How Does a Solar Panel Work?

Small retail solar panel
A solar panel or photovoltaic module, is composed of individual PV cells. This crystalline-silicon panel has an aluminium frame and glass on the front. (Photo credit: Wikimedia Commons)

Most people aren’t aware of how long the technology behind solar panels has actually been around. Way back in 1839, French physicist Edmund Bequerel discovered the photoelectric effect that is the basis of the modern solar panel.

However, the first real use of the photo electric effect to generate power happened over 100 years later at Bell laboratories in 1954. By 1958, solar power was being used to produce power on U.S. spacecraft. Since that time, the methods have stayed the same, but the components of today’s solar cells are so much more efficient that they have become a major source of alternative energy around the globe. But how do solar panels work?

solar panel
A solar panel or photovoltaic module, is composed of individual PV cells. This crystalline-silicon panel has an aluminium frame and glass on the front. (Photo credit: Wikimedia Commons)

Solar Panel BasicsThe basic mechanism behind a solar panel is something you learned about in high school science, electron shells and valence bonding. Bet you never thought you’d need to know about that in your everyday life. Here is a quick refresher.

  • Molecules seek to attain a balance between the number of protons and electrons in each of their atoms.
  • When they are in balance, the molecule is stable.
  • When the molecule is not in balance, from either gaining or losing an electron, it seeks to remedy this by returning to balance.

When sunlight hits a solar panel, photons from the light dislodge electrons from the molecules in the upper layer of the solar panel. These electrons are the source of the electricity that is generated by the panel.

Composition of the Solar Cell

soldering solar cells
A homemade solar panel (half completed) created from individual solar cells soldered together (Photo credit: Wikimedia Commons)

The smallest unit of a solar panel is an individual solar cell. Several cells are wired together to create a module. Each module is placed within a panel and is designed to supply electricity at a particular voltage, most commonly 12 volts.

Every solar cell consists of several major components sandwiched together in a thin wafer. They can be assembled as follows:

In a traditional solar cell

  • Glass panel
  • N-Silicon layer
  • P-Silicon layer
  • Glass panel

In an organic solar cell*

  • Thin film plastic or acrylic layer
  • Carbon nanotube layer
  • Organic electrolyte layer
  • Thin film plastic or acrylic layer

Titanium dioxide dye panel

  • Upper shell
  • Electrical conductor
  • Electrolyte layer
  • Catalyst layer
  • Lower shell

*in organic solar cells there can be multiple layers of organic electrolytes to absorb different portions of solar radiation.

Traditional Solar PanelsIn traditional solar panels, the shell layers were, up until quite recently, made primarily of silicon. Silicon is not a very efficient natural conductor, so it must be prepared in a process known as “doping.” The two shell layers are combined with different compounds to make them more efficient. One layer is doped with phosphorous for the positively charged (N-Silicon) panel, and the other is doped with boron for the negatively charged (P-Silicon) side.

How does a solar panel work when it is made of silicon? Instead of using a dye sensitive layer, the solar cells use a direct transfer of electrons from one layer to the next. The N-Silicon top layer of the solar cell is hit by sunlight and electrons are pushed directly into the P-Silicon layer. The P-Silicon layer pushes these electrons directly out of the panel through a conductive wire at the back. The wire routes the electrons back to the top N-Silicon layer. While it is a simple cell with few parts, the maximum efficiency of these cells is about 29 percent, and the panels have a life expectancy of about 25 years.

New Organic PanelsUnderstanding how solar panels work in the traditional sense will help you understand why the new organic solar panels are getting such a buzz. Traditional solar panels are very rigid and costly to produce. New organic panels have the potential to eliminate both of these issues.

Researchers are working on organic solar cells that replace the rigid silicon with much thinner, flexible carbon based nano structures. These are expected to double or even triple the life expectancy of a single solar cell to upwards of 75 years. They are also expected to reach much higher efficiency levels than that of the silicon versions. Currently, the maximum efficiency of these organic cells is at around 12%, but this technology is still in its infancy.

The Chemistry of Titanium Dioxide Solar CellsIn one new type of cell, a small amount of sunlight is absorbed into a hardened acrylic top layer. Just beneath this layer is a dye sensitized layer of titanium dioxide. This is the molecule that the electrons are knocked off from by absorbed photons. These electrons are routed out of the cell via electrical conductive wires attached directly to the titanium dioxide layer of the cell. The electrons travel through this wire creating a direct current – this is the electricity. The electric current can be routed to a converter to power alternating current tools or to a battery bank for later use.

This is the first part of the process. The titanium dioxide which has lost electrons now needs to acquire new electrons to replace the ones that were knocked off. Here’s how that happens. The electrons that were originally knocked off and created the electric current, continue past the tool or battery that they are powering and follow a wire back into the lower layer of the photovoltaic cell. These electrons displace electrons in the catalyst layer of the cell.

The electrons in the catalyst layer move toward the electrolyte layer (almost always made of Tri-iodide). In this layer, negatively charged iodine atoms are created through the infusion of the extra electrons. The electrolyte layer is filled with negatively charged iodine and the layer directly above is full of positively charged titanium dioxide trying to regain electrons. The titanium dioxide takes the extra electron from the iodine and returns to its natural state.
This reaction happens thousands of times every second, creating a steady electrical current. The beauty of this system is that there is no waste created because all that is happening is that electrons are being moved from one place to another through a series of chemical reactions started by the photons from sunlight.

Which Type Will Win Out?As solar technology continues to improve, we will see the death of the traditional silicon based solar panel. Whether activated die or organic solar panels become the industry standard will likely be determined by how efficient the organic offerings can become. They have the advantage of being thin enough to be flexible and adaptable enough to be placed on several different types of material. Only time will tell, but either way it goes, solar power is going to be a huge part of future power generation. One day, the power of the sun might be directly powering your espresso machine.