How Do Wind Turbines Work When It’S Not Windy?
Wind energy is one of the fastest growing and most promising renewable energy sources in the world today. Wind turbines harness the power of the wind to generate clean, emissions-free electricity. Unlike traditional power plants fueled by coal, gas or oil, wind turbines don’t release any harmful pollutants into the atmosphere while operating. As concerns about climate change and energy security rise globally, wind power offers a sustainable solution by diversifying energy supply and reducing dependence on fossil fuels.
Wind turbines work by converting the kinetic energy of the wind into mechanical power which then drives an electrical generator. A modern wind turbine consists of rotor blades that capture the wind, a shaft, a gearbox, a generator, a controller, a tower and foundation. As the rotor blades turn, they spin a shaft connected to the gearbox which increases the rotational speed to drive the generator. The generator uses magnetic fields to convert the mechanical rotation into electrical energy. The power output from a turbine depends on the turbine’s size and the wind’s speed through the rotor.
How Wind Turbines Work
Wind turbines convert the kinetic energy in wind into mechanical power to generate electricity. The main components of a wind turbine are:
Blades – The blades are attached to the rotor and spin when wind blows over them. Modern wind turbine blades are made of composite materials like fiberglass and usually have three blades.1
Rotor – The blades connect to the rotor, which spins when the blades are turned by the wind. The rotational speed is controlled by the generator.1
Nacelle – The nacelle sits atop the tower and contains the gearbox, generator, controller, and brake. It allows the turbine to rotate to face into the wind.2
Generator – The generator uses electromagnetic induction to convert the rotational energy into electrical energy. Generators may be direct-drive or use a gearbox.1
Tower – Towers are made of tubular steel or concrete and hold the turbine high in the air where winds are stronger and more consistent.
Yaw System – This system keeps the turbine facing into the wind as wind direction changes.
Generating Electricity
Wind turbines harness the kinetic energy in wind to generate electricity. Wind turns the blades of the turbine, which spins a shaft connected to a generator inside the turbine housing. The spinning shaft causes magnets inside the generator to rotate around a set of fixed conducting coils. This motion generates a flow of electrons, or electricity. The stronger the wind blows, the faster the turbine blades spin, and the more electricity is generated. Most turbines also have a gearbox which increases the rotational speed from the turbine to the generator. This allows the generator to produce electricity at wind speeds that are lower than the turbine’s start-up speed. The electricity generated is then fed into power cables, connecting the turbine to a transformer where the electricity is stepped up to a higher voltage suitable for transmission to the utility grid.
Modern wind turbines are designed to start generating electricity at wind speeds as low as 3-5 meters per second (6-11 mph), with power output continuing to rise as wind speed increases up to around 25 m/s (56 mph). At very high wind speeds, turbines have braking mechanisms and control systems that limit rotor speed to prevent damage. The most productive wind speeds for energy generation by a wind turbine are in the range of 12-25 m/s (27-56 mph).
The amount of energy in wind varies with the cube of wind speed. So even a small increase in wind speed results in a large increase in power. This is why taller towers provide access to higher wind speeds and substantially boost the electricity generation of a turbine. Offshore turbines placed in coastal waters benefit from faster, less turbulent wind speeds, enhancing productivity compared to an identical turbine on land.
Sources:
https://www.sciencedirect.com/science/article/pii/S0960148119306196
https://medium.com/@bookshelf007/green-energy-solutions-a-path-to-a-sustainable-future-e0f0677c17fd
Storing Energy
Wind turbines are able to store excess electricity generated on windy days for later use when wind conditions are less favorable. There are a few main methods used for energy storage with wind turbines:
Batteries are one common way to store electricity from wind turbines. Large battery storage facilities can be built alongside wind farms to accumulate surplus energy production. The batteries then discharge electricity back into the grid when needed during periods of low wind. Lithium-ion batteries are a popular choice given their high efficiency and fast response times.
Flywheels are another storage technology sometimes paired with wind turbines. A flywheel is a mechanical device that spins at very high speeds to accumulate rotational energy, which can be converted to electricity on demand. The kinetic energy stored in the spinning flywheel is dispatched to the grid when required.
Compressed air energy storage is another option being explored. This involves using excess electricity to compress air into an underground cavern. The pressurized air is then released to turn a turbine and generate electricity when needed. Some wind farms are experimenting with this method to even out power delivery.
Ultimately, combining wind turbines with battery storage and other technologies helps maximize the utilization of wind energy and ensures a consistent supply of electricity around the clock.
