A power plant is described as black-start capable if it can be restarted completely independently in the event of a power grid failure, without any external voltage input.
The safe and reliable operation of the electricity supply system and thus a secure energy supply is the responsibility of the distribution system operators and transmission system operators. In addition, the transmission system operators maintain measures throughout Europe to prevent a grid collapse in critical situations. Despite all these security measures, in extreme cases a (partial) collapse of the electrical supply network can occur ("blackout"). In this case, the network operators coordinate the reconstruction of the network with the help of black-start capable power plants.
In the event of a major disruption, the coordinating responsibility lies supraregionally with the transmission system operator. The transmission system operators are obligated to maintain network reconstruction plans, to check them regularly for up-to-dateness and function, and to coordinate them with the connected network operators and the relevant plant operators. Grid reconstruction begins with generators that have the necessary control capability, can be deployed from the grid operators' control center, and thus fulfill the technical requirements for the fastest possible resupply. Today, these are mainly large-scale power plants, such as gas or hydropower. In the further course of grid reconstruction, renewable energies will be used depending on the power available today, which is mainly provided by conventional power plants Control services. In addition, in the further course of grid reconstruction, electricity consumers are successively connected and the power grid is thus reconstructed bit by bit. The grid frequency must be kept stable at all times. The grid operator coordinates the interplay between power production and power consumption until normal conditions are fully restored.
Which and how many plants are currently black start capable?
There are currently 174 black-start-capable plants in Germany with a rated output of at least 10 MW. Some of these are held in reserve for blackouts, i.e. they are on standby, or they are active and also produce electricity for the normal case. Of these 174 black-start capable plants, only 26 actually have a contractual agreement with the TSOs for grid reconstruction. Most of these plants are hydroelectric plants. In addition, natural gas power plants are used. However, these black-start capable conventional power plants as well as hydropower plants also require a small amount of starting energy (pumped storage power plants, for example, to control the actuators to regulate the water flow), which is provided by local batteries, for example. The most important task of black-start capable plants is to provide the thermal power plants with the necessary starting power to resume grid operation. Therefore, gas turbines are also kept at sites of large conventional generators for black start capability.
What does black start capability look like in a renewable future?
Due to the transformation of the energy system in the context of the energy transition, grid reconstruction will be subject to changes in the coming years. On the one hand, more conventional generation plants will come under profitability pressure and go off the grid. If such black-start capable conventional power plants were to be kept on the grid for black-start capability alone, the costs for the overall system could increase. A market for black start capability should be designed so that a plant remains on the grid for black start capability only if it continues to be the most economical option for meeting the given level of safety. These changes in the wake of the energy transition create opportunities for grid reconstruction - for example, by bringing in new players and plant types for black start.
In addition, these new types of plants must be able to cover the released demand for required Control power to cover this demand. This is because control energy is required for the step-by-step connection of generators and consumers during network reconstruction. If this is not available in sufficient quantities, grid reconstruction slows down. Since this balancing power is currently provided to a large extent by conventional large-scale power plants such as gas-fired power plants, there will be an opportunity for new players to take over this role in the near future.
Energy storage in general, and large-scale battery storage in particular, therefore offer themselves as a natural alternative: They can be used independently of geographic conditions, so they do not need a gradient like a pumped storage power plant, and they can deliver large amounts of energy in a matter of seconds at the "push of a button." Thanks to their multifunctionality, large-scale battery storage systems are able to provide both black start capability and balancing power and can thus make a decisive contribution to security of supply. In addition, large-scale battery storage represents a sustainable alternative to black start supply: After all, stored solar and wind energy can also be used for black start. This makes it possible to use the entire range of renewable energies also for grid stabilization and grid restoration. As a black start-capable technology, large-scale battery storage can ideally replace the gaps in black start-capable power plants that arise due to the disappearance of conventional power plants.
How big is the market for black-start power plants?
The market size can be estimated from the costs associated with black start capability in the BNetzA's monitoring report. In 2018, these amounted to €7.4 million. According to the study on aspects of electrical system stability in the German transmission grid up to 2023 (RWTH Aachen University, 2015), 4.6 GW of potential black-start-capable power plant capacity was contracted in 2019. According to statements by transmission system operators and the German government (as publicly confirmed in Printed Paper 19/16714, 2020), 26 plants, mainly pumped-storage and natural gas-fired power plants, and occasionally coal-fired power plants, are currently contracted by transmission system operators. In total, there are 174 black-start capable plants, but the majority of these have comparatively small outputs. In coordination with the transmission system operators, additional plants are held in reserve by the distribution system operators for their own use cases, such as the reconstruction of supply to critical infrastructure. The costs for the latter are passed on via the distribution grid charges, since the plants are not included in the control area-wide reconstruction.
What might be the role of large-scale battery storage in a system for market-based procurement of black start capability in the future?
In the future, a new procurement concept for the system service black start capability in Germany is to be developed. This will be done against the background of Directive (EU) 2019/944 (Electricity Market Directive), which calls for the market-based, transparent and non-discriminatory procurement of non-frequency-based system services (NF-SDL). Black start capability is procured today through bilateral negotiations and contracts. The main issue is to improve transparency and non-discrimination. At the same time, a new procurement concept aims to improve on the status quo, especially in terms of incentives for innovation and investment.
Such a procurement concept offers large battery storage facilities the opportunity to participate in this market, which is important for supply security. For example, black start capability could be put out to tender in a standardized procedure after a technically based regional differentiation. All facilities that meet the minimum requirements for black start facilities should be able to participate in these tenders and be awarded the contract after weighing price and technical and system benefits. Such a procedure, as well as the implications described above due to the transformation to a sustainable energy supply, will promote market development as well as active competition among all providers of black start capability. In order to maintain security of supply in the long term, grid operators also need planning certainty with respect to the available black start facilities. For large-scale battery storage, this creates the opportunity to conclude multi-year contracts and thus secure revenues as part of a multi-use strategy.