The Impact of Polish Pumped-Storage Plants on Operation of the National Power System on Working Days and Holidays

Transcription

1 1 Paper N 0 : II.14 The Impact of Polish Pumped-Storage Plants on Operation of the National Power System on Working Days and Holidays Jan Wróblewski Abstract: The analysis of current changes of power demand in the power system is conducted for characteristic days. The investigations are based on daily power balances of the power system made in the national dispatching center. The impact of pumped-storage plants on the load distribution in the national power system is investigated for two basic options: when the national power system operates without pumped-storage plants and when pumped-storage plants take part in the national power system, which is the real situation. The most recent investigations conducted at the Department of Hydro and Marine Engineering Gdańsk University of Technology, have also been focused on analysis of the effect of pumped-storage plants on the curve of daily generation of power and energy in the national power system. The analysis of current changes in demand for power in the national power system will be carried out for characteristic days selected from the period The following studies have been carried out for the characteristic working and holidays: analysis of contribution of pumped-storage plants to increase the minimum base load of the national power system - N min, analysis of contribution of pumped-storage plants to reduce peak demand for power and intermediate load of the system in the power range between N max and N min, analysis of contribution of pumped-storage plants to reduce intermediate generation of the system, analysis of contribution of pumped-storage plants to reduce minimum intermediate load, analysis of increase of the load coefficient in the system. Keywords: Pumped storage plants; Power System; Peak and minimum demand; Load demand of the power system.

2 204 Wróblewski 1. The effect of pumped-storage plants on the curve of daily generation of power and energy in the national power system Data found based on readings on the hours throughout the day and two half-hour readings during the evening peak (and every 15 minutes since 2003) extend on the following parameters of the national power system: country generation, pumping (in all pumped-storage plants simultaneously), country generation not including power consumption for pumping, generation of hydro power plants of the system (6 pumped-storage plants of: Żarnowiec MW, Porąbka-Żar MW, Żydowo MW, Solina MW, Czorsztyn - since MW, Dychów - 80 MW and two water- plants of: Włocławek MW, Rożnów - 50 MW), peak generation of all hydro power plants of the system, country generation not including generation of pumped-storage plants, normal demand not including power consumption for pumping, total generation of thermal power stations. The results contain: total power generation [MW] from all national pumped-storage plants, total country power generation minus generation from pumped-storage plants [MW], country generation of active energy for half-hour intervals (and every 15 minutes since 2003) throughout the day [GWh], country generation of active energy minus generation from pumped-storage plants for half-hour intervals of the day [GWh], energy consumption for pumping for half-hour intervals of the day [GWh]. These data form a basis for subsequent calculations within the subject of investigations. Table 1 gathers results of calculations for an exemplary holiday - November 11, 2003 (Independence Day). The calculations were carried out for two main operational configurations of the national power system: national power system not equipped with pumped-storage plants (column 3 in Table 1), and national power system operating with pumped-storage plants (column 4 in Table). The results of calculations divided into 9 groups separated by horizontal lines are gathered in Table 1. In the first group (rows 1 3), there are values of generation in the national power system, with and without energy consumption for pumping, which enables the determination of percentage increase of generation in the national power system due to this consumption. In the second group (rows 4 10), values of normal peak demand P max and minimum demand P min (corresponding exactly to the frequency of 50,000 Hz) are gathered, based on which the percentage rates of P min /P max were determined (rows 7 and 8). Also the percentage share is evaluated of maximum power consumption for pumping (loading night lows) P pump.max

