Need for Electricity storage

Transcription

1 Electricity Storage

2 Need for Electricity storage Electricity travels at the speed of light Electricity shall be used instantaneously Power plant producers ramp up power generation and ramp down generation based on demand Variations in Voltage and frequency Variations in Energy(peak load) demand during day, night, weekdays and holidays

3 Need for Electricity storage (contd.) Thermal power plants need more time to cater to sudden fluctuations of load demand Renewable energy options like Wind energy is seasonal and has lot of variations during the course of the day/week/month Solar energy is available only during the day and energy demand is more during the late evening All these variations can be addressed by levelling up load curve i.e. lower cost for power usage during off-peak hours. But this is not feasible for Power distribution companies

4 Possible modes of Electricity Storage DC batteries Compressed air Energy storage Liquefied air Energy storage Flywheel storage Supercapacitors

5 Possible modes of Electricity Storage Thermal storage Superconducting magnets Gravitational potential energy storage with solid masses Chemical storage-hydrogen, Biofuels Molten salt

6 Pumped Storage Increasingly important role in providing peaking power and maintaining system stability in power system Base load requirements from Thermal/Nuclear power plants Peaking load requirements: conventional Hydro projects along with pumped storage plants- Hydel power plants connection to grid within 5 minutes (4-6 hours for thermal Power plants) Relevance of Pumped storage: Decline of available sites in a conventional hydro-electric generation The availability of water decreases in the river system due to upstream consumptive uses Lower capital costs compared to other peaking units Adaptable to automation and remote control

7 Pumped Storage The original concept - conversion of relatively low cost off peak energy generated in thermal plants into high value peak power. Pumped storage plants improve overall economy of power system operation, increase capacity utilization of thermal stations reduce operational problem of thermal stations during light load period. availability of large reactive capacity for regulation Voltage and Power factor corrections availability of spinning reserve at almost no cost to the system regulating frequency to meet sudden load changes in the network

8 Pumped storage Installations Zurich-1882 Germany-1931-Reversible pump-turbine Acute need of Peaking stations USA-Tennesse valley auhority- Francis type Reversible pump-turbine Ohira-Japan-Head 513 m-single stage high head plant Ludington-USA-2053 MW

9 Principle of Operation Store energy by pumping water from a low level reservoir downstream into high level energy storage reservoir during times of low demand Utilize stored water of upper reservoir to generate hydroelectric power during peak load periods Turbine-generator set is designed to operate as pump Peak load hours- Function as Power generating unit-utilize potential energy of water Low load-pumping Water conductor path is common for both modes

10 Principle of Operation

11 Principle of Operation

12 Pumped storage schemes Pure pumped storage scheme-recirculation type Power generation only at peak load Feasible for regions with hydroelectric potential Mixed Pumped Storage scheme: Conventional Hydro power plant + Pure pumped storage Inflow to upper reservoir is large Conventional mode- More water is available Pumped storage-dry period Underground Pumped storage scheme: Economical to link-reservoirs-via shortest route

13 Pumped storage schemes Both reservoirs along same river in tandem manner (e.g. Takase river- Tokyo) Reservoirs on two separate rivers flowing at different elevations Higher reservoir on artificially constructed pool with help of dykes all around on a high level plateau/ levelled hill top Lower reservoir on natural river-most common type- e.g Revin France ; Lower reservoir- Conventional hydro development Lower reservoir-natural lake; Upper- artificial-eg-lake Michigan-USA Sea is also being considered as a lower reservoir

14 Basis of pumped storage Relative arrangement of turbines and pumps Initially-Four units installation-pump-motor-generator-turbine Three Unit system-pump-turbine-generator(functions as motor) Present trend-two unit installation-generator(operate as motor) coupled to Turbine (operates as pump-rotating in reverse direction)- Reversible-Pump-Turbine-Installation

