What is Solar Power?

How Does Solar Power Work?

Part 1- The Sun as Energy Creator

 

Most people understand that the sun gives life to all things on this planet through its light and heat, but the sun also produces many other things. The process of solar energy began in the center of the sun, almost a million years ago. Photons are created through the fusion of atoms in the sun's core. They will eventually be what generates solar power, but not until they are able to escape from the sun.

 

It generally takes a photon over a million years to escape from the center of the sun to the sun’s surface. Once at the surface, the photons are sent hurtling out into space in all directions, and some of them are aimed directly at the Earth.

 

The photons are sent out at such an incredibly fast speed, that the ones which reach Earth travel over 93 million miles in under 8 minutes. They are basically tiny packages of sunlight, also known as quanta - which is where the term quantum mechanics comes from.

 

 

Part 2- Converting Photons into Energy

 

Once the photons reach Earth, we must harness them in order to create electricity from them. This is done through the use of photovoltaic cells which react with the photons. These PV cells are coated with a material -  usually silicon in most modern cells - which displays the photovoltaic effect.

 

The photovoltaic effect is used to describe the process in which energy is created by certain materials when they are exposed to solar radiation or sunlight. This process was first discovered by the French scientist Alexandre-Edmond Becquerel in the mid 1800’s. These PV cells are stimulated by sunlight and then produce direct current electricity. However, this energy must still be made useable.

 

Part 3- AC/DC

 

Most all appliances and electronics use alternating current or AC power, which differs from the direct current or DC power that is generated by solar panels. In order to transform this DC power into AC power, it is necessary to have a solar power inverter connected to your solar panels. This inverter allows the energy generated to be consumed, fed back into the grid, or used to charge a battery depending on what type of solar energy generating unit you have.

 

Part 4- Solar Energy Consumption and Storage

 

Once the solar energy is converted into AC power, it is possible to use this energy to power your home or business. If you have a grid tie solar system, the electricity you produce will be fed directly back into your local power grid. When you are producing electricity, any energy you consume will come directly from your solar system and any excess will go back into the grid.

 

When you are not producing electricity, then any electricity you consume will come directly from the power grid. If you have an off-grid solar system, then your system will have a rechargeable battery in the loop, right after the inverter. This battery is charged by your solar cells and stores any excess energy, which guarantees that you will always be using the energy you generate yourself, and that you’ll always have energy as long as you produce sufficient amounts.

 

How Does Silicon Produce Energy?

 

Silicon is the most common conductor used in PV cells nowadays, for several reasons. The main reasons lie in the extremely low price of silicon and the fact that it’s widely available worldwide.

 However, pure silicon is not an excellent conductor due to its crystalline structure. A silicon atom has 14 electrons in three different layers (or shells), with 2 electrons in the first, 8 in the second, and 4 in the third layer.

 

This third layer is only half full and the atoms always seek to fill up their layers with electrons by sharing them with other atoms around them.

 

However, because of the even number of electrons, each silicon atom will have a full share, which leaves less room for free electrons to go. When energy is added to silicon, some of these electrons break free and look for holes left by other free electrons.

 

This movement of electrons is what actually generates electricity. The photons strike the PV cell and ideally, each photon will knock one electron free and send it searching for a hole to fill, thus conducting electricity. Because silicon has an even number of electrons, all modern solar cells use impure silicon as a way to free up extra electrons to conduct energy better.

 

All solar companies have a patented crystalline structure that they use in their own panels, and these are made by adding other atoms into the silicon, although usually only a few parts per million. The two main types of atoms that are added to silicon to form solar cells are usually phosphorous and boron.

Solar modules

 

Photo (light) + voltaic (produces voltage) = photovoltaic (PV) system

 

Solar cells are interconnected in a matrix to form a module. One solar cell produces electricity at a voltage of approximately 0.5 volt at room temperature, so 36 cells connected together in a module produce enough voltage to charge a 12-volt battery. However, the solar cell heats up while exposed to the sun, reducing the operating voltage to about 14-15 volts. A 12-volt battery needs about 14 volts to charge it, so the 36-cell module is the standard used in charging 12-volt batteries. The cells are connected and placed between a tough glass front and a back surface within a frame and sealed, as shown in the illustration.

Loss of Energy in Solar Cells

 

It is possible to divide light into many wavelengths. The light that affects the cell contains photons consisting of a large variety of energies. Not all of them have energy enough to modify the opening-electron pair. However, there are other electrons that contain lots of energy. Only a specific portion of this energy, measured in terms of eV or electron volts is necessary to knock an extra electron loose. This is commonly known as a material’s band gap energy. If a photon contains excess energy than what is required, the additional energy gets lost. However, if the incremental energy is equal to the required amount, there is possibility of the formation of more than one electron – hole couple. But, the latter effect does not seem to be of much significance. Just these two outcomes account for more than 70 percent loss of the incident concerning radiation energy on the cell.

 

There are more losses involved in the process. The electrons need to drift from one side to another of the cell using an outer circuit. The bottom can be covered using a metal, leading to effective conduction. But in case the top is completely covered, the photons are unable to pass through the opaque conductor and lose most of their current.

Structure of a Photovoltaic Cell

 

Two individual pieces of silicon happen to be electrically neutral. But when two impure silicon pieces -– the P-type and N-type -– are brought in contact with each other, an electric field is formed. The free electrons present on the N side seeing all the holes on the P side rush to fill them fast. All free electrons are unable to fill the free openings. The entire arrangement would, in fact, be wasted if they had. But, exactly at the opening point, they mix successfully to form a kind of barrier which makes it increasingly tough for electrons located on the N side to make the move to side P. Gradually, the process reaches a point of equilibrium and there exists an electric field dividing the different sides. This field serves as a kind of diode, permitting and even forcing electrons to drift from the P to the N half, instead of the other way round.

 

 

When light in proton form hits the solar cell, the energy results in dividing the hole-electron couples. Each photon carrying sufficient amount of energy will usually be able to free just a single electron, leading to a free opening as well. If this occurs very close to the field of electricity, or if free opening and free electrons tend to flow into influence range, the field is likely to shift the electron to side N and the hole to side P. This results in even more disruption of neutrality of electricity, and if an external charged path is presented, electrons make use of the path to travel to the P side to combine with openings sent by the electric field, carrying on work in the process. The flow of electron results in the current and the electric field of the cell results in the formation of a voltage. Power is formed as a product of both voltage and current.

 

A few elements remain before the cell can be used. Silicon is a highly shiny substance that can push photons away prior to the completion of their job. In order to remedy this, it is normal to apply an anti-reflective coating which lessens the losses. The ultimate step is the installation of a cover plate made of glass or any other object that can offer protection to the cell from the elements. The amount of energy absorbed from sunlight by the solar cell is not very much.

In order to reduce these losses, cells are normally covered using a contact grid made of metal that lessens the distance required to travel by the electrons, covering just a limited part of the surface of the cell. Even then, the grid blocks a few electrons.

 

 

Common Solar Power Issues

A portion of the power generated by the photovoltaic panels can be collected using chemical batteries. However, the setup suffers from a lack of additional power initially. The photon-producing sunlight is also responsible for infrared and harmful ultraviolet waves which result in the physical degradation of the panels. The panels need to be exposed to the harsh elements of nature, are also capable of affecting efficiency in a serious manner.

 

The necessity of light in the emission of electrical current can be deduced from the name of the photovoltaic cell. Future scientists will face the challenge of creating regular-sized and further developed solar panels that can be used to produce additional energy for the times when there is no sunlight.

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