Experiments on Horizontal and Vertical Axis
Water Turbines for Harnessing Marine Currents:
Technological and Economical Aspects
D. P. Coiro
Department of Aerospace Engineering (DIAS)
Università di Napoli “Federico II"
www.dpa.unina.it/adag/
ISLENET 2007
BRUXELL, OCTOBER 9th 2007
H
Diameter
Swept
Area
WATER
OR
AIR
Speed=V
D
Theoretical Power of the air stream hitting the rotor = 0.5 ρ V3 S
ρ is the water or air density (water has a density about 1000 times higher than air)
V is the speed of air stream hitting the rotor
S is the frontal surface swept by the stream (S=π*R2 –Horiz. or S=D*H-Vertical)
Example:
ρ = 1000 Kg/m3
V = 2 m/s
S = 30 m2 =>
Ptheoretical = .5 * 1000 * 8 * 30 = 120000 Watts = 120 Kw
BASIC CONCEPTS
Theoretical power of the stream hitting the rotor = 0.5 ρ V3 S (Watts)
Effective electrical power produced Pelectrical (Watts)
Pelectrical
Pelectrical
Global efficiency of the system = η =
η=
Ptheoretical
.5 ρ V 3 S
Example(water): ρ = 1000 Kg/m3 V = 2 m/s
S = 30 m2 =>
Ptheoretical = .5 * 1000 * 8 * 30 = 120000 Watts = 120 Kw
Pelectrical= Ptheoretical * ηRotor * ηGearbox * ηGenerator * ηElectrical System
If the global system efficiency is:
η = ηRotor*ηGearbox*ηGenerator* ηElectrical = = 25%
Pelectrical = .25 * 120 = 30 Kw
=>
TIDAL CURRENTS
Alta marea
Bassa
marea
Bassa
Alta marea
marea
Messina Strait
Change of direction every 6h and 12min
Maximum Speed = 2.5 m/s
Related to Earth-Moon gravitational
fields, they are present where
channels are located
1) They are not dependent on climate
variability. The current speed,
during the whole year, can be known
in advance as well as the energy that
will be collected at the end of the
year.
2) The maximum speed is known in
advance so complex mechanical
system to break-down the turbine
can be avoided
BASIC CONCEPTS
1 meter
WATER
1 meter
With only 1 square meter (11.1
square feet) of intercepted water
flowing at 6 knots (17.6 miles/h),
it is possible to produce about
3.3 kW (with system efficiency
η=.25)
AIR
An
equivalent
air
stream
intercepting 1 square meter, to
produce the same 3.3 kW, must
flow at a speed of 56 knots
(63 miles/h)!!!!
VERTICAL AXIS TURBINES
Savonius
Gorlov
Darrieus-straight blade
Pinson
Darrieuscurved blade
DUCTED VERTICAL AXIS TURBINES
BlueEnergy
Shaped Channel
Ducted Kobold
Straight Channel
Northern Territory-AU
HORIZONTAL AXIS TURBINES
GEM-Italy
Tyson turbine-AU
Lunar Energy-UK
Marine Current-UK
Aquantis-cable anchored
Pinson
POSSIBLE LOCATIONS FOR THE TURBINES ?
Rivers or Gulf Stream (Flow Unidirectional)
Tidal Current Sites
In Existing Barriers (Flow Bi-Directional)
VERTICAL AXIS TURBINES
Darrieus (curved blades)
Cicloturbine (straight blades)
Advantages:
•Not dependent on current direction
Disadvantages:
•Efficiency little lower than horizontal
•Blades very easy to build
•The blade span can be easily increased
•The Darrieus (fixed blade) does not start spontaneously
HORIZONTAL AXIS TURBINES
Similar to standard wind turbine
Advantages:
•Efficiency little higher
•Very well known the aero-hydro dynamics
Disadvantages:
•They depend on the current
direction
•Complex mechanism needed for
blade rotation
Ocean’s Kite Project Main Goal
To design a marine current horizontal axis turbine rated at 300 Kw of
electrical power with a marine current of 2.5 m/s.
This is part of the GEM project that aims to develop a tidal current
device hosting two horizontal axis turbines. The whole system will
behave as a big ocean kite, floating under the sea level and anchored at
the bottom with a winched chain
Project’s Main goal
General Data of full scale turbine:
R=5.5 m
Blade number=3
Tip Speed Ratio ~ 4
Depth of turbine axis ~ 15 m under the sea surface
Cavitation number n= 3.7 with V∞=2.5 m/s and water temperature of 10°
Blade and Rotor Design
Root
Twisted Blade & Rotor Characteristics:
Tip
Root chord: 0.136 m; Tip chord: 0.05 m
Length: 0.4 m;
Area = 0.5 m2 ; Diameter = 0.8 m
Number of Blade = 3; Solidity = 0.2
Scaled Model
The model has been designed to measure rotational speed, rotor torque and thrust
Blades manufactured
in aluminum using
C.N.C. machine
Experimental Tests
The experimental tests have been carried out at the Naval department’s
Towing Tank of the University of Naples Federico II.
