How Does a Solar Panel Work?
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 renewable energy around the globe. But how do solar panels work?
Solar Panel Basics
The 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.
What is a Solar Panel?
A solar panel is an assembly of photovoltaic cells capable of converting light directly into electricity. By combining several solar panels into a larger grid (mounted on a roof or in a field) you can create a solar array with an expandable capacity.
How do Solar Panels Work?
Solar cells and solar panels make use of the “photovoltaic effect” (and are alternately known as “PV cells” and “PV Panels”). They are based on the following scientific principle:
- 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.
How Do Solar Panels Work at Night?
Solar panels can’t generate electricity by themselves without sunlight (daylight) to power them. But the energy from a solar panel grid can be stored in battery banks and used at night in the absence of the sun.
Composition of the Solar Cell
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 Panels
In 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 phosphorus 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 silicon 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 Panels
Understanding 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 nanostructures. 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 Cells
In 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 electrically 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 retain 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 of Solar Panel Will Win Out?
As solar energy 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. As more of the public power grid makes use of advances in solar technology more large-scale solar power plants will enter service, generating renewable energy for future generations. One day, solar energy might be directly powering your espresso machine.
How Many Solar Panels Do You Need?
The number of solar panels required to successfully power a specific installation will depend upon several factors:
- the power requirements of the device (or devices) to be run on your grid
- the storage capacity (batteries) in place to optimize power usage and ensure no excess energy is wasted from the grid
- the generating capacity of the individual solar cells being used on that grid
When electricity generated by the solar array exceeds the user’s needs, the excess energy is either stored via a high-capacity battery system or else it can be sold to the local electric utility via a system known as “net metering.”
One way to determine your potential energy needs is to calculate the average energy usage in kWh (kilowatt hours). By studying your electric bills over a 12 month period you can determine the average number of kWh used in a typical month, By dividing that number by 30, one can estimate potential daily usage.
Average 250 Watt rooftop solar panels can produce around 1kWh per day (each) of renewable energy under optimal conditions (4+ hours of solar exposure). By determining the number of kWh (kilowatt hours) your home requires, you can match that with the wattage power output of your collected cells to meet your projected needs. You’ll need to design a solar array specific to your roof installation, taking into account the weather patterns of your regional location. Some areas, where sunny days are fewer and farther between, might require a larger roof grid system that would be needed in a sunnier locale to meet the power requirements of a specific user.