing energy surplus to immediate requirements for later use – the batteries themselves have special backup inverters that manage the flow of power to and from the battery.
The second type is grid-tie inverters, which work in conjunction with the grid, and as such, are usually not available in case of power outages due to failsafe mechanisms manufactured to halt energy flow known as anti-islanding protection – important in the event of electrical maintenance.
The third type of inverter is a hybrid, combining the best attributes of both the stand-alone and grid-tie inverters, managing backup storage, PV panels, and grid; more intelligent, and versatile, but not cheap.
The alternating current, now coming from your inverter travels through copper wires to your distribution board where it is divided into separate circuits, usually distinct areas of your home; lighting, heating, air conditioning, power outlets, upstairs and downstairs, etc.
Circuit breakers or fuses in your distribution board protect your home from energy overload.
Energy relayed from the distribution board carries on through more copper wiring, to your socket, to plug to your computer (or smart device), and you have just spent the last few minutes reading an article powered by particles of light older than civilization.
We have covered everything from the moment of conception of minuscule particles of light, in the very heart of our sun, to the end of the electrical cycle, where the culmination of six stages of a journey results in hot cups of morning coffee; movie nights-in with family; and fully charged electric cars.
Recap of the Main Points
- Nuclear fusion in the sun creates light particles called photons
- The photons zig and zag their way through the sun for roughly 40,000 years.
- Our particles of light are finally ejected at 186,282 miles per second toward Earth.
- Semiconducting lattices of ‘doped’ crystalline silicon (or other chemical combinations) in a solar cell capture the photons’ energy to direct a flow of displaced electrons, generating a current of electricity.
- The current of electrons combine from other cells in the solar panel and is directed through a junction box to form a unidirectional flow of direct current (DC) electricity.
- Unified streams of electricity from all the junction boxes in a solar array are fed into solar inverters, where the direct current is converted into alternating current (AC).
- The current then travels to a distribution board and is divided into circuits for different purposes.
And that is how solar power works, step by effulgent step.