Due to the finite nature of non-renewable energy sources and the increasingly pronounced effects of climate change, securing alternative power sources is becoming a huge issue.
One solution is wind turbines which convert the kinetic energy of the wind into electric energy for consumption. Wind turbines recover the kinetic energy of the moving air by utilizing propeller-like blades, which are turned by wind. The power is transmitted via a shaft to a generator which then converts it into electrical energy. Typically, a group of wind turbines will be installed in the same location known as a ‘farm’.
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Average sized onshore wind turbines can produce 2.5 to 3 MW of power, offshore wind turbines can produce around 3.6 MW. To put that into perspective, a single offshore turbine can power more than 3,300 average EU households.
Onshore wind has the lowest average levelized cost of all renewable energy sources with an average value of £62/MWh. Power can be generated 24 hours a day, but requires a wind speed of at least 13 mph for utility scale turbines so windy areas of the world are obviously better suited. Off-shore locations where winds are stronger and more persistent are ideal locations for wind farms. However, putting farms offshore presents complications in their construction/maintenance and in distributing the power via subsea cables.
How is Wind Power Distributed?
Electricity generated from a wind farm will travel to a transmission substation, where it is stepped up to a high voltage in the region of 150-800 kV. It is then distributed along the electricity grid power lines to the consumer.
Wind is a form of solar energy, the result of uneven heating of the earth’s atmosphere by the sun and it is a relatively variable power source. The amount of power generated varies greatly at hourly, daily or seasonal timescales which means that often the supply of electricity will outweigh the demand. In a regular wind farm configuration, the power is distributed straight onto the electrical power grid. With no energy storage capability, this requires the turbines to be slowed to sub-optimal speeds when more energy is produced than is required.
How can Wind Energy be Stored?
Through several different storage processes, excess energy can be stored to be used during periods of lower wind or higher demand.
Electrical batteries are commonly used in solar energy applications and can be used to store wind generated power. Lead acid batteries are a suitable choice as they are well suited to trickle charging and have a high electrical output charging efficiency.
Compressed Air Storage
Wind turbines can use excess power to compress air, this is usually stored in large above-ground tanks or in underground caverns. When required the compressed air can be used through direct expansion into a compressed air motor. It can also be injected in an internal combustion turbine, where it is burnt with fuel to provide mechanical energy which then powers a generator.
Hydrogen Fuel Cells
Hydrogen fuel cells can also be used to store excess energy. A hydrogen generator is used to electrolyse water using power generated from the wind turbine, storing the resulting hydrogen and converting it back to electricity using a fuel cell power system when needed.
Pumped storage is associated with hydroelectric power generation but is yet to be used with wind power generation. Water could theoretically be pumped up to an elevated reservoir utilizing excess generated power and then be used to drive a water turbine when required. The technology is proven and has been used for centuries, giving a relatively high overall efficiency of 70%. Existing hydroelectric power plants could be utilized if they are in an area suitable for a wind farm.
Image Credits: Marko Poplasen/shutterstock.com Conclusion
The cost of wind-generated electricity is falling, currently wind farms are being installed at record rates across the world. Almost 633 advanced energy storage projects are presently under development or in full operation around the world. This is to address the major downfall of conventional wind power – that it cannot produce energy on demand.
However, cost will be the main stumbling block for wind energy storage; the American Wind Energy Association (AWEA) has said that flexibility in the form of fast-growing gas plants and hydroelectricity already exists on a lot of grids, and that building new energy storage facilities is almost always more expensive. This certainly will not always be the case; as the technology behind energy storage advances, costs will likely fall and fossil fuel plants are by nature finite so cannot supplement wind-generated electricity forever.
Sources and Further Reading