Reactive power is that part of the power provided by the grid that is generated by the interaction between voltage and current in an AC system and cannot be actively used by consumers. Reactive power is generated or consumed in many electrical devices (capacitors, electric motors, generators). Reactive power plays a role in building up the electric and magnetic fields of motors or capacitors. Reactive power must be distinguished from power loss, which represents the energy that is lost as heat energy due to friction losses, for example. Reactive power, on the other hand, is not "lost", but is "temporarily stored" and returned to the network when the fields are reduced. The reactive power cannot do any useful work, but it is still a burden on the grid, which is why it is generally kept as low as possible.However, it is unavoidable in order to build up the electric and magnetic fields that are important not only for the operation of numerous electrical devices, but also for the transport of electricity.
Just as large-scale battery storage facilities can participate in the balancing energy market, it would also be possible for storage facilities to participate in such a free reactive power market without difficulty. The provision of reactive power is not only limited to times when energy is stored or withdrawn. After all, the technical connection guidelines stipulate that reactive power must be provided during these times anyway.
In addition, large-scale battery storage systems have the technical capability to provide reactive power even when the plant is idle,when no active power is being injected or withdrawn. In these idle phases, reactive power can be provided on a contractual basis, which enables a revenue stream during the idle phases. The end customer also benefits, because the additional supply of reactive power reduces the procurement prices for the grid operators and thus the grid charges for the customers.
In general, it is the responsibility of the grid operators to provide the required reactive power by requesting the generation plants available in the grid. Up to a certain range, the provision of reactive power for generation plants is regulated in the grid connection conditions of the respective grid operators or in the Technical Connection Guidelines ('TAR') issued by the VDE. These stipulate that generation plants may only be connected to the grid if they can provide part of the power as reactive power. The exact proportion to be supplied is often in the order of 10% of the connected power, depending on the grid operator. For example, if a large-scale battery storage system feeds in 10 MW of active power, it must provide an additional 1 Var (=1 MW) of reactive power for a static reactive power provision of 10%. However, the generation plants are not additionally remunerated for this provision of reactive power, although increased line resistance and wear and tear result in additional costs for the generation plant.
The demand that goes beyond this "forced" procurement measure of reactive power is currently often regulated via bilateral contracts between conventional large power plants and the respective grid operators. Pricing takes place in individual negotiations between the parties and is not presented to the public. It is correspondingly non-transparent. According to the BNetzA, the agreed prices differ significantly in some cases and vary from €0.08 to €2.27/MVArh (source: discussion paper "Reactive power provision for grid operation", BNetzA). As early as 2019, the legislator legally stipulated in Section 12h of the EnWG that, as with many other electricity products such as balancing energy, trading of reactive power should also be based on a transparent, non-discriminatory and market-based procedure. However, the reality is quite different, due to non-transparent price negotiations of the network operators with a few large conventional power plants. In the course of the introduction of § 12h, the Ministry of Economics commissioned an expert opinion that examined the economic efficiency of such a procedure. The result shows that reactive power can generally be procured via a market-based, transparent procedure. The industry is currently waiting for the Federal Network Agency to specify exactly how the future reactive power market is to be structured. Unfortunately, the timetable for this is still open.
Currently, reactive power is mainly offered by large power plants. There is continuous communication between them and the grid operators in order to calculate requirements as accurately as possible. However, renewable energy generation plants and large-scale battery storage systems are also able to provide reactive power. In the meantime, they are even obliged to supply a certain amount. Due to the expansion of renewables and the gradual shutdown of conventional power plants, this is particularly important as grid operators can thus draw on more and more generation plants. In this way, the power grid can also be stabilized in the future through reactive power.