Towing Tank of the University of Naples Federico II (135 X 9X 4.5 meters )
The tests have been performed at a combination of speed and depth
to obtain the same cavitation number of the full scale turbine. This
has been immersed at a depth of 1.5 m. Nominal V∞= 2.5 m/s.
VIDEO
Experiments
Efficiency (Pitch 0°)
0.45
0.4
0.35
0.3
0.25
0.2
1.5 m/s
0.15
2 m/s
2.5 m/s
0.1
3.0 m-s
0.05
0
0
1
2
3
4
TSR
5
6
7
8
VERTICAL AXIS HYDRO TURBINE “KOBOLD”
Buoy built by “Ponte di Archimede S.p.A.”. The
rotor and its innovative working principle has
been developed by our research group ADAG
An international patent has been issued.
Patent n. WO 2005/024226 A1
It is installed in Messina Strait.
Copyright ImageFactory/Quark n.26
Mean current speed = 1.5 ÷ 2 m/s
Main Characteristics
3 straight blades partially freely of oscillating
Rotor Diameter
= 6m
Blade span
= 5m
Blade chord
= 0.4 m
High lift airfoil – cavitation free
Buoy diameter
= 10 m
Buoy height
= 2.5 m
Sea depth
= 18 – 25 m
Global efficiency
= 25%
BASIC WORKING PRINCIPLE
Videoclip
ANIMATION
Videoclip
FROM AN IDEA TO THE PROTOTYPE
¾ WIND-TUNNEL TESTS OF TURBINE MODEL
Model dimensions :
Turbine Diameter
Blade height
Blade chord
2.10 m
0.80 m
0.17 m
Blade airfoil
NACA 0018
2–3–4–6
Blade configurations
PROTOTYPE DESIGN AND CONSTRUCTION
The blades are made of an inner steel structure, extending
only around the attachment points, composed by
longitudinal spars and ribs. Around the structure a carbonresin “skin” has been stratified. Glass fibre cover was
necessary to avoid corrosion problem.
PROTOTYPE DESIGN AND CONSTRUCTION
The holding arms have also been streamlined by means of an
“ad hoc” airfoil made of glass fibre structure
PROTOTYPE DESIGN AND CONSTRUCTION
Steel Attachment System, blade mass balance and blade
rubber stops
THE WHOLE SYSTEM (Turbine + Floating Platform)
The whole system has been designed to have characteristics of
solidity and high efficiency.
Turbine in the sea
Turbine and buoy on dock
UNDER THE BUOY
Turbine rotor on dock
INSIDE THE BUOY
Mechanical overdrive (1:162) and electrical equipment
The generator is brushless three-phases -synchronous -4 poles160Kw -connected to a control system capable of delivering
energy directly to the electrical line
Data Acquisition System and Control
Current-meter
Torque-meter
1
3
PLC
2
Generator
PC
Experimental Data - Kobold
C p a l l ' a l b e ro m o to re d e l l a tu rb i n a
0 ,3 5
0 ,3
0 ,2 5
0 ,2
0 ,1 5
The tilting of
the buoy and
of the turbine
has been taken
in account in
the numerical
code
0 ,1
0 ,0 5
0
1 ,4
1 ,5
1 ,6
1 ,7
1 ,8
1 ,9
2
2 ,1
2 ,2
2 ,3
2 ,4
2 ,5
2 ,6
2 ,7
la m b d a
Measured Rotor Efficiency-Cp
V m e dia c or r e nte m is ur a ta 1 .2 m /s
exp (Vaver. + ΔV = 1.4 m/s)
0 ,4
0 ,3 5
numerical V = 1.4 m/s
0 ,3
Cp
0 ,2 5
0 ,2
0 ,1 5
0 ,1
exp (Vaver. + ΔV = 1.7 m/s)
0 ,0 5
0
1 ,3
1 ,4
1 ,5
1 ,6
1 ,7
1 ,8
1 ,9
2
2 ,1
2 ,2
2 ,3
2 ,4
2 ,5
2 ,6
2 ,7
la m b d a
Experimental and numerical data comparison
2 ,8
VIDEO
Turbine producing electricity
Areas of current investigation to improve the efficiency
and to lower the unit cost of energy: MYTHOS project
•Unsteady viscous numerical methods to include flow curvature
effects on airfoils and rotor design.
•Gearbox ratio brought to 1:5 or none
•Development of a new axial flow PM generator operating at low
rpm
•Improvement of the hydrodynamic efficiency of the rotor thanks to
an innovative (under experimentation in these days...) rotor working
principle: new patent is expected!
