Wind Energy – Renewable energy by harnessing wind power – Answer for Emission problem:

Wind Energy – Renewable energy by harnessing wind power – Answer for Emission problem:

People try to make many assumptions against wind turbines for generation of wind energy; but the fact remains, wind energy is most suitable form of renewable energy we can have to replace coal fired / nuclear powered / and even oil fired power plants in the near future. In support various points are discussed below:

1. Wind power is a clean, renewable source of energy which produces no greenhouse gas emissions or waste products. Power stations are the largest contributor to carbon emissions, producing tones of CO2 each year. We need to switch to forms of energy that do not produce CO2. Just one modern wind turbine will save over 4,000 tones of CO2 emissions annually.

2. The average wind farm will pay back the energy used in its manufacture within 3-5 months of operation. This compares favorably with coal or nuclear power stations, which take about six months.

3. A modern wind turbine is designed to operate for more than 20 years and at the end of its working life, the area can be restored at low financial and environmental costs. Wind energy is a form of development which is essentially reversible – in contrast to fossil fuel or nuclear power stations.

4. A modern wind turbine produces electricity 70-85% of the time, but it generates different outputs depending on the wind speed. Over the course of a year, it will typically generate about 30% of the theoretical maximum output. This is known as its load factor. The load factor of conventional power stations is on average 50%. A modern wind turbine will generate enough to meet the electricity demands of more than a thousand homes over the course of a year.

5. All forms of power generation require back up and no energy technology can be relied upon 100%. Variations in the output from wind farms are barely noticeable over and above the normal fluctuation in supply and demand.

6. The cost of generating electricity from wind has fallen dramatically over the past few years. Between 1990 and 2007, world wind energy capacity doubled every three years and with every doubling prices fell by 15%. Wind energy is competitive with new coal and new nuclear capacity, even before any environmental costs of fossil fuel and nuclear generation are taken into account. As gas prices increase and wind power costs fall – both of which are very likely – wind becomes even more competitive, so much so that some time after 2010 wind should challenge gas as the lowest cost power source. Furthermore, the wind is a free and widely available fuel source, therefore once the wind farm is in place, there is no fuel requirement or no waste related costs.

7. In future, we will need a mix of both onshore and offshore wind energy to meet the challenging targets on climate change. At present, onshore wind is more economical than development offshore. However, more offshore wind farms are now under construction. Thus, prices will fall as the industry gains more experience.

8. Wind energy is a benign technology with no associated emissions, harmful pollutants or waste products. In over 25 years and with more than 75,000 machines installed around the world, and there is no report of any body has ever been harmed by the normal operation of wind turbines.

9. The evolution of wind farm technology over the past decade has rendered mechanical noise from turbines almost undetectable with the main sound being the aerodynamic swoosh of the blades passing the tower.

10. We need to act now to find replacement power sources - wind is an abundant resource, and therefore has a vital role to play in the new energy portfolio all over the world.

Average onshore turbines discussed here is of capacity 1.8 MW. For many on-going projects at present the capacity over 2 MW turbines are being installed. Offshore, turbines currently being installed are rated at 3 MW, and it is expected that this will rise to a typical 5 MW per machine by 2010.

Cleaner Coal-fired ‘Supercritical Power plants’

High performance Coal-fired ‘Supercritical Power plants’ – Promotes cleaner environment

As name suggests, Coal-fired Supercritical power plants operate at very high temperature and pressure (580 degree centigrade temp. and at a pressure of 23 MPa) resulting much higher heat efficiencies (46%), as compare to sub-critical coal-fired plants which operates at 455 degree centigrade temp., and efficiency of within 40%. Some of the benefits of advanced supercritical power plants include:

• Reduced fuel costs due to improved plant efficiency;

• Significant improvement of environment by reduction in CO2 emissions;

• Plant costs comparable with sub-critical technology and less than other clean coal technologies;

• Much reduced NOx, SOx and particulate emissions;

• Can be fully integrated with appropriate CO2 capture technology.

In other words, supercritical power plants are highly efficient plants with best available pollution control technology, reduces existing pollution levels by burning less coal per megawatt-hour produced, capturing the vast majority of the pollutants. This increases the kWh produced per kg of coal burned, with fewer emissions.

Because of the above techno-economic benefits along with its environment-friendly cleaner technology; more and new power plants are coming-up with this state-of-the-art technology. As environment legislations are becoming more stringent, adopting this cleaner technology have benefited immensely in all respect. As LHV (lower heating value) is improved (from 40% to more than 45%); a one percent increase in efficiency reduces by two percent, specific emissions such as CO2, NOx, SOx and particulate matters.

"Supercritical" is a thermodynamic expression describing the state of a substance where there is no clear distinction between the liquid and the gaseous phase (i.e. they are a homogenous fluid). Water reaches this state at a pressure above 22.1 MPa. The efficiency of the thermodynamic process of a coal-fired power describes how much of the energy that is fed into the cycle is converted into electrical energy. The greater the output of electrical energy for a given amount of energy input, the higher the efficiency. If the energy input to the cycle is kept constant, the output can be increased by selecting elevated pressures and temperatures for the water-steam cycle.

There are various operational advantages in case of supercritical power plant:

• There are several turbine designs available for use in supercritical power plants. These designs need not fundamentally differ from designs used in sub-critical power plants. However, due to the fact that the steam pressure and temperature are more elevated in supercritical plants, the wall-thickness and the materials selected for the high-pressure turbine section need reconsideration. The supercritical plant needs once-through boiler, where as drum type boiler is required by sub-critical power plant. In fact, once-through boilers are better suited to frequent load variations than drum type boilers, since the drum is a component with a high wall thickness, requiring controlled heating.

• The performance of supercritical plant depends on steam condition. Steam conditions up to 30 MPa/600°C/620°C are achieved using steels with 12 % chromium content. Up to 31.5 MPa/620°C/620°C is achieved using Austenite, which is a proven, but expensive, material. Nickel-based alloys, would permit 35 MPa/700°C/720°C, yielding efficiencies up to 48%. Lot R&D inputs and allying with suppliers are required to achieve higher performance.

• Moreover, fuel Flexibility is not compromised in Once-Through Boilers. A wide variety of fuels have already been implemented for once-through boilers. All types of coal as well as oil and gas have been used.

• Current designs of supercritical plants have installation costs that are only 2% higher than those of sub-critical plants. Fuel costs are considerably lower due to the increased efficiency and operating costs are at the same level as sub-critical plants. Specific installation cost i.e. the cost per megawatt (MW) decreases with increased plant size.

Because of the high performance, efficiency and preservation of much cleaner environments than sub-critical coal-fired power plants, more than 400 supercritical coal-fired power plants are operating in the developed countries like US, Europe, Russia and in Japan. Most of the new power plants coming up now-a-days are of supercritical coal-fired technology.