Coal Fired Power Station

---

Coal-fired power stations produce electricity by burning coal, to boil water, to produce high pressure steam, to drive a turbine, connected to a generator that produces electricity. They belong to the family of thermal power stations along with oil and gas-fired stations. They are easy to power up and down to meet changing load.

Pulverised coal is burned in a furnace where feedwater in boiler-tubes is heated to produce steam at very high temperature (>500°C) and pressure (>150 bar). The steam flows through a set of turbines which spin a generator to create electricity. The steam is then cooled, condensed back into water and returned to the boiler to start the process over. This water stays in a closed circuit to ensure that it stays clean for the turbine. The cooling water is a separate circuit where the water either cools down in large cooling towers, or into a nearby water source (river, ocean etc.).

The turbines spin the generators at 3 000 (3 600 USA) revolutions per minute to make 50 Hz (60 Hz) alternating current (AC) electricity at tens of thousands of volts. Typical generator sizes are a few hundred megawatts (MW) and a typical power station produces a few gigawatts (GW). That equates to some 10 billion kWh per year, enough to supply nearly one million homes.

Burning about 15 000 tons of coal a day produces a lot of ash, smoke and gases. The ash has several industrial uses, but the gases require special treatment, both mechanical and chemical, to reduce harmful components before release through tall stacks high into the atmosphere.

Hydro Power

---

Hydropower, or hydroelectricity, is generated from the energy of flowing water. For water to flow requires a slope like a river or pressure from deep water like a dam or lake. Hydropower is a renewable energy source because the sun is constantly evaporating water back into the clouds in the so-called water cycle.

Early uses of hydro power were waterwheels for mechanical milling such as grinding grains. Modern hydro plants produce electricity using water turbines and generators. Water under pressure causes a turbine to rotate. The turbine is connected to an electromagnetic generator and the mechanical energy is converted to electrical energy when the turbine rotates.

Dams have been created on many rivers around the world, to harness the energy of water flowing to the sea. Large turbine halls are excavated in the hillsides adjacent to the river or constructed within the dam wall. Excess water is released, often dramatically, into a spillway.

Hydro power facilities can be categorized into three sizes: large (>30 MW), small (100 kW < 30 MW), or micro (<100 kW). Some countries are fortunate to be mountainous and have an abundant supply of clean, cheap hydroelectricity.

In pumped-storage schemes the turbines are reverse-running pumps that can pump the water back where it came from using the generator as a motor. This is done at night using cheap off-peak electricity to be available for additional power during day-time periods of peak demand.

Nuclear Power

---

Nuclear power stations produce electricity using the heat from a nuclear reaction, to boil water, to produce high pressure steam, to drive a turbine, connected to a generator that produces electricity. They belong to the family of thermal power stations. They prefer to run continuously and provide the base-load power supply.

Most nuclear power stations utilise the heat produced by the nuclear fission of uranium and plutonium. This takes place in nuclear reactors which produce and control the release of energy from splitting the atoms. The main design, originally developed for propelling submarines and used in 85% of nuclear power stations, is the pressurised water reactor (PWR) which has water at over 300°C under pressure in its primary cooling/heat transfer circuit, and generates steam in a secondary circuit. As nuclear fission creates radioactivity, the reactor core is surrounded by a protective shield and the high temperatures and pressures require strong steel pressure vessels.

Nuclear is the second largest low-carbon source after hydro-electricity., there are 450 fission reactors in 30 countries with a combined electrical capacity of 395 Gigawatt (GW) – approx. 10% of world energy demand. 60 GW of ‘generation III’ reactors are under construction and another 120 GW planned

The debate about nuclear power is that it is clean in terms of carbon emissions, but the disposal of used fuel and the operational risks to people and the environment, as witnessed in a number of accidents, are of concern.

There is considerable international collaboration on research and development towards greater efficiency, safety and recycling of spent fuel in future ‘generation IV’ reactors.

