Sustainable peaking power development planning of Sri Lanka with hydropower

Transcription

1 Sustainable peaking power development planning of Sri Lanka with hydropower M.T.K.De Silva Ceylon Electricity Board No.5, Sir C.A.G. Mawatha Colombo-2 Sri Lanka Abstract Catering of peak power demand of Sri Lanka in 225 forecasted system with hydro power is analysed in this paper. Reservoir based hydro power, Pump storage and small hydro with daily ponds are identified as the options for catering peaking demand. Capacity expansion of existing hydro power stations and operating of pump storage are discussed in this context. A study of economic feasibility of peaking power options by a model with daily load demand distribution in half hour time step has been carried out. Base load plants, economic merit order dispatching of the thermal power plants were analysed in the dispatch model. Further to the economic evaluation indices as NPV, EIRR, B/C, marginal cost has been calculated for the operation of sustainable peaking power options. Introduction Consumer categories of Sri Lanka basically can be divided into four sectors as domestic, industrial, commercial and religious purposes. Electricity energy demand has been forecasted to grow at 6-7% every year and peak is expected to grow at 5-6%. Daily load profiles for the last 2 years were compared and it can be observed that the daily peak demand occurs from 6.3pm to 9.3pm and off peak demand occurs from 11.3pm to 4.3am. There is no drastic change in the shape of load curve in last 2 years. Improvement of the load factor is projected for the 225 system. After the 3 years civil war was over, country is heading to service oriented economic structure, day time demand growth is projected. But slow growth in off peak demand and maximum demand at evening peak is projected for the 225 system. Presently Sri Lanka has exploited the hydro power potential for great extent and other potentials are very limited due to the socio economic reasons. CEB is in the process of diversifying the fuel mix used for power generation with the introduction of coal. Base load power plants as coal power, will be economical at high plant factors without varying loads. Also Continuous operations of combined cycle power plants are expected for the economic operation of power system. As per the long term generation expansion plan of CEB, 225 will have continuously operable 37MW of coal power plants and 677MW wind and unregulated small hydro power plants. Whereas our base load will be around 24MW leaving about 19MW excess capacity during off peak. Also Peak load will be around 24MW and no enough capacity for the peaking power. Currently peaking power requirement is met by a combination of hydro power plants and gas turbines. The existing hydro power plants with regulating reservoirs are not sufficient to meet this peak demand and existing Gas Turbines which has very high production cost will also be retired within 1 years. Sustainable peaking power development is planned to achieve with the following options. 1. plant 21 MW capacity expansion to 42MW 2. Pump Storage power plant of 6MW 3. Conversion of unregulated 377MW small hydro power plant to regulated daily pond type power plant. The first two options, smart way of operating Hydro power with cheap base load power plants are discussed under this paper.

2 The long term generation expansion plan ( ) was prepared according to the.822% maximum Loss of Load Probability, 1.2 USD/KWh Not Served value and 3% maximum Reserve Margin reliability levels. Also the largest plant capacity value of Spinning Reserve will be achieved at 225 projected power system. Generation Planning branch used the latest version of the Wien Automatic System Planning Package (WASP IV) developed by International atomic Agency for the planning studies. It utilizes probabilistic estimation of system production costs, expected cost of unserved energy and reliability to produce the optimal generation expansion sequence for the system for the stipulated study period. The Area of optimizing in the study is shown in Figure 1. Figure 1: Optimization area of capacity expansion plan WASP-IV model is loaded by monthly Load Duration Curve to represent the load variation over the time. From this paper it is further analysed the dispatching of power plants in daily load profile. Methodology The daily load profile of 225 has been projected in 3 minutes considering the energy and power demand projections using econometric techniques and load factor improvements. The load curve has been projected for the Peak day and Average day for the study. Economic dispatching cost of power plant operation is considered. Since, daily cycling of coal power plants are not possible with the plant characteristics, 4% minimum load of coal power capacity considered for the base load. Also Run of River type hydro power such as Kukule, Upper Kotmale and small hydro and wind power considered as the base load power generation. Each and every major hydro power plant have been modelled in 5 types of hydro conditions such as Very dry, Dry, Medium, Wet and Very wet. Total of 225 Hydro power capacity without considering the power station capacity expansion is shown in the Table 1. Year 225, total small hydro power capacity and energy for 5 hydro conditions are shown in the Table 2. Wind capacity availability also analysed under the five conditions with different probability values. Therefore under the one hydro and wind condition base load is equal to the constant and fill up the bottom of daily load curve. Base Load Capacity: Base load = (Puttlam+Trinco+Other total coal)*4% + (Total ROR Hydro)*β + (Total Small Hydro)*α + Wind*µ The factors β, α, µ are determined by the hydrological and wind condition of the analysed representative day.

