Energy is essential to our daily lives. It heats our homes, fuels our transport and supplies our electricity, but how many of us actually think about where energy comes from?
Energy can never be destroyed, it simply changes from one form to another. For example, to change ice into water, you need to add energy in the form of heat. This is a physical change, but energy can many other forms, such as mechanical energy (the physical force required to move something) and chemical energy (energy created through chemical changes in an organism).
The Energy Chain
All around us energy is constantly changing form as it goes through a never-ending cycle of use. Through the process of photosynthesis green plants use light, a form of electromagnetic radiation, to cause chemical changes in the carbon dioxide which they take from the air and the nutrients drawn from the soil, in order to grow. By eating the plants animals, and humans, can use this energy which the plants have stored as chemical energy, in order to generate heat.
Many millions of years ago land-plants and algae in the sea took energy from sunlight. Fish and other animals consumed the plants, and when they died they slowly became fossilised. Under intense pressure and heat deep underground the plants became coal, and the animals formed crude oil & natural gas trapped in tiny pores in sandstone rock.
By burning these fossil fuels to release heat from the chemical energy they contain - which originally came from sunlight millions of years ago - we can raise steam in a power station boiler. The heat and pressure energy in the steam is turned into work in a turbine, which drives a generator to produce electricity.
Not all the energy in the fuel can be changed into electricity; some heat escapes up the chimney in the gases formed when fuels are burned, some is radiated from the outside of the boiler, and some is lost through the mechanical work of the turbine (friction in the generator). So, although energy cannot be destroyed, it can easily be "lost". The percentage of the original chemical energy in the fuel which emerges from the power station as useable electricity is called the energy efficiency of the station.
When we have used up all the coal, oil & natural gas it will take millions of years for new reserves to form. Even peat, a "young" fossil fuel, takes several thousand years to mature. Burning these fuels also releases carbon dioxide into the atmosphere at a rate greater than today's forests can re-absorb it for growth; too much of this gas in the air will trap heat in the atmosphere & cause 'global warming'. So there is increasing interest in the development of what are called renewable energy sources.
- Moving materials possess kinetic energy. The kinetic energy in flowing water has been used to drive waterwheels for grinding corn and other tasks for centuries. Modern water turbines for driving electricity generators were first developed over one hundred years ago, and there are large hydro-electric power stations at Ardnacrusha & Poulaphouca.
- Waves too, have kinetic energy. Development of practicable machines for harvesting this energy is still in its infancy, but there is already a wave-generator serving a light-house in Ireland.
- Old windmills used the kinetic energy in the wind; modern wind turbines are being used for electricity generation in several places in Ireland.
- The energy in the tides of the sea can also be harnessed. Water trapped behind a dam at high-tide has potential energy. At low tide the water is released to flow through water-wheels or turbines; a medieval tidal mill still exists in Wales, and there is a modern tidal electric power station in Brittany.
- We can also use the radiation fom the sun directly. Solar thermal panels use the infra-red ('heat radiation') in sunlight to heat water for heating houses & offices, or special types can raise steam to drive a generator. Solar photo-voltaic panels convert the visible light & ultra-violet rays directly into electricity.
- Wood and other plant material was mankind's earliest source of 'artificial' heat; trees or other biomass crops can be specially grown and burned to produce energy; the carbon dioxide released will only be that which the plants have recently used up in growing, and an equivalent amount will be absorbed again by the following "energy crop".
To find out more about sustainable energy and the different technologies that have been developed, please visit some of our sections on the left.