A steady balance between production and consumption is the prerequisite for a stable electricity grid and guarantees secure supply at a frequency of 50 Hz. This means production and consumption need to be coordinated. As far as production is concerned, this is relatively simple: the production of electrical energy is largely foreseeable, apart from the new renewable energies. Consumption (so-called grid load) is a different matter, however: it can be estimated but never accurately predicted. An unforeseen cold spell, for example, can drive up electricity consumption in contradiction to plans.
Grid load Switzerland
All electricity withdrawals from the electricity grid are referred to as grid load. The electricity withdrawal is the quantity of produced energy distributed from the electricity grid. Swissgrid makes the following distinction in terms of electricity withdrawal:
- Load on the transmission system: load which is distributed from the high-voltage grid to subordinate grids (grids with lower voltage level, distribution systems) or to directly connected consumers. These include, for example, pumps or frequency converters linked to the high-voltage grid.
- Total load: total grid load of all consumers, irrespective of the grid level (high-voltage grid, grids with lower voltage levels).
There is a difference between the load on the transmission system and the total load. Many power plants do not feed the energy they produce into the high-voltage grid. They transport the energy produced to the consumer via subordinate grids.
Example of feed-in to subordinate grids:
A river power plant close to a city seldom feeds the energy it has produced into the high-voltage grid, but rather into a lower voltage level. The city draws its electricity from this voltage level. Because of the short distances between the river power plant and the city, no detour via the high-voltage grid is necessary. The electricity can be transmitted directly via a lower voltage level. This electricity withdrawal therefore does not feature in the «load on the transmission system».
Grid operational safety and photovoltaic plants
Small, decentralised generating plants, primarily photovoltaic plants, have a distinctive feature: they disconnect from the grid as a result of even the smallest fluctuations in grid frequency. Plants like these feed into subordinate grids.
This means that when the grid frequency reaches 50.2 Hz, many existing plants disconnect at the same time. If conditions are unfavourable, this could trigger anything from a critical grid status to blackouts. Further information is available here (in German).
Example of feed-in to high-voltage grid:
An efficient pumped storage power plant in the Alps has to transport large volumes of produced energy across large distances. Because transport is more efficient on a high voltage level this power plant feeds the energy produced into the high-voltage grid.
When this power plant goes into pumping mode and pumps water up into the higher reservoir in order to store energy, it becomes an additional consumer (load). Consequently, the power plant will feature in the «load on the transmission system” when in pumping mode.
Load flows across the border (exchange)
The exchange of electricity between different high-voltage grids is referred to as load flows across the border. Switzerland has more than 30 connections to the high-voltage grids of neighbouring countries. Electricity is constantly exchanged via these connections. The electrical flows and direction of flow change depending on where electricity is produced and consumed in Europe. The load flows between Switzerland and its neighbouring countries are calculated for each border.
The sum of all load flows across the border yields the balance for Switzerland.
The balance for Switzerland indicates how much electrical power (electricity) Switzerland currently exchanges with its neighbouring countries. The balance states whether Switzerland imports or exports more electrical power overall.
The balance for Switzerland does not refer to the overall production or the total consumption of energy in Switzerland.
Electricity consumption in Switzerland rises significantly with the operation of a large factory. If the required energy is supplied by a power plant within Switzerland there is no additional load flow across the border. There is no additional exchange of electricity with grids belonging to neighbouring states. The balance consequently remains unchanged.