Faculty of Science and Technology of Nova University of Lisbon
Wave power conversion systems for electrical energy production March 2008
Wave energy is the capacity of the waves for doing work. It is a renewable energy. Ocean waves are generated by the influence of the wind on the ocean surface. Outline
Origin of Sea Waves
Sea Wave Characteristics
Power Associated to a Sea Wave
Resource of Wave Power
Types of Wave Power Mechanisms
Pelamis Energy Converter
Wave Energy Market
Origin of Sea Waves storm swell wind wave direction fetch Sea waves formation due to a storm trough Waves - The combination of forces due to the gravity, sea surface tension and wind intensity are the main factors of origin of sea waves. Fetch - distance over which the wind excites the waves To distances far from the fetch, sea waves have a regular shape and the phenomenon is called swell . Water particle Sea Wave
wavelength - distance between two consecutive crests , or two consecutive troughs
height H - distance crest to trough. It is proportional to wind intensity and its duration.
wave period T - time in seconds needed for the wave travel the wavelength
frequency f = 1/ T - indicates the number of waves that appears in a given position.
wave speed –The ratio wavelength/period or v = /T = f .
declivity – the ratio /2 H
When this value is greater than 1/7 the wave becomes unstable and vanishes .
In deep water, the energy in waves can travel for thousands of miles until that energy is finally dissipated on distant shores.
crest crest trough H
Power Associated to a Sea Wave The power associated with a wave of wavelength and height H and a front b is given by H b Power per metre (b = 1 m) of front wave is approximately When wave height is doubled then generates four times as much power.
The world resource of wave power is estimated in about 2 TW. Resource of Wave Power Europe represents about 16% of the global wave power resource (320 GW) Only about 10 to 15% of the global estimated resource can be converted in electrical energy. Global wave power distribution in kW/m Increased wave activity is found between the latitudes of 30° and 60° on both hemispheres Height (m) Period (s) A good wave have ~50 kW/m Equator
5000 MW Resource of Wave Power in Portuguese coast Povoa do Varzim
Types of Wave Power Mechanisms The sea wave’s motion can be converted into mechanical energy by using proper wave power mechanisms
turbine Wells 0,35 0,30 0,25 0,20 0,15 0,10 0,0 1,0 2,0 3,0 4,0 5,0 Rendimento Ângulo de calagem das pás Sem válvula de alívio Com válvula em paralelo Com válvula em série Air output Wave Structure Parallel valve Generator Turbine Series valve
Floating cylinder oscillating movement converter electric generator waves Escone sea level under sea This converter unit, called Escone, after his inventor Esko Raikano, is the heart of the system and converts the reciprocating motion to a rotating shaft connected direclty to a generator for generating electrical energy with high efficiency .
Bristol cylinder for
wave energy extraction
One of t he first methods to extract mechanical energy from the waves was invented in the 1970s by Professor Stephen Salter of the University of Edinburgh, Scotland, in response to the Oil Crisis. It can be moored, to distances of 80 km of the cost. The cam rotates about its axis and is shaped to minimize back-water pressures.
Pelamis Converter Profile view Top view Sea snake Pelamis
Some aspects of Pelamis construction Rolling the steel plate Steel tubes of 3.5 m in diameter Transportation Articulation
Pelamis layout Power module of 250 kVA D/ 3 Power transformer de 950 kVA 6.6/15 kV Three phase cable 15 kV Three phase cable 15 kV T D = 3.5 m Articulation Power Module 120 m ~ 30 m 5 m Nose P-750 Articulation
Power module Inside view of the power module Efficiency = 35 % Hydraulic arm High pressure container Motor/ generator set Distributor Reservoir Vertical articulated axis Horizontal articulated axis
Hydraulic circuit Electric generator Gas under pressure HP Valve 1 Hydraulic motor Hydraulic arm 1 Hydraulic arm 2 Fluid under pressure Reservoir LP force force Valve 2 High pressure Low pressure Hydraulic arms
Pelamis wave energy converter of 750 kW Pelamis Wave farm of Aguçadora of 2.25 MW Association of Pelamis units in a total of 30 MW (waiting for legislation) 2100 m 600 mof Wave direction Pelamis Seabed Anchorage Pelamis anchorage to the seabed Flexible cable
Pelamis installation Total power = 2.25 MW. (3 units of 750 kW) 15 kV 2001 2002 2003 3 year average Jul Aug Sep Oct Nov Dec Jan Feb Mar Apr May Jun 150 125 100 75 50 25 0 Wave Seasonal Variability Average incident power (kW/m)
Costs distribution for a wave power plant Wave Energy Market mechanical and electrical equipment 49% structures 27% assemblage 13% grid connection project management 2% 5% anchorage 4%
Wave energy is not expensive to operate and maintain, no fuel is needed and no waste is produced. However, it depends on the intensity of the waves and needs a suitable site where waves are consistently strong. The infrastructure must be able to withstand very rough weather.
Wave power lies not in huge plants but in a combination of on-shore generation and near-shore generation (using a different technology) focused on meeting local or regional needs. If this system prove to be economically possible, only 0.1% of the renewable energy within the world's oceans could supply more than five times the global demand for energy.
The Pelamis Wave Energy Converter is a revolutionary concept resulting from many years of engineering development. It was the world’s first commercial scale machine to generate electrical energy into the grid from offshore wave energy and the first to be used in commercial wave park projects. In Portugal, Pelamis System is now proving to be successful.