Technical – Page 3 – Wind Turbine Magazine

It sounds like a strange question, but I quite often get asked 'Do wind turbines work when it's not windy?' No, wind turbines do not generate electricity when it’s not windy. They also don’t generate electricity when the wind speed drops below what’s called the ‘cut-in-speed’. That’s the minimum wind speed below which the wind turbine stops generating electricity. Cut-in speed varies among different types of wind turbines. For example, the 225kw Vestas V27 wind turbines—which we operate on our various sites around the United Kingdom—all cut-in (i.e. start generating electricity) as soon as the wind speed reaches 3.5 metres per second (mps), or about 8 miles per hour (mph). Much larger turbines, like the 2MW ‘Vestas V90’—which stand over 100 metres tall—have a slightly higher cut-in-speed of 4 mps, or 8.95 mph. Some Enercon wind turbines have a much lower cut-in speed of just 2 mps, but at that wind speed they only generate 2kw. Most turbines don’t start generating significant levels of electricity until they reach at least 8 metres per second. Many medium size wind turbines need wind speeds of at least 14 metres per second before they start generating at their full rated output. Rated output simply means if a turbine is sold as a 225 kilowatt turbines, and its rated output is 14 mps, then it will need wind of at least 14 mps to generate the full 225 kw of production. That’s why turbines ideally need siting in the windiest locations possible. Small residential wind turbines for homes and private properties, like the Automaxx 1500W, or the AirForce 1 Wind Turbine System, also have a similar cut-in speed of around 3 mps. Now, just to confuse things slightly… Wind Turbines Do Still Function When It’s Not Windy! I know that contradicts what I said above, but wind turbines do technically still ‘operate’ when it’s not windy. I’m making the distinction that when people ask ‘do wind turbines work when it’s windy’, what they’re really asking is ‘does it generate electricity when its not windy’. As I already explained above, no they don’t. However, although they don’t generate electricity, even if the wind drops below the cut-in-speed, all of the internal electrical components and computer systems inside a wind turbine do continue working, to keep the turbine operational. Most turbines still rotate, and pitch and yaw to change the angle at which the blades face the wind. Internal monitoring systems and sensors continue operating to provide instant alerts and feedback in case of a mechanical error. To power these internal systems when the turbine’s not generating electricity requires the turbine to actually import a very small almost negligible amount of electricity from the grid. However, this is totally offset when the turbine starts generating electricity again, when the wind rises above the cut-in-speed. Why Do Wind Turbines Stop Working When Its Extremely Windy? I also frequently get asked this question too! If you’ve ever seen a wind turbine that isn’t spinning (or only ‘freewheeling’ — spinning very slowly) when there is a storm, it’s actually not broken down, like many people mistakenly think. In storm force winds, most wind turbines simply ‘pause’. This is to protect themselves from ‘getting out of control’, in the event a problem occurs while the wind is too strong. That’s because when a wind turbine malfunctions, most turbines have disk brakes (similar to those on a car) which are automatically applied to stop the blades from spinning until a repair is made. However, let’s say there’s a storm, and the wind is so fast that there’s a huge amount of air pressure blowing on the turbine blades. If there was then an internal malfunction, and the turbine suddenly had to apply the brakes, there’s a chance that the air pressure would be so high, the brakes wouldn’t be able to stop the blades spinning. Of course, a malfunctioned turbine that continues spinning after an error occurs could cause serious problems! It’s actually one of the main reasons why in—thankfully—very rare cases, a wind turbine collapses, or sets on fire. The brakes either didn’t work, or worked but the blades were spinning so fast the brakes couldn’t stop them. So, that’s why wind turbines are designed to automatically pause, and stop generating electricity, in extreme wind. Also, the wind speed at which the turbine is designed to automatically pause is called, you guessed it, the ‘cut-out’ speed. Most medium and large size wind turbines’ cut-out speed is around 25 mps, or 60 mph, although some larger turbines have additional control systems which allow them to continue operating at even higher wind speeds. All wind turbines have a wind speed above which they must be paused, for safety reasons. Anyway, now you know! If you ever see a wind turbine that isn’t spinning when it’s very windy, it’s probably not broken. It’s just having a rest until the wind dies down a bit!