15 Relative Merits Reversible unit-lesser Initial costs Generally single stage, Multi stage pump-turbines also developed head upto 1000 m Three unit installation-optimum efficiency for both pump and turbine Reversible machines lesser efficiency for pumps as against turbines Operation : Three unit system is simpler-identical direction of rotation-switching from pumping mode to generating mode- shorter time-2-3 minutes Lesser cavitation in three-unit system due to multi stage

16 Three-Unit arrangement Turbine-Generator-permanently locked-pump-coupled during pumping phase (using power operated mechanical gear coupling) Vertical setting-generator at top-pump at bottom Eg- san fiarana-ps plant-italy-head 1438 m; 105 MW pumps(6 stage) Special arrangement for pump starting(small turbine to run the empty pump upto synchronous speed and then couple with rotating-t-g set)

17 Reversible Pump-Turbines Kaplan Turbines(Head < 20 m), Francis turbines(< 500 m) and diagonal flow Deriaz turbines(<150 m) act as reversible flow machines Different operating characteristics pump, turbine For same rotational speed discharge during pumping is lesser; maximum efficiency at different heads; Eg Racoon Mountain-USA-Turbine-305 m; Pump-296 m Discharge-115 m 3 /s. (400 MW) Need for reversing rotation-stop-dewater-restart-time 10 minutes

18 Operational problems Cavitation Pump-Negative suction head; Power house located such that pump operates in submerged conditions Underground power house Reversing rotation, flow direction, frequent starts stops fatigue

19 Criteria Minimal ratio L/h (Length between the two pools to the head difference <10) upper Reservoir capacity hrs of pumping capacity Design for Treatment of earthern dykes to avoid seepage losses Optimum size of penstock-greater than hydro power plant Max flow velocity in head race tunnels m/s Underground Power house-submergence requirements m

20 Revin pumped storage 760 mw underground pumphouse-4 x 190 MW; Head-230 m; L-1200 m; L/h-5; Upper reservoir-7,00,000 sq.m embankment; Lower reservoir-7,00,000 cu. M embankment Conveyance- tunnels large dia vertical shaft-9 m dia dividing to two 6 m dia tunnels Machine hall- 17 m x 114 m x 30 m 200 MVA generators; 13 KV-rotor weight-350 MT

21 Revin pumped storage Discharge-Generating mode cumecs Discharge-pumping mode cumecs Hydraulic efficiency-90 % Starting time-generator-full load-2 minutes- Changeover time-16 minutes Cost-550 francs/kw in 70 s 40 % for machinery and equipment; 27 % for reservoirs; 15 % for waterways; 8 % powerhouse; 10 % roads, land etc.

22 Potential for pumped storage in India

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26 Further, 3 pumped storage plants with aggregate installed capacity of 2100 MW are under Survey & Investigation in the country. Details of these schemes are given below:

27 Pumped storage-cons The fact that energy gained from the pumped storage development is always less than energy input should not obscure the fact that this loss to the system is small when compared with substantial savings in the fuel which are made when these stations are operated in an integrated manner. Since the energy gained from Pumped Storage Plants (PSP) is less than the energy input, it is necessary that off-peak power to be used as input may be available at reasonable tariff for making the Pumped Storage Plant commercially viable.

28 Pumped storage-pros Ingenious method to conserve limited water resource Balancing the load on the distribution system Same water recycled again and again with some amount of make-up Allows flexibility in operation schedules of the system Efficiency 70 % attainable

29 Future Scope For grid stability, reliable supply and quality power, Peak load plant to base load plant ratio:60:40-can be achieved by Pumped storage schemes Study reports-optimum installed capacity of PSS 4-5 % of total installed capacity As per Reports from Power Ministry, India is to be Power surplus in This surplus power shall be used in development of PSS. Pump-Turbines, generators, starter motors, Switch gears, Control equipment Transmission equipment in BHEL context Environment friendly technology

30 References Wikipedia Electrical India Large Scale Grid Integration of Renewable Energy Sources - Way Forward - Central Electricity Authority Water Power Engineering MM Dandekar K N sharma

31 Thank You