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An Introduction to Renewable Ocean Energy Generation in Ireland & Comparing the use of Wave Power Vs. Tidal Power.
John Conroy
11212251
Contents
1. Abstract
2. Introduction
3. Literature Review
3.1 Introduction to Ocean Energy
3.1.1 What is Ocean Energy
3.1.2 Potential of Ocean Energy
3.1.3 Types of Ocean Energy Systems
3.1.3.1 Tide Systems
3.1.3.2 Wave Systems
3.1.3.3 Temperature Gradient Systems
3.1.3.4 Salinity Gradient Systems
3.2 Wave Energy Generation – The Hinged Contour Wave System
3.2.1 Physical concepts
3.2.2 Case Study – The Pelamis Wave Generation System
3.2.3 Potential
3.2.4 Challenges
3.2.5 Wave Energy of this type in use/proposed for use in Ireland today.
3.3 Tidal Energy Generation – The Venturi Turbine Tidal Power System
3.3.1 Physical concepts
3.3.2 Case Study – The OpenHydro Tidal Energy Generation Plant
3.3.3 Potential
3.3.4 Challenges
3.3.5 Tidal Energy of this type in use in Ireland today.
4. Ocean Energy in Ireland
4.1 The benefits of using Renewable Ocean Energy in Ireland
4.2 The position of Ocean Energy within Irelands Renewable Energy plans
4.3 The potential of Ocean Energy in Ireland
4.4 Ireland proposed roadmap into the use of Ocean Energy
4.4.1 Security
4.4.2 Environmental Concerns
4.4.3 Costs Etc.
5. Conclusion
6. References
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Abstract
Introduction
This assignment will focus primarily around Renewable Ocean Energy which compromises technologies that convert kinetic tidal and wave energy into electricity. Within this topic I hope to examine Ocean Energy as a concept as well provide some detail about its position within the field of renewable energy generation specifically within Ireland. I am also intending to examine in detail two advanced methods of Renewable Ocean Energy Generation and make an assessment on which has the greatest potential for growth given all the factors within the systems.
First though I would like to spend some time considering the historical utilization and forecasted demand of energy in an attempt to emphasize the importance of Renewable Energy to the population of the world.
According to Aldo V. Da Rosa [1] with the start of the industrial revolution at the beginning of the 19th century the growth in energy utilization per capita accelerated dramatically as indicated in figures 1.1/1.2 below.
Fig.1.1 Estimated plot of the increase of per capita energy utilization. [1]
Fig.1.2 Demonstrates how the annual rate of increase was flat until the 19th Century [1]
It is clear from this data that in the last century we have become heavily dependent on energy for growth and if we are to assume this growth will continue it would be safe to assume that we will continue to see an upward trend in the need for energy.
Ideally through better energy use and management the energy demand growth rate would become more sustainable as shown by the World Energy Outlook (WOE) 2010.[2] Prediction of the world’s future energy demand is a difficult process due to the numerous scenarios that play into such a projection. The IEA (International Energy Agency) have projected this growth in Mtoe (Million tons of oil equivalent) based off a number of scenarios in Fig 1.3 below.
Fig.1.3 Projected energy demand by scenario. [2]
Inevitably the world’s governments dictate the energy demands by the policies they drive within their individual countries and the IEA have built these policies into 3 possible projections in Fig 1.3.
The scenarios show us that with no change the ‘Current policies’ in place today the energy demand continues to grow at a rapid rate of 1.4% per year reaching 18,000 Mtoe by 2035. Assuming that today’s governments continue with existing energy policies as well as declared intentions the second projection is yielded (New Policies Scenario) with a 1.2% average growth rate reaching 16,750 Mtoe.
Finally the IEA show the ‘450 scenario’, an aggressive energy demand profile which was first presented in detail at the WEO 2010 sets out pathways that if were to be introduced provides a reasonable chance to achieve only a 2° Celsius increase in global temperature. This scenario shows a much reduced 0.7% average growth rate per year peaking at a 22% increase in 2035 from 2008 compared to the 36% in the ‘New policies scenario’. [2]
In summary all of the projections out there for future energy demand show a strong growth profile no matter what actions or policies are undertaken. This now leads us to examine how do we satisfy this demand profile with the resources and in turn fuel sources at our disposal today.
Global energy intensity (the amount of energy needed to produce each Gross Domestic Product - GDP) has gradually fallen over the last number of decades due to a number of reasons including energy efficiencies improvements and fuel switching. Even with all this activity and with the expectation that the world is to become more efficient in its energy production fossil fuels still play the primary role in energy demand in each of the scenarios in Fig 1.4/1.5.[2]
Fig.1.4 IEA Projected primary energy demand by fuel and scenario (Mtoe). [2]
Fig.1.5 IEA Shares in projected primary energy demand by fuel and scenario (Mtoe). [2]
In each of the IEA’s New & 450 Policies scenarios we can see that it is expected that through these policies it is expected that the share of fossil fuel energy demand will be significantly reduced. We have already seen at the beginning of this chapter that there is no expectation that the energy demands are not expected to decline so obviously we must replace the reduction in fossil fuels with an alternative, in all cases a major part of this alternative are ‘Other Renewables’ in which Ocean & Marine Energy plays a role.
