Analysis of wind energy with pumped storage systems in autonomous islands George Caralis Mechanical Engineer NTUA National Technical University of Athens Department of Mechanical Engineer Fluids Section, Wind Energy Laboratory

Contents of the presentation Description of the problem Methodological approach Evaluation criteria Application in three autonomous Greek islands 1 st case –Analysis of the wind power penetration in autonomous islands without pumped storage 2 nd case –Analysis of the combined use of wind energy with pumped storage systems –Operational targets and Architecture of WPS –Optimization procedure Conclusions - Recommendations G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 2

Description of the problem Autonomous islands face the problem of wind energy rejection during the hours of low demand from the system operator. The ability of local power stations to balance out both the variability of the demand and the wind power, defines the wind power which can be directly absorbed by the grid. G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 3

Methodological approach The simulation of the whole electrical system based on the steady-state (non-dynamic) analysis and the convolution of the demand and the wind data is proposed as the main methodological approach for the design and the decision process. The following data are needed for the application: –the special characteristics of the energy demand (hourly data series), –the local conventional units (technical minimums, cost, fuel consumption) –the technical restrictions for the smooth and safe operation of the network –the wind characteristics (hourly data series) –the wind installed capacity and –the design of the Pumped Storage Unit. G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 4

Objectives of the current work Create a computational tool –Simulation of the autonomous electrical system –Simulation of the various subsystems (conventional units, wind farms, pumping station, hydro-turbine, etc) Present comparable results for three Greek islands –Analysis of wind power penetration (without storage) and –Analysis of the combined use of wind power with pumped storage systems. G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 5

Current situation in the autonomous Greek islands 4% of the national demand with 1 million citizens Weak autonomous electrical grids, based almost entirely on oil High rates of increase of the energy demand (due to tourism development) High variation of demand between summer and winter and during the day (low load factor of the conventional units, high Electricity Production Cost) Abundant wind potential (annual wind speed 8-9m/s) High investor’s interest for wind applications Constrain in the wind installed capacity Wind power rejection during low demand G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 6

Current situation in the autonomous Greek islands

1 st Case study: Analysis of the wind power penetration in autonomous Greek islands G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 8

Case study: Analysis of the wind power penetration in autonomous Greek islands Simulation Wind power is absorbed in priority with respect to the technical minimums of the conventional units and until the maximum permitted instantaneous wind penetration (i.e. 30%) The maximum ability of the committed conventional units should be able to meet the demand (even all the wind power is lost) G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 9

Case study: Evaluation of the wind power penetration in autonomous Greek islands In order to take comparable results, the wind installed capacity should be introduced dimensionless: by the peak demand, or by the mean annual load? Using the mean annual load, similar results for different in size systems are achieved G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 10

Case study: Evaluation of the wind power penetration in autonomous Greek islands Crete / Lesvos / Serifos Three wind velocities (8.1 / 7.2 / 6.3m/s) corresponding to different initial capacity factors (23%, 30% and 38%) Wind installed capacity: 0%-200% of the mean annual demand Evaluation indexes –The real capacity factor CF R (%) –The percentage of wind energy absorbed (%) –The contribution of wind energy (%) –The Conventional units production cost (EPC C - €/kWh) –The Electrical system’s production cost (EPC S - €/kWh) –The Wind power’s production cost (EPC W - €/kWh) G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 11

G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 12 Crete

Lesvos G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 13

Serifos G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 14

Sensitivity on the allowed instantaneous wind penetration G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 15 allowed instantaneous wind penetration: 30% / 40% / 50% For wind velocity 8.1m/s For Brent price: 54$/b (mean value 2005)

Crete G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 16 Lesvos Serifos

Sensitivity on the electrical system’s EPC on the Brent price G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 17 Allowed instantaneous wind penetration: 30% / 40% / 50% For wind velocity 8.1m/s For Brent price: 54$/b / 75$/b / 100$/b (mean value 2005)

Crete G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 18 Lesvos

G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 19 Serifos

Conclusions There is a very specific level of penetration of wind energy which is different for each island and provides the maximum benefits to the electrical system. According to the existing infrastructure and the current technical constraints, even with significant wind penetration the decrease of the EPC S is negligible, and the dependence on the oil remains high. G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 20

2 nd Case study: Analysis of the combined use of wind power with pumped storage systems in autonomous Greek islands G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 21

Current electrical system G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 22

Wind energy combined with pumped storage unit (WPS) G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 23

Simulation 1.The hydro-turbine’s set-point, the number of conventional units committed 2.The wind power absorbed directly and the wind power rejected by the grid 3.The conventional units set-point, Available grid power for pumping 4.The pumping - turbine operations and the water flows G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 24

