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How do solar panels work? The science of photovoltaic effect made easy.

The earth receives 173,000 terawatts of solar power daily, ten thousand times more than the power used by the whole planet’s population. 

But,  most of it goes without being utilized. 

Globally, solar power accounts for only 1% of power generation; in the United States, this figure just touches 3%

Primarily, there are three types of technologies that harness solar radiation: 

  1. Photovoltaic (PV) technology. It directly converts sunlight into electricity. Rooftop solar panels most commonly use PV technology. 
  2. Concentrating solar power. It uses large mirrors to focus sunlight onto a receiver for generating utility-scale electricity. 
  3. Solar heating and cooling systems. It collects sunlight to provide hot water and air heating or conditioning. 

Understanding all these technologies is important. But for homeowners interested in going solar, understanding how solar panels work (PV technology) is more important, as it directly concerns them. 

In this article, we explain the science of how solar panels generate usable energy for your home. 

How do solar panels work?

Particles of sunlight, called photons, fall on solar panels, knocking electrons free and setting them in motion. 

What happens when electrons move? An electric current is produced. 

This current, known as direct current (DC), is captured by conducting plates and sent for use through wires. But since our home appliances are rated for alternating current (AC), the DC is sent to an inverter where it is converted to alternating current. The electricity produced by the sun is now ready to power your home. 

This is only a simpler answer.   There is more to it. To get to the nitty-gritty of how solar panels work, we first need to understand the photovoltaic effect, the mechanism responsible for converting solar energy into usable electricity. 

Photovoltaic effect 

When exposed to solar radiation, certain materials produce electric current or voltage.   This is called the photovoltaic effect, a phenomenon discovered accidentally by Edmond Becquerel in 1839. The material used in the PV effect has to be a semiconductor, a material that normally doesn’t conduct electricity but can be made a conductor under certain circumstances. 

The role of solar cell

At the most basic level in a solar panel system is the solar cell, also called the PV cell. The photovoltaic effect occurs precisely in this smaller cell. A solar cell is made by sandwiching two slices of semiconducting material, most commonly silicon. 

LET’S GET GEEKY

Doping. No we’re not talking about drugs!

Doping means adding impurities on purpose to pure silicon to make it a better conductor. 

The top layer of a solar cell is made of silicon but doped with an element with more electrons, such as phosphorus. Since there are more electrons in the top layer, it is called the n-type layer. On top of this layer, thin metal lines, usually silver, are printed for the purpose of conduction when an electric current is produced. 

The bottom layer of a solar cell is also silicon but doped with an element with fewer electrons, such as boron or gallium. Since there are fewer electrons, this lack of electrons may be described as an effective positive charge. Hence, it is called a p-type layer. Below this layer, an aluminum plate is connected to complete the circuit. 

When these two layers are combined, the electrons from the n-type layer rush to fill holes in the p-type layer. But,  not all electrons can cross to the p-type side. As soon after this rush, a sort of equilibrium is reached at the junction. This junction is called the PN junction. The stage is now set for electricity generation—we just need sunlight. 

Pending Image

When the sunlight hits the solar cells, photons— found in the sunlight—break the electron-hole bonds, setting them free. After these free electrons and holes enter the range of the electric field, i.e., PN junction, the field sends electrons to the n-type region and holes to the p-type. This process is continuous—the sunlight knocks off electrons, and the field sends them to the n-type. 

At this stage, too many free electrons are moving inside the solar cell. Give a free passage to these electrons, and we have an electric current. In our case, we have already installed thin metal lines at the top of the n-type layer. Through this external path, these electrons cross over to the p-type layer and combine with holes that were sent by the electrical field. Now, we have current and  voltage—voltage is responsible for making the electric charges move.  

With both voltage and current, we get electric power, the product of the two (P=IV). So far, we have described only the working of how electricity is generated inside the cell. But how does it power our homes and businesses? 

How does a solar panel system work?

A solar cell produces only a minimal amount of electricity, enough to power a calculator but not a refrigerator or a whole home. To produce electricity on a bigger scale, many cells are connected in series to form solar modules—also called solar panels, which we see on rooftops. 

Today, most solar panels come in two standard sizes: 60-cell solar module and 72-cell module. 60-cell modules have an output of about 270 to 300 watts; in contrast, 72-cell panels come with a power rating of 350 to 400 watts. 

But again, one panel would still not be enough. So many panels are combined to form solar arrays. Have you seen a row of panels installed on a rooftop or on the ground? That’s a solar array. 

How many solar panels in one array you need hinges upon the amount of electricity you need. A typical American home requires an array of 21 to 34 panels to cater to its needs. 

The role of inverters 

Irrespective of how many solar panels are in your system, the current it produces is direct current (DC), not of much use to our home appliances, as they are prepared for alternating current (AC). 

Our electricity  grid uses alternating current; if we use a grid-tie system, we will have to convert this DC to AC for smoother integration. This is what inverters do—convert DC into AC.

Solar inverters can be attached directly to each panel, where DC is converted to AC at the source. Or, you can also have central inverters, where the direct current from all the panels is converted to AC. 

The role of batteries 

Solar panels do not produce electricity at night or when the weather is too cloudy. 

If you don’t want to rely too much on your grid, you can have an energy storage system—batteries—in place. 

During the daytime, your solar system generates more electricity than you need, so you can store the excess energy in batteries for use at night or when there is a blackout.

After installing our first rooftop solar system, we cut our electric bill in half. We also learned that the appliances that use tons of electricity are water heater, washer and dryer.

So, no more long showers. Wash and dry clothes when it’s nice and sunny!

Parichatra R. (Business Owner)

How do solar panels work? A quick recap

A step-by-step process of how solar panels work looks like this: 

  • The sunlight falls on solar panels 
  • Solar panels absorb the sunlight, where photons knock the electrons free and set them in motion 
  • A current is produced, which is captured by the circuit attached to solar panels 
  • Since this current doesn’t have much utility for our homes, it is converted to alternating current using one central inverter or a set of string inverters

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