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Solar Energy: How do Solar Panels Work?

SUAOKI SUAOKI

Posted on June 12 2018

 

You have probably read dozens of online articles or heard people around you talking about green & renewable energy sources such as solar energy, along with their pros and cons.  While many people can effortlessly name the different types of green energy sources, very few can tell how they actually work. Rest assured that understanding this process is not rocket science.

Today, we will focus on solar energy and how do solar panels work. This article will explain how solar panels use solar energy to generate electrical current. Hopefully, this article will help you understand the process by which solar panels convert solar energy.

So, what is solar energy? In middle-high school, during one of your biology courses, you have probably come across the process of photosynthesis. For those who were asleep during biology classes, photosynthesis is the process by which plants, algae, and even some microorganisms take advantage of sunlight to synthesize nutrients from carbon dioxide and water. Simply put, it is the process by which plants' leaves use free solar energy to make their own food and grow.

Turning solar energy into electricity for daily use is the exact thing that we humans have tried to accomplish by inventing solar panels and many other green energy technologies.

 

What are the Different Types of Wavelengths?

On a non-stop basis the sun emits solar energy in the form of waves.  These waves can range in length from short ultraviolet waves through the rainbow of the visible spectrum to long infrared waves. The sun emits shortwave radiation directly to the earth. On the other hand, the earth re-emits longwave radiation in the form of infrared waves towards the atmosphere. When the visual light spectrum hits the solar panel or more specifically the photovoltaic cell, it transforms solar energy into electricity.  This physical and chemical phenomenon is the photovoltaic effect.

[caption id="attachment_241" align="aligncenter" width="787"]Electromagnetic spectrum wavelength by khanacademy[/caption]

Solar panel: made up of many smaller units called solar cells or photovoltaic cells.

Solar cell: a.k.a photovoltaic cell converts sunlight (photon) directly into electricity (Voltage).

Photovoltaic effect: is the creation of electricity in a material upon exposure to light.

 

What Solar Panels are Made of?

The active part of a solar cell is a wafer containing semiconductive material such as silicon. A semiconductor is a material which does not conduct electricity well but can become more conductive, under certain conditions. The semiconductor part of the solar cell has 3 distinctive layers.

[caption id="attachment_242" align="aligncenter" width="792"]n-type and p-type semiconductor layers by valuewalk[/caption]

Top layer: Also called negative (N) type; contains silicon and a very tiny amount of phosphorus, which has more electrons than silicon. Giving the top layer an excess of electrons, that move freely and makes it more conductive.

Thin bottom layer: Also called positive (P) type contains both silicon and Boron; which has fewer electrons than silicon. This provides the bottom layer fewer electrons that are free to move, therefore making it less conductive.

Thick middle layer: Has only slightly fewer electrons, which makes it marginally P-type.

 

How Solar Panels Generate Electricity?

Generally, the solar grid has thin metal lines printed on the top N-type layer and the bottom P-type layer is in contact with an aluminum plate.

When the solar energy in the form of light waves hits the top surface of the silicon photovoltaic cell, only lights with wavelength from a specific window of the solar spectrum (350 to 1140nm) are absorbed into the middle layer. This range of waves length includes the visible spectrum. Ultraviolet wavelengths are so short they stop at the surface. Infrared wavelengths are so long they can't be absorbed and pass right through the cell or are reflected back.

Every time this occurs the light wave knocks an electron off a silicon atom, this set the electron loose and leave an area of positive charge a hole.  The loose electron then moves towards and reaches the top N-type layer, which readily accepts electrons. In a similar way, the loose hole moves towards and reaches the bottom P-type layer which readily accepts holes. This process keeps repeating as long as the sun is shining on the solar cell.

[caption id="attachment_248" align="aligncenter" width="542"]N-type and P-type movement within a solar cell by science[/caption]

Now that the electrons and the holes have been separated, a wire connected between the top and bottom metal electrodes provides a pathway for the electrons to move towards the hole. A flow of electrons is what gives us electrical current.

FYI one solar cell can generate few watts of power, sufficient to charge small units e.g a phone or calculator. For practical use several solar cells, typically 32, are wired together to make a solar panel and generate more watts. It needs several solar panels to generate enough electricity to power a household.

 

What are the other solar energy technologies?

It's important to note that the photovoltaic system is just one of many solar energy technologies. For those avid of knowledge, below is a small list with a brief description.

1.Solar Hot Water

Solar Water heating systems a.k.a solar thermal system, is the process of converting sunlight into sustainable energy for water heating using a solar thermal collector. Directly heated or via light-concentrating mirrors.

2.Solar Electricity

The PowerPot. Thermoelectric power converts heat (temperature differences) directly into electrical power. It uses a solid-state device, thermoelectric generator (TEG), also called Seebeck generator. Its technology is built into the bottom of the pot and generates electricity from a wide range of heat sources. It results from 2 physical effects, namely the Seebeck effect and Peltier effect.

3.Passive Solar Heating and Daylighting

Has to do with building design. Whereby windows, walls, and floors are designed to collect, store, reflect and distribute solar energy. The design of the building attracts solar energy in summer and rejects it during winter.

4.Solar Process Space heating and Cooling

Widely used in large commercial and industrial buildings. Solar process heating systems provide a large amount of hot water or space heating for nonresidential buildings. A classic system usually comprises of solar collectors, a heat exchanger, and one or more large storage containers. The heat collected, from a solar collector, also helps cooling down buildings.

 

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