Parameters for optimization – Dimensioning The most important parameters: –the wind potential (mean wind velocity) and –the hydraulic head between the two reservoirs. The main parameters for optimization are: –the wind capacity to be installed, –the capacity of the two reservoirs, and –the capacity of the hydro-turbine Less critical parameters are: –Rating and number of pumps –Diameter of the Penstock G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 25

Optimization procedure - Example: Crete G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 26

Operational design and Architecture of WPS Issues to be defined: –Energy supply of the hydro-turbine Peak demand supply (when the demand exceeds one predefined level) Supply of a stable percentage of the demand Stable operation at the technical minimums (as a spinning reserve) –Single or double penstock –Definition of the allowed wind penetration Stable instantaneous wind penetration (simple control) Increasing the wind penetration use the hydro-turbine as a spinning reserve (advanced control) –Pumping using conventional power At the hours of low demand Given the rest ability of the committed conventional units Whenever (aiming at the minimization of the reservoir volume) G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 27

Operational design and Architecture of WPS a.Peak demand supply (when the demand exceeds one value) b.Supply of a stable percentage of the demand c.Stable operation of the turbine at its technical minimums as a spinning reserve G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 28 Options of the hydro turbine operation

Operational design and Architecture of WPS Single or double penstock Single penstock –Cheaper solution –Turbine priority –Pumping priority Double penstock –Operational flexibility –Independent pumping and turbine operation –Quick response of the turbine when it is needed G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 29

Operational design and Architecture of WPS Instantaneous wind penetration permitted “Simple control”: Stable maximum instantaneous wind penetration “δ” –(i.e. δ = 30%), as it is used today in most autonomous islands with concrete wind installed capacity. “Advanced control”: Increase the wind penetration by an amount equal to the rest ability of the hydro- turbine. –Two-sided communication (The EUO should know the rest capacity of the hydro-turbine, in order to permit equal increase of wind penetration). –The turbine should be in operation. G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 30

Scenarios definition G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 31 Scena rio Single/ Double penstock Operational targetWind penetration permitted 1Single penstock/ turbine priority Peak demand supplyStable δ=30% 2Double penstockPeak demand supplyStable δ=30% 3Double penstockPeak demand supplyAdvanced control 4Double penstockStable supply of a percentage of the demand Stable δ=30% 5Double penstockStable supply of a percentage of the demand Advanced control 6Double penstockStable operation of the turbine at its technical minimums Advanced control Conventional power given the rest ability of the committed conventional units is used for complementary pumping

Main assumptions H=300m, L=3000m Wind velocity: 8.1m/s at the hub-height. Financial evaluation without any subsidy Oil price: 54$/b (annual mean for 2005) Basic parameters introduced dimensionless: –The wind installed capacity as a share of the mean annual load demand (50% - 430% by step 20%) –The volume of the reservoir in respect with the maximum hourly water pumping ability (30 to 100 by step 10). –The maximum operational target (as a percentage of the peak) is calculated using an iterative procedure. A bigger target could be set, but it would be achieved in less than 100% of the year. G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 32

Indexes for the evaluation Turbine’s EPC Conventional unit’s EPC Electrical system’s EPC Energy supply G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 33

Results - Crete G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 34

Results - Lesvos G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 35

Results - Serifos G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 36

Comparison of the three islands (scenario 3) G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 37

Proposed solutions for the examined islands G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 38 IslandPeak (MW) Wind Capacity (MW) Reservoir (10 6 m3) Turbine (MW) % peak supply % energy supply Crete %46-72% Lesvos %51-79% Serifos %80-98%

Sensitivity analysis of the allowed instantaneous wind penetration G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 39 Crete

Sensitivity analysis of the allowed instantaneous wind penetration G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 40 Lesvos Serifos

Sensitivity analysis of the Brent price G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 41

Sensitivity analysis of the Brent price G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 42

Sensitivity analysis of the Brent price G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 43

Conclusions The proposed architecture of the WPS (scenario 3): –Double penstock / “Peak demand supply” / “Advanced control” With the introduction of the WPS the system’s EPC is decreased This benefit should be shared between the pubic utility and the investor, by the definition of a suitable price. The basic parameters in issue are: –Hydraulic head and the Wind potential –Plant size, Island size –Current cost –Duration curve of the demand. The production cost is quietly defined The introduction of the WPS is proposed and expected to have very positive results G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 44

Thank you for your attention G.Caralis, “Analysis of Wind Energy with Pumped Storage systems in autonomous islands” 45