What is Energy?

Energy makes things happen - it causes changes!

For example, to change ice into water, you have to put energy in the form of heat into it. If you remove the same amount of energy from the water, it  will freezes again. These are "Physical Changes".

If you want to change the position of a shopping trolley from the check-out to the car, a "Mechanical Change", you have to do some work (mechanical energy). The greater the force required to move the trolley and the further away you've parked the car, the more work you have to do.

To put it mathematically: work = force x distance moved

Energy cannot be destroyed, but it can be changed from one form to another:

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. This is called photosynthesis.

By eating the plants animals like us can use this energy which the plants have stored as chemical energy, in order to generate heat to keep warm and also to do work like pushing shopping trolleys around!

Many millions of years ago growing land-plants and algae in the sea took energy from sunlight; the fish and other animals ate the plants; when the plants and animals died they became buried in mud and fossilised. Under intense pressure and heat deep down in the earth 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, a very versatile form of energy which can be turned back into work, heat and light as required. 

Not all the energy in the fuel can be changed into electricity; some heat goes up the chimney in the gases formed when fuels are burned, some more is radiated from the outside of the boiler, and some of the work done by the turbine will be turned to heat by friction in the generator. So although energy cannot be destroyed, it can all too 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 so-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.

And we can now use the radiation from 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". Will the Irish farmer become a energy producer in the future?