SOURCES OF ENERGY

SOURCES OF ENERGY

Non RenewablePrimary Energy Source

Coal
                    The major use of coal in electricity generation is as a fuel burnt in the furnace of a large steam generator. The high pressure and temperature steam is then supplied to a turbo-generator which produces the electricity. The overall process is simple but there is a large amount of associated plant and equipment used to optimise the cycle efficiency and minimise environmental pollution.

Fuel Oil
                  The term fuel oil covers a wide range of petroleum products from heavy oil which requires preheating for burning and handling through to a light petroleum fraction similar to kerosene. It is a product of an oil refinery after crude oil has been processed.

Fuel oil contains no (or very little) ash and this makes the furnace design much easier compared to a design for coal fired plant. The combustion of the oil can be completed in a smaller volume resulting in smaller furnace size and lower cost.

              Heavy fuel oil (also known as residual or bunker C) is difficult to use since it has a very high viscosity and must be heated to about 40°C for pumping purposes. It is usually burnt in the furnace of a steam generator which supplies steam to a turbo-generator.

Distillate
               

       Distillate is a lighter fraction of fuel oil having a low viscosity and which may be pumped at ambient temperature. 

        Distillate is used to generate electricity by being burnt in a gas turbine or a reciprocating engine, the output of which drives a generator.

Jet Fuel
 

           Jet fuel (also known as kerosene) is the lightest fraction of fuel oil having the lowest viscosity and which may be pumped at ambient temperature.

Jet fuel is usually burnt in the combustion chamber of a gas turbine (aero-derivative type) which then drives a generator.

Gas
 

          Gas is an important energy resource, which plays an increasingly significant role as a fuel source for electricity generation, industrial processes, business and residential consumers.

The term "gas" usually encompasses:

       Two types of related, naturally occurring gases (natural gas and coal seam methane), both of which contain mainly methane (CH4).
LPG (liquefied petroleum gas) is one of the petroleum products produced in the oil refining process.

Renewable Primary Energy Sources 

 Solar
         

          Solar systems are powered by energy from the sun. Solar radiation reaching the earth's surface is called insolation and has two components - direct normal insolation (DNI) is that part of the radiation coming directly from the sun (usually 80%) and diffusion insolation is that part that has been scattered by the atmosphere or is reflected off the ground or other surfaces. Systems in which the solar radiation is concentrated use only direct normal insolation.

      

           Insolation is typically given as a power density in kW/m2 and average daily insolation as an energy density in kWh/m2-day. For much of the earth's area, the instantaneous insolation on a surface oriented towards the sun at noon on a very clear day is typically in the range of 0.9 kW/m2 to 1.1 kW / m2. The insolation may be reduced by clouds, atmospheric haze or by the angle of the sun to the surface. It quickly increases in the early morning and just as quickly falls away in the late afternoon and varies throughout the day.

         

           The best information on insolation resource for a particular location is measured data at that location. Direct normal insolation is measured with a pyroheliometer, a device that tracks the sun.

Electricity generation using solar energy is by means of two quite different methods - solar photovoltaic and solar thermal.

       

               Solar photovoltaic systems convert solar radiant energy directly to electricity through the use of solar cells which are typically solid-state semiconductor devices, usually containing silicon. Sunlight striking the solar cell produces an electric current which may be transmitted to the external load. A vast amount of research effort has been expended in recent years in developing solar cells which are cheaper to produce, are more efficient and which can produce more energy than is used in their manufacture.

               Solar thermal technologies convert radiant energy from the sun to thermal energy. All of these technologies include a collector which redirects and concentrates the insolation on to a receiver. In the receiver, the solar energy is absorbed, heating a fluid that powers a heat engine to generate electricity. There are several different arrangements of solar thermal systems incorporating different shapes of collectors and varying mechanisms of heat transfer. Many demonstration plants have been or are currently being performance tested within Australia and throughout the world.

Wind
 

           Wind energy systems convert the wind's kinetic energy into mechanical or electrical energy. The energy flow rate per unit area is proportional to the wind velocity cubed - this means that a doubling of the velocity results in an eight times increase in available power. Hence the economics of a wind power system are extremely sensitive to the wind velocity resource. The wind velocity at a particular location varies with the height above ground level and the nature of the terrain.

          

          The actual amount of energy that can be extracted from the wind is less than the theoretical amount of energy available with the theoretical limit being about 60%. A typical efficiency for a wind turbine is about 40%; that is, about 40% of the power available in the area swept by the wind turbine blades is converted to electricity.

           

            On a global scale, winds result from temperature gradients between the equator and the poles and between the land and seas. On a smaller scale, thermal winds can be generated by local thermal effects. Local factors such as high altitude, unobstructed terrain and natural wind tunnelling features cause some areas to have inherently higher wind speeds. At present, areas with a mean wind speed greater than 6 metres per second are considered suitable for wind energy projects but it is anticipated that improvements in technology will permit areas with lower wind speed to be developed.

           Electricity generation using wind as the energy source uses a wind turbine consisting of a large rotor, a gearbox and a generator. Wind turbine technology has developed significantly is the last 25 years and one of the latest turbines has done away with the gearbox since this was a major cause of failure in some early machines.

           The tendency is to construct wind farms consisting of a number of interconnected turbines in a cluster to achieve an economy of scale. The wind farm must be carefully located so as to prevent objections from residents on the grounds of visual or noise pollution. Care must also be taken in the site selection so as to avoid bird kills, particularly to threatened and/or migratory species.

Water
 

            Water energy systems use the energy contained in the water resource. The energy may be in the form of the potential energy stored in an upper water reservoir which can be released as the water falls to a lower reservoir. It may also be potential energy resulting from the changes in the level of ocean water during tidal cycles.

             Another form of water energy resource is associated with the kinetic and potential energy of ocean waves. The kinetic energy of waves is associated with the velocity of the water mass; the potential energy is associated with the displacement of water above or below the mean sea level. The greatest resource for wave power typically occurs between 40 degrees and 60 degrees latitude in each hemisphere. The west coasts of the United States, Europe, New Zealand and Japan are considered suitable for wave energy extraction.

A hydro-electric plant is used to generate electricity from the potential energy stored in the water. As the water is released from the upper to the lower reservoir it passes through a water turbine which drives a generator. There are numerous hydro-electric schemes throughout the world, with some having a capacity of thousands of megawatts.

              A tidal energy conversion plant typically consists of a tidal basin created by a dam, a turbo-generator and a sluice gate in the dam to allow the tidal flow to enter or leave the tidal basin. Tidal energy using conventional hydro-electric technology has been demonstrated on a large scale.

There are a number of different devices used to generate electricity from ocean waves. One arrangement uses a water oscillation chamber incorporating a Wells turbine. The rise and fall of waves in the chamber cause air in the chamber to pass backwards and forwards through a Wells turbine, thereby generating electricity. The Wells turbine spins in the same direction irrespective of the direction of the air passing through it.

Biomass
 

              Biomass is regenerative organic material used for energy production. Sources for biomass fuel include agricultural and forestry residues and municipal and animal wastes. Bagasse (the waste from the crushing of sugar cane) has been used for many years in the sugar industry as boiler fuel for the generation of steam and electricity for use in the sugar mill during the crushing season. Its use, together with other agricultural/forest wastes, is now being promoted in facilities that operate all year and which, in the non-crush season, generate electricity for sale back to a retailer. Such schemes depend on Government subsidy and/or generous buy back prices for their viability. S

              

                 Biomass has a number of advantages over traditional fossil fuels with its primary advantage being that it is renewable. The growth and combustion cycle of biomass does not increase the atmospheric carbon dioxide level (however, cultivation and harvest of biomass requires the use of fuels that may increase the carbon dioxide level). It is usually a low cost fuel since many biomass sources are agricultural or industrial residues that, if not used for energy production, would result in disposal costs.

                Electricity production from biomass generally uses direct combustion of the biomass in a steam generator which supplies a turbo-generator. Allowance must be made in the design of the materials handling system and the steam generator for the specific properties of the biomass to enable satisfactory plant operation. For example, bagasse, which is the fibrous residue from sugar cane milling, is a light-weight material with a high ash content and demands special consideration in the design stage.

An alternative method is to process the biomass in a gasifier with the gaseous output being burnt in a combined cycle gas turbine plant.