1. COMBINATION OF HYBRID WAVE & WIND ENERGY CONVERTION APPLIED TO AN OFFSHORE PLATFORM
MS. AFROKOMI-AFROULA STEFANAKOU, THEODOROS LILAS & PROF. NIKITAS NIKITAKOS UNIVERSITY OF AEGEAN DEPARTMENT OF SHIPPING TRADE AND TRANSPORT CHIOS
6 TH INTERNATIONAL SCIENTIFIC CONFERENCE ON "ENERGY AND CLIMATE CHANGE",
ATHENS 2013

2. The Problem of Water Scarcity
The 1/3 of the planet faces water scarcity due to mismanagement of water resources and their extensive use.
According to data of World Health Organization, about 1.1 billion people do not have access to clean drinking water, and the future does not look so good, as the number of people who live in areas with absolute water scarcity will increase to 1.8 billion by 2025 (UN-Water 2011).
A prime example of the severity of the situation is the statement of the vice-president of the World Bank, Ismail Serageldin, who said:
“The Next World War will be over water.” (Mosey, 2009, p. 9).

3. Water Scarcity Map

4. The common characteristics of these areas are:
Water Scarcity
According to World Health Organization the great part of countries which encounter water scarcity are:
Middle East
Mediterranean basin.
The common characteristics of these areas are:
Fairly high temperatures during the whole year
Intense drought conditions, which sometimes verge on desertification

5. Water Scarcity In Greece & the Temporary Solution
Greece is one of seven countries of EE which face scarcity problems together with Malta, Spain, Cyprus, Belgium, Portugal and Italy
The problem became more intense in our islands due to:
low touristic development
the lack of drinking water in these areas
The State has chosen as a temporary solution of the problem, the water transfer to islands with ships. However, the amounts which are spent for this practice are increasing, as the problem is still unsolved

6. The Solution of Desalination
So, the most advantageous & feasible solution is the desalination of water, given that the 97% of planet water comes from the sea, desalination seems to be the only solution to effectively deal with the problem of water scarcity. Desalination is the conversion process of seawater into drinking water A typical desalination plant consists of a water pre-treatment system, the desalination unit and a post-treatment system. The most important desalination processes are split into two main categories: Thermal (or distillation) Multistage Flash Distillation (MFS) Multiple Effects Distillation (MED or ME) Vapor Compression (VC) processes Membrane processes. Reserve Osmosis (RO) Electro Dialysis (ED) processes.

7. Reverse Osmosis
Osmosis is the movement of a solvent through a semi-permeable membrane into a solution of higher solute concentration that tends to equalize the concentrations of solute on the two sides of the membrane.
Reverse Osmosis is a method of producing pure water by forcing salt water through a semi-permeable membrane (which allows some molecules through, but not others) that salt molecules cannot pass through (Almeida, 2006)

8. Desalination Using Renewable Energy Sources
In recent years the research in the field of desalination has focused on the combination of desalination units with R.E.S, so as to reduce:
Energy cost
Cost of desalinated water.
R.E.S can produce:
Thermal energy (solar panel, geothermal)
Electrical energy (solar panel, wind turbines)
Mechanical energy (wind turbines).
The best choice is the combination of 2 renewable energies the system is called Hybrid

9. Possible Combinations of Desalination Systems with Renewable Energy.
Source: (Gude, Nirmalakhandan & Deng 2010).

10. The Best Coupling of R.E.S to Desalination Systems
System’s Efficiency
Investment & Operational Cost
Availability of Operational Personnel
Suitability of the System to the Characteristics of the Location
Possibility of the Future Increase of the System Capacity (Mathioulakis, 2007).
The selection of the appropriate R.E.S desalination technology depends on a number of factors, including:
Required quantity of potable water
Feed water salinity
Remoteness
Availability of grid electricity
Technical infrastacture
Type and potential of the local renewable energy source.

11. Desalination with Wave Energy
In order to harness the power of the waves, there needs to be a device that transforms wave energy to a more useful type, usually to mechanical energy, from which e.g. electricity can be made (Mc Cormick, 2007).
Wave energy converters (WECs) can be classified:
by their positions (on-shore, near-shore or offshore)
by their size (point absorbers, versus large absorbers) or by their operating principle (Falcão 2010).
Nearshore Devices are situated between meters of water from the shore. The most common device for this situation is the oscillating water column.
Offshore Devices are situated in deep water, with typical depths of more than 40 meters.

12. Desalination Plants with Wave Energy

13. Desalination with Wind Energy
Wind turbines aim to provide effective use of the kinetic energy of wind. Wind turbines came back into the foreground of energy technology in the mid-70s, mostly like a consequence of the energy crisis but also due to environmental degradation.
Nowadays the coupling of wind turbines with desalination systems is technically feasible.
Prime examples are:
Hybrid system equipped with wind turbine and photovoltaic panels which was made by the Center for Renewable Energy Sources & Saving which is located in Laurio since 2007
Idriada, which has been located in the Aegean Sea since 2007, which is floating and has got photovoltaic panels and one wind turbine at the centre of a platform.

14. The Project
The idea of our project is based on the fact that a wind turbine, which is located in a floating platform, consisted of a four-peripheral cylinders grid with a bigger cylinder at the center and combined with a wave energy conversion close to the platform for producing electricity for a desalination plant’s energy needs.

15. Wind Turbine &Wave device design characteristics:
Features of Wind Turbine:
30 Kw
Variable pitch of blades
Variable speed
Features of Wave device
Wave Front 8 meters
25 KW Hydraulic Power
Also: While wind varies significantly even at 5 minutes intervals, waves remain stable enough for long periods

16. Power Curve of Wind Turbine

17. Wave Device Power v.s. Wind Turbine Power Kw

18. Wave Energy Device

19. Production of Water

20. Floating platform design features:
Features of Floating Platform:
Semi-submerged which consists of :
4 peripheral cylindrical
1 central shaft
Metal mesh-grid
Automatic control via GPRS for monitoring and remote control
Operation even in adverse weather conditions.

21. Floating wind turbine platform

22. Conclusions
Water scarcity and the resulting desertification is a phenomenon that threatens many areas of the world and our country and this problem becomes especially visibly in our islands due to their low touristic development and the lack of drinking water in these areas.
The solution of transfer of water by ships is characterized particularly ineffective and especially costly
So, the desalination of water with the use of wave and wind power which are plentiful in our country is considered the most suitable method for producing pure water ensuring lower cost & lower cost of desalinated water

23. Thank you