5 questions about... Remote controllability of wind and solar systems

1. Why do wind and photovoltaic systems need to be remotely controllable?

The expansion of renewable energies has accelerated in Germany in recent years: At the beginning of 2025, almost 100 GW of solar power, 9 GW of offshore wind power and almost 64 GW of onshore wind power have already been installed.^[1]

If renewables produce simultaneously on windy and sunny days, there can be significant generation surpluses - especially if such a generation situation meets low consumption at the weekend or on a public holiday. On such days, electricity is exported, stored or electricity consumption is increased where possible. However, these measures are not always sufficient to completely balance supply and demand. In such situations, systems are curtailed by the legally prescribed remote control in order to avoid overloading the electricity grid. At the same time, negative revenues from renewable energies are to be avoided.

According to Section 10b EEG 2023, remote control is mandatory for all systems that are in subsidised direct marketing under the market premium model. System operators must equip their systems with a technical device via which the direct marketer or a third party can call up the actual feed-in and via which the output can be remotely controlled in stages or, if technically possible, continuously.

2. Who is responsible for remote controllability?

The system operator is responsible for establishing remote controllability. In most cases, operators commission a service provider to establish a remote control connection, i.e. to equip the wind or solar farm with the necessary hardware. In addition to a stable internet connection, this requires suitable hardware for system control and remote access, e.g. data loggers with a direct marketing interface.

3. How does remote control work and who carries it out?

As a rule, control is carried out via radio ripple control receivers or telecontrol technology. A separate interface must be set up for direct marketing so that the direct marketer can control the park's output independently. The interface must include an Internet connection and hardware for the transmission of real-time data and control.

At Vattenfall, we work together with the control service provider emsys VPP GmbH. Plant operators usually have an interface service provider who has to contact us or emsys to establish the connection. As soon as this has been done, we carry out a remote control test. In this test, we test the remote access and check whether the park transmits the actual real-time data. Once the remote control capability has been successfully tested, a remote control certificate is issued. This certifies to the system operator and the distribution grid operator that the park has the mandatory remote control capability. 

A draft bill on the ‘Amendment of energy industry law to avoid temporary generation surpluses’ is currently being finalised^[2] in the parliamentary process. According to this, direct marketers are to be obliged to notify the grid operator of breaches of taxability obligations by system operators so that the grid operator can impose penalties. ^[3]

4. Grid-orientated vs. market-orientated control

Control systems can be divided into two categories:

1. On the one hand, grid operators have the option of curtailing renewable energy plants to avoid grid congestion and ensure grid stability. In this case, the measures are referred to as Redispatch 2.0 measures.
2. In addition, direct marketers can curtail plants via remote control technology in order to avoid negative revenues from renewables or to optimise their portfolio. These cases are referred to as market-induced controls or market-induced curtailments.
    

5. Market-related curtailments

In contrast to the grid operator, who regulates for reasons of grid stability, for example, the direct marketer has the right to control for market-related reasons - i.e. to react to price signals and thus utilise the flexibility of the installations.

Market-driven control can make sense for the direct marketer if it is more expensive for them to continue operating an installation than to curtail it. This can be the case in three scenarios in particular:

1. The EPEX SPOT price is below the settlement price of the system (often also referred to as the limit price or strike price). The plant is then not marketed in the day-ahead auction. If the prices on the subsequent intraday market do not rise above the limit price either, the plant is switched off for the period.
2. The market prices on the intraday market fall to such an extent that it makes sense for the direct marketer to curtail its own production by shutting down plants and buying back the shortfall on the intraday market at negative prices.
3. The direct marketer has a long position in its portfolio and can compensate for the imbalance most favourably by curtailing installations in the balancing group.

In all cases of market-induced curtailment, the direct marketer must fully compensate the system operator for the loss of production. Vattenfall pursues the principle that the operator should be in the same economic position as if the measure had not taken place.

In addition to the economic aspects, the direct marketer acts in a system-friendly manner by curtailment and supports the grid. In statements by experts^[4] with regard to the above-mentioned draft bill on the ‘Amendment of energy industry law to avoid temporary generation surpluses’, it is noted that installations in direct marketing, which should actually already be controllable under the current legal situation, sometimes do not react to negative price signals. There are three possible reasons for this: firstly, a non-functioning control system, secondly, the consideration of compensation payments by the direct marketer in the event of shutdowns or, thirdly, demands by the plant operator to reduce the control system to minimise wear and tear. In view of the legal objective of reducing future generation surpluses, the above-mentioned reasons that restrict market-related curtailment in new direct marketing contracts must be evaluated critically.

Do you have questions about remote controllability or market-induced curtailment? Please get in touch with us!

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^[1]BNetzA: Statistiken ausgewählter erneuerbarer Energieträger zur Stromerzeugung - November 2024

^[2] Bundestag, Drucksache 20/14235,https://dserver.bundestag.de/btd/20/142/2014235.pdf.

^[3] § 10b Abs. 6 EEG 2023-E.

^[4] https://www.bundestag.de/ausschuesse/a25_klimaschutz_und_energie/anhoerungen/1037770-1037770