pumped hydro energy storage system

pumped hydro energy storage system

1. Energy storage systems Pumped Hydro Energy Storage System Dr. Mohamed Hassanain

2. Pumped-Hydro Energy Storage  Potential energy storage in elevated mass is the basis for pumped-hydro energy storage (PHES) Energy used to pump water from a lower reservoir to  an upper reservoir Electrical energy input mechanical energy Pumps transfer energy potential energy to motors converted to rotational  to the water as kinetic , then 

3. Pumped-Hydro Energy Storage  Energy stored in the water of the upper reservoir is released as water flows to the lower reservoir Potential energy converted to kinetic energy Kinetic energy of falling  water turns a turbine  Turbine turns a generator Generator converts mechanical energy to electrical  energy 

4. Pumped-Hydro Energy Storage  Typically, pumping would take place by buying electricity during times when prices are low, which is when demand is low or the availability of electricity from other sources is high (e.g. a windy and sunny day). Generation would take place during times of high demand (such as during evenings) when prices are high. This pattern of buy-low and sell-high is called arbitrage. The power companies make a lot of money by selling the generated power during peak hours at higher rates.

5.  Typically, pumping would take place by buying electricity during times when prices are low, which is when demand is low or the availability of electricity from other sources is high (e.g. a windy and sunny day). Generation would take place during times of high demand (such as during evenings) when prices are high. This pattern of buy-low and sell-high is called arbitrage. The power companies make a lot of money by selling the generated power during peak hours at higher rates. Pumped Storage Hydro Power Plants

6. HISTORICAL DEVELOPMENT The history of pumped storage plant can be traced as far back 1 st as 1882 , in which year the hydroelectric plant making use of pumped storage started functioning at Zurich in Switzerland . 1 st In 1931 , the reversible pump-turbine was installed at Baldeneyesee in Germany . 1 st The major reversible diagonal turbine (Deriaz) was installed at Niagara in 1955 . I n Europe, in 1962, Ffestiniog (Great Britain) with a total capacity of 360 MW and Provindenza (Italy) with a head of 284 m, were the major landmarks in the progress of pumped storage plants.

7. Conventional river-based PHES (open-loop) Many existing PHES systems have been developed in conjunction with a conventional river-based hydroelectric system. Two reservoirs are created, at different altitudes, but close to each other. Often, the lower reservoir is large and located on a substantial river, while the upper reservoir is smaller, and located higher up on the same river or in a high tributary or parallel valley. Most river water passes through the system, generating electricity, and then flows on down the river. Some water is cycled between the two reservoirs to create energy storage.

8. There are alternative methods of constructing PHES that do not require significant modification to river systems. One method is to connect closely spaced existing reservoirs using underground tunnels and powerhouses. With care, there is low disturbance at the surface An off-river PHES system comprises a pair of artificial reservoirs spaced several kilometers apart, located at different altitudes, and connected with a combination of aqueducts, pipes and tunnels. The reservoirs can be specially constructed ('greenfield') or can utilize old mining sites or existing reservoirs ('brownfield’). Off-river PHES utilizes conventional hydroelectric technology for construction of reservoirs, tunnels, pipes, powerhouse, electromechanical equipment, control systems, switchyard and transmission, but in a novel configuration. Off-river (closed-loop) pumped hydro systems

9. An off-river PHES system has the advantage that flood mitigation costs are minimal compared with a river-based PHES system. Heads are generally better than river-based systems because the upper reservoir can be on a high hill rather than higher in the same valley as the lower reservoir. Environmental costs of damming rivers are avoided with off-river PHES, which helps with social acceptance. The much greater number of off-river sites compared with on-river sites allows much wider site choice from environmental, social, geological, hydrological, logistical and other points of view. Another advantage is that construction of off-river pumped hydro can be much faster than other storage methods Work can proceed in parallel on the two reservoirs, the water conveyance, the powerhouse and the transmission Off-river PHES vs river-based PHES

10. The first requirement is to find places where reservoirs can be constructed that store a large amount of water compared with amount of rock and other material used to construct the reservoir walls. The second requirement is to find closely spaced pairs of sites that have large differences in altitude ('head'). The former requirement is because pipes and tunnels connecting the two reservoirs are expensive, and the latter requirement is because doubling the head doubles the storage energy volume and storage power capacity but does not double the system cost. Off-river PHES location requirement

11. Components of a PHES Plant Lower re s er voi r

12. PHES Components – Reservoirs  Upper and lower reservoirs separated by an elevation difference  Two configurations: Open-loop :  At least one of the reservoirs connected to a source of natural inflow  Natural lake, river, river-fed reservoir, the sea Closed-loop :  Neither reservoir has a natural source of inflow  Initial filling and compensation of leakage and evaporation provided by ground water wells  Less common than open-loop  

