How electricity is generated

The moment you flip a switch, things start happening. Lights come on to allow you to see. Heat is generated, so you can cook and keep warm. A whole range of electronic items just work! As if by magic, energy flows into your home and into your life. What's the trick?

Let us show you, simply, where electricity comes from and how it gets into your home, whatever its origin.

What is electricity?

Everybody uses it, almost without thinking, but how many of us can actually define what it is?

Electricity is the energy generated by the movements of electrons (negative charge) and positrons (positive charge) within conductive materials.

Opposites attract. Positive and negative charges come together, creating two types of energy: Static electricity (generated by friction) and dynamic electricity (known as a current).

Where does electricity come from?

Electricity’s journey to your plug is very long, but occurs at astonishing speed. It is not magic; it is not science fiction. It is a step-by-step process which explains many of the doubts that arise with regard to the electricity sector:

• Generation: electricity is produced in plants capable of drawing electrical energy from primary energy sources. These primary energies may be renewable (wind, solar power, tidal power, etc.) or non-renewable (coal, natural gas, oil, etc.). The companies which (fully or partly) own the various power plants sell the energy generated to companies which supply it commercially.
• Transmission: once the energy has been processed and turned into electricity, it is sent through overhead or underground wires from the plants to substations. There, transformers ensure sufficient electrical voltage. Substations tend to be above ground near to power plants, or on the outskirts of cities, though if they are not too large, they may also be within the actual city, inside a building.
• Distribution: from the substations, electricity is distributed to the homes in the surrounding area. As a consumer, you cannot choose your electricity distributor; it is determined by where you live. That company is responsible for ensuring electricity reaches your home properly, and takes care of repairs when needed. It is also the company which owns your electricity meter, and sends readings from it to your commercial energy supplier.
• Commercialisation: what you certainly can choose is your commercial energy supplier. It is the supplier who sends you the bill: the supplier buys the energy from the generation companies, and sells it to you. Commercial suppliers are the ones who offer various rates and offers, although in Spain, there is a free market (you pay under the terms of your contract, as happens with your mobile bill) and a regulated market (what you pay is set by a system designed by the Government).

Types of electricity plant

As we said earlier, in order to generate electricity, we need to release the energy contained in primary materials. How do we do this? It depends entirely on the type of electricity plant we are talking about:

• Conventional cycle thermo-electric plants (coal, diesel oil and natural gas): energy is liberated by burning coal, natural gas or diesel oil. As they burn, they are used to heat a tank of water. That water transforms into steam, which is used to drive a turbine. It is this movement which generates electricity, by means of an alternator, which turns the mechanical energy into electrical energy. Finally, the steam passes through a condenser, turning back into liquid water, and starting the cycle anew.
• Combined-cycle thermo-electric plants (coal, diesel oil and natural gas): these plants work in a very similar way to conventional-cycle ones. Like these, they have a turbine which is driven by steam from heated water. However, they also have another turbine, driven by air drawn in from outside and heated by the same fossil fuels. The major advantages of combined-cycle over conventional-cycle plants is that they are more efficient, more flexible (they can work at full capacity or at "half throttle" as required) and more ecologically friendly (producing less emissions into the atmosphere).
• Nuclear power plants: the heat released by nuclear fission in a reactor is used to heat large quantities of high-pressure water. The resulting steam produces electricity as it passes through a turbine connected to a generator. The fuel used tends to be uranium.
• Geothermal power plants: the system is similar to the previous ones (water is heated to create steam which drives a turbine), but in this case, we use the natural heat within the planet through pipelines in the subsoil.
• Biomass plants: in this case, heat is generated by burning organic material, be it plant matter or any kind of waste (animal, industrial, agricultural and urban waste products).
• Hydro-electric plants: these plants do not require heat, as these are the evolved version of the windmills of old. What they do use is a significant water drop to move a hydraulic turbine. They are typically built in barrages and reservoirs.
• Wind farms: in this case, it is the wind which drives a turbine to obtain electricity.
• Solar power farms: there are two types. Las Thermo-solar installations use the heat from the sun to heat water and use the steam to drive a turbine. Photovoltaic installations transform solar energy directly into electricity, using photovoltaic cells.
• Tidal power plants: the movement of water caused by high and low tides drives a turbine, which produces electricity by means of a generator.
• Wave power plants: similar to the previous technology, but using the force of waves instead of tides.

The major difference between renewable and non-renewable stems from the primary energy being used to generate electricity. Do we need to replace the so-called “fuel”, or is it no longer necessary, because nature provides it for free?

At present, the most commonplace power plants use non-renewable energies: that is, they use primary energy which must be extracted from the ground (coal, natural gas, uranium, etc.). However, the future looks much more renewable.

How is wind power produced?

Wind power is difficult to explain briefly, but we’ll give it a go: the force of the wind on three-bladed wind turbines creates mechanical energy, which is transferred to a series of copper wires, where it is turned into (yes) electrical energy.

