intermittency

What happens when the wind doesn’t blow?

In the last decade, wind turbines out to sea and on land have gone from producing less than 2% of our electricity to 11% in 2015. Sometimes it’s windy and the turbines produce more power, sometimes it’s not that windy and they produce less. But they still produce enough electricity to power 30% of UK homes. And they haven’t caused any blackouts.

Wind turbines do cause some variations in electricity supply for the National Grid. But it’s predictable (we’re pretty good at predicting the weather these days!). We can plan for wind generation with a high level of certainty. Plus, energy secretary Greg Clark thinks the concerns about wind power’s intermittency have been ‘overblown’ and we’re more than able to deal with them.

What about as we build more wind turbines? Germany and Denmark are streets ahead of us when it comes to renewables - in 2015 Danish wind turbines contributed 42% of their electricity needs. And yet these are two of the most reliable energy systems in Europe, with four times fewer power cuts than the UK (pdf). A more diverse electricity grid (rather than one based on a small number of centralised power stations) means if something does go wrong with one part of the system, it is far less likely to cause big power cuts.

As we build more wind turbines in the UK, we can use demand management, interconnection (linking up with other parts of the country or other countries) and energy storage to help us manage. It will need a bit of thinking, but it’s well within our capabilities, and something we need to do as we move towards the cleaner, smarter, more efficient energy system of the future. And the government are already investing in it.

Wind would never be the only electricity source we use - it complements other sources like solar, hydro and tidal. But it is a pretty good one, especially in windy places like the UK. Wind turbines deliver two and a half times as much electricity (pdf) during periods of high demand (like cold winter nights) compared to times of low demand. There’s plenty we can make the most of.

If you’re wondering what happens when it’s too windy - we’ve also written about that!

Banner image: One Fine Stay, creative commons

What happens when it’s really windy?

On a blustery day, wind turbines will be turning and generating lots of lovely clean power. Last summer the Met Office issued a yellow weather warning for wind in Scotland. A few bridges were shut and ferries cancelled, but that was the day wind turbines produced 100% of Scotland’s power needs.

But when extreme weather and very strong winds hit, turbines sometimes need to be shut off. All modern wind turbines are are set to stop turning automatically if there’s too much energy in the wind. Some will shut down if the average speed of the wind is over a certain level for a period of time, while others will stop after a super strong gust (something like 100mph).

It’s pretty rare that we’ll see strong enough winds in the UK to stop the turbines - and certainly not to stop all of them. High winds affecting 40% or more of the UK’s turbines would occur in around one hour every ten years (pdf).

The reason turbines shut down like this is for safety - if the wind is too fast it can put major stress on the blades and mechanisms inside the turbine causing lots of friction and long term damage. It’s much safer to have the turbines stop and then start again when wind is a bit slower and safer.

It’s pretty straightforward to predict, too, so the National Grid know when there will be lots of wind power produced, and when they will have to switch off. That means they can easily plan for the variation.

The other reason turbines may stop turning on windy days is when there’s too much renewable energy being fed into the National Grid. The grid was originally built around a few centralised power stations, rather than lots of small generators feeding in. When it’s too windy and turbines are producing lots of clean power, the grid people ask some wind turbines to switch off to stop the grid from getting overloaded. This isn’t a problem with wind turbines, they’re just doing their job, the real a problem lies with the grid which needs to be upgraded to support a new smarter energy system.

If you’re wondering what happens when it’s not windy - we’ve also written about that!

Banner image: Nigel Goodman, creative commons.