Building and operating a grid stabilization plant

The power grid can only be stably operated if the energy generated corresponds to the energy consumed at any given moment. A change in consumption must be instantly balanced on the generation side, which is why power plants have balancing reserves and quickly controllable power plants can balance this change in consumption at short notice.

Fluctuating generation from renewable energy sources (such as photovoltaics or wind power) must also be balanced by conventional power plants, nuclear power plants or pumped-storage power plants.

Even if certain equipment (i.e., a system such as a switch, a power line or a transformer) fails, the power grid can still be operated in a stable manner. This is known as (n-1) security. The remaining lines/systems then take on the task of transmitting the electricity. The circuits are usually not overloaded, meaning that the failure is safely controlled – as long as no further equipment fails during this phase. That is why so-called (n-1) security must be restored as soon as possible. This is achieved by easing the load on the power grid locally through generation capacity that can be activated quickly.

In the past, power grids were rarely operated at the limits of (n-1) security because the transmission distances were significantly shorter than they are today due to power being generated close to where it was consumed. Even after the failure of equipment, (n-1) security was often still guaranteed – helped by the grid’s normally unused overload capacity in those days. Today, the grids are increasingly being operated at their technical limits. As a result, the number of interventions required to ease the pressure on the grid has increased significantly in recent years.

The situation on the generation side will change significantly in the future due to the following factors:

• The phaseout of nuclear power
• Further expansion of renewable energy capacity increasingly leading to a generation surplus in northern Germany, which has to be redirected toward southern Germany
• Delayed grid expansion of high-voltage lines between northern and southern Germany

These factors are having a particularly serious impact in southern Germany. Additional generation plants are therefore needed to guarantee grid stability and security of supply. However, these will not be used to compensate for the lost capacity previously provided by nuclear power plants, but will only be used for a relatively brief length of time to support the power grids in the event of problems in the transmission grid if equipment fails (see also question 2).

The capacity of conventional generation plants and pumped-storage plants has been factored into the calculations for new grid stabilization plants when determining the power needed. In an analysis, the Federal Network Agency concluded that an additional 1,200 megawatts (MW) of rapidly accessible generation capacity are needed in southern Germany to guarantee security of supply in the event of a fault in the grid.

The current reserve power plants are used to balance any power deficiency in the power grid and support grid stability as a preventive measure, even if no equipment within the power grid has failed and the grid remains stable.

The new grid stabilization plants, meanwhile, will only be used if one or more system elements (such as a switch, a power line or a transformer) have actually failed within the transmission grid, placing the power grid in a critical condition. Grid stability will then be restored with the help of these new plants. The grid stabilization plants are also available much more quickly than the existing grid reserve, which is usually made up of older plants.

The grid stabilization plant will only be started up in the event of an equipment failure within the transmission grid. In most cases, they are used secondarily to all existing power plants. As such, in our view, a very small number of operating hours can be expected.

However, the operator (in the event of being awarded the contract in the tendering process: EnBW) has no influence on the plant’s use and operating life. This is the responsibility of the transmission system operators, who decide entirely independently how the grid stabilization plant is used.

The operative word “gas” describes the medium that drives the turbine. Steam drives a steam turbine and wind drives a wind turbine. A gas turbine, meanwhile, is driven by hot combustion gas, which is why it is known as a “gas turbine” – regardless of which fuel is used to produce the hot combustion gas.

No, the gas turbine is built as a new block at the Marbach site and will not replace any of the existing plants.

Back in 2013, EnBW applied for the final decommissioning of all generation plants in Marbach. Since the plants have been classified as having system relevance by the transmission system operator since 2013 (most recently in 2018), they have been subject to a decommissioning ban ever since and are started up at the request of the transmission system operator.

The operating license for some of the existing plants (MAR II gas turbine and MAR III boiler and steam turbine) expires at the end of 2023, so we must assume that these plants will be decommissioned at the end of 2023.

The plant will be kept available for a period of ten years.

The emissions and in particular the gas turbine’s impact on the environment have been examined as part of the immission control approval process. Approval will only be granted if operating the gas turbine has no significant impact.

In our view, light fuel oil is more suitable as a fuel than natural gas in Baden-Württemberg. This will avoid any short-term supply bottlenecks, which could occur if natural gas were used. Furthermore, security of supply in southern Germany should not depend on a single primary energy source like natural gas. In conjunction with the large (already existing) oil storage facility in Marbach, we consider light fuel oil to be the ideal fuel for this purpose.

Since the grid stabilization plant is not expected to be used very often, the fuel will have no significant impact on the environment. Gas turbines that run on fuel oil are also subject to much lower emission limits today than they were around 20 years ago.

This will be examined and evaluated in the course of the approval process. We currently do not expect there to be any significant impact on water resources.

Oil will still be supplied by ship via the Neckar. Due to the low number of expected operating hours, we do not currently expect any significant increase in activity.

• During operations:
  The impact of the gas turbine power plant on surrounding areas will be examined and evaluated in detail as part of the approval process. Approval will only be granted in accordance with regulations governing emissions if the gas turbine can be operated within the permissible limits.