Analysis of wind energy with pumped storage systems in autonomous islands George Caralis Mechanical Engineer NTUA

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National Technical University of
AthensDepartment of Mechanical EngineerFluids
Section, Wind Energy Laboratory
Analysis of wind energy with pumped storage
systems in autonomous islands George
CaralisMechanical Engineer NTUA
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Contents of the presentation

• Description of the problem
• Methodological approach
• Evaluation criteria
• Application in three autonomous Greek islands
• 1st case
• Analysis of the wind power penetration in
  autonomous islands without pumped storage
• 2nd 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
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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
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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
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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
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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 investors interest for wind applications
• Constrain in the wind installed capacity
• Wind power rejection during low demand

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Storage systems in autonomous islands 6
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Current situation in the autonomous Greek islands
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1st 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
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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
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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
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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 CFR ()
• The percentage of wind energy absorbed ()
• The contribution of wind energy ()
• The Conventional units production cost (EPCC -
  /kWh)
• The Electrical systems production cost (EPCS -
  /kWh)
• The Wind powers production cost (EPCW - /kWh)

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Storage systems in autonomous islands 11
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Crete
G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 12
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Lesvos
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Storage systems in autonomous islands 13
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Serifos
G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 14
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Sensitivity on the allowed instantaneous wind
penetration

• allowed instantaneous wind penetration 30 / 40
  / 50
• For wind velocity 8.1m/s
• For Brent price 54/b (mean value 2005)

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Storage systems in autonomous islands 15
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Crete
Lesvos
Serifos
G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 16
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Sensitivity on the electrical systems EPC on the
Brent price

• 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)

G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 17
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Crete
Lesvos
G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 18
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Serifos
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Storage systems in autonomous islands 19
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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
  EPCS is negligible, and the dependence on the oil
  remains high.

G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 20
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2nd 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
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Current electrical system
G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 22
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Wind energy combined with pumped storage unit
(WPS)
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Storage systems in autonomous islands 23
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Simulation

• 1. The hydro-turbines set-point, the number of
  conventional units committed
• The wind power absorbed directly and the wind
  power rejected by the grid
• The conventional units set-point, Available grid
  power for pumping
• The pumping - turbine operations and the water
  flows

G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 24
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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

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Storage systems in autonomous islands 25
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Optimization procedure - Example Crete
G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 26
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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)

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Storage systems in autonomous islands 27
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Operational design and Architecture of WPS
Options of the hydro turbine operation

• 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

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Storage systems in autonomous islands 28
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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

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Storage systems in autonomous islands 29
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Operational design and Architecture of WPS

• Instantaneous wind penetration permitted
• Simple control Stable maximum instantaneous
  wind penetration d
• (i.e. d 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.

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Storage systems in autonomous islands 30
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Scenarios definition
Scenario Single/ Double penstock Operational target Wind penetration permitted
1 Single penstock/ turbine priority Peak demand supply Stable d30
2 Double penstock Peak demand supply Stable d30
3 Double penstock Peak demand supply Advanced control
4 Double penstock Stable supply of a percentage of the demand Stable d30
5 Double penstock Stable supply of a percentage of the demand Advanced control
6 Double penstock Stable 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

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Storage systems in autonomous islands 31
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Main assumptions

• H300m, L3000m
• 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.

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Storage systems in autonomous islands 32
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Indexes for the evaluation

• Turbines EPC
• Conventional units EPC
• Electrical systems EPC
• Energy supply

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Storage systems in autonomous islands 33
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Results - Crete
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Storage systems in autonomous islands 34
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Results - Lesvos
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Storage systems in autonomous islands 35
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Results - Serifos
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Storage systems in autonomous islands 36
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Comparison of the three islands (scenario 3)
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Storage systems in autonomous islands 37
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Proposed solutions for the examined islands
Island Peak (MW) Wind Capacity (MW) Reservoir (106 m3) Turbine (MW) peak supply energy supply
Crete 563 825-1314 60-120 310-405 55-75 46-72
Lesvos 58 84-145 4.4-14 30-46 57-81 51-79
Serifos 2.9 2.2-3.6 0.2-0.3 2.3-2.9 75-100 80-98
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Storage systems in autonomous islands 38
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Sensitivity analysis of the allowed instantaneous
wind penetration
Crete
G.Caralis, Analysis of Wind Energy with Pumped
Storage systems in autonomous islands 39
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Sensitivity analysis of the allowed instantaneous
wind penetration
Lesvos
Serifos
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Storage systems in autonomous islands 40
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Sensitivity analysis of the Brent price
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Storage systems in autonomous islands 41
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Sensitivity analysis of the Brent price
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Storage systems in autonomous islands 42
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Sensitivity analysis of the Brent price
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Storage systems in autonomous islands 43
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Conclusions

• The proposed architecture of the WPS (scenario
  3)
• Double penstock / Peak demand supply /
  Advanced control
• With the introduction of the WPS the systems 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

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Storage systems in autonomous islands 44
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• Thank you for your attention
• gcaralis_at_central.ntua.gr

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Storage systems in autonomous islands 45