1. Energy production from oceans
SCHOOL OF SCIENCE & TECHNOLOGY
Energy production from oceans
Pagana Adamantia
Dr D. Missirlis
MSc in ICT Systems – October 2011

2. Introduction
The aim of this work is to present methods which can be used for energy production from ocean power and to provide information about the development status and the trends in the technology of ocean energy systems.
This thesis is based on a detailed literature review. 2

3. Presentation Outline
In this work the four basic ways to reclaim energy from the ocean are presented and analyzed. These are the following:
Ocean's high and low tides
Ocean's waves
Temperature differences in the water
Marine Wind 3

4. Tidal Energy
- Tidal power is extracted from the Earth's oceanic tides.
- A tidal generator converts the energy of tidal flows into electricity. 4

5. Tidal Energy Principle of operation
An estuary or bay with a large natural tidal range is identified and then artificially enclosed with a barrier.
The electrical energy is produced by allowing water to flow from one side of the barrage, through turbines, to generate electricity. 5

6. Tidal Energy
A combination of sluices which, when open, can allow water to flow relatively freely through the barrage, and gated turbines, the gates of which can be opened to allow water to flow through the turbines to generate electricity.
Single basin barrage
Ebb generation mode 6

7. Tidal Energy Double basin systems
Two-way generation on both ebb and flood (double effect cycle)
Two-Way Generation 7

8. Existing tidal energy plants8

9. Average annual wave power levels as kW/m of wave front
Wave Energy
The energy that can be extracted form waves is a renewable type of energy called “Wave energy”. It is technically feasible to capture this energy in offshore locations.
Average annual wave power levels as kW/m of wave front 9

10. Wave Energy - Oscillating Water Column (OWC)
This device is based on the pressure of the enclosed air in a cavity (column of air). 10

11. Wave Energy - The Pelamis Length = 120m Diameter = 3.5m
Overall power rating = 0.75MW
Nominal wave power = 55kW/m
Annual power production = 2.7GWh
Water depth = >50m
- The Wave Dragon
Width and length = 390x220m
Reservoir = 14,000 m3
Rated power/unit = 11MW
Annual power production/unit = 35GWh
Water depth = >30m 11

12. Wave Energy - The Archimedes Wave Swing (AWS)
The only moving part is an air-filled floater. Waves create an ‘up and down’ movement due to applied pressure on the floater which is located in a lower fixed cylinder. 12

13. Wave Energy - The McCabe Wave Pump
Hydraulic pumps attached between the center and end pontoons are activated as the waves force the end pontoons up and down.
- The PowerBuoyTM
Inside the buoy, a piston follows the movement of the waves’ rise and fall to output energy from the internal generator (immobile part). 13

14. Wave Energy - The AquaBuOYTM
The vertical movement of the buoy drives a broad, neutrally buoyant disk acting as a water piston contained in a long tube beneath the buoy. 14

15. Wave Energy - The case of Greece
There are plans for deploying a full scale, semi-commercial demonstration plant for fresh water and electricity production at the island of Amorgos in the South Aegean Sea, Greece. 15

16. Ocean Thermal Energy Conversion (OTEC)
Ocean thermal energy conversion (OTEC) is a method which consists of extracting energy from the difference in temperature between shallow and deep waters by way of a heat engine.
Map of temperature difference between surface and depth of 1000m 16

17. Ocean Thermal Energy Conversion (OTEC)
- Closed cycle OTEC
This cycle uses a working fluid (with a low boiling point) which is cooled down and heated up in a full cycle. 17

18. Ocean Thermal Energy Conversion (OTEC)
- Open-cycle OTEC
The open-cycle process does not use an intermediate fluid like the closed-cycle but directly uses the sea water 18

19. Ocean Thermal Energy Conversion (OTEC)
Block diagram of all applications from OTEC technology 19

20. Marine Wind Energy Conversion Systems
Research on offshore wind technologies for shallow water, transitional depth, and deepwater 20

21. Marine Wind Energy Conversion Systems
Marine wind turbines off the shores of Copenhagen
The "Alpha Ventus" wind park, 45 kilometers (28 miles) north of the island of Borkum in the North Sea 21

22. Marine Wind Energy Conversion Systems
Semi-submersible platform.
Spar Platform
Tension Leg Platform
Free Floating Platform (FFP)
IDEOL 22

23. General Economics for the main ocean energy sources
TIDAL ENERGY
Tidal power incurs relatively high capital costs, and construction times can be several years for larger projects. Although plant lifetime can be very long (120 years for the barrage structure and 40 years for the equipment), the high capital costs and long construction time are considered to be a barrier for the construction of large tidal schemes.
OCEAN THERMAL ENERGY CONVERSION (OTEC)
OTEC has high capital costs. Economic analysis indicated the early market for OTEC to be islands and near-shore communities requiring 15 MW or less. Cost analyses showed that the closed cycle OTEC would be cost effective for only very large-sized plants (greater than 40 MW). 23

24. General Economics for the main ocean energy sources
WAVE ENERGY
It is difficult to estimate the unit costs of electrical energy produced from the waves, given that the few existing schemes are prototypes and there are additional costs incurred by such a preliminary stage of development.
However, the estimated costs have shown a steady decrease with time, despite the little financial support received in recent years. It appears that several devices have already the potential to provide cheaper electrical energy for small islands and remote coastal communities that depend on expensive Diesel generation. 24

25. Conclusions
Each system has its own advantages and disadvantages. Several common points to these four main technologies stand out.
The positive aspects of using ocean energy are:
- Reduction in the dependence on fossil fuels.
- Source of energy is free, renewable and clean.
- Clean electricity is produced with no production of greenhouse gas or pollution (liquid or solid).
Energy produced is free once the initial costs are recovered.
The negative aspects of using ocean energy are:
At present, electricity produced would cost more than electricity generated from fossil fuels at their current costs.
- Technologies are not fully developed.
- Problems exist with the transport of electricity to onshore loads. 25

26. Thank you for your attention!

27. Energy production from oceans
SCHOOL OF SCIENCE & TECHNOLOGY
Energy production from oceans
Pagana Adamantia
Dr D. Missirlis
MSc in ICT Systems – October 2011