•Flow Increaser (diffuser). It can double the ouput power
•Avoid the tilting of the buoy and of the turbine
Theory states that vertical axis turbine can reach at least the same
maximum efficiency of horizontal axis ones: our goal is to prove that
this is possible in reality!!
Mythos Vertical Axis Turbine
•Innovative rotor shape, new airfoils, simpler
geometry and a new PM generator
•Wind tunnel test next month.
Water test at the end of the year
• Expected
•Patent expected
rotor efficiency around 42%
Rotor Diameter = 6 m;
Blade chord = 0.4 m;
Rotor Diameter = 6 m;
Blade chord = 0.4 m;
Blade span = 5 m;
Number of blades = 3
Current speed = 2 m/s
Current speed = 2 m/s
0.35
50
KOBOLD (exp)
MYTHOS-2 (num)
KOBOLD (exp)
MYTHOS-2 (num)
0.3
40
Power [kW]
0.25
Efficiency
Blade span = 5 m;
Number of blades = 3
0.2
30
20
0.15
10
0.1
0
0.05
1
1.5
2
TSR
2.5
3
6
7
8
9
10
11
12
13
14
15
16
Ω [rpm]
Comparison between KOBOLD and MYTHOS performances
17
18
19
Cost Analysis - Tidal Current behavior in time
Available Energy from the tide
2,5
Month
Total
Energy
kWh/m^2
Current Speed(m/s
2
1,5
January
467.767
380.567
February
382.433
294.633
March
467.367
367.634
April
439.500
342.333
May
467.833
374.267
June
689.100
606.467
July
878.933
793.433
August
406.433
311.267
September
405.300
305.567
October
417.333
319.600
November
524.133
435.633
December
759.497
672.467
1
0,5
0
-0,5
0
5
10
15
20
25
30
35
40
45
Time (hours)
1
1
P
P
P ⎛ kW⎞
Ptheoret. = ρV 3S ⇒ V 3 = theoret. = theoret. = theoret. ⎜ 2 ⎟
2
2
Sρ S1000 S ⎝ m ⎠
7
6
Power density(kW/m2
Extractable
Energy
kWh/m^2
5
50
4
3
2
1
Working Factor =
0
-1
0
5
10
15
20
25
30
Time (hours)
35
40
45
50
number of working hours
1760
=
= 0 .25
yearly inactive period
8760 − 1760
ECONOMICAL FEASIBILITY STUDY
Simplified Economic Analysis Methods
Simple Payback Period Analysis:
AAR = Average Annual Return = Ea X Pe
Ea = Annual Energy Production = 156116 kWh/yr
SP =
Pe = Price Obtained for Electricity = 0.10 €/kWh
Cc
125000
=
=
AAR 15612
8 years
Cc = Total Capital Cost = 125000€
Cost of Energy Analysis (EPRI TAG):
FCR = Fixed Charge Rate = 8% Cc
is an average annual charge used to
account for debt, equity costs, taxes
COE =
Cc ⋅ FCR + CO&M 125000 ⋅ 0.08 + 3000
=
=
Ea
156116
CO&M = Operation & Maintenance Costs = 3000€/yr
= 0.083 €/kWh
Costs per installed kW of power: comparison between existing turbines
Vertical Axis (Kobold, IT)
Horizontal Axis (MCT, UK)
Buoy anchored
Monopile foundation
Total Cost/Kw=2400 $
Total Cost/Kw=8000 $
Rated Power
Design&Testing
Machine Cost
Installation Cost
Grid Connection
TOTAL (excl.
design)
Manufacturing($/kW)
MCT, UK
300 (kW)
3.1 Ml $
1.3 Ml $
.83 Ml $
0
2.4 Ml $
Kobold, IT
160 (kW)
.05 Ml $
.34 Ml $
.05 Ml $
0
.39 Ml $
5200 $
1133 $
Costs: summary
¾
Main factors influencing the cost of energy:
1. The capital cost (fabrication, installation, permissions,etc.)
2. Operation and Maintenance – annual costs
3. Energy output per year
4. Discount rate (i.e. the cost of the capital)
5. Scale economy (producing many units will lower the price)
¾
Difficulties:
¾ Lease of seabed
¾ Navigation and shipping interests
¾ Marine environment and usage
¾ Electrical cables at the sea and connections on land
¾ Fishing interests
Note: In Italy at least 10 public entities have to give a permission! Many of
them have no idea under which regulation this type of installation falls!
¾
Lessons Learned
¾Keep the machine as simple as possible!
¾Do not underestimate the bureaucracy: this is a
novel technology and there is not past experiences
(permissions, rent, etc.)
¾Do not underestimate the difficulties related to
cable connection to the grid
¾Maintenance should be as simple as possible!!
¾Accurate evaluation of site (sheltering, depth,
mooring difficulties, etc.)
coiro@unina.it
www.dpa.unina.it/adag/