Hydraulic Storage: A New Storage Concept for Wind Turbines

Kasra Zarisfi Impressive Engineering Limited

AGENDA

• Introduction • Hydraulic Accumulator • Gravitational Storage • Efficiency and Design life • Production Credit • Construction • Cost Reduction Credits • Innovation in Sealing Mechanism • Other Applications • Questions

INTRODUCTION

• Tower Height: 100m to120m

• Rotor Blades Diameter:150m

• Storage Shaft Diameter:8m

• Storage Shaft Depth: 500m

• Working Pressure: 50barg

• Weight of Each Cylinder:

1000 tonne

• Turbine Output: 6MW • Charge Time: 6hr • Hydraulic Storage Capacity:12.6MWhr

(6x6x0.35)

• Storage Output: 2-4-6MW (according to grid

connection/trading strategy)

Technology Gap

Novel Seal

HYDRAULIC ACCUMULATOR

• Hydraulic Accumulator is invented by Lord Armstrong in1846

• Hydraulic press with capacity

of 18500 tonne is commonly used in heavy industries however displacement is limited to few meters

Friction Material Strength Integrity

50 bar

>50 bar

10

m

• Dynamic seal is a key element and shall move with low

friction while holding the hydraulic liquid

• Machining requirement limits the size of

hydraulic cylinder. This issue cannot be resolved by using a pressure seal. because:

GRAVITATIONAL STORAGE

• Gravity, simple physics but

fundamental fact for storing energy

• Pump Storage, about 99% world capacity, however is limited by: The geographical

and environmental constraints Limitation in number

of suitable sites

• Underground storage, Has already suggested by many different designs.

99%

1%

World Energy Storage Capacity

Pump Hydro Others

US patent

application

1917

EFFICIENCY AND DESIGN LIFE

• High Efficiency

• Long Design Life, Structural Parts >30 Years

• Minimal Degradation Over Time

Rotor Mechanical

Energy

X 95% Gear Box

X 90% Generator

X 96% Convertor

X 94% Storage (Battery)

= 77% Overall

Efficiency

Rotor Mechanical

Energy

X 95% Pump

X 95% Hydraulic Storage

X 90% Turbine / Hydraulic Motor

X 95% Generator

= 77% Overall

Efficiency

Conventional Wind Turbine With Energy Storage

Wind Turbine With Inherent Hydraulic Storage

Equivalent electrical round trip efficiency for Hydraulic Storage

Same generators: the first one is operate at variable speed, the second one is operated at constant optimum speed

PRODUCTION CREDITS

• High value electricity • High quality electricity • Increase in annual production

Avoid curtailment & Increase the rated power input, <10% increase is expected

• Ancillary Service • Predictability and Controllability

Wind

Turbine WT+ HS

WT+ Lead

Acid Battery

WT+ Nickel

Cadmium

Battery

WT+

Flywheels

WT+

Pump

Hydro

Production

Efficiency 82%* 77.9%* 82% 82% 82% 82%

Round Trip

Storage

Efficiency

- - 80% 90% 90% 75%

Overall

Efficiency 82% 77.9% 65.6% 73.8% 73.8% 61.5%

Harvesting

Capacity (MWh) (Normalised)

1 1.1 1 1 1 1

Generated

Electricity

(MWh)

0.82 0.85 0.66 0.74 0.74 0.62

Curtailment 10% 0% 0% 0% 0% 0%

Grid Input

(MWh) 0.74 0.85 0.66 0.74 0.74 0.62

COST REDUCTION CREDITS

Mechanical Equipments

Electrical Equipments

Transmission System

Hydraulic Storage Batteries Pump Hydro

600MW 600MW 600MW 280MW 280MW

Gearbox Pump

Turbine Motor

Transformers Transmission Cables

Sub Stations

Generator Convertor

De-rating of an offshore wind farm facilities

• Capacity factor 18/24=75% vs 0.35%(conventional wind turbine)

• Same production with de-rated equipments

A 600MW offshore wind farm can be de-rated to 650 x35%=280MWx75%

• Elimination of costly components Gearbox 12.9%, Convertor 5.0% of the turbine cost

• Optimisation of components Tower 26.3%, Generator3.4% Transformed% Brake System 1.3% of the turbine cost

• Storage as the foundation 12% to 16% of the project cost

• Grid Connection 11% to 20% of the project cost

CONSTRUCTION

• Drilling is the main cost and challenge

• Storage bore is an extension to

the foundation

• Typical mono-pile foundation, 6-8m diameter, 50-100m depth

• Technology is exist, Reversed Circulation

Drilling (RCD) can be modified for deeper applications

• Preliminary assessment has been

performed.

Further R&D work is ongoing

INNOVATION PRESSURE BALANCE SEAL

• Leakage is a function of pressure not density

• Solid Parts are submerged in a heavy density liquid with

same density as the solid

• Pressure is kept balanced at the seal faces by controlling of

dense liquid level

• Dynamic Seal functions as a separator and not a pressure

seal

INNOVATION METAL POWDER - OIL SUSPENSION

• Made of oil and metal powder • Density: 2800 -3000 kg/m3

• Test model energy loss: 0.088J in 10 min

• Power loss: 2.6x10-4 W/kg=0.26W/tonne

• Efficiency reduction due to suspension

energy loss: 0.002% (based on lab test)

• Suspension optimisation, many variables shall be

considered like: Powder density and grain size, oil viscosity and density, operating temperature and pressure, etc

CG

CG

INNOVATION TEST MODELS

• One successful lift test • Challenges: Agitation mechanism, suspension settlement, iron–oil

paste, minor suspension leakage

• Seal design tested and modified

• New test model with air agitation system and suspension level

control mechanism is under design

• Test Model: Helical Lift Mechanism No suspension level

control mechanism Piston Weight: 10kg Piston Height: 500mm Displacement: 800mm Tower Height: 1500mm Test Pressure: ˜0.3bar

OTHER APPLICATIONS HYDRAULIC STORAGE FOR HEAT PUMPS

Condenser Evaporator

Expansion Valve

Compressor Storage Pump

Turbine/Motor Generator

Grid

Cylindrical Weights

Technology Gap: Innovative Pressure Balanced Seal

Wate

r

Underground Shaft

Control Valves

Dis

charg

ing

Charg

ing

Wate

r Power

Heavy Density Suspension Liquid

• Heat pumps are

important green technology with high COP

• Storage reduces the Heat

Pump load from the grid. Two full Charging cycle per day

• Capacity: 6 kWh = 2x3kWh

• Depth: 200m, Diameter: 400mm

Many Thanks

Any Questions Please?