Solar Energy Made Simple

By Osei, Kwabena | New African, December 2003 | Go to article overview
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Solar Energy Made Simple

Osei, Kwabena, New African

This is the second part of our major series on solar energy which we began in the July issue. Africa gets 365 days of glorious sunshine a year, and yet the majority of our people (at least 85% or so) who live in rural areas have no electricity. In this article, Kwabena Osei (left), our solar energy expert and engineer, takes us through the very basics of solar energy generation.

You can call this the ABC of solar energy. As in every field, the jargon can be technical and confusing. But I am going to do the best I can to break them all down to the lowest denominator for the ordinary reader to understand this very important subject (solar energy), which, to me, holds the key to Africa's second liberation. The "first liberation was political, the "second liberation" will be economic and how we use energy (of gain access to abundant and cheap electrical power) for economic development and domestic use.

Thus, in the piece, I will explain how a Photovoltaic (PV) system functions. I will also highlight the components that are brought together to make up the PV system.

Photovoltaic (PV) is the term used to describe the complete system for generating electricity from the sun. The basic components are the PV generator, the battery and the controller unit, and the cables that join all these components together.

A PV generator churns out electricity so long as the sun shines. To understand how solar cells work, we must first know something about the nature of the sun.

Sunlight is a form of electromagnetic radiation similar to radio waves and microwaves. The sun radiates simply because it is hot. The sun is a black body whose radiation is composed of a broad mixture of different wave lengths. If the sun were cold, it would appear black simply because it would only absorb radiation.

Solar cells are electronic devices without any moving parts, which convert light energy (sunlight) directly into electricity. The idea is so fascinating that Africans should make good use of this energy from the sun. Poor street lighting in most African cities can dramatically be improved. PV systems can be installed anywhere the sun shines.

A major component of this system is the solar cell, which is made from semiconductors such as silicon, usually in the form of thin slices (wafers) about 1/4 mm thick. The positive contact is a layer of metal on the back of the wafer, while the negative contact on the top of the cell collects the current but alto allows as much light as possible to enter the device. The top contact is made in the form of a grid.

To know how solar cells work, we must understand the term electricity. Electricity is a form of energy. It is simply the flow of electrons. All matter consists of atoms. The centre of an atom, known as the nucleus, contains both positively-charged particles known as protons and uncharged particles known as neutrons.

The nucleus is surrounded by negatively-charged particles called electrons. An atom is stable when there is a balancing force between the negative and positive charged particles.

The number of electrons in an atom is normally equal to the number of protons. When an outside force, for example light energy (sunlight), disturbs the balancing force, an atom may gain or lose an electron. A repeated upset by an outside force results in free movement of electrons and this represents an electric current.

A solar cell produces electric current and voltage by "photovoltaic effect"--a process in which two different materials in close contact act as an electric cell when struck by light or other radiant energy.

Light striking such crystals as silicon of germanium provides the energy needed to free some electrons from their bound condition, which result in electrons moving from atom to atom within the crystal.

A PV-generator generates direct current (DC), normally 12 volts, The system may contain a supplementary of back-up generator (for example a diesel generator) to from a hybrid system.

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