Record generation of wind energy and its impact on the National Electric Power System

by Piotr Mrowiec

3 March 2017

3 January 2017 went down in the history of Polish wind power industry. Due to the heaviest storm the Baltic sea saw in many years, caused by Alex – a strong low pressure system, the hourly output of wind farms reached its record-breaking level.

Wind energy generation record

Owing to the favourable weather conditions, wind farms in Poland were able to produce a record-breaking hourly amount of energy. According to the data updated as soon as 9 January 2017 on the Exchange Information Platform the amount of wind energy actually generated in the evening of 3 January 2017 reached its highest level ever. The output peaked at 10 p.m. when 5006 MW were produced in an hour. This was the first time more than 5 GW were produced. The previous record of nearly 4900 MW was set at the end of the previous year (26 December 2016). Such an amount of wind energy put the National Electric Power System to test as it never before had to accept such a large amount of energy from an unstable source. It was a particular challenge because the record amount was generated during the so-called valley hours, that is, at night when the demand for electricity is lowest.

Power generating units in the National Electric Power System

Electricity circulating in the electric power system may be divided into two basic types when it comes to the power generation units. The first type of electricity is produced in centrally controlled power generating units run by the Transmission System Operator (the so-called CCPGUs which include coal-fired power plants, large hydroelectric power plants, gas-fired power plants, pumped-storage power stations). These are stable sources which are generally insensitive to weather conditions. The power obtained from these sources provide the so-called technical minimum, which stands at about 10 GW as of 3 January 2017. This is a guaranteed amount of energy fed into the system and is a sort of security for the electricity consumers.

The second type of electricity is produced in uncontrolled power generating units or units controlled by the Transmission System Operator to a limited extent. These sources are called non-centrally controlled power generating units (nCCPGUs). They include without limitation photovoltaic plants, biogas power plants and wind farms.

Generation planned vs actual

The Transmission System Operator estimates the demandfor electricity. Then, it develops the so-called Daily Coordination Plan. That is why the Exchange Information Platform shows two parallel graphs, one of which shows the planned generation in a day (planned demand), while the other one shows the actually generated power. The values are usually very close and the power generated by the centrally controlled power generating units must never drop below the technical minimum.

If the actual generation is lower than the actual demand for electricity, the National Electric Power System uses the output from reservoir power plants, that is, plants that can quickly produce the lacking electricity. In Poland, it is the pumped-storage power stations that function as reservoir power plants. Then, even if the reservoir power stations cannot supply enough power to satisfy the demand, a blackout may happen. The opposite situation is when the supply of electricity exceeds the demand. Then, some sources of power must be shut off due to the redundant costs of power generation. Noteworthy, the technical minimum must always come from the CCPGUs. Therefore, if e.g. at some point the current demand is lower than the current supply of electricity, the technical minimum is ensured and the remaining power comes from wind farms, some of the wind turbines will have to be switched off. For instance, the demand for electricity on 3 January 2017 at 10 p.m. was about 16 GW. The technical minimum required about 10 GW and wind farms supplied 5 GW. Therefore, all of the generated electricity was consumed. However, if the demand was for 13 GW, the surplus of 2 GW from wind farms would be squandered. Moreover, the operator of the National Power Electric System would have to order some of the wind turbines to be switched off to balance the power in the grid. At the same time, wind farm owners would not earn on the electricity they produced. Polish law lacks provisions dealing with such a situation. In this context, we cannot rule out that wind energy producers might seek compensation for opportunity costs and losses caused by the limitation or shut-down of ready to use wind farms on the basis of civil law. The losses are then particularly high because wind farms are shut down during excellent wind conditions so the amount of potentially unused electricity is considerable.