3 Month Very Wet Wet Medium Dry Very Dry Average Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Table 1: Year 225 Expected Major Hydro and Capacity for Different Hydro Conditions Very Wet Wet Medium Dry Very Dry Average Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Table 2: Year 225 Expected Small Hydro and Capacity for Different Hydro Conditions Hydro dispatching According to Economic loading order rest of the demand first supplied by the remaining hydro energy which is not included in the Runoff River hydro category. Hydro energy is distributed exponentially according to the total demand of the day. Therefore maximum available capacity is of hydro power dispatched at the peak time of the day. d t b 1 1 p(t) hydro capacity within the period d(t) demand b base load e ph hydro energy γ hydro dispatching factor varied according to the total system demand Mathematical Model for Daily Dispatch Scheduling, System Economic Analysis and Alternative Generation Planning Based on the Daily Load Profile by Mr.BWHA Rupasinghe and Mr.AS Wickramasinghe (Annual Transactions of IESL,pp.( ), 212) is used for the analalysis of Hydro and Thermal power dispatching.

4 Thermal dispatching Thermal plants are dispatched according to the economic loading order. Unit generation cost of each plant which reflect fuel price has been calculated. To load the i th thermal generator, maximum Load share of i th plant has to be less than or equal to the demand requirement of the system. Also maximum Load share of i th plant, single generator has to be less than equal to the 2% of off demand of the system. Increment of thermal plants from i=1 upto m where, Dispatching of power plant in 225 Average Day under Average Hydro condition is Shown in the Figure 2. 5, Load Share 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 Hydro Non base No Oil fired Thermal power Other Future Coal Trinco Coal Puttalam Coal Base Coal Wind :3 2:3 4:3 6:3 8:3 1:3 12:3 14:3 16:3 18:3 2:3 22:3 Figure 2: Plant dispatch 225 average day, average hydro condition Dispatching of power plants in 225 Peak day under Very dry hydro condition is shown in Figure 4. Load Share 5,5 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 Hydro Non base No Oil fired Thermal power Other Future Coal Trinco Coal Puttalam Coal Base Coal Wind Small Hydro :3 2:3 4:3 6:3 8:3 1:3 12:3 14:3 16:3 18:3 2:3 22:3 Figure 3: Plant dispatch 225 peak day, very dry hydro condition

5 Modelling of capacity expansion of victoria power station CEB has carried out the feasibility study for capacity expansion of existing Hydro power station up to 42MW by using existing reservoir capacity. Therefore electricity energy output will be the same as existing power station, but higher capacity to be operated at the peak demand of the day. Expected capacity and energy of expansion under 5 hydro conditions are shown in Table.3 Very Wet Wet Medium Dry Very Dry Average Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec Total Table 3: Expansion Expected and Capacity for Different Hydro Conditions Since hydro energy is exponentially dispatched according to the demand over the day, maximum potential capacity of dispatched at the Peak time. This avoid the dispatching of small GT plants at Kelanitissa at peak and Marginal cost of the system will be reduced to 37.55USCents/kWh. But still system requires to dispatching Gas Turbines to cater peak power. Load Share 5,5 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 Expan Hydro Non base No Oil fired Thermal power Other Future Coal Trinco Coal Puttalam Coal Base Coal Wind Small Hydro Upper Kotmale Kukule :3 2:3 4:3 6:3 8:3 1:3 12:3 14:3 16:3 18:3 2:3 22:3 Figure 4 :Plant dispatch year 225: peak day, very dry hydro condition with expansion