13. PHES Components – Penstock  P e n st oc k Conduit for water flowing between reservoirs and to the pump/generator Above-ground pipes or below ground shafts/tunnels  5 -10 m diameter is common  One plant may have several penstocks  Typically steel- or concrete-lined, though may be unlined Flow velocity range of 1 – 5 m/s is common Tradeoff between cost and efficiency for a given flow rate,  Larger cross-sectional area:  Slower flow  Lower loss  Higher cost     𝑄𝑄

14. PHES Components  T ailr a c e t unn el  Typically, larger diameter than penstocks  Lower pressure  Lower flow rate  Downward slope from lower reservoir to pump/turbine  Inlet head helps prevent cavitation in pumping mode  S u r ge t a n k s  Accumulator tanks to absorb high pressure transients during startup and mode changeover  May be located on penstock or tailrace  Especially important for longer tunnels  Hydraulic bypass capacitors

15. PHES Components – Power House  Power house Contains pump/turbines and motor/generators Often underground T y pi c ally b e l o w the l e v e l o f the l o w e r r e s e r v o ir t o p r o v ide r e qui r e d pump inl e t h e ad Three possible configurations  Binary set : one pump/turbine and one motor/generator  Ternary set : one pump, one turbine, and one motor/generator  Quaternary set : separate pump, turbine, motor, and generator    

16. Power Plant Configurations – Quaternary Set  Quaternary set Pump driven by a motor Generator driven by a turbine Pump and turbine are completely decoupled Possibly separate penstocks/tailrace tunnels Most common configuration prior to 1920 H igh e quipm e n t / i n f r a s t r u c tu r e costs High efficiency  Pump and turbine designed to optimize individual performance       

17. Power Plant Configurations – Ternary Set  T er na r y s e t Pump, turbine, and motor/generator all on a single shaft  Pump and turbine rotate in the same direction Turbine rigidly coupled to the motor/generator Pump coupled to shaft with a clutch Popular design 1920 – 1960s N o w a d a y s , u s ed when he a d e x c eeds stage pump/turbine     the usable range of a single-   High-head turbines (e.g., Pelton) can be used Pump and turbine designs can be individually optimized 

18. Power Plant Configurations – Ternary Set  T er na r y s e t Generating mode:  Turbine spins generator  Pump decoupled from the shaft and isolated with valves Pumping mode:  Motor turns the pump  Turbine spins in air, isolated with valves Both turbine and pump can operate simultaneously Turbine can be used for pump startup  Both spin in the same direction  Turbine brings pump up to speed and synchronized with grid, then shuts down  Changeover time reduced    

19. Power Plant Configurations – Binary Set  Binary set Single reversible pump/turbine coupled to a single motor/generator Most popular configuration for modern PHES Lowest cost configuration  Less equipment  Simplified hydraulic pathways  Fewer valves, gates, controls, etc. Lower efficiency than for ternary or    quaternary sets   P ump /t urbine runner de s i g n is a c o mp r o mi s e b e t w een pump and turbine performance

20. Power Plant Configurations – Binary Set  Binary set Rotation is in opposite directions for pumping and generating Shaft and motor/generator must change directions when changing modes  Slower changeover than for Pump startup:   ternary or quaternary units   Pump/turbine runner dewatered and spinning in air  M o t o r brin g s pu m p up t o sp ee d and in s yn c h r o nism w i t h g rid b e f o r e pu m ping o f wa t e r b e g ins the

21. Turbines  H y d r o t u r b i n e d e s i gn s ele c tio n b a s e d on  Head  Flow rate  P H E S p la n t s a r e t y p i c all y s i t e d t o h a v e la r g e  Energy density is proportional to head  Typically 100s of meters  R e v e r s i b l e F r a nc is pump/tu r bine  Most common turbine for PHES applications head  Single-stage pump/turbines operate with heads up to  F o r h i g h e r h ea d:  Multi-stage pump/turbines  Ternary units with Pelton turbines 700 m

22. Turbine Selection Source: rivers.bee.oregonstate.edu/turbine-sizing

23. Francis Turbine – Components  Volute casing ( scroll casing ) Spiral casing that feeds water from the penstock to the turbine runner Cross-sectional area decreases along the length of the casing  Co n s t a n t f l o w r a te m ai n t ain e d al o ng t he l e n g t h  Francis turbine casing – Grand Coulee: 

24. Francis Turbine – Components  Gu ide v a n e s a nd st ay v a n e s Direct water flow from the casing into the runner Stay vanes are fixed Guide vanes, or wicket gates , are adjustable    Open and close to control flow rate Power output modulated by controlling flow rate Set fully open for pumping mode    Source: Stahlkocher Source: Stahlkocher

