تشخیص چرخه حیات گازهای گلخانه ای از سیستم های تولید برق باد Characterization of the life cycle greenhouse gas emissions from wind electricity generation systems

Introduction Wind energy may be defined as the energy harnessed by a wind turbine that converts the kinetic energy of the wind to mechanical energy and then to electricity. A wind turbine is comprised of different components such as the tower, the rotor blades, the yaw mechanism, the wind speed and direction monitor, and the gear box. The tower is mostly cylindrical and made of steel with heights varying from 25 to 75 m. The rotor blades are prepared with fiberglassreinforced polyester or wood-epoxy and have a diameter varying between 30 and 80 m. As the length of the rotor blade increases, the electricity generation capacity of the wind turbine also increases. The yaw mechanism turns the turbine to face the wind. The power is automated to vary with the wind speed and stopped at very high wind speeds to prevent damage. The sensors monitor the wind direction and the tower head is turned to line up with the wind. The gear box helps increase the rotational speed from a lowspeed rotor to a higher speed electrical generator. The total electricity generation in 2012 across the world was reported to be 21.53 trillion kilowatt hours (kWh) [1]. The projected world electricity generation for 2040 is 39 trillion kWh (81%) [2]. The renewable energy sources have been projected to account for 9.6 trillion kWh (25%) of the world’s total electricity generation in 2040. With the continuing depletion of traditional non-renewable energy sources, the necessity for generating electricity through the use of renewable energy sources (wind, hydro, biomass, solar, geothermal) increased manifold. Wind energy accounted for only 0.52 trillion kWh (2.42%) of the world’s total electricity generated in 2012. Based on the 2012 statistics, wind energy was identified to be the second largest renewable energy source for electricity generation after hydro (3.646 trillion kWh) [1]. The global wind energy based electricity generation is projected to account for 25–30% of the global electricity supply in 2050 [3]. In the United States of America (USA), wind energy based electricity generation is projected to account for the largest absolute increase in renewable electricity generation to displace hydropower in becoming the largest renewable electricity generation source by 2040 [4]. These statistics indicate that there is ample scope to generate electricity on a large scale using wind energy. Considering the projected increase in the use of wind electricity generation systems across the world, one needs to evaluate the life cycle greenhouse gas (GHG) emissions resulting from the adoption of different categories of wind electricity generation systems. The life cycle assessment (LCA) approach helps evaluate the net GHG emissions resulting from the use of wind energy as a fuel. LCA is an analytical method that provides an assessment of the environmental impacts of the considered products and technologies from a ‘cradle to grave’ systems perspective utilizing the detailed input and output parameters that operate within the designated system boundaries.