overview
The overarching goal of wind turbines is to convert Earth’s natural wind into electricity. The way a wind turbine converts wind energy into electricity is through the use of the aerodynamic force from the rotor blades of the wind turbine. They are made up of many airfoil cross-sections that consist of different sizes and shapes from the root all the way to the tip. These airfoils employed by the blades make the wind turbines turn. As the wind flows, the pressure on one side of the blade decreases. This imbalance that is generated creates lift and drag. In other words, a lift force is produced when a fluid moves over the airfoil.
Through this lift force, the wind turbine is able to rotate. The rotation of the wind turbine isn’t directly connected to a generator as these turbines have a very low rate of rpm (rotations per minute). If we were to connect the blade to a generator, we wouldn’t be able to generate much electricity and it would be a huge waste of money and space. However, to ensure that this doesn’t happen, the blades are connected to a gearbox. Within this gearbox, the speed is increased through the use of a planetary gear set arrangement. By using this, a high-speed ratio is produced; this ratio is approximately 1:90. There’s also a brake in the nacelle to ensure that during windy conditions, wind turbines don’t over-generate electricity and break down. Following this, power cables are connected all the way to the base. At the base of the wind turbine, there’s a transformer that acts as a connection between the wind turbine and the overall distribution grid.
Problem 01. Efficiency
Out of all the major drawbacks of wind turbines, their poor efficiency is what is stopping wind turbines from being our sole source of energy supply. For context, wind efficiency is essentially the amount of kinetic energy in the wind that is converted into electricity that we can use. However, there are limitations to how efficient wind turbines can be due to the laws of physics. The laws of physics that prevent wind turbines from being efficient is called Betz's Limit. This limit says that the maximum efficiency of a wind turbine is 59.3%; this is a theoretical limit. However, this number is a theoretical value and most wind turbines only reach an efficiency between 25 and 45%. Wind turbines can’t be 100% efficient/extract all the energy from wind as that would mean that the wind velocity would be reduced to 0. With no velocity in the wind, the air/wind particles would all pile in the surrounding area of the wind turbine. Another major drawback is that it’s not possible for a wind turbine to convert all 59.3% of the kinetic energy into electricity. In this conversion process, some of this energy is lost. This is due to the way that the modern day generators are produced and engineered. On average, a generator is able to convert about 80% of the total kinetic energy that a wind turbine captures. To understand this from a mathematical perspective, if the wind turbine captures 50% of the available energy and the generator converts 80% of that: 0.5 x 0.8 = 0.4. This would mean the wind turbine is only 40% efficient.
Problem 02. Cost
Another major drawback is how expensive a single wind turbine is. On average, a commercial wind turbine (2 megawatts) costs anywhere between $2.6–$4M. The typical cost is $1.3M per megawatt of electricity producing capacity. The costs of the wind turbine increases as the size of the wind turbines increase; wind turbines have an average height of 280 feet.
The upfront capital cost of wind turbines makes up about 84% of the total installation cost.
For these turbines, the biggest components are the rotor blades, tower and the gearbox. Putting these 3 items together, they can account to anywhere between 50% and 60% of the turbine cost. The rest of the items make up for a total of 13%. Overall, the turbine itself can cost between 64% and 84%; the grid connection, civil works and other costs account for the rest.
Along with these initial costs, there are manufacturing costs as well. Per wind turbine, it costs about $42000-$48000 to maintain annually. However, this number doesn’t stay consistent throughout the life span of a wind turbine; it increases as the wind turbine ages. This is because the wind turbine wears down due to the harsh environments and weather conditions they often face. The maintenance cost is broken down further into 6 costs: Insurance; Land rent; Service, repair and spare parts; Administrative tasks; Power; Miscellaneous
Problme 03. Space
The third major problem with a wind turbine is that they require a lot of space. On average, a single wind turbine requires 1.5 acres of space. To put this into context, that’s about a football field, just for a single wind turbine. The scary part is, wind turbines are only going to continue growing in size and taking up space. Since 2000, wind turbines have been growing in height and blade length.
Average turbine hub height, rotor diameter, and nameplate capacity for land-based wind projects from the Land-Based Wind Market Report: 2021 Edition
Another factor that impacts the amount of space a wind turbine takes up is its hub height. The hub height is the distance from the ground to the middle of the turbine. This contributes greatly to how much space a wind turbine takes up. The hub height has increased 59% since 1999; as of 2020, the hub height is about 90 meters. To put this into perspective, that’s as tall as the statue of liberty. Research has shown that the hub height for offshore turbines is projected to grow even taller to almost 150 feet.
