As electricity becomes ever more significant to our daily lives and the future, it is increasingly important that we have a functioning and stable electricity supply that we can trust, at all hours of the day and in all weather conditions. So that society and the economy can keep functioning and continue to develop every day of the year.

Grid stability easily explained 


This video explains grid stability easily. What would happen if suddenly there were disturbances in Sweden's electricity system?

A balance of various energy sources makes the electricity system stable

What do we really need for the electricity system to function optimally? To be able to rely on consistent and stable access to fossil-free electricity at the right price, we need a balance of the different energy sources in our electricity system. It requires both stable and dispatchable energy sources such as hydro and nuclear power, and weather-dependent energy sources such as solar and wind power, which lowers the price of electricity when the weather is favorable. Every power source has its strengths and weaknesses, and it’s a matter of finding an optimal mix that works, both technically and economically – to create overall stability and security.

Furthermore, ancillary services are required to ensure that the electricity is always of a sufficiently high-quality – 50 Hertz. Ancillary services are a collective term for various technical resources that can be mobilized rapidly when the electricity system is exposed to strains. For example, when the wind suddenly stops or there are disruptions on the grid. Ancillary services are primarily delivered by our dispatchable energy sources: nuclear power and hydropower. In other words, they ensure that we have electricity when we need it, while creating stability and reliability in the electricity system.

Ancillary services from flexible production provides support when required

In the past few years, the share of weather-dependent power sources, such as wind and solar power, has increased. This development increases the risk of imbalances occurring in the electricity system – which can result in electricity shortages or serious disruptions in the electricity grid. It could be said that the more weather-dependent power we utilize, the more important it is that we also have access to hydro and nuclear power, which, jointly with our various ancillary services, can also balance and stabilize the system when required.

Disturbance reserve – a quick starter that kicks in when the frequency falls

The disturbance reserve is an ancillary service procured by Svenska kraftnät, which is Sweden’s system operator. The disturbance reserve consists of electricity generation resources that can be rapidly activated to restore balance to the system. At present, the disturbance reserve primarily comprises gas turbines that produce electricity and which can be fully operational in a couple of minutes in the event of a frequency drop. Uniper is a contributor of this reserve.

Frequency control enables a power plant to be ramped up or down

In the event of a deviation in frequency, it is paramount to stabilize the frequency quickly. To achieve this, various methods of frequency control are utilized as an ancillary service. The frequency can be regulated both automatically and manually. Automatic frequency controls are featured in many hydropower plants. The equipment that is linked to a power plant turbine cab automatically increase or decrease electricity generation based on the prevailing frequency.

Rotational energy – kinetic energy that buys time while imbalances are corrected

A third vital ancillary service that is required to quickly offset frequency deviations is rotational energy – a kinetic energy that can only be provided by the turbines and generators of major power plants. As the power plant stops driving the generator, the turbines continue to spin for a while, due to kinetic energy. This allows for the power plant to continue generating electricity for a little longer. Simplifying it somewhat, it could be said that rotational energy buys time that can be used to regulate the frequency. The heavier the generator and turbine, the longer it continues to spin. The more rotational energy we have in our electricity system, the easier it is to maintain the frequency and thereby stabilize the electricity system. Hydro and nuclear power provide considerable amounts of rotational energy, while weather-dependent power sources such as wind and solar power lack this characteristic.

Power reserve – when insufficient electricity is generated

A fourth support for the electricity system is the power reserve, which has a somewhat longer planning horizon. The power reserve is used temporarily when our electricity consumption is deemed to exceed the electricity being generated. The power reserve is usually used on very cold winter days, when our demand for electricity is particularly high. Uniper’s Karlshamnsverket power station is part of Svenska kraftnät’s power reserve during the winter season. The power plant can be started up quickly and produce electricity on short notice when needed. It only takes two hours for Karlshamnsverket to go from standby to production.

We ensure that the electricity system remains stable

As part of the global Uniper Group, we are a major electricity and power producer for Swedish base industry and a guarantor of stable and reliable electricity generation. We have power plants throughout the country for fossil-free hydro and nuclear power, as well as the Nordic region’s greatest peak power and reserve power. Uniper’s electricity is used to ensure that our society and industries function, regardless of the weather and time of year. In terms of hydropower, we are the third-largest producer in Sweden. Our 76 wholly and jointly owned hydropower plants, distributed from Lycksele in the North to Kristianstad in the South, account for approximately 12% of Sweden’s total hydropower production. The Uniper Group is a co-owner of all three of Sweden’s active nuclear power plants.

Find out more

In line with the global climate goals, the Swedish parliament has decided that Sweden will have net zero emissions of carbon dioxide by 2045. For Sweden to achieve this goal, the electricity system must be developed at a rapid pace.

A functioning and stable electricity system requires access to the right amount of electricity throughout the country, and that the electricity is of sufficiently high quality. Consequently, rotational energy – the kinetic energy that remains in our large generators when they have been set in motion – is important to us.

The gas turbines of the disturbance reserve, which are controlled by Svenska kraftnät, are activated in the event of a sudden production failure at a baseload power plant. 

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