Black start capability


A power plant is described as black-start capable if it can be restarted completely independently in the event of a power grid failure, i.e. without an external voltage supply. 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 there may be a (partial) collapse of the electrical supply grid ("power outage"). In this case, the grid operators coordinate the restoration of the grid with the help of black-start capable power plants.  

Where is this battery storage system used?

In future, a new procurement concept is to be developed for the black start capability ancillary service in Germany. This will take place against the backdrop of Directive (EU) 2019/944 (Electricity Market Directive), which requires the market-based, transparent and non-discriminatory procurement of non-frequency-based ancillary services (NF-SDL). Black start capability is currently procured via bilateral negotiations and contracts. The main focus is therefore on improvements in terms of transparency and non-discrimination. At the same time, a new procurement concept is intended to achieve an improvement on the status quo, particularly with regard to incentives for innovation and investment. Such a procurement concept offers large-scale battery storage systems the opportunity to participate in this market, which is important for security of supply. Alongside hydropower plants or gas-fired power plants, which will be undesirable in the future, large-scale battery storage systems are almost the only systems that can be black-started. For example, black start capability could be put out to tender in a standardized procedure after a technically determined regional differentiation. All plants that meet the minimum requirements for black start plants should be able to participate in these tenders and be awarded the contract after weighing up the price and the technical and systemic benefits. Such a procedure and the implications of the transformation to a sustainable energy supply described above will promote market development and 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 security with regard to the available black-start facilities. For large-scale battery storage systems, this provides the opportunity to conclude multi-year contracts and thus secure revenues as part of a multi-use strategy.  


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 as grid reserves for blackouts, i.e. they are on call, 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 also 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. However, 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. 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 be taken 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 types of plants for black start. Energy storage in general, and large-scale battery storage in particular, therefore present 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, for example, and they can deliver large amounts of energy in 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 control energy 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.