Impact of prediction uncertainty of intermittent power generation on frequency control costs

Rast vlaganja v obnovljive vire električne energije, predvsem v izrabo energije vetra in sonca, se je v zadnjih 15 letih zelo povečala. To je v veliki meri posledica političnih odločitev, ki so naklonjene izrabi obnovljivih virov. Evropska unija preko programov, katerim se je zavezala, stremi k čim večjemu deležu obnovljivih virov. Najbližji je strategija do leta 2020 oziroma »20 20 20 do leta 2020«, ki predvideva 20% zmanjšanje emisij CO2 v primerjavi z letom 1990, 20% delež obnovljivih virov v porabi primarne energije ter povečanje energetske učinkovitosti za 20%. Za dosego teh ciljev so potrebna vlaganja v nove tehnologije in obnovljive vire. Pri vlaganju v sončne in vetrne elektrarne veliko pripomorejo spodbude – subvencije, ki jih ponujajo države v Evropski uniji. Avstrija je ena izmed vodilnih držav v Evropski uniji po deležu obnovljivih virov za proizvodnjo električne energije. Večinski delež predstavlja izkoriščanje vodnih virov. V zadnjem času pa se je povečalo vlaganje v sončne in predvsem vetrne elektrarne. Delež instalirane moči vetrnih elektrarn v Avstriji predstavlja nezanemarljiv delež. Značilnost Avstrije je ta, da je območje, kjer so vetrovne razmere primerne za postavljanje vetrnih elektrarn, strnjeno na vzhodni in severovzhodni del države. Tako ima država večino vetrnic postavljenih na relativno majhnem območju, kar privede do zelo nestanovitne proizvodnje iz vetrnih elektrarn ob spremenljivih vetrovnih razmerah. To pa lahko privede do neravnovesja v sistemu, torej da proizvodnja ne sledi porabi. Ko pride do neravnovesja v sistemu, mora sistemski operater aktivirati regulacijo frekvence. Najprej pride do samodejne aktivacije primarne regulacije, nato sekundarne. Če neravnovesje traja več časa, je potrebna aktivacija še terciarne regulacije oziroma minutne rezerve, ki razbremeni primarno in sekundarno regulacijo za primer, da v sistemu ponovno pride do nestabilnosti. Od leta 2010 do leta 2015 se je v Avstriji vsako leto povečeval znesek namenjen za aktivacije terciarne regulacije. To je posledica tako povišanja povprečne cene za aktivacijo po letih kot tudi povišanja števila oziroma količine aktivacij terciarne regulacije. Istočasno se je v tem času povečala instalirana moč vetrnih elektrarn za več kot dvakrat in sicer iz 1011 MW na 2306 MW. Pri primerjanju podatkov o napovedani ter dejanski proizvodnji električne energije iz vetrnih elektrarn, smo ugotovili, da je v nekaj primerih, ko pride do aktivacije terciarne regulacije, prisotno precej veliko odstopanje med napovedjo in proizvodnjo iz vetrnih elektrarn. Tako smo ugotovili, da nestanovitnost proizvodnje iz vetrnih elektrarn vpliva v Avstriji že do take mere, da je potrebno aktivirati terciarno regulacijo frekvence za izravnavo odstopanj v omrežju.The value of investments in renewable resources of electrical energy, mainly in using wind and solar energy has increased greatly in the last 15 years. It has been mainly a result of political decisions, which were inclined to the idea of using renewable resources. Through the programs the European Union has committed itself to, it strives to the highest possible share of renewable resources. The most current one is a Europe 2020 Strategy, which predicts a 20% decrease in CO2 emissions in comparison to the year 1990, a 20% share of renewable sources in primary energy consumption and a 10% increase in energy efficiency. For accomplishing these goals, a lot of investments in new technologies and renewable resources are needed. Financial incentives or subsidies, offered by EU countries, play an important role in investing in solar and wind power plants. Austria is one of the leading EU countries in the share of renewable resources for electrical energy production. The majority share is represented by using water resources. In the recent years the country increased investments in solar and especially wind power plants. The installed capacity of wind power plants in Austria represents a significant share of total installed capacity of the country. Austria’s main feature is that the areas where the wind conditions are appropriate for power plants are condensed in the eastern and north-eastern parts of the country. The power plants are therefore placed on a relatively small area, which results in a very inconsistent production of energy from wind power plants in case of changeable wind conditions. This can lead to an imbalance in the system, meaning that the production does not follow the consumption. When such imbalance in the system occurs, the system operator has to balance the system. If the imbalance lasts for a longer period of time, then the tertiary control or minute reserve has to be activated. Tertiary control thus relieves the primary and secondary control for the case of repeated instability in the system. Between the years 2010 and 2015 Austrian costs intended for tertiary control activations increased annually. This rise is due to an annual increase of average price of activation and an increase in number of tertiary control activations. At the same time the installed capacity of wind power plants more than doubled, from 1011 MW to 2306 MW of installed capacity. When comparing the data of predicted and actual production of electrical energy from wind power plants, I found out that in some cases of tertiary control activations there has been a significant deviation between the prediction and actual production from wind power plants. Thus, I reached the conclusion that the inconsistency of production from wind power plants affects Austria to the extent that tertiary control activations are needed for balancing the electrical power grid