In the planning phase of the grid development process, the Swiss Federal Office of Energy (SFOE) drafts an energy policy scenario framework for Switzerland. It is approved by the Federal Council and used as the future basis for planning the Swiss electricity grid – with the aim of ensuring that the electricity grids are optimally aligned with the future energy policy developments in Switzerland. The scenario framework contains three scenarios that reflect the range of possible energy policy developments.

Swissgrid then uses this scenario framework to determine the need for adjustments to the transmission system. These changes are documented in a multi-year plan, the «Strategic Grid». Expansion planning for the distribution system operators’ high-voltage grids is also based on the scenario framework. The planning phase is repeated every four years, which means that the high-voltage grids (distribution system) and the extra-high-voltage grids (transmission system) can be continuously adapted to changing framework conditions in parallel and by mutual agreement.

In the project planning phase, Swissgrid develops specific projects covering the demand identified in the Strategic Grid report. Every project normally passes through a national sectoral plan process for transmission lines at the SFOE as well as a planning approval procedure with the Federal Inspectorate for Heavy Current Installations (ESTI). Decisions on the transmission technology to be used (overhead lines, cables or a combination of the two) and routing are also made in this phase.

Once all the necessary approvals are in place, Swissgrid starts the implementation phase with the construction of the relevant projects. After commissioning the installations, Swissgrid also checks whether the project costs assumed in the Strategic Grid and their expected benefits reflect reality and possible reasons for deviations. The findings from these analyses are incorporated into the recurring planning process.

Swissgrid is not expanding the grid to accumulate reserve capacity. The existing grid is operated as efficiently as possible. Wherever possible, Swissgrid first optimises the existing grid and enhances it as necessary. Obsolete lines and substations are dismantled wherever possible. If a new line is required, Swissgrid takes into account the spatial and environmental impact, as well as technical aspects and cost-effectiveness, when searching for the best line corridor and selecting the transmission technology (overhead line or cabling).

The bundling of transmission and distribution lines with trunk roads and railway lines reduces the number of parallel routes. The need for expansion between grid nodes is determined as part of the Strategic Grid. The line corridor and transmission technology are definitively determined within the framework of the subsequent «Spatial Coordination (National Sectoral Plan Procedure)».

Swissgrid identifies grid elements where regular congestion is likely to occur in the future. For this purpose, Swissgrid refers to findings from current grid operations, as well as to a grid simulation for the target year being analysed. Existing and future congestion will be eliminated by means of grid optimisation, grid enhancement and grid expansion.

The dismantling of large power plants all over Europe reduces the rotating mass on the transmission system. The inertia of large generators, such as those found in nuclear or coal-fired power plants, still stabilises the frequency of the grid today. Swissgrid and foreign transmission system operators conduct stress tests to determine whether grid stability can still be guaranteed in the future or whether measures need to be taken as part of grid planning.

In grid planning, Swissgrid can only take into account the potential for flexibility offered by artificial intelligence, decentralised consumption control and smart peak shaving in photovoltaic and wind production if this potential can be activated and used by Swissgrid at any time. To achieve this, the regulatory framework conditions must be created, products developed, technical requirements met and contracts concluded. This has not yet happened to a sufficient extent.

For every grid project costing more than CHF 1.0 million, Swissgrid carries out and documents a uniform cost-benefit comparison. The benefit of each grid project is shown in monetary, quantitative or qualitative terms according to various criteria.

Swissgrid coordinates long-term grid planning with all the relevant stakeholder groups. These include, for example, the transmission system operators of neighbouring countries, the distribution system and power plant operators connected to the Swiss transmission grid, the Swiss Federal Office of Energy (SFOE) and the Swiss Federal Electricity Commission (ElCom). Swissgrid communicates the procedure and results of the Strategic Grid in a transparent and comprehensible manner.

The starting point for the grid planning process is known as the “start grid”. This European grid model includes all grid elements that will continue to be in operation or that will be put into operation by the target year.

The reference grid is formed with the help of market and grid simulations. This is done by adding new grid projects to the start grid until there is no longer any relevant grid congestion in the various scenarios. The grid expansion requirements identified during this process are coordinated both with the DSOs connected to the transmission system and with foreign transmission system operators in order to enable coordinated planning of the entire grid.

• The result obtained from the market simulation shows the hourly power plant deployment per bidding zone (a country can consist of one or more bidding zones) and the resulting cross-border electricity exchange. The target function is to cover the load in each bidding zone, at minimum generation cost, taking into account the maximum cross-border capacity between bidding zones. The results per bidding zone from the market simulation are allocated to the nodes of the European grid model by means of mapping. This means that the hourly generation and the consumption per grid node are taken as input values for the grid simulation.
• For each scenario, grid simulations are calculated with the European grid model, and any congestion (n-1/tension violations) is detected. The utilisation of the grid elements per scenario is created from this, at which point it becomes clear where there is still a need for grid expansion. The NOVA principle is always applied when upgrading the grid. The NOVA principle stands for grid optimisation before grid enhancement before grid expansion. It aims to minimise the impact of grid expansion on the environment and the landscape.

After the finalisation of the reference grid, the target grid is formed. All additional grid projects in the reference grid are evaluated with the help of the cost-benefit analysis. The evaluation of each individual grid expansion measure is carried out from an economic as well as an environmental and technical perspective and serves as a proof of need. In principle, only those projects where the benefits prevail will become part of the target grid.

The totality of the additional grid projects in the target grid compared to the start grid forms the Strategic Grid.