25. Francis Turbine – Components  Turbine runner  Reaction turbine  Pressure energy is extracted from the flow  Pressure drops as flow passes through the runner  Flow enters radially  Flow exits axially  Typically oriented with a vertical shaft  Draft tube  Diffuser that guides exiting to the tailrace flow Source: Voith Siemens Hydro Power

26. High-Head PHES Two-stage pump/turbine:  Options for heads in excess of 700 m: Two-stage Francis pump/turbines  Typically no wicket gates two-stage configuration  in  No mechanism for varying generating power Ternary unit with Pelton turbine  Source: Alstom

27. Pelton Turbines  Pelton Turbine Suitable for heads up to 1000 m Impulse turbine  Nozzles convert pressure energy to kinetic energy  High-velocity jets impinge on the runner at atmospheric pressure  Kinetic energy transferred to the runner  Water exits the turbine at low velocity Cannot be used for pumping  Used as part of a ternary set   Source: BFL Hydro Power  Source: Alstom

28. PHES Losses  Typical losses for PHES:

29. ADVANTAGES

30. Relatively low capital cost; thus economic source of peaking capacity. Rugged & dependable; can pick up load rapidly in a matter of few minutes. Readily adaptable to automation as well as remote-control. Hydel power is free from effects of environmental pollution—thus contributing a part in curbing air & water pollution. ADVANTAGES

31. Allow great deal of flexibility in operational schedules of system. Power r eq u i r ed for pu m p i ng is av a i l able at a ch e ap e r r a t e ( s l a c k ho u r s ’ ra t e); power p r oduced can be so l d at pri m e r at e (p e a k hou r s ’ ra t e) - this co m pensates the low hy d rau l ic ef f ic i ency. They allow entire thermal or nuclear power generation to take up base load; thus load factor improves giving overall greater system efficiency. Little effect on the landscape. ADVANTAGES

32. Disadvantages of PHES  Disad v a n t ages o f P H E S  Environmental issues  Water usage  River/habitat disruption  Head variation  Pressure drops as upper reservoir drains  Efficiency may vary throughout charge/discharge cycle  Particularly an issue for lower-head plants with steep, narrow upper reservoirs  Siting options are limited  Available water  Favorable topography  Large land area  P o ss i b l e al t er n a ti v e p o t e n tial  Rail energy storage energy storage:

33. OBLEMS OF PR OPERATION Once it's used, it can't be used again until the water is pumped back up. Cav i t a tion p r ob l e m s; pow e r h ou s e l o c a t i on has to be so fix e d that pu m p ope r at e s under sub m e r ged cond i t i ons ( m agni t ude depends on spec i fic speed & net head). Reversing of direction of flow gives rise to runner cracking due to fatigue. Trash racks vibrate violently during pumping operation. Flow during pumping mode tends to lift the machine axially causing tensile stresses in bearings; specially guide vanes.

34. Density=mass/volume W=m x g Density of water =1000Kg/m 3 hydraulic efficiency x electrical efficiency= overall efficiency General Formulas

35. The power that can be extracted from a waterfall depends upon its height and rate of flow. The available hydro power can be calculated by the following equation: P= ρ *Q*g*h P=available water power[W] Q=water rate of flow [m 3 /s] h= head of water [m] Ρ = water density [ kg/ m 3] g = 9.81 [m/s 2 ] Available Hydro Power

36. The energy used to pump a water volume (V) to a height (h) with a specific pumping efficiency ( η p ) is given by: E pumping =  · g · h · V η p Overall efficiency of the energy storage system = E generator / E pumping The energy supplied to the electrical network by a generator of efficiency (η g ) can be obtained by: E generator =  · g · h · V · η g P pumping =  · g · h · Q η p P generator =  · g · h · Q · η g Pumped Hydro Energy

37. A large hydropower station has a head of 324m and an average flow of 1370m 3 /s. The reservoir of water covers an area of 6400Km 2 . Calculate the available hydraulic power the number of days this power could be sustained if the level of the impounded water were allowed to drop by 1m. Example 1

38. The available hydropower can be found using the equation P= ρ *Q*g*h P=1000*9.8 x 1370 x 324=4350MW (b) we have to find the number of days ? Using the 1 m drop we find the corresponding volume of water Volume = area x height =6400x10 6 m 2 x 1m=6400x10 6 m 3 Solution

39. Rate of flow= 1370m 3 /s By looking at the units of rate of flow we can deduce that time in seconds would be volume divide by rate of flow Q=V/t  t=V/Q t=6400x10 6 /1370 = 4.67x10 6 s = 1298h =54 days Solution

40. 40 Assignment :

41. 41

42. Then the power cost of the pump, the revenue generated by the turbine, and the net income (revenue minus cost) per year become 42 Solution

43. Discussion It appears that this pump-turbine system has a potential annual income of about $70,000. A decision on such a system will depend on the initial cost of the system, its life, the operating and maintenance costs, the interest rate, and the length of the contract period, among other things. 43 Solution