Renewable Energy has been growing rapidly in the last decade due to the numerous benefits it yields including reduced greenhouse gas emissions as well as offsetting the always increasing fossil fuel prices.
The IEA, within the WEO 2010, have in the 450 scenario predicted a total primary energy demand of modern renewable growth of four fold between the 2008 to 2035 time frame per Fig 1.6 below for electricity generation trends. [2]
There are many types of renewable energy generation types contained within this profile including Hydro/Wind/Solar/Biomass/Geothermal/CSP and finally Marine. Each of these renewable sources will have a significantly contribution to the total predicted energy generation profiles.
As in this case we are considering Ocean & Marine energy Fig 1.7 shows its predicted growth by region. Although this renewable energy type contributes a relatively small part within each of the regions captures below primarily down to the fact that the technology is in its infancy compared to other generation types. [2] Also see Fig 1.8 below shows an assessment of the position of Ocean energy within the development of renewable energy systems. From this we can conclude that much of the Ocean renewable energy field is still in development.
We can also take from this that in every region there is a predicted growth in Marine energy generation, although small compared to the other sources it does demonstrate that there is significant potential across the globe and in all regions initially between now and 2035 and even greater beyond this time frame.
Fig.1.6 Predicted electricity generation from renewables by scenario. [2]
Fig.1.7 Share of renewables in electricity generation by type and region within the ‘New Policies scenario’. [2]
Fig.1.8 Assessment of Renewable Energy Technology Development. [11]
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Literature Review
Introduction to Ocean Energy
What is Ocean Energy?
Ocean Energy (OE) involves the generation of electricity from the waves, the tides, the currents, the salinity gradient, and the thermal gradient of the sea or the ocean. [3]
The oceans hold energy in numerous ways and this is resulting in numerous different technologies being used to exploit these energies. As discussed above we have defined 5 different high level categories of energy available in the sea as listed below;
· Tides
· Tidal Currents (Marine Currents)
· Waves
· Temperature Gradients
· Salinity Gradients
We will expand these on each of these ocean energy generation mechanisms in the coming chapter after a brief look at an assessment of the potential of ocean energy.
Potential of Ocean Energy
Due to the enormous volumes of energy contained in the world’s oceans as well as the numerous types in theory, in the future (but hopefully not too far in the future), the oceans could largely meet the world’s energy needs in their totality.
According to Gouri S.Bhuyan through the IEA the ocean contains the following theoretical energy values per annum;
o Tide and marine current resources represent estimated annual global potentials exceeding 300 TWh and 800 TWh per annum, respectively.
o Wave energy, the theoretical potential is estimated at between 8,000 TWh and 80,000 TWh per annum. These high potentials are attributable to the strong wind variations observed within the band between 30o and 60o latitudes, and to the occurrence of circumpolar storms near the southern latitudes, which account for high-energy ocean waves in those areas.
o The global theoretical potential of ocean thermal gradients is estimated to be 10,000 TWh per annum. Significant temperature gradients in tropical coastal areas indicate good opportunities for OTEC within the Tropic of Capricorn and the Tropic of Cancer.
o The potential of salinity gradients is estimated at 2,000 TWh per annum.[4]
If we consider that in 2008 the total world power generation was 20,181 TWh [6] then the sum total theoretical energy available in the world’s ocean well exceeds that of today’s total generation.
In reality today we only extract a very small fraction of the potential energy the worlds Ocean, this shows that Ocean Renewable Energy is really in its infancy compared to other types of Renewable Energy, Fig 2.1 shows the current Ocean related research and activities further demonstrating the early stages of this energy type.
Fig.2.1 Technology maturity of various ocean energy conversion systems. [4]
Types of Ocean Energy Systems
There are a large number of different technologies and concepts currently within the area of Renewable Ocean energy and not all are at the same level of development. Quite a number are still only concepts and do not yet have proven scale systems but fortunately there are a number of countries that are leading the implementation and further research of Ocean Energy projects, See Fig 2.2 below detailing the quantity of projects from the leading countries.
Fig.2.2 Ocean energy-related research, demonstration and commercial activities,
as of December 2007. [4]
Fortunately for the advancement of this energy type, several countries are already setting a good example by encouraging the development of ocean energy. A number of governments have implemented national policies for ocean energy and have adopted longer-term targets for deployment of ocean power. [4]
The United Kingdom, for example, has adopted an energy policy designed to attract and support technology developers, including a program for wave and marine-current energy development. At the end of 2007, the UK had by far the largest number of companies operating in this sector. In Ireland, a government strategy has been designed to accelerate development of wave energy through financial support for Irish technology developers. Three Irish companies have developed technologies that have advanced to the sea-tests phase. Portugal’s strategy has created attractive conditions that facilitate the development of a wave energy industry. [4]
We are now going to spend some time reviewing some of the existing concepts and projects available in the field of renewable energy today.
