The Power You Need
The electricity powering your home is a flow of electrical charge created by the movement of tiny negatively charged subatomic particles called electrons. Though it’s often claimed that electrical current is composed of the electrons themselves, this isn’t really true.
Your appliances run on AC or alternating current, meaning the flow of electrical charge is constantly switching directions. AC current in the U.S. switches back and forth a remarkable 60 times every second. That’s so fast that the electrons in your wiring never even get a chance to flow in either direction and wind up simply vibrating back and forth instead. But their back-and-forth vibrations do, nonetheless, cause an alternating current of electrical charge to flow through your outlets.
One factor complicating solar power systems is that the panels themselves don’t produce the AC current you need. Instead, they generate DC or direct current, which flows continuously in just one direction. So, in addition to panels, devices called inverters are necessary to convert the panels’ DC output into the alternating current required to run your appliances.
Because the flow of electrical charge in DC current never changes direction, the electrons aren’t stuck in place vibrating like they are in AC. Instead, they flow in the same direction as the electrical charge they carry – albeit at a much slower rate.
Turning sunshine into cost-free electrical power became possible when scientists and engineers developed efficient two-sided solar cells. When exposed to sunlight, these miraculous wafers generate a continuous flow of electrons through a wire running out of the top side, to your inverters which convert the DC current to AC for you to use or sell, and back to the bottom side.
Electrons & Photons
Electrical wiring conducts electricity because it’s composed of metals like copper containing relatively free electrons that aren’t bound too tightly to any particular molecule. So, when a force that pushes electrons is applied to one end of a copper wire, even if it’s relatively weak, it can break some electrons in the copper completely free and cause them to flow through the wire like a pump pushing water through a pipe. Plastic and other poor conductors are like permanently frozen pipes – all their electrons are bound tightly and, hence, “frozen” in place. So, it takes massive amounts of electrical force, or voltage, to get the electrons in plastic to move at all.
Generating solar power is possible because light is composed of incredibly small particles called photons that can interact with electrons. If the photons in a beam of light striking a metal surface have enough energy, any electrons they impact not bound too tightly to their molecules will be “knocked” free. Some will even be “knocked” off and emitted from the metal’s surface. Albert Einstein was awarded his Nobel prize for explaining this scientific phenomenon, known as the Photoelectric Effect.
But it’s also possible to channel the Photoelectric Effect into another scientific process called the Photovoltaic Effect. That’s when electrons impacted by sufficiently energized photons of light, instead of being randomly knocked around, get channeled into wires by an electric force, creating DC electrical current.
Generating Solar Power
That’s how solar power is generated. A solar panel is constructed out of several dozen wafer-like solar cells each composed of two different types of material:
- A negatively charged top layer that contains extra electrons.
- And a positively charged bottom layer that is missing electrons and, hence, attracts the extra electrons in the top layer.
The attraction between the top and bottom layers of a solar cell creates an electric field between them. The electric field in turn exerts an electrical force. So, when an electron in a solar cell is knocked free by a photon of light, it’s channeled toward a wire running from the top layer of the solar panel, to your inverters, and back to the bottom layer. When enough electrons are knocked free by sunlight, voilà! A flow of electrons producing DC current is created.
Next time, we’ll talk more about how the two kinds of materials composing solar cells create the force that channels electrons freed from their molecular bonds by the sun into free and clean electrical power.