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Energy Systems and Technologies for the Coming Century ...

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different gusts <strong>for</strong> <strong>the</strong> individual turbines, inertia of <strong>the</strong> large rotors as wells as <strong>the</strong>variable speed turbines absorbing <strong>the</strong> variations <strong>and</strong> <strong>the</strong>re is no correlation between <strong>the</strong>variations of geographically dispersed wind farms. As a result, wind power variationswithin seconds or few minutes, in <strong>the</strong> order of <strong>the</strong> activation notice of primary reserves,have very small effects on system operation even at considerable penetration [10, 11].For regulating power <strong>and</strong> secondary reserves with an activation time of maximum 15minutes, <strong>the</strong> impact of wind power <strong>for</strong>ecast errors is significant but never<strong>the</strong>less lowerthan <strong>the</strong> impact of hourly wind power variations [22].The remaining wind power impacts are in <strong>the</strong> following analysed using projected hourlynet load variations <strong>for</strong> West Denmark in 2025. The length of negative <strong>and</strong> high net loadperiods 2 is investigated based on two different approaches:1) Length of consecutive negative/high net periods <strong>and</strong>2) Rolling averages indicating periods with negative/high net loads on average.2.3 Negative <strong>and</strong> high net load periodsThe results suggest that negative net load periods in 2025 will be ra<strong>the</strong>r pronounced,occurring in 22 %, 15 % <strong>and</strong> 10 %, of <strong>the</strong> year <strong>for</strong> consecutive net load periods below 0MW, -500 MW, -1000 MW, respectively (see Fig. 3). A significant part will coverperiods with a length of up to half a day, i.e. 34 %, 40 %, 54 %, 82 % <strong>and</strong> 100 % of <strong>the</strong>periods with net loads below 0 MW, -500 MW, -1000 MW, -1500 MW <strong>and</strong> -2000 MW,respectively. However, periods of 0.5-3 days will comprise <strong>the</strong> majority of <strong>the</strong>consecutive negative net load periods below 0 MW <strong>and</strong> -500 MW <strong>and</strong> hereof, asignificant part of <strong>the</strong> periods have lengths above one day.Pct. of <strong>the</strong> year25%20%15%10%5%0%Net loadbelow0 MWNet loadbelow-500 MWNet loadbelow-1000 MWNet loadbelow-1500 MWNet loadbelow-2000 MW2.5-3days2-2.5days1.5-2days1-1.5days0.75-1days0.5-0.75days0-0.5daysFig. 3. Consecutive negative net load periods expected <strong>for</strong> West Denmark in 2025.As illustrated in Fig. 4, consecutive high net load periods will not exceed a length of oneday. Hereof, periods of lengths below <strong>and</strong> above half a day, respectively, will both besignificant.2 After subtracting of 300 MW minimum power productions on large <strong>the</strong>rmal plants.Risø International <strong>Energy</strong> Conference 2011 Proceedings Page 4

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