Swansea University

An Introduction to Marine Renewable Energy

Summary

There are 2 main forms of marine renewable energy; wave power and tidal power. Energy contained in a wave depends upon its size, with a high density of wave energy on the Welsh coast. Energy from the tide is obtained in 2 forms, exploiting changes in the sea level (tidal range) and utilising the flow of the water (tidal stream). This project has focuses on tidal stream energy.

Tidal stream power generation requires a flow rate of ≥ 2 m/s in order to drive a turbine and achieve power generation. These sites are generally found around land, or in straits. Studies examining flow rates located around Wales have shown several suitable locations for tidal stream energy

The UK has an estimated 18 TWh per year of tidal energy resource, 5% of the UK electricity demand, helping towards renewable energy targets of 20% by 2020. The UK tidal resource is approximately half the total extractable power for the whole of Europe. Initial installations at the most attractive sites are targeted at 1-2.5GW in Europe, at a price of 9-18p/KWh, falling to 5-7p/KWh as technologies mature.

Many tidal stream turbine designs (including Swanturbines, Marine Current turbines) are in development, with research, testing and commercialisation boosted by the creation of the European Marine Energy Centre (EMEC) in Orkney. Further support under the Renewables Obligation (RO) could lead to tidal stream devices qualifying for a premium of around 10p/KWh produced.

What is Marine Renewable Energy?

Marine renewable energy consists of two main types; wave power and tidal power.

Wave power

Energy in a wave varies in phase with each wave. The amount of energy available from a wave depends on its size, predictable around 120 hours in advance. A high density of wave energy exists on the Welsh Atlantic coast due to the large waves created by the long fetch of the Atlantic coming to shore in this location.

Tidal stream power

Tidal stream power is available whenever a tidal current is flowing in the sea. The tide cycle lasts approximately six and a half hours and normally power can be generated on both the ebb and flood. A high power density occurs where water is restricted by land, such as near headlands or through channels.

Examples of Wave Power Generators

Pelamis

Long, tube shaped device (200m long)
Articulated joints
Wave travels along device, moves joints, drives hydraulic system
Power converted to electrical energy

Wave Dragon

Reservoir floating just above sea level
Waves focussed by ‘arms’ up ramp into central reservoir
Turbine at base of reservoir
Water returns to sea through turbine, generating power.

Tidal Power and the Tidal Stream Resource

Tidal power includes both tidal range and tidal stream energy.
Tidal stream energy requires peak flow rates of 2m/s.
Tidal power can contribute to UK base power load.
The tidal resource can provide around 5% UK electricity demands.
UK has half the total extractable tidal power of Europe

Tidal power is the production of electricity from the natural power contained in tidal flows. This energy is renewable, predictable and produces no emissions, making it a very attractive source of power. There are two main methods of harnessing the power from tides, by exploiting the change in sea level such as tidal barrage systems, and by harnessing the flow of water; such as tidal stream systems. Both of these methods pass water through devices that convert the energy in the water to electrical energy. The rest of the information here will focus on tidal stream energy.

As previously mentioned, there are points, generally near land, where geographical restrictions increase the speed of the water flow, and concentrating flow energy density. Locations of interest for tidal stream energy are the points where the peak flow rate exceeds 2m/s. Because the tide does not flow at the same time everywhere and these sites are located around Britain, the net result of the electrical energy obtained could contribute to base load power in the UK. A study examining flow rates showed Wales has several sites identified as being suitable for capturing tidal stream power.

It has been estimated that the UK alone has around 18TWh per year of tidal power resource; approximately five percent of the nation’s electricity demand, greatly helping towards the government target of achieving 20% renewable energy by 2020. Investment in the region of three billion pounds is required over the next fifteen years to fully exploit this resource. The UK has an excellent density of extractable tidal power with approximately half the total extractable power for the whole of Europe. A significant proportion of this power is around the Welsh coastline.

Government Policy on Tidal Power in the UK

New legislation for marine management of energy extraction.
Anticipated production at 5-7p/KWh as technology matures.
Many devices in early stages of development.
Potential support of 10p/KWh produced using tidal stream energy.

Current UK policy in marine renewables focuses on the challenges of climate change and security of supply, specifically the 2007 Energy White Paper and the proposed Climate Change Bill. These focus on reduction of CO2 emissions whilst ensuring