Solar Power

Energy

We keep talking about energy, but what does energy actually mean, and how do you measure it?

You need energy: 

• to accelerate a body or 
• to move it against a force, 
• to heat up a substance, 
• to compress a gas, 
• to cause an electric current to flow or 
• to emit electromagnetic waves.
• Plants, animals and people need energy to live. 

The unit used to measure energy and work is the joule (J). 
If you want to learn more about energy, you can find interesting articles online and in reference books.

From coal to nuclear power

And where does all that energy come from? We generate the majority of it from fossil fuels like gas, oil and coal. Some of our electricity also comes from nuclear energy. However, these types of energy do have various disadvantages:

• The Earth’s reserves of fossil fuels are limited.
• When we burn oil and coal, this produces harmful substances that pollute the environment, like CO2, which is responsible for the ongoing warming of the Earth's atmosphere.
• Despite high safety standards, nuclear energy does carry with it the risk of a nuclear meltdown. In addition, it also produces nuclear waste which remains radioactive for thousands of years.

However, there are forms of energy that are unlimited, that create no environmental pollution, and that do not come with any risk of nuclear disaster. We will explain these in the following section.

Fundamentals of solar Energy

Solar energy is energy generated by the sun through nuclear fusion, 
some of which reaches the earth as electromagnetic radiation (radiant energy). The majority of this energy is used to warm our planet. 

We can also use solar technology to harness solar energy for a variety of purposes: 

• solar collectors generate heat and warmth 
• concentrated solar power systems generate electricity by converting heat into water vapour 
• solar cookers and solar ovens heat food 
• solar cells generate direct current (photovoltaics)

Converting solar energy into electricity 

A solar cell or photovoltaic cell is an electrical component that converts the radiant energy in light (generally sunlight) directly into electric energy. The physical principle behind this conversion is the photovoltaic effect. A solar cell should not be confused with a solar collector, which uses the sun's energy to heat a transmission medium (usually hot water). 

Solar cells are made of silicon. Silicon blocks are cut into thin slices approx. 0.5 millimetres thick. The slices are then contaminated with different impurity atoms, which creates an imbalance in the structure of the silicon. This produces two layers, the positive p-layer and the negative n-layer.

To put it simply, the flow of electricity is created when electrons from the n-layer, excited by the incident light, move through the connected device (such as a solar motor) to the p-layer. The more light (energy) hits the cell, the more the electrons move. 

When a solar cell is connected to a device, it will move in this direction. You can imagine the flow of electricity as a circuit, where electrons are continuously arriving at the n-layer, then moving back to the p-layer. This flow of electrons causes current to flow and makes the motor turn.