6 Modelling of pump storage power plant Figure 2 shows even in the Very dry hydro condition of the Peak day, off peak hours (.-4.3) system demand is less than the base capacity power plants. Therefore cycling of coal power plants from full load to 4%, which is not possible in real operational conditions to be required to follow in the dispatch schedule. Therefore filling of the valley with energy storage is required and 6MW pump storage power plant with 7% efficiency can be operated during this period. Comparison of original load curve with modified load curve for pump storage power plant is shown in Figure 3. Off peak demand has been shifted upwards and coal power dispatching capacity also shifted. 5,5 5, 4,5 4, Load Share 3,5 3, 2,5 2, 1,5 1, 5 Forecast Demand Demand with PSP F :3 2:3 4:3 6:3 8:3 1:3 12:3 14:3 16:3 18:3 2:3 22:3 Figure 5 : Year 225 Demand and demand with pump storage power plant Load Share 5,5 5, 4,5 4, 3,5 3, 2,5 2, 1,5 1, 5 :3 2:3 4:3 6:3 8:3 1:3 12:3 14:3 16:3 18:3 2:3 22:3 Pump Storage Expan Hydro Non base No Oil fired Thermal power Other Future Coal Trinco Coal Puttalam Coal Base Coal Wind Small Hydro Upper Kotmale Kukule Forecast Demand Demand with PSP Figure 6: Plant dispatch 225, peak day, very dry hydro, pump storage and expansion

7 It can be noticed that with Pump Storage and Expansion requirement of oil fired thermal power requirement is not necessary. Also Plant factor of coal power plants improved more than 8% in daily dispatch. Therefore economic cost of operation of the system will drastically reduced with implementation of two hydro power options together with the addition of cheaper base load plants. 6 PSP.VicEx Full load heat rate of coal plants = 2626kcal/kWh 4% heat rate of coal plants = 31kcal/kWh Benefit USD PSP pumping generating -1 Time -2 Figure 7: Benefit from PSP, expansion energy generation Taking into the efficiency improvement of coal power plants pumping cost and avoided cost of oil fired power plants cost at peak demand are calculated and shown in the Figure 7. Load Share 2, 1,75 1,5 1,25 1, :3 2:3 4:3 6:3 8:3 1:3 12:3 14:3 16:3 18:3 2:3 22:3 Figure 8: Year 225, Hydropower dispatch peak day, very dry hydro condition Pump Storage Expan Gingganga Moragolla Broadlands Uma Oya Rantambe Smanalawewa Bowatenna Ukuwela Randenigala Kotmale Polpitiya New Laxapana Old Laxapana Wimalasurendra Canyon Small Hydro Upper Kotmale Kukule It can be observed that in addition to the ROR plants, major power plants associated with daily ponds will be dispatched in the whole day while keeping maximum plant capacity at the peak period. full capacity will be dispatched at the peak and the rest of period also one or two units will be run for the system operation requirements.