3 The Impact of Polish pumped-storage Plants on operation of the national Power System on Working Days and Holidays 205 referred to the minimum demand P min that could take place if not for the pumping (row 10). In group 3 (rows 11 13), the increase of minimum load in the national power system (minimum country generation) N min owing to pumping in pumped-storage plants is determined. Table 1 The effect of 6 Polish pumped-storage plants (PSP) on the load distribution in the national power system on November 11, 2003 (Independence Day) Parameter of the national power system Unit without PSP System with PSP Remarks Country energy [GWh] 418,50 425,17 2 Energy consumption for pumping [GWh] - 6,67 3 increase of energy consumption [ % ] - 1,6 4 Maximum demand Pmax [MW] Minimum demand Pmin [MW] Pmax-Pmin [MW] Pmin/Pmax [%] 74,0 79,3 8 Increase Pmin/Pmax [%] - 5,3 9 Loading night lows (Maximum power consumption) Ppum.max [MW] Increase of Ppum.max/Pmin [%] - 7,7 11 Minimum load Nmin [MW] Increase of Nmin [MW] Increase of Nmin [%] - 5,1 14 Peak load Nmax [MW] Nmin/Nmax [%] 73,1 76,9 16 Increase of Nmin/Nmax [%] - 3,7 17 Nmax without PSP [MW] Reduction of evening peak [MW] Reduction of evening peak [%] - 4,6 20 Intermediate load [MW] * 21 Intermediate load [% of peak] 26,9 18,5 22 Reduction of intermediate load [MW] Reduction of intermediate load [%of peak] - 8,4 24 Relative reduction of intermediate load [%] - 31,2 25 Basic energy [GWh] 359,98 378,43 26 Intermediate energy [GWh] 58,52 46,74 27 Share of intermediate energy in the country energy [%] 14,0 11,0 28 Reduction of intermediate energy [%] - 3,0 29 Daily-average load Nav [MW] Load coefficient m=nav/nmax [%] 85,0 86,4 31 Increase of load coefficient m [%] - 1,4 32 Minimum intermediate load 33 Nmin.aftern.l. Nmin.nigh.l. [MW] % of peal load [%] 12,5 8,8 35 Reduction [%] - 3,7 * generation and pumping in pumped-storage plants (PSP) subtracted

4 206 Wróblewski The increase of minimum load in the national power system (minimum country generation) N min referred to the peak load N max is determined in group 4 (rows 14 16). The reduction of evening peak load owing to generation from pumped-storage plants is determined in group 5 (rows 17 19). In group 6 (rows 20 24), the reduction of intermediate load, being a difference between the maximum and minimum power in the national power system is evaluated. Group 7 (rows 25 28), shows results of energy generation in the base of the system (below N min ) and in intermediate generation, that is between N max and N min. In group 8 (rows 29 31), values of the daily-averaged power and load coefficient for the system are determined. In the final group 9 (rows 32 35), the reduction of minimum intermediate load, that is a difference between the minimum load in the afternoon and night low load period (N min.aftern.l. - N min.nig.l. ) referred to the peak load is evaluated. Based on the above data, daily graphs of country generation, country generation minus load consumption for pumping and country generation minus power generation from the pumped-storage power plants were elaborated. A sample graph for November 11, 2003, is shown in Figure 1. The picture illustrates selected results of calculations gathered in Table 1. Besides indicating (by arrows) the regions of pumping, the following quantities are indicated and described in Figure 1: percentage reduction of power generation in the system during the evening peak due to operation of pumped-storage plants, percentage increase of the minimum power generation in the night low due to pumping, percentage reduction of intermediate load (difference between the maximum and minimum load throughout the day) referred to the peak load, reduction of intermediate generation (generation between the daily minimum and maximum load) referred to the country generation, reduction of the minimum intermediate load (difference between the minimum load during the afternoon lowload period - N min.aftern.l. and minimum load during the night low - N min.nig.l ) referred to the peak load. The conducted investigations revealed a number of interesting results and led to a number of conclusions, which will be formulated below (Wróblewski, 2003). A general principle of loading pumped-storage plants in the national power system follows from the programmed function of these plants in the system. In a daily cycle they are loaded for generation in the period of peak demand for power (morning peak and evening peak) and for pumping in the period of minimum demand for power (night off-peak and relatively rare afternoon off-peak - practically only on Sundays and some holidays). The level of generation and pumping load and its duration depend on the season of the year, atmospheric conditions (temperature, cloudiness, rainfalls or snowfalls), and on the day of the week.