Photovoltaic Energy

---

Photovoltaics (PV) are special semiconducting materials that convert light into electricity. They have gained in popularity as their efficiency and reliability have increased and the cost of manufacture has decreased. From small localised systems they are now viable to provide power into the national grid.

A PV system for the grid requires millions of panels, each comprising hundreds of solar cells. The PV panels can be mounted on the ground, rooftops, walls or even floating. The mounts may be fixed, in which case their output will vary as the sun moves, or use a solar tracker to follow the sun. A single PV cell only produces about 0.5V so they are assembled and arranged in series and in parallel to get the desired voltage and current output. They produce direct current electricity and require large powerful inverters to produce electricity for the grid.

Solar PV has specific advantages as an energy source: once installed, it produces no pollution and no greenhouse gas emission; it is very modular to satisfy power needs and silicon is abundant in the Earth's crust.

Photovoltaic systems have been used (since 1950s) in specialized stand-alone applications, notably satellites in space. Grid-connected PV systems have been in use since the 1990s.

More than 100 countries now use solar PV. In terms of global capacity PV is currently the third renewable energy source, after hydro and wind. In 2018, world-wide installed PV capacity increased to more than 515 gigawatts (GW) providing approximately two percent of global electricity demand.

Wind Turbines

---

Wind turbines produce electricity from the energy of the wind. Quite simply the wind turns a propeller, which spins a generator that creates electricity.

Wind is a renewable energy source, deriving energy from the weather (caused by the sun). Early examples were mechanical windmills for grinding flour, using sails made from fabric on wooden frames.

Modern wind turbines use aerodynamic blades, which work like an aeroplane wing or helicopter rotor blade. When wind flows across the blade, the air pressure on one surface of the blade increases. The difference in air pressure across the two surfaces of the blade causes the rotor to spin. The rotor is connected, through a gearbox, to an electric generator that produces electricity.

The whole wind turbine itself can be turned on top of its mast so that it can face the wind. When the wind is too strong the turbine can be turned out of the wind and a brake applied to prevent the rotor from turning.

Overland Power Transmission and the Electricity Grid

---

Have you ever wondered how the lights turn on in your home or how your TV gets power? It all starts from a power station and travels through the electricity grid to reach your home. Let's break it down!
Power Stations: The Source of Energy

At power stations, electricity is generated using various sources like coal, hydro, nuclear, wind, or solar energy. Once electricity is created, it travels a long way to reach our homes. This journey starts with overland power transmission.
Overland Power Transmission: The Superhighway for Electricity

Imagine electricity as a group of cars traveling on a superhighway. To make sure it travels quickly and efficiently over long distances, we use very high voltages. In South Africa, electricity starts its journey at an enormous 800,000 volts (800 kilovolts)! This high voltage helps the electricity move smoothly over long distances without losing much energy.

From Highways to Streets: Bringing Electricity to Your Town/District

Once the electricity reaches your town, it needs to be reduced to a safer level. This happens at substations where the voltage is lowered from 800 kilovolts to 11,000 volts (11 kilovolts). Think of this step as moving from a superhighway to the main streets in your town.

Final Step: Into Your Home

Before electricity enters your home, it needs to be reduced even further to a safe level. Another substation, now in your suburb, lowers the voltage to 240 volts, which is the level we use in our homes. Now, the electricity is ready to power your lights, TV, and all your gadgets safely.

How It All Connects

1. Power Station: Generates electricity.
2. Overland Transmission: Electricity travels at very high voltages (up to 800,000 volts) over long distances.
3. Substation 1: Voltage is reduced to 11,000 volts for the district and industrial consumers. 
4. Substation 2: Voltage is reduced again to a domestic voltage (400-500 volts) within the suburb.

And that's how electricity travels from the power station all the way to your home! It's like a journey from a superhighway to the streets and finally to your doorstep, making sure you have the power you need for all your daily activities.