8 Economic evaluation According to the detailed Economic evaluations for Pump Storage plant and Expansion projects, which were done comparing avoided cost of Gas Turbine for peaking power and dispatch of coal base loads at high efficiency full load levels the two projects are Economically feasible. The information are shown in the Table 4 and Table 5. Evaluation Index Evaluation Criteria Criteria 3.1 Discount Rate 5% B/C 2.9 Discount Rate 1% > Discount Rate 15% 2.6 5% high Coal power 21 % Discount Rate 5% EIRR 21 % > Opportunity cost of Discount Rate 1% 25 % capital Discount Rate 15% 21 % 5% high Coal power (Economic Evaluation Operating Pump Storage Plant in the System of Sri Lanka, CEPSI 212, MTK De Silva) Table 4: Economic Evaluation Indices for Pump Storage plant Vic Evaluation Index Evaluation Criteria Criteria 2.8 Discount Rate 5% B/C 2.3 > 1 Discount Rate 1% 1.9 Discount Rate 15% EIRR 19.4 % Discount Rate 5% > Opportunity cost of 19.8 % Discount Rate 1% capital 2.2 % Discount Rate 15% (Feasibility Study for Expansion of Hydropower Station,JICA,28) Table 5: Economic Evaluation Indices for Capacity Expansion This results are further analysed in the daily dispatch model to calculate the Marginal cost of the system at different Hydro conditions. No. Case Marginal Cost (USCents/kWh) 1 Peak Day, Hydro condition Very Dry, No Ex, No PSP Peak Day, Hydro condition Very Dry, with Ex, No PSP Peak Day, Hydro condition Very Dry, No Ex, with PSP Peak Day, Hydro condition Very Dry, with Ex, with PSP Average Day, Hydro condition Average, No Ex, No PSP Conclusion Hydropower play major role in the Sri Lanka power generation sector from the history. Until early 199s total demand was supplied by the hydro power. Since country has exploited high share of economically, technically and socially feasible hydro potential thermal power has to cater to the increasing demand. Operation of thermal base power plants are highly economical than the thermal peaking power plants. Limitations of addition of thermal base power plants with the load curve has been analysed in this paper. Without energy storage during off peak period, operation of base load power plants are not feasible. Also to keep the system reserve margin and spinning reserve, high capacity peaking plants are required. Capacity expansion of hydro power station and energy dispatching exponentially according to demand requirement will smooth the operation of the system with frequency regulation according to demand variation and non conventional renewable power generation variation. Operating of thermal base load power plants at high efficient higher capacity levels and difficulty of cycling is the challenge. 2% Non Conventional Renewable generation addition target will also be challengeable in low off peak demand. Pump storage is the best environment friendly solution identified for the high energy storage requirements. With the blessing of nature potential sites for pump storage power plants are already identified in the Sri Lanka.

9 From the results of dispatching model, it is proved that the requirement of operating high cost Gas turbine plants in absence of the Expansion and Pump storage power plants. Marginal cost of the system will be USCents/kWh without two projects. This value will be reduced to USCents/kWh with the addition of two projects. Economic evaluation of projects B/C is around 2, at 15% discount rate. EIRR indices are around 2%. Therefore projects are economically feasible for the development. Promotion of developing indigenous resource and reduction in the dependency for imported fossil fuel has been identified in the National policy and strategies. Environmental effects from fossil fuel burning also reduce with the hydro power peaking options. Therefore sustainable peaking power development options power station capacity expansion and Pump storage power plant are highly recommended. The Authors M.T.K.De Silva graduated in Electrical Engineering from University of Moratuwa, Sri Lanka in She obtained her Master of Engineering and Master of Business Administration from the same University. She worked for Government and private sector consultancy companies before joining the Ceylon Electricity Board. During her carrier at CEB, she has been involved for long term generation expansion planning and several hydro and thermal power feasibility studies. Demand projection with econometric and end user methods, energy and power sector modelling and optimization are her specialized areas. Also she has been involved several hydro power feasibility projects including expansion and pump storage power. References: 1. Mathematical Model for Daily Dispatch Scheduling, System Economic Analysis and Alternative Generation Planning Based on the Daily Load Profile, Annual Transactions of IESL,pp.( ), 212 by Mr.BWHA Rupasinghe and Mr.AS Wickramasinghe 2. Economic Evaluation Operating Pump Storage Plant in the System of Sri Lanka, 19th Conference on Electric Supply Industry CEPSI 212, by MTK De Silva 3. Long Term Generation Expansion Plan , Transmission and Generation Planning Branch, Ceylon Electricity Board, International Atomic Agency, Vienna, 1984, Expansion Planning for Electrical Generating Systems (Guidebook) 5. Feasibility Study for Expansion of Hydropower Station in Sri Lanka, Japan International Cooperation Agency, Ceylon Electricity Board, 28