(Source: https://renewablesystems.org/how-do-wind-turbines-store-energy/)
When There’s No Wind
Wind turbines need consistent wind to generate electricity. What happens when the wind stops blowing? Modern wind turbines are designed with advanced power electronics to address the intermittent nature of wind.
First, wind turbines have inertia that keeps the rotor blades spinning even when wind speed drops. The rotational kinetic energy helps maintain momentum to continue producing some electricity during brief lulls in wind. However, this only lasts for a short time.
Forecasting tools can predict when winds will slow down hours or days in advance. This allows grid operators to plan ahead and bring other power plants online to compensate. Turbines may also curtail their output to conserve power when needed. Additionally, some turbines can provide reactive power or grid support when not producing electricity.
While wind turbines do rely on consistent wind patterns, they employ various strategies to manage fluctuating resources. Advanced power electronics, forecasting methods, and grid integration provide ways for turbines to operate with minimal disruption during periods of low wind.
Inertia
Wind turbines have rotational inertia that helps keep the blades spinning even when wind speeds are low. The turbine blades and shaft have significant mass, and the kinetic energy stored in these rotating parts acts as a flywheel to provide continuous power output (Skeleton Technologies, 2020). This property of objects in rotational motion to resist changes in speed is known as rotational inertia. Traditional power plants with large spinning turbines, like coal, nuclear, and hydro, also rely on inertia to stabilize grid frequency. Inertial response describes the immediate increase in power output from the release of kinetic energy when grid frequency drops. Variable speed wind turbines can also provide inertia response by briefly increasing output when wind speeds are low (Morren, 2006). The inertia response helps grid stability during a disruption, though it only lasts for a short time before the turbine slows down.
Forecasting
Being able to accurately forecast when the wind will slow down or stop is crucial for wind farm operators. Advanced forecasting algorithms analyze historical weather patterns and real-time data from sensors across the wind farm. This allows operators to predict hours or even days in advance when wind speeds will decrease and generate less power. Forecasting helps them schedule maintenance, estimate future electricity production, and coordinate with the grid. If turbines are forecast to have low output at a certain time, the operator can schedule maintenance tasks during the lull rather than at full power. Accurate wind forecasting maximizes turbine uptime and electricity generation when the wind is blowing.
One forecasting technique uses “evolutionary product unit neural networks” to predict wind speeds at individual turbines based on sensor data. In a study described at https://sci2s.ugr.es/keel/, researchers forecast wind speeds up to 4 hours in advance for multiple turbines in a wind farm. Their model successfully predicted decreases in wind, allowing the operator to prepare. Sophisticated forecasting will only improve as more historical data becomes available.
Curtailment
Curtailment refers to slowing down or stopping wind turbines when there is low wind or high energy supply relative to demand. This helps stabilize the electrical grid and prevents overloading the system. Wind farm operators may curtail turbines based on commands from system operators or based on software algorithms that optimize grid stability and economics. Curtailment typically occurs at night when energy demand is lower. One study found curtailment reduced bat fatalities by 44-93% while lowering annual power generation by only 0.3-1.4% (Curtailment as a successful method for reducing bat fatalities). While curtailment lowers energy production, it provides important grid balancing services and reduces wildlife impacts.
Grid Support
Wind turbines can provide important stability services to the electrical grid, helping maintain reliable power delivery during disruptions. Although wind power output varies with wind conditions, modern wind turbines are equipped to support grid reliability in a variety of ways. This includes providing reactive power or voltage control, frequency regulation, and frequency response and control. These services are needed to balance load changes and ensure stability on the grid system. By providing these grid support services, wind turbines can help regulate grid operation and prevent outages.
For example, wind turbines can supply reactive power to the grid to help maintain proper voltage levels and support security and reliability of the power system. The reactive power capabilities of wind turbines are present even when the turbine is not generating active power. This allows wind turbines to dynamically respond to the grid’s voltage needs. The inverters used in wind turbines also allow them to supply or absorb reactive power rapidly. Overall, wind power plants are well suited to provide reactive power and voltage control on an as-needed basis to promote grid stability (source).
Conclusion
In summary, wind turbines utilize the power of the wind to generate electricity. Even when the wind is not blowing, turbines employ various methods like inertia and grid support to continue producing energy. Forecasting wind conditions and curtailing output during high winds also help maximize power generation.
Looking to the future, innovations in turbine design, materials, data analytics, and storage will further improve the efficiency and reliability of wind power. With steady cost reductions and technological advances, wind energy is poised to play an expanding role in the global renewable energy mix.