5 The Impact of Polish pumped-storage Plants on operation of the national Power System on Working Days and Holidays 207 The distribution of load changes between working days, Saturdays, Sundays and holidays, as well as some other days neighboring with holidays (e.g. May 2, Christmas Eve, New Year s Eve). The distribution of load in pumped-storage plants on working days is not the same for all days. Mid-week days Tuesdays, Wednesdays and Thursdays are different than Mondays and Fridays. Mid-week working days are characterized by the largest demand for power of all weekdays. The peak power usually takes place on Tuesdays or Thursdays. The difference between Mondays or Fridays and other working days consists in some extension of the period of generation during the evening peak on Fridays, and delay in pumping during the Friday/Saturday night off-peak, and in some prolongation of pumping during the Sunday/Monday night off-peaks and delay in generation work on Monday mornings. Another difference is a deeper Sunday/Monday night off-peak as compared to other weekdays. The analysis was also extended on variation of maximum power generation and maximum peak demand for power during morning and evening peaks of characteristics days over 12 months of both investigated years. The lowest values of power demand, and country generation, in both peaks occur during summer months: from June to August, the largest power demand is in winter: from November to February. Particular attention is due to the fact that during summer month s values of peak demand during the evening peak are below those of the morning peak. 2. Analysis of contribution of the pumped-storage plants to increase the minimum base load demand of the national power system It follows from the conducted investigations that the pumped-storage plants considerably change the shape of the daily curve of power generation in the national power system. The power demand during night low-load periods increases. The minimum power demand P min increases thanks to pumping operation of all pumped-storage plants in the country from 73.8% to 80.7% of the peak demand P max, that is 6.9% of P max. The considered increase oscillates during the analysed days between 1.8% (Holiday on November 1, 2003) and 10.6% P max (on June 3, Corpus Christi day) (Biliński, Wróblewski, 2001 and Wróblewski, Tararuj, 2005). Values of maximum loading of the night low due to pumping range between 769 MW and 1577 MW (for MW of total pumping power of the 6 pumped-storage plants), with the average value equal to 1195 MW, which constitutes 8.7% of the minimum power demand N min. The limits of the range are 5.1% and 12.3% of N min, respectively. The discussed percentage increase of the minimum load in the national power system due to pumping in national pumped-storage plants is indicated and quantitatively described in Figure 1. Owing to the increase of the minimum load N min, the daily ratio of this load to the peak load N max also increases. During the considered days, N max changes between MW and MW (the latter value referring to December 3, a peak day in 1998). The percentage ratio N min /N max during the analysed days increases. The extreme values of the increase were 3.7% and 9.0% of N max.

6 208 Wróblewski Figure 1 The effect of 6 national pumped-storage plants on the balance of power and energy in the national power system on November 11, 2003 (Independence Day) 3. Analysis of contribution of the pumped-storage plants to reduce the peak power demand and intermediate load of the system For certain, pumped storage plants not only increase the demand during the night lows, but also reduce the peak demand. The reduction of the evening peak due to generation from pumped-storage plants ranges from 408 MW (August 18, 1998) to 1489 MW (April 4, 1996) (Wróblewski, 1999), which amounts to 2.6% do 9.5% of the maximum load N max (April 20, 2003 Sunday, Easter). The percentage value of the considered reduction is also indicated in Figure 1. The increase of the minimum load and reduction of the peak causes that the range of load between N min and N max, called the intermediate load (Adam,Neill, 1984) is reduced twice. The intermediate load (N max -N min ) is reduced from about 1400 MW (7.7% of the peak load N max ) down to 2866 MW (13.5% of N max ). The relative reduction intermediate load oscillates between 24.2% and 55.3% of the intermediate load of the national power system. The value of reduction of the intermediate load expressed in % is indicated in Figure 1.

