Insufficient inertia will increase the risk of power cuts

An increasing proportion of wind and solar energy will make the electricity system more vulnerable to disruptions.
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According to Ulf Moberg at Svenska Kraftnät (Sweden’s national grid), a lack of so-called inertia in the future could at worst lead to parts of the power grid going dark.

Development towards an increasing amount of renewable production will present many challenges to the electricity system in the future. One of the most significant ones to address, according to Ulf Moberg, CTO at Svenska Kraftnät and member of the Steering Committee for Electricity Crossroads, is the issue of inertia. 

“We have never before needed to discuss inertia. It is something that has been abundant in the Swedish and Nordic electricity systems. But when we change our electricity system we don’t want it to become less robust or reduce delivery reliability. Inertia will be an important issue here,” says Ulf Moberg.

At the beginning of June, IVA’s Electricity Crossroads project presented a special study on inertia. Inertia is crucial for a stable electricity system. But most people are unfamiliar with the concept. Historically, Sweden’s electricity production has been dominated by hydropower plants and nuclear reactors. In electricity   production, mechanical energy is converted into electric energy in generators. Stored in the rotating parts of the generators are large amounts of mechanical kinetic energy – also called inertia. In the case of significant disruptions in the electricity system, for example when a nuclear reactor is shut down, the stored energy (inertia) is used to ensure, within a split second, that production and consumption remain in balance.

Solar cells and wind turbines are not constructed in the same way and do not contribute inertia to the system. Now that our nuclear power reactors are being decommissioned and replaced by wind turbines and other power sources, the total inertia in the system is declining and the ability of the system to handle disruptions is thereby also being reduced.

“Sometimes it seems like many people think the electricity system can be adapted to any changes that happen without it affecting delivery reliability. But the electricity system is very complex and a number of functions in the system, such as inertia, have a very substantial impact on how robust the system is.”

Up to now there has been a good amount of inertia in the Swedish and Nordic systems. But according to Svenska Kraftnät’s assessment the situation could be unacceptable by 2025 if nothing is done about it.

“The worst case scenario is that a decline in production will result in power cuts and parts of the grid going dark,” says Ulf Moberg.

There is no simple solution to this problem. Some are hoping to be able to equip wind turbines with special electronics to created so-called synthetic inertia. Handling large fluctuations by simply stopping production is another possibility.

“Many are arguing in favour of various methods to replace physical inertia. Right now I do not see any satisfactory solution. But we will be forced to take action to ensure operational reliability,” says Ulf Moberg.

In recent years, Svenska Kraftnät has been focusing on drawing attention to the importance of inertia as one of several contributing factors in a reliable electricity system – now and in the future. Despite the technical nature of the issue, Ulf Moberg believes that the efforts are bearing fruit.

“We have tried to teach people about it and I’m hearing more politicians talk about inertia today than just a few years ago. I think the importance is beginning to sink in.”