An Introduction to Photovoltaics

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Photovoltaic technology has been continually fine tuned since the early 1900s. Progress in technology has not only made photovoltaics more effective but also much cheaper for the masses to use.

Newer semiconductor materials are being explored to expand on the possibilities of greater solar energy applications. Being green and grid-free energy source, it is a necessity for remote locations and a critical, greener option over fossil fuels in light of global warming.

As such, we seek to help you understand photovoltaic technology a little better through this introductory article to the topic.

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What does the term ‘photovoltaic’ mean?

The term is derived from two root words: ‘photo’ and ‘volt’.

The former comes from the Greek word for ‘light’, as in photosynthesis. The latter is the unit of electromotive force, one of the measurements for electric power.

‘Photovoltaic’ can mean either the ability to produce electricity from light, or related to the process of doing so. 

Photovoltaic or PV in short is used to describe the process of converting light (photons) to electricity (voltage).

Examples of photovoltaics

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The first solar-powered application was for satellites and space technology, as photovoltaic technology involved very high production costs in the early days.

Over time, it was made more commercially viable. For regular consumers, the first applications of photovoltaics was the roof solar panel for water heaters.

Later on, photovoltaics was applied to smaller items such as solar-powered calculators, which have now totally replaced the need for battery-powered versions.

Since the calculator, a myriad of applications has been created. These range from solar-powered pumps to light-weight mobile charging panels.

What is photovoltaic energy?

It is electrical energy generated using the solar spectrum as the natural raw material which is then processed by photon-absorbing materials. 

A clean, renewable energy, it is based on what is called the photoelectric effect. Photovoltaic materials are needed in order for photovoltaic effect to occur.

What is solar spectrum?

The sun emits energy in the form of radiation or electromagnetic waves which are visible and non-visible. It is the visible radiation which is relevant to the production of photovoltaic energy.

Visible radiation appears to us as a rainbow of colours when shone through a glass prism or when seen in a rainbow. Half of the sun’s energy is in these visible wavelengths.

Visible radiation, or sunlight, is composed of photons. A photon is a particle of solar energy so it contains energy. Different wavelengths of the solar spectrum have different amounts of energy.

In order for solar energy to be harnessed properly, a photovoltaic system is required. 

Photovoltaic system

A photovoltaic system consists of several components in order for the system to be functional. The components are:

  • PV cells
  • PV module
  • Electrical circuit
  • Solar inverter
  • Battery (for instances where electricity generated needs to be stored)

What is a PV cell?

A photovoltaic (PV) cell is the basic building block of a photovoltaic system. Each cell is a self-contained package consisting of PV materials.

Sandwiching the PV materials are two layers which form the ‘skin’ of the PV cell. The top layer facing sunlight is an anti-reflective coating while the bottom layer is a reflective layer.

These layers help to protect PV materials from the elements and from other physical damages. They are often made from a combination of glass and/or plastics.

The PV materials in the PV cell act as semiconductors. Fine wiring touching the PV materials function as conductors which link to an electrical circuit.

The size of a cell can vary from about half an inch to 4 inches across. Each can produce only 1 or 2 Watts worth of electrical power. This amount of electricity can power only small items such as calculators and wristwatches.

PV cells produce the most electricity when they are directly facing the sun. The type of material used to form the PV cell also determines the effective rate of sunlight to electricity conversion.

Some PV cells can even convert artificial light into electricity.

What are photovoltaic materials?

These are materials used to make the semiconductors in a PV cell. When PV energy was first used, there were only two options: monocrystalline silicon and polycrystalline silicon.

Modern photovoltaic technology has more and more options being created each year. For example, amorphous silicon, gallium arsenide, metal chalcogenides, organometallics, perovskite and mesoscopic solar cells.

Silicon solar cells are the initial prototypes. The newer version is the thin-film PV cell.

Thin-film solar cells are made from some of the newer materials, including cadmium telluride and copper indium gallium diselenide.

An even newer prototype is called the III-V solar cell. It is named after the two groups of elements that are used to make the semiconductors.

Group III elements of the table include gallium and indium. Group V of the table includes the elements arsenic and antimony.

III-V solar cells are the most expensive to produce but they are the most efficient in converting sunlight into electricity. Therefore, they are normally only used for space technology.

What is the working principle of a photovoltaic cell?

The working principle of photovoltaic cells is the photovoltaic effect. The following is a detailed explanation of this effect in layman’s terms.

When sunlight is shone on PV cells, the photons in its rays pass through the transparent top layer of the PV cell and strike the semiconductor material in the cell.

This causes the outer electrons of the photon atom to break free of their atomic bonds. The semiconductor material forces the electrons to move in one direction.

The bottom layer of PV cells is reflective. This then causes the free electrons in the PV material to bounce back up through the top layer.

This to-fro movement of electrons creates a current in the PV cell. In other words, electrical energy is created.

However, not all the photons in a sun’s rays are completely absorbed by PV cells. Some photons may bounce off the cell or pass through it. This is due to the fact that some PV materials are not 100% efficient.

Furthermore, the effectiveness depends on the light spectrum that is being captured. Infrared rays are too weak while ultraviolet rays create heat instead of electricity.

Electrical conductors are connected to PV cells to absorb these moving electrons. The PV energy is then passed through an electrical circuit to an external load such as a battery, a power grid or an electrical device.

What is a PV module?

A photovoltaic module is a solar panel. It consists of a number of PV cells connected together and packaged in a weather-tight rectangular panel.

There are various sizes of PV modules and corresponding electrical output. The more PV cells there are in a panel, the higher the output.

When PV modules are strung together, they are called a PV array.

There are three varieties of solar panels for different purposes:

  1. Photovoltaic – to generate electricity from solar rays
  2. Thermal – to generate heat from solar rays
  3. Thermodynamic – to generate electricity from solar rays and ambient temperatures

Read about the types of solar photovoltaic panels in greater detail.

Photo by Mariana Proença on Unsplash

Photovoltaic arrays

The development of photovoltaic technology has created new computations of PV arrays to increase efficiency and aesthetic appeal.

Concentrating PV arrays are an example. These have lenses and mirrors which concentrate sunlight onto high-efficiency cells.

Another is the building-integrated photovoltaic (BIPV) system. A BIPV system is designed to serve as both the outer layer of a structure as well as generate electricity. For example, BIPV roof tiles.

What is a solar inverter?

An inverter is a device which adapts electrical energy from PV cells into a form which can be used by devices that run on alternating current (AC).

PV cells generate electricity in the form of direct current (DC). However, most devices and electricity distribution systems use AC.

An inverter converts DC electricity to AC electricity.

How was the photovoltaic effect discovered?

The photovoltaic effect was first discovered by Edmond Becquerel, a young French physicist who was, at the time, assisting his father who was also a physicist.

Edmond was interested in light. He was studying the phenomena of fluorescence and phosphorescence in 1839.  

During an experiment, he placed two electrodes in an acidic solution and exposed one of the electrodes to light. The device generated electricity. The first photovoltaic cell was incidentally created.

However, the discovery was not furthered by Edmond. It was only decades later that scientists managed to figure out the mechanism behind the photovoltaic effect.

Which country uses the most solar energy?

The country with the highest capacity of solar power is China followed by the U.S. and Japan. 

China was reported to have a cumulative capacity of 204 gigaWatts of solar electricity in 2019. In the same year, the U.S. had a cumulative capacity of 76 gigaWatts while Japan had 63 gigaWatts.

Photo by Mariana Proença on Unsplash

Conclusion

The future of photovoltaics is bright and its economic potential is vast. Over time, PV cells and solar-powered products will only become more efficient, cheaper and innovative.

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