More specifically, wind is turned into electricity by the so-called aerogenerators or wind turbines, which have an electrical generator on board, alongside their control system and grid connection system.

Thinking clearly about it, though, we seem to have jumped the gun a little, forgetting about a crucial question: where does the wind come from?

It is something so utterly everyday that we never stop to think where it comes from. Wind is caused by the effects of the sun on our planet. Between 1% and 2% of solar radiation absorbed by the planet becomes wind energy. This is due to the fact that the earth’s crust releases a large portion of solar energy into the air, causing the air to warm up, become less dense, expand and rise. At the same time, the cooler, denser air – sitting over seas, rivers and oceans – comes sweeping in to fill the gap left by the warm air.

Wind is simply the movement of air. Masses of air which move from areas of high atmospheric pressure to areas of low pressure move at speeds proportional to the pressure differences between the two areas (the greater the difference, the more powerfully the wind blows).

To transform sunlight into energy, metal semi-conductor sheets are needed: these are called photovoltaic cells.

These cells have one or more layers of a semi-conductive material, and are covered by transparent glass which allows solar radiation in and helps minimise heat losses.

The solar panels that can be seen on the rooftops of many houses are made up of these photovoltaic cells. Whilst they may seem costly to install, data show that they pay for themselves in the long run, offering savings of around 30% on electrical consumption; in the longer term (25 years), this represents and a saving of between €20,000 and €30,000! Another of their advantages is that they do not require much maintenance.

The sun’s rays are made up of photons which strike the panel’s photovoltaic cells, generating an electrical field between them and, hence, an electrical circuit. The more intense the light, the greater the flow of electricity.

The photovoltaic cells convert sunlight into direct current (DC) electricity, with an intensity ranging between 380 and 800 volts. To improve the result, an inverter is used to turn that energy into alternating current (AC), which is the form of energy we use in our homes.

Finally, this alternating current passes through a meter that quantifies it and supplies it to the general electrical grid.

Hydroelectric energy

A study by NASA states that the origin of life may be found in the electricity generated naturally on the sea floor some 4,000 million years ago. Water and movement are a source of life and, thus, also a source of energy.

Our ancestors knew this and used the currents in rivers to move large mills. More sophisticated versions of these water mills are used in hydro-electric power plants. A dam blocks a river with a concrete wall, flooding the area around the plant and creating an artificial lake. The retained water harbours enormous potential energy.

Water is one of the strongest and most powerful forces of nature. That torrent can be converted into kinetic energy (the energy of a body in motion). Under the force of gravity, the water travels downward through a series of large pipes called penstocks. This makes the blades of the turbines spin quickly.

The turbines supply mechanical energy to the plant’s electric generators. A transformer increases the electric power and transmits it to the power grid, which then supplies power to your TV or washing machine.

Tidal energy

A lesser-known variant of hydroelectric energy in tidal energy.

This system utilises the vertical movement of seawater, which is caused by the gravitational force of the moon and sun on the sea. The ebb and flow of the tides generates tidal power.

At present, there are three different types of tidal power plants:

• Tidal barrages: built at river mouths, tidal barrages are quite similar to hydropower plants. They harness the potential energy generated by the difference in height between high and low tides. Although they produce large amounts of energy, these facilities are quite costly to build and maintain.
• Tidal stream generators: the tidal flows drive a series of axial turbines, similar to wind turbines, which generate mechanical energy. This is the simplest and most economical method, with the lowest impact on nature. As no dam needs to be built, it does not alter the ecosystem in the sea.
• Dynamic tidal power: this method is merely theoretical, as it has never yet been successfully applied. It would combine the two methods described above. To do this, dams would be built off the coast and further out to sea creating a T-shaped structure that, on one side, would retain the force of the high tides and, on the other, the energy of the low tides.

Tidal energy stems from the movement of water caused by the high/low tide cycle.

Geothermal energy

Moving out of the water and onto dry land, let us know look at geothermal energy, a system which uses the heat stored inside the earth, in hot rocks and/or hot springs.

The thermal energy contained under our feet is tremendous. By simply digging to a depth of some 10 metres, we find temperatures of around 17°C year-r due to the thermal inertia of the soil.

To harness this energy, geothermal heat pumps are used to extract heat from the earth or release heat into it, depending on whether the goal is to heat or cool the air, or to heat water.

One of the most precise methods is to inject liquid water deep into the earth to raise its temperature; the water is turned to steam and returns to the plant carrying a great deal of energy, ready to be transformed into electricity.

This energy can be used for different purposes depending on the characteristics of the source:

• Resources at high temperatures (over 150°C) are used to generate light.
• Below 100°C they are used to supply electricity to heating/air conditioning systems.
• At very low temperatures (less than 30°C) they are used directly for heating water.