7 The Impact of Polish pumped-storage Plants on operation of the national Power System on Working Days and Holidays Analysis of contribution of generation from the pumped-storage plants to intermediate generation of the national power system Integration of the load of the national power system over 24 hours of the day in the limits between N min and N max enables the determination of intermediate generation for each day. Owing to the operation of pumped-storage plants, the amount of intermediate generation is considerably reduced. The percentage value of intermediate generation referred to the total daily generation for both configurations of operation of the system, with and without pumped-storage plants, is also indicated in the figure. Values of reduction of intermediate generation for the analyzed days oscillate between 3.0% and 8.0% of generation in the national power system. 5. Analysis of increase of the load coefficient in the system The 24 hour-averaged load N av of the system was calculated for each considered day. The operation of pumped-storage plants in the national power system acts to increase the average load of the system. The degree of equalization of the load throughout the day can be expressed by the so called load coefficient of the system m, calculated as a ratio of the average load N av to the maximum load N max N m = av 100%. (1) N max Hypothetically, in a practically impossible case of constant load over the day, the load coefficient m would be equal to 100% (the average load would equal the maximum load and the daily distribution of load would be a horizontal line). Owing to the operation of pumpedstorage plants in the national system, the load coefficient increases on average from 88.4% to 90.0%, that is by 1.6% and maximal 2.7% N max. 6. Minimum intermediate load during off-peak periods For each considered day, a reduction of the minimum intermediate load, that is a difference between the minimum load during the afternoon low N min.aftern.l. and night low N min.nig.l. (N min.aftern.l. - N min.nig.l. ) referred to the peak load N max was determined. The minimum off-peak intermediate load due to operation of pumped-storage plants decreases on average from 3000 MW (16.0% of the peak load) down to 1900 MW (9.5% of the peak), that is by 6.5% of N max. The maximal observed reduction was 9.1% of the peak (N max ).

8 210 Wróblewski 7. Increase of energy consumption in the national power system due to pumping In order to fully illustrate the effect of pumped-storage plants on the operation of the system, it is also useful to determine the daily percentage increase of energy consumption for pumping related to the country generation. Considering numerous advantages for the system coming from the operation of pumped-storage plants discussed in the preceding sections, this seems to be the only disadvantage. The increase of energy consumption for pumping in all 6 pumped-storage plants amounts on average to 1.9%. For the analysed days, it changes between 1.0% and 2.7%. Summary Pumped-storage plants considerably reduce the intermediate load. The reduction of the evening peak due to generation from pumped-storage plants ranges from 400 MW to 1500 MW, which amounts to 2.6% do 9.5% of the maximum load N max. The intermediate load (N max -N min ) is reduced from about 1400 MW (7.7% of the peak load N max ) down to 2870 MW (13.5% of N max ). The relative reduction intermediate load oscillates between 24.2% and 55.3% of the intermediate load of the national power system. Values of reduction of intermediate generation for the analyzed days oscillate between 3.0% and 8.0% of generation in the national power system. The calculations are valuable as they concern real loads that occur in Polish power system. References Adam P.J., Neill G.V. (1984). The Impact of Pumped Storage Operation on Economic Resource Commitment, Proc. International Symposium and Workshop on the Dynamic Benefits of Energy Storage Plant Operation; Boston, May 7th-11th, Biliński W., Wróblewski J. (2001). The effect of pumped-storage plants on the curve of daily generation of power and energy in the power system. Proceedings of the VII International Symposium on Water Management and Hydraulic Engineering. Międzybrodzie Żywieckie, Poland. September 10-12, University of Technology in Gdańsk. Wróblewski J. (1999). Contribution of Polish pumped-storage plants to the national power system. Conference Proc. Hydropower into the Next Centaury - III. Gmunden, Austria October 2000, The International Journal on Hydropower & Dams. Wróblewski J. (2003). The comparative study of daily loads of Polish pumped-storage plants in relation to the curves of daily power generation in the national power system. Proceedings: VIII. International Symposium on Water Management and Hydraulic Engineering. Podbanské, Slovakia. October 5-9, Slovak University of Technology in Bratislava. Wróblewski J., Tararuj A. (2005). The role of pumped-storage plants in demand for curve of daily generation of power in the national power system. Conference Proc. Market of Electricity Energy. Kazimierz Dolny, April 25th 27th Technical University of Lublin. (in Polish). Author Ph.D., Eng. Jan Wróblewski: University of Technology, Faculty of the Civil and Environmental Engineering, jwro@pg.gda.pl