Keeping the lights on: how Austria’s power grid remains stable
Without electricity, modern-day life would grind to a halt. Public and private transport, food supplies, healthcare, communication and even the water supply: none of it would work if the power grid went offline. To make sure this does not happen, electricity production and consumption need to be precisely balanced – throughout the entire European electricity system. So at any given time, exactly the same amount of electricity needs to be generated as is being consumed. How electricity moves from one place to another has nothing to do with who is selling it to whom; electricity flows only follow the laws of physics, regardless of what is happening on the trading exchanges.
Small drop in frequency poses risk of blackouts
In the physical electricity system, voltage and frequency need to be at the same level, otherwise outages can occur. The system frequency in Europe is 50 hertz. The largest power outage in recent years was in 2006, when the frequency dropped but did not even touch 49 hertz. This happened because too little electricity was injected in southwest Europe, while northern Europe was oversupplied. Parts of Europe were left without electricity for up to two hours.
The problem was due to an error in the load flow calculations and forecasts following the scheduled shutdown of high voltage power lines. These calculations usually ensure that additional electricity from power stations is injected into the system in case of undersupply, while production is scaled down if there is excess supply. This is called control energy and its purpose is to keep the grid stable.
Control power in Austria
In Austria, ensuring grid stability is the job of Austrian Power Grid (APG), which operates the upstream European electricity network in cooperation with transmission system operators (TSOs) from other countries.
International electricity transmission takes place at this level, which also forms the basis for security of supply. During the 2006 power outage, large-scale industrial consumers were also taken offline and additional pumped storage power stations were ramped up in order to restore balance in the network. In Austria and Germany, between 2,500 and 3,500 MW of control energy is available at any given time.
The TSOs purchase this control reserve from producers on the basis of tenders. The producers’ electricity is called off in accordance with the price, so cheaper photovoltaic power is more likely to be procured than that from gas-fired power stations, which are expensive to fire up.
Storing control energy in the form of water
Pumped storage and gas-fired power stations are the most influential participants on Austria’s control energy market. The country currently has 16 gas-fired power plants – although they are expensive to ramp up, on the plus side they are also a quick and reliable solution to system imbalances. By contrast, pumped storage power stations can store energy in the form of water, meaning that power can be called off quickly when it is needed. Because energy is required to pump water up to reservoirs at higher altitudes for storage, pumped storage facilities are not only in a position to supply control energy, but can also make use of any excess electricity in order to bring the system back into equilibrium in case of oversupply.
Congestion management takes the load off power lines
Liberalisation of the electricity market and the growing proportion of renewable energy are placing grids under increasing pressure. This is where congestion management comes in, dealing with impending oversupply on certain sections of power lines. Redispatching measures are put in place specifically in order to reduce the load on particular connections within the grid. To prevent imbalances in the system, electricity generation is reduced at one end of a transmission line and a power station is fired up at the other end at the same time to make up for the shortfall in supply. APG is responsible for coordinating these measures. When congestion occurs, APG instructs power station operators to adjust their generating schedules by either increasing or reducing capacity at their power stations.