Wind, Water and Solar Power

TASK 1: HOW DO WIND AND WATER GENERATE ELECTRICITY? 

We all know what water is, but what exactly is wind? Wind is created by the sun. Land absorbs heat energy from the sun and warms the air around it. as the warm air rises (because it is less dense than cool air), cool air rushes in to take its place. The fast moving air is wind.

So how can water and wind generate electricity? The answer is all about the transfer of energy. Everything has energy of some form. It can't be created or destroyed, but it can be converted from one form to another when it is transferred between things.

When water is lying still in a reservoir, it has potential (stored) energy. But when it is rushing down towards the turbines of a hydro-electric power plant, the potential energy is converted to kinetic (moving) energy. In the same way, still air has potential energy that is converted to kinetic energy when a wind develops. To turn the huge blades on a tower, wind speeds need to be at least 15km/h.

To look at, hydro-electric power plants and wind farms are very different but the way in which they generate electricity is very similar.

When moving water or wind hits the blades of a turbine, the kinetic energy converts to mechanical energy and causes the blades to move. The turbine is attached to a shaft. As the blades turn, their mechanical energy is converted to rotational energy, causing the shaft to spin. The spinning shaft is attached to a generator, which is a magnet surrounded by copper coils.

The principle of electromagnetism is used to generate electricity. Just as a current in a wire generates a magnetic field around itself, so a moving magnetic field generates a current. Inside the generator, a magnet spinning inside a coil of copper wires generates a current in the coil - electricity!

Electricity loses some of its power as it travels over a distance. To make sure it still has enough power when it reaches its destination, a step -up transformer boosts its voltage to a very high level. Huge metal towers called transmission towers support insulated cables that carry the electricity at this dangerously high voltage. Before it is connected for use, the electricity is passed through a step-down transformer, converting it to lower voltages that are safe for domestic and commercial use.

 

TASK 2: HOW DO WE GET POWER FROM THE SUN?

Solar power is a reliable source of sustainable energy generated from the light of the sun. It requires no fossil fuels, produces no noise and little pollution, and once installed, it requires no maintenance. 

How does solar power work?

Light energy from the sun is collected in solar panels. Each panel contains a number of special cells called photovoltaic (PV) cells. Solar panels are always located where they will receive the maximum amount of sunlight. Power is harnessed from the light of the sun, not from the heat. As such, the cells work well in winter even when the heat is less intense.

Less electricity is produced by solar panels in winter because there are fewer hours of daylight and there is more chance of cloudy skies, which reduce the intensity of the suns rays.

The output of power from solar panels is measured in sun hours. One sun hour is equivalent to the amount of power that would be generated in one hour of strong midday sun.

On a cloudy day, it may take a few hours for a panel to produce one sun hour of power.

As sunlight strikes a solar panel, some of its energy is transferred to each PV cell. The construction of the cells allows them to instantly convert the light energy into electricity. This is called the photovoltaic effect, which means electricity from light.

The electricity passes through the cells in each solar panel and then among the panels, along insulated cables, into an ammeter. This measures the magnitude (amount) of an electric current at any given moment.

If a dark cloud hides the sun for a short while, the reading on the meter drops and then rises again when the cloud moves away.

When the solar panels do not produce enough electricity for all appliances being used, electricity is supplied by the main electricity grid.

When the solar panels produce more electricity than is needed, the excess is transported to the main electricity grid.

The electricity passes through the main switch board, which supplies all the energy for all household appliances. 

The kilowatt per hour meter records total the amount of solar energy produced by the solar panels.

The type of electricity produced by PV cells is called direct current (DC). The type we use in our homes is called alternating current (AC). 

An inverter transforms the electrical current from the solar panels into the type needed for electrical appliances in the home, such as lighting, cookers, computers and televisions.

 

TASK 3: WHICH ENERGY SOURCES FOR THE FUTURE?

Electricity is needed to power electrical appliances, machinery and different forms of transport. The source of energy has to come from somewhere and it can be either sustainable or unsustainable.

Sustainable sources of energy will not run out. They are available for this generation and all generations that follow. Examples of sustainable energy sources are the sun (solar energy), wind, water, tides and heat from the earths core (geothermal energy). Producing electricity this way creates relatively little pollution. 

Unsustainable sources of energy are those produced by fossil fuels; coal, oil and natural gas which formed millions of years ago from the remains of dead plants and animals. They are unsustainable because once they are used up, they cannot be replaced. We now know that burning fossil fuels to generate electricity creates environmental problems that damage the health of the planet; for example: 

TOXIC WASTE

Toxic waste from fossil fuel combustion can seep into soil and water, damaging plant and animal life and destroying eco systems.

ACID RAIN

Burning fossil fuels releases damaging gases that rise into the atmosphere and can combine with water vapour and fall as acid rain. Acid rain damages plant and animal life and the soil, inhibiting crop growth.

GREENHOUSE GASES

The gases released from fossil fuels have the effect of trapping heat within the earths atmosphere. This may cause global warming and changes to the climate. If changes to the climate do occur, rainfall may decline and average temperatures may rise.

OZONE LAYER DEPLETION

The earth is protected from certain types of harmful sun rays by the ozone layer, which works like a protective blanket within the atmosphere. The build up of certain manufactured gases has depleted the strength of the ozone layer and allows greater amounts of types of harmful solar rays to reach the earths surface.

OIL SLICKS

Transport accidents involving liquid fossil fuels have caused environmental disasters; for example, oil slicks from damaged oil tankers have spread across beach and ocean, destroying local habitats and wildlife.

Access to sustainable sources of energy varies across the globe:

• Regions with high volcanic activity can make use of geothermal energy.
• High altitude areas or those with exposed coatlines favour wind energy.
• Areas in the tropics where the hours of daylight are relatively constant throughout the year could effectively utilise solar power

We need electricity but we don't need to burn fossil fuels to produce it. Renewable energy sources can be used to generate electricity with minimal impact on the environment.