The national power grid is a massive piece of complex infrastructure that delivers the electricity required by millions of homes and businesses around the country, literally at the flick of a switch. Yet is also an incredibly delicate mechanism which requires an enormously precise balancing act to function.
That’s because the system is designed to work at a frequency of 50hz – or cycles per second. Every electrical device we use is designed to use power at that frequency while conventional power-generating stations are built to deliver electricity at the same frequency. Margins for error are very tight. If the rate of change of the frequency from any generating source is more than just one cycle per second, it is disconnected from the network.
And if demand and supply should go out of balance for any reason – a surge in demand during a major sporting event or an outage at a generating station, for example – the frequency changes too.
Power system operators like Eirgrid therefore need to carefully manage the power coming onto the system and match it the level of demand on a moment by moment basis. That’s a tricky enough task but it is made all the more challenging by the addition of renewable power sources like wind and solar onto the system.
Accommodating these intermittent power sources effectively requires power systems to do something they were not designed for. That makes Eirgrid’s achievement of running the electricity grid with up to 75 per cent of the electricity flowing through it coming from renewable sources all the more remarkable. This is the result of a ground-breaking project carried out by Eirgrid in collaboration with Northern Ireland power system operator Soni along with industry partners over the past decade.
“We started out at zero and then got to 50 per cent,” says Eirgrid Group chief innovation officer Liam Ryan. “Over the last 11 years we have gone in incremental steps of 5 per cent to get it to 75 per cent.”
Challenges
Ireland’s size and relatively remote location present further challenges. “Ireland has a very small synchronous power system,” Ryan notes. “On the continent the systems are all interlinked. That gives them more stability. If you are bringing on more renewables in one country, you know that power is available from another if the wind drops, or the sun doesn’t shine. The balancing act we have had to perform here is almost unique.”
The task involves a fundamental transformation in how the power system is operated. “The system was designed for a small number of large generating stations, and we are now moving to a large number of small ones. Ireland is leading the world in that area. To my knowledge, no other power system anywhere in the world has 75 per cent renewables.”
Putting that in context, he points out that Europe has set a target of 55 per cent renewables on the system by 2030. “And because there is a lot of hydro-electric power in northern Europe, the non-synchronous element will only amount to about 35 to 40 per cent.”
The project involved a number of highly technical changes to the system. Power users also play an important role through what are known as demand-side units (DSUs) and system services. DSUs see users either reducing demand or supplying power back onto the system from their own generating plants in response to requests from the system operator.
Anticipating changes
The ability to anticipate accurately changes in demand or supply has also been crucially important. “We have always done a lot of forecasting, but we looked at things like the possibility of lightning striking a power station or of a cold snap causing an increase in demand. We now have to look at the output of wind farms in different areas of the country so that we can turn on or off conventional generation or use batteries as we need them. We also need to look at cloud cover across the country to forecast solar output.”
Ryan describes the successful outcome of the project as a hugely significant milestone in the decarbonisation of the electricity sector on the island of Ireland as well as the decarbonisation of the economy. “We will now begin work on increasing the figure to 95 per cent by 2030 in order to achieve the government’s target of having 80 per cent renewables on the system by that date. We are very prudent in what we do. We want to make sure the system is resilient, that all customers get the quality of electricity supply they are used to, and that we meet the government’s target in a structured and measured fashion.”