by David Roper (LVI, SATIS A/S)
What is meant by energy efficiency ?
It is all to do with converting energy from one form to another. Normally we need a device for doing this, such as a generator, or electric light bulb. The total energy going into to a device is always equal to the total amount of energy from the device. This is known as the conservation of energy, which states that energy cannot be creates or destroyed, but merely changes from one form to another. Now, in order to define the efficiency of a device we need to identify the useful form of energy we need from the device. Then we express this as a fraction of the total energy into the device, in the same time . Therefore , we have
Energy Efficiency = (Useful Energy Out / Total Energy In)
Which can have a value from 0 to 1. A value of 0 would mean we obtain no useful energy from the device. The energy has been converted into other forms of energy that we do not require ! Normally we call this the 'wasted' energy. 'Wasted' energy = (total energy in - useful energy out). Multiplying the number we obtain from the equation will give us the percentage efficiency of the device. We can also write the efficiency in terms of useful power obtained
Energy efficiency = (Useful Power Out/ Total Power In)
Again , by multiplying the number we obtain from this expression by 100 will give the percentage efficiency . Normally we would consider a filament light bulb to be very inefficient, because most of its energy is converted into heat. However, if we define the heat from the light bulb as the useful energy we need, then all of a sudden we have an efficient device !
One of the greatest challenges facing our 'modern' world is no only to save energy resources, but to develop devices which convert the source energy into a greater percentage of useful energy.
Energy efficiency throughout the world is falling to its lowest in the latter half of this century . One of the worst energy wasters is Japan, having an overall energy efficiency of approximately thirteen percent. The other inefficient energy users are West Germany and the United States of America. This is because the demand for energy has increased with the population explosion . As a result, there are no new energy sources to help to recover the losses. Inefficient devices include cars and computers.
The more widespread use of energy-efficient technology is not yet a standard throughout the world . The losses of energy resources such as fossil fuel, coupled with the lack of any large scale efficient new energy sources being developed, has presented a scenario where the world is in for a large shock when its non-renewable resources run out in the mid-twenty first century.
One extrapolation of events is that our planet's non-renewable energy resources will soon be exhausted and there will be nothing to replace them permanently. Therefore, the world's population will find that there will be no power to run the important machinery and that we will be unable to use the technology which is needed for these machines to work.
Other Sources Of Energy.
There are several different sources of energy which with research can be used to supplement or even replace the energy sources that are being used today. These include nuclear fusion and wind power but these are either to hard to control or do not produce enough energy. The other types of energy production that are being researched and in some cases even used are Tidal Power, Hydroelectric power, Geothermal energy and solar energy. These are all renewable energy sources and can be harnessed to provide power for the population of a country but in some cases they cannot produce enough energy to supply the demand created by they energy intensive lifestyles of the modern household. Solar energy can only produce small amounts of energy at one time and for obvious reasons only during the day when the sun is shinning. It depends greatly on the weather at the time . If the weather is poor then the amount of electricity from the solar panel is greatly reduced.
Biomass
Biomass is provided by the decomposition of waste products such as straw, wood waste, refuse and landfill gas. Useful energy can be obtained by the burning of the gases that are released when these products decompose. The main gas produced is methane. The solid waste itself can also be used . For example the burning of straw and wood waste in special burners to provide hot water for use in a house heating system.
Hydroelectric Power.
This is an energy source which is currently used in North Wales to great effect. There are two power stations one of which is Dinorwig power station which makes a reasonable contribution to the national grid in britain. The process of producing energy this way involves holding water in a reservoir and allowing it to fall under gravity to spin a turbine as it flows through the station. This then turns a generator to produce electricity. This type of energy source can be widely exploited in areas where there are large amounts of rain and it has the required geography to allow a reservoir to be built so that the water can be stored and be allowed to fall under gravity.
Geothermal Energy
This is where water is pumped down into the ground and flows through hot rocks. It is then allowed to come back up to the surface as high pressure steam. This steam turns a turbine which then turns a generator to produce electricity.
Tidal Energy.
This uses the energy given to the the sea and oceans by the gravity of the moon which causes the tides to rise and fall as it orbits the Earth.These systems use a dam across an estuary or a bay and as the tide rises the water pushes turbines in the dam round as it flows past them to fill the estuary or bay. The tide then falls again and the gravity of the earth causes the water to turn the turbines again as the water leaves the estuary or bay.At the moment the largest of these schemes is in France and generates 240MW and there are smaller schemes in Canada and in the Soviet Union. China also has tide powered pumping stations along its coastline.
Wave Energy.
This type of energy is different to tidal power but still uses the sea to produce energy. It uses the vertical displacement caused by waves to generate electricity by turning turbines. It is usually done by a long string of floating barrages which as the waves pass under them they rotate around there connections turning a turbine within the float. This way of producing energy has never seriously been looked at and for now it is not in use anywhere in the world.
Environmental Impact Of Renewable Energy Sources.
Many renewable energy sources affect the environment and some have been said
to be Eye-sores such as wind farms full of wind turbines and hydroelectric
power stations altering the countryside by having to create artificial lakes
but in the long run the beneficial effects of having these renewable sources
of energy far out way the problems of what the look like or whether they
change the current environment.