Fossil energy resources
The commonly accepted fact is that the earth's fossil energy resources are limited and in the next decades, oil, coal and gas production will come to an end stage. At this point of time, renewable sources of energy should contribute to the world's ever rising need of energy . (Wind Energy Systems for Electric Power Generation By Manfred Stiebler) Wind generation is the valuable source of renewable power used in most of the countries around the world. The hunt for pollution free sustainable energy has encouraged the wind generation industries worldwide. If the mechanical energy is transferred to electricity, then the machine is called wind turbine, wind generator, wind energy converter, wind power unit or aero generator. Around 5000 B.C, wind energy was first used to propel boats along the river Nile. In the 7th century, simple windmills were used in Persia for milling grains and for irrigation purposes. In countries like America, Russia and Australia, wind generator supplied the power needed for farming etc. The wind generation process does not use up any resources and thereby it makes certain inexhaustible supply of energy. Renewable sources of energy like wind generation produce very less carbon dioxide emissions and so it is a preferable source of energy. Fossils fuels like coal, gas and oil are also used for energy generation. But these fossil fuels produce a high carbon dioxide rate which is the major contributor of greenhouse gas in the issue of global warming.
Over the last three decades, wind energy technology has developed rapidly with the use of power electronics which allows functioning at variable rotor speed . (Wind Energy Generation: Modelling and Control By Olimpo Anaya-Lara, Nick Jenkins, Janaka Ekanayake, Phill Cartwright) In Australia, there has been a tremendous increase in the number of wind farms. The encouragement for setting up more and more wind farms is provided by Australian Government's mandatory Renewable Energy Target. (MRET). There were only twenty wind turbines in Australia during 1996 with capacity of 2.7 megawatts. Australia has witnessed a dramatic development of wind power with 2120 percent increase with 444 wind turbines and 638 megawatts capacity at present and there are another 130 turbines presently under construction. A typical wind turbine satisfies the energy needs of 1000 homes in Australia. A wind turbine 50 megawatt wind farm can decrease greenhouse gas emissions between 65,000 and 115,000 tonnes per year. The size of wind energy projects has enhanced extensively. The average size of commercial projects has grown from 10-20 turbines with a capacity of 10-15 MW in 2000 to 30-50 wind turbines with the capacity of 50-90 MW in 2005.
Best Wind Resources in Australia:
Australia has excellent wind resources when compared to other countries. Hundreds of sites have average wind speeds above 8 m/s at 50m above ground and the southern coastline lies in roaring forties. The Southern South Australia, The southwest of Western Australia, Western Victoria, elevated areas of New South Wales, Queensland and Northern Tasmania have very good wind resources.
Key steps to wind farm resource calculations:
Based on many logical steps, the location of windy sites and arraying of wind turbines in a wind farm can be simplified.
Preliminary selection of region is based on using available broad-scale regional maps, knowledge of climatology, existing background wind data and applying basic constraints to development.
By using wind measurements in several locations or regional climatology based wind prospecting modeling tools together with local wind resource mapping, the possible sites are selected.
Exact wind farm location depends on vast range of planning issues, local wind resource map and constraints like proximity to power line infrastructure, amenity of area etc.
To confirm the level of wind resource, wind is monitored at or near hub height with quality calibrated instruments.
Using a numerical model such as WASP, production of a high resolution wind resource map, local variations in wind including wind speed changes with effect and height of local roughness can be calculated.
To lay out the complete turbine design, in addition to strength and location of the wind resource it includes many other factors like visual impact, noise propagation, ease of turbine erection and foundation engineering issues.
This wind resource map of Australia was released on October 17th 2008. The red color indicates the better wind resource. According to the map, the best wind resources are The Alps of eastern Victoria and southern NSW, sections of the coast of Queensland, Central Tasmania and the NE and NW corners of island, Bass strait and its islands, area around Ballarat in Victoria, The Peninsulas, Kangaroo Island, Mount Lofty/Flinders Ranges areas of South Australia, area within about 100km of coast from Shark Bay to Moora. This map deals with the areas that are having first rate wind resources. The map visibly says that the sections of the Queensland and Southern coasts are windy. Generally, highlands have good wind resources than lowlands. Particularly good wind resource can be located in any line of hills which lies across the direction of the prevailing winds .
Technical Aspects of Wind Turbines:
Over the years of product development and experience, improvements have been made to all parts of the wind turbine. But from the past 10 to 15 years, there have no fundamental changes to central wind turbine principles. In 1980s, the output of mass-produced wind turbines were rated between 25 and 50 kW and now it has been developed to 600kW and it produces between one and two million kWh per year. The latest generation of mass produced wind turbines has seen twice the growth in size and generators are between 1.0 and 1.65 MW. Over the past15 years, there has been 5% annual increase in energy yield per square meter of wind turbine rotor area particularly in research and product development within aerodynamics. There is 50% decrease in weight and noise level reduction over the past 5 years. Mass produced wind turbines has been developed since 10 to 15 years specifically with regard to limitation of damage and operating safety in the following respects.
- Open generators are no longer used and due to this corrosion damage caused by humidity is reduced.
- The gearboxes have been improved in such a way that it can resist impact caused by changing speeds.
- To increase power transmission and reduce noise, the gear wheels in the gear boxes have inclined toothing.
- To increase the useful lives of gears and extend the intervals between oil changes, the gears have fixed with oil coolers.
- Previously, the noise insulation in nacelle was inflammable but now it is replaced with flame retarded materials.
- To avoid scattering of sparks in nacelle, the disc brakes have been shielded.
- The risk of lightening cannot be decreased only by insulation and so rotor blades have configured with lightening conductors.
- In order to slow down the use of the generator, the brake strategy has been changed.
- For ongoing control of the vital components, modern wind turbines allow remote monitoring of production data.
There are some technical aspects required for the wind generation. A wind turbine cannot generate wind until there is adequate wind generally about 4 m/s which is known as ‘cut-in' speed. Until 15 m/s, the machines do not reach peak generation. For safety reasons, the turbine controls the speed and stops the turbine. This is known as cut-out wind speed. This speed is generally set to 25m/s . (Developing wind power projects: theory and practice By Tore Wizelius)A constant output with increasing speed should be maintained up to safety cut-out speed of 25 m/s. to take advantage of stronger wind, a rotor can be allowed to idle below cut-in speed. The nominal maximum output is referred as ‘installed capacity'. A wind turbine converts kinetic energy of moving air into mechanical work. The power output, P, of a wind turbine can be well understood by this expression:
Where the density of air, Cp is the power co-efficient, A is the rotor swept area and U is the wind speed. The power co-efficient explains the fraction of wind power which may be converted in to mechanical energy by the turbine . (Wind energy: handbook By Tony Burton, David Sharpe, Nick Jenkins) The theoretical electrical output is connected to the mass of air passing through the rotor. The amount of power available doubles when the area of the rotor doubles. This is because the area of the swept circle is pi x radius squared, the output is proportional to the blade-length squared. A wind turbine requires spacing at 8-10 rotor diameters and some others suggest even greater spacing.
The decline in the nuclear power plant development or new coal and high price of energy from fossil fuels has made the increase in renewable type of energy tremendously important. These renewable energy sources produce energy without harmful emissions and help to feed the power grid. Renewable energy sources decrease our country's dependency on fossil fuels and protect our environment. The mostly used renewable form of energy is the wind. Australia is a nation which is extremely dependent on energy both for international competitiveness and domestic use. Australia is one of the highest carbon emitters and it has the third cheapest energy prices. To meet the growing demand in electricity infrastructure, renewable technologies like biomass, geo-thermal and wind are seen as substitute methods of electricity generation. The Federal Government has implemented the Mandatory Renewable Energy Target (MRET). This scheme has developed renewable industry development initiative and greenhouse gas abatement program. According to MRET, 9,500 GWh of energy in Australia needs to be generated using renewable sources by 2010. The economical issues of wind energy start from the investment to generate the electricity. The costs have changed a lot since the past decade. As the technology improved, there was a slow and long decline in the costs. The cost has been increased during past three years as the cost of commodities like steel increased. As the demand for the turbines increased, the manufacturers also raised the costs. All these can be noticed in the below graph.
According to the International Energy Agency, wind power generation costs $80 per MWh. It is important to note that in case of wind; most of the costs are upfront. Money needs to be invested to manufacture the wind turbine and then install it. After this, there are only few costs now and then for the maintenance and for the spare parts. The price of wind generation does not only depend on cost of generating, it also includes different factors like energy, taxes and subsidies which effect the market. The cost of generating electricity from wind generation consists of three steps.
Capital costs - the cost of construction of the power plant and connecting it to the power grid.
Running costs-this costs include maintenance, operation and buying fuel.
Cost of financing - this cost include the way in which the capital costs are repaid.
With the wind, the fuel is free of cost. For onshore projects, the capital is between 75% to 90% and it is considered very high. The below figure shows capital cost breakdown of a 5 MW onshore project.
The economical issues of the wind turbines also depend on the number of blades of the wind turbine. Wind turbines do not have more blades. The number of blades depends upon the job of the turbine. Turbines which are used to produce electricity do not need turning force or much torque but they need to operate at high speed. The majority of wind turbines now-a-days have three blades; it has a great aesthetic appeal. But the disadvantage of more blades is that it adds the weight and in economical perspective, the overall cost of the turbine increases and it is difficult to install particularly in the offshore areas. But in low wind conditions, a 5 blade wind turbine will improve annual energy production. But when it is compared with three blade wind turbine, more than 60% of annual energy output is increased.
There are two main factors which influences the price of the wind generated electricity. They are technical factors and the financial perspective. The cost of the electricity is low when the turbine provides more electricity. The electricity generation costs vary with the wind speed. The energy generation increases eight fold if the wind blows twice the speed . (Renewable energy focus handbook By Bent Sørensen, Paul Breeze, Aldo V. Da Rosa, Harsh K. Gupta, Mukesh Doble, Soteris Kalogirou) For example, a turbine where the wind speed is 8 meters per second produces 80% more electricity than turbine where the wind speed is 6 meters per second. For efficient production of electricity, the turbines must be arranged in such a way that they do not shadow each other. The economics of grid attached wind power depend on the perspectives. The feasibility of the wind project depends on the investors and the rate of returns they require. The levelised cost of wind is dependent on the discount rate. The marginal cost of wind is zero, which means it costs nothing to create an extra MWh. As per the graph below, when compared to the cost structure of wind, the gas-fired plants are completely different. One consists of finance costs and the other consists of fuel costs. The nuclear energy is closer to the economics of wind and the coal is closer to the economics of gas .
The price of natural gas has enhanced since 1996 and the cost of gas-fired power plants is higher. In January 2001, in certain markets the price of natural gas produced power was very high up to 20 cents per kWh. In the meantime, the cost of wind power declined. There are four important factors why the wind generation has been considered so important when compared to other sources of energy.
First, the cost of wind generation has powerful influence by the size and wind speed of a wind farm. The energy that the wind contains is a function of the cube of its speed. Though there are small differentiations from site to site in average wind, it results in large difference in production and hence in the cost.
Second, wind energy is considered as the highly capital-intensive technology. The cost invested on wind energy reflects the capital involved in plant construction and equipment manufacturing. Hence, wind economics depend upon the interest rate charged.
Third, the cost of conventional generation is higher when compared to the cost of wind energy. During 1990's, the capacity of the wind farm has been doubled three times and the cost of wind has fallen down by 15 percent and in 2006, the cost is supposed to decline by another 35-40 percent.
Fourth, if the cost of the wind power is calculate according to the environmental costs, and then wind energy's competitiveness would have increased further because wind energy has very low environmental impacts. There is no damage to the public health or environment due to the wind energy as associated with the production of electricity from conventional power plants .
Developments of this generation:
Wind energy has become a substantial part of energy generation in several countries. At present, it is not regarded as the marginal source of electricity. The development of wind energy in Australia is very high due to low price of the primary fuel. Wind power in Australia is in rapid growth phase and it is supported by G-Gas abatement scheme and legislated renewable energy target in New South Wales and also in other states .. Greenpeace and AusWEA are members of the international alliance and they planned to construct 5,000 MW for Australian wind power manufacturing industry by 2010. That means it is 50 percent increase in capacity with in 10 years . (Year book, Australia, Issue 87 By Australian Bureau of Statistics) In the southern areas of Australia, the government incentives played an important role in the development of the wind generation. The technology of the wind turbines has been developed and it is being applied in the production of wind energy. To control the energy production, power electronic devices are broadly used. Wind farms are connected to the local distribution networks at this period of wind energy development in Australia. These networks have been designed to supply loads. To ensure generator ride through and to prevent extreme disturbance to customer voltage, power electronic devices are being used. This is used to help with subsequent line clearance and to stay connected to the network during faults and not to cause disconnection of the wind generation.
An innovative wind turbine has been designed by Graeme Attey in Australia. This invention helps in making cheap micro-generation through wind power. If this model is developed in to consumer product as the West Australian Government is planning to launch next year, it can be a efficient model working .
When compared with the wind generation in Australia and other countries, Australia has only state run schemes and it has no nationalized program. Australia has less than 0.5% of Grid connected solar power compared to Germany's capacity. Germany has 2,500 MW of solar power capacity and developed its wind generation. Due to the generous feed in tariff program, Australia is lagging behind the countries such as Germany.
The efficiency of wind energy generation can be improved by following some suggestions. They are:
The Practical resource in Australia is small but the industry thought to have 10GW potential. Offshore locations have small potential when compared to other countries because of lack of shallow continental shelf. Fine splitting and substantial extension of the connecting grid is of greater importance. By unpredictability of supply and lack of commercial space, in Australia, wind is limited to 50% of minimum annual grid load. In economically attractive locations, bird strikes can be an issue.