The August power cut: what was supposed to happen?

Posted in: Energy

Posted on: 27.08.2019

On a Friday afternoon this August, the UK electricity grid saw significant outages. So what was supposed to happen?

National Grid, the company which manages the UK’s energy networks, faces a daily challenge: matching demand for electricity with generation in constant real-time. A big part of this is creating a grid which can cope with faults and shutdowns of generators — imagine the fuses tripping in your house, but on a much bigger scale.

No system is infallible, generators will sometimes fail with no notice. What is important is that the system can cope with these shutdowns.

The recent power outages which impacted millions of people in Britain were caused by a lightning strike and two large generators failing within seconds of each other. National Grid usually has plans in place to cope with one generator failing; to have two almost simultaneously is rare.

Power plants are generally operated in four different ways. Imagine four different cars.

Car one: Driving on the motorway at 70mph, can react very quickly to reduce speed but cannot increase speed.

Car two: Travelling on the motorway at 50mph, can react very quickly and speed up, probably unwise to go any slower on a motorway.

Car three: Parked with the engine running in neutral, can speed up but needs a few seconds to do this — check mirrors, put in gear, handbrake.

Car four: Driver reading about grid balancing in their house, car parked in drive. Can increase speed but will take longer to do this — find keys, put shoes on, lock house, get in car.

Car one is useful if the grid has more power than expected and needs to reduce power. Cars two, three and four are useful if there’s a fault in a generator like there was on the 9th of August.

So, if a generator has a fault and disconnects from the grid, car two automatically increases speed for a few seconds as car three sets off. If the fault is expected to last longer, then National Grid asks the driver of car four to set off too.

It is an effective system, but an expensive and unnecessarily pollutive one.

This means the grid always has some generators only running at half capacity — car two —  and some even being paid to burn fuel to stay warm but not generate — car three. This creates resilience in the grid — the more plants we have running like car two and car three, the less chance of power cuts we will have. But this resilience comes with costs and extra carbon emissions. It is an effective system, but an expensive and unnecessarily pollutive one.

Running plants this way not only emits more carbon, it leads to wind turbines being shut down overnight. This is because it can be dangerous to turn off nuclear power plants at night, and it would be unwise to shut-down the corresponding backup gas power plants as that would risk blackouts – combined, these generators are labelled ‘must run’. This is one reason why wind turbines are turned off when it is ‘too windy’, even if wind is only generating enough to meet about half of our demand.

This ultimately means using half capacity power plants as backup leads to us turning off renewable power which has no fuel cost, so we can keep burning expensive, carbon emitting gas to generate electricity. Does that sound like a sensible way of operating to you?

How do we improve this?

First, we need to stop building large power stations; smaller generators cause less stress on the grid as it is highly unlikely a large enough portion of them will have a fault at the same time. The equivalent of a large nuclear plant tripping out would mean about 1,000 wind turbines would have to experience faults simultaneously. Extremely unlikely.

We must also ask ourselves: is this expensive but very effective resilience required? The Friday 9thAugust blackout caused so much chaos because infrastructure does not expect power cuts, so it is not designed to cope with them. A good way of dealing with power cuts like this is to prioritise power correctly — traffic lights turning off can be very dangerous but if every other streetlight turned off for a short while this may not be problematic. I can cope if my fridge turns off for an hour but the lights in a medical operating theatre should never turn off.

Lastly we have to support lower carbon ways of providing flexibility. This could either be demand side response — turning all of the fridges in a supermarket down, for instance, batteries, or other methods like installing control systems to let wind turbines generate a little extra during a fault period. Lots of methods are available, there just needs to be leadership to encourage National Grid to transition from its effective, expensive and polluting old way of operating to a smarter, cheaper, cleaner, and greener method.

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