HSB’s solar park outside Strängnäs can in a few seconds reduce its electricity production if needed for the electricity system. As the first Swedish solar park, it has been approved to regulate the frequency in the main grid.
The solar cell park outside Strängnäs is one of Sweden’s largest. Today it has an installed capacity of 14 MW and this summer it will be expanded to 22 MW. Then it is expected to be the largest in Sweden.
Now it is also unique in another way. It has been the first Swedish solar park to be approved for regulating the frequency in the electricity grid.
The frequency in the Nordic electricity system must always be 50 Hz. If it rises above that level, power must be drained, if it falls, power must be applied.
In practical terms, this is done with support services that system operators Svenska kraftnät buys in advance. So far, it is mainly hydropower that has assisted with such support services.
HSB’s solar park outside Strängnäs. Photo: Energy commitment
But now Svenska kraftnät is carrying out a pilot project to bring in more types of energy that can deliver support services. Ny Teknik has previously reported on the first wind farm that was approved for frequency regulation.
Activated in the event of a fault in the electrical system
At the end of April, HSB’s solar park also received the green light, after undergoing the pilot project’s simplified process for pre-qualification. The solar park will participate with frequency regulation of a maximum of 6 MW.
This is mainly because the tests in the pre-qualification were done in March, when the sun does not shine very much, says John Diklev at the energy service company Flower, which was previously called Krafthem.
– In March, we were a bit limited in how big tests we could do, so we may re-qualify the park later, he says.
Axel Dellenby from Flower programs the local control unit on site in the solar park’s network station. The picture shows the control unit in the form of the orange jar on top of the cabinet. Photo: Flower
The support service that the solar park will assist with is called FCR-D Ned. It is only activated if a disturbance occurs in the electrical system which causes the frequency to become too high. Then the solar park can quickly reduce its electricity supply to the electricity grid, so that the frequency returns to 50 Hz.
“Solar cells have a variance in themselves naturally”
The park has already had time to submit bids and been called off by Svenska kraftnät. This meant that the park for one hour on April 30 was ready to cut off electricity production by 600 kW for the sake of the electricity grid.
From the summer of 2022, the solar park will have an installed capacity of 22 MW. Photo: Jonas Weissglas
Flower will handle the bidding for Svenska kraftnät and has also developed the control system that is used when the solar park regulates the frequency.
The control system receives a signal from the surrounding electricity grid about the value of the frequency, but also from a divided reference area in the solar park. The reference area covers just over 1 MW and serves as a stopping point for determining how much electricity the park could have delivered at most.
– The challenge for solar cells is that they have a variance in themselves naturally, says John Diklev and takes a support service offer of 1 MW as an example.
“We need to compare their forecasts with actual delivery”
If the bid is activated by Svenska kraftnät, this means that the solar park will choke 1 MW.
– But if at the same time it becomes semi-cloudy and the reference point goes down to 800 kW, we will consider that the 1 MW that we have switched off has also gone down, so that we do not live up to what we have sold. Therefore, we turn off another 200 kW in the rest of the park to reach the bid, says John Diklev.
John Diklev. Photo: Christian Åslund
During the pilot project, Svenska kraftnät primarily wants to investigate how well the players’ forecasts agree with what they can actually deliver in the operating hour.
– We need to compare their forecasts with actual delivery and see that they agree well so that we can trust that we will not be there during operation and not get the delivery we have planned, says Jorunn Cardell, power system analyst at Svenska kraftnät.
Jorunn Cardell. Photo: Svenska kraftnät
In addition, Svenska kraftnät hopes that the pilot project will lead to good processes being developed for pre-qualification, so that it will be easy for similar players to start delivering support services.
“The cost of support services should go down”
The solar cell park has been built by Energiengagemang and is owned by HSB. Johan Skördare, CEO of Energiengagemang, sees the park’s support services as a way to tackle the electricity deficit in southern and central Sweden.
– We can not connect more electricity consumption or electricity production without it becoming very expensive and it takes a very long time to expand the electricity grid. In such a situation, we must have a dynamic use of electricity and electricity production instead, he says.
If more solar parks can start delivering support services, he believes that more solar parks can be allowed in the electricity system. In this way, Johan Skördare hopes that the pilot project will lead to the conversion to renewable electricity production going faster.
John Diklev’s hope is that it will become standard for solar parks to deliver support services to the electricity system.
– We need balance in the electricity system even when we have a higher and higher share of renewables in the electricity mix. The support services cost consumers and producers a lot of money and if more resources meet that demand, the cost of the services should go down, he says.
The support service FCR-D Ned
FCR-D Ned is a new support service that was introduced in 2022. It is activated in the event of a disturbance that causes the frequency to be between 50.1 and 50.5 Hz.
The abbreviation stands for Frequency Containment Reserve – Disturbance. In Swedish, the formal frequency maintenance reserve is called disrupted operation, down-regulation.
FCR-D Down refers only to down-regulation.
Today’s requirement for FCR-D Ned is that the bid must include at least 0.1 MW, the resource must be able to be activated to 50 percent within five seconds and to 100 percent within 30 seconds, and the endurance must be at least 20 minutes.
If a bid is called, it means that the player is paid because the resource is available for a certain hour. If the player’s bid is activated, it means that down-regulation is made for the sake of the electricity system.
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