Tide Systems
As detailed earlier in this chapter there are two particular categories of tidal energy systems;
Tides - The potential energy linked to the force of tides can be harnessed by building systems involving fixed or floating barrages either at an estuary or offshore. The Earth's tides are ultimately due to gravitational interaction with the Moon and Sun and the Earth's rotation, tidal power is practically inexhaustible. The magnitude of the tide at any given location is the result of the changing positions of the Moon and Sun relative to the Earth. Tidal energy can also vary significantly by locations due to the unique geographic formations in all coastal regions therefore a tidal project would need to be targeted for a strong tidal region. For example where barrages (dam-like structure used to capture the energy from masses of water moving in and out) are used, as the level of water rises and falls with the tides, a difference in water level develops on either side of the barrage and water is allowed to flow with the force of gravity through the barrage, thus turning turbines to produce power. [4][5]
Tidal Currents (Marine Currents) – Different to the potential energy within the tides section above as this is the kinetic energy present in tidal (marine) currents can be turned into electricity by using modular turbine systems, which can be placed directly in-stream to generate power from the flow of water. The turbines can be either horizontal-axis or vertical-axis turbines. These systems can be submerged or floating or fixed to the seabed. [4]
We can now examine some of the primary types of Tidal energy systems or Tidal Energy Convertor (TEC) systems;
Tidal Stream Generators
A) Horizontal axis turbine
This device extracts energy from moving water in much the same way as wind turbines extract energy from moving air. Devices can be housed within ducts to create secondary flow effects by concentrating the flow and producing a pressure difference. Fig. 2.3.[7]
Fig.2.3 Impression Horizontal Axis Tidal Turbine Farm. [8]
B) Cross-axis turbine
Horizontal - This device is essentially a vertical cross axis turbine orientated horizontally. This turbine configuration allows for deployment in shallow water.
Vertical - This device extracts energy from moving in a similar fashion to that above, however the turbine is mounted on a vertical axis.[7]
In Fig 2.4 we can see the configuration of the horizontal type tidal power system as described by a company called TidGen.
Fig.2.4 ORPC’s TidGen™ Shallow Cross Axis Tidal Power System. [9]
C) Oscillating Hydrofoil
A hydrofoil attached to an oscillating arm and the motion is caused by the tidal current flowing either side of a wing, which results in lift. This motion can then drive fluid in a hydraulic system to be converted into electricity. [7]
Fig.2.5 Pulse Tidal’s Pulse-Stream100 Concept Oscillating Hydrofoil Power System. [10]
D) Enclosed Tips (Venturi)
By housing the device in a duct, this has the effect of concentrating the flow past the turbine. The funnel-like collecting device sits submerged in the tidal current. The flow of water can drive a turbine directly or the induced pressure differential in the system can drive an air-turbine. [7]
When the water level outside of the basin or lagoon changes relative to the water level inside the turbines are able to produce power as shown in Fig 2.7/2.8 below as well as the artists impression of the Severn barrage in Figure 2.9.
Fig.2.6 Lunar Energy’s Rotech Tidal Turbine (RTT) Concept Venturi Turbine Power System. [12]
Tidal barrage
This method of extracting tidal energy involves building a barrage across an estuary bay or river. As water flows into and out of the estuary/bay it carries an enormous amount of kinetic energy. The job of the barrage is to extract as much of that energy as possible.
A tidal barrage is really just a long, fairly low dam wall. It has tunnels cut into it to let water flow through it in a controllable way. In the tunnels are huge turbine-generators that spin as the water rushes through them to make electricity. [16]
Fig.2.7 Tidal Energy Ltd. concept Electricity Generating During Outflow. [14]
Fig.2.8 Tidal Energy Ltd. concept Electricity Generating During Inflow. [14]
*********ASSIGNMENT EMAILED 19/12/2011 DUE TO SPACE ISSUES WITH THE WIKI PAGES***********
Dynamic tidal power
The very new and theoretical dynamic tidal power invented and patented (WO 9801670 (A1) )[20] by H2iD of the Netherlands proposes to build a dam is a long dam of 30 to 60 km which is built perpendicular to the coast, running straight out into the ocean, without enclosing an area. The horizontal acceleration of the tides is blocked by the dam. In many coastal areas the main tidal movement runs parallel to the coast: the entire mass of the ocean water accelerates in one direction, and later in the day back the other way. A DTP dam is long enough to exert an influence on the horizontal tidal movement, which generates a water level differential (head) over both sides of the dam. The head can be converted into power using a long series of conventional low-head turbines installed in the dam. [17][18]
Fig 2.10 below shows an artists impression [19] of a top-down view of a DTP dam. Blue and dark red colors indicate low and high tides.
Fig.2.9 Artist impression of the proposed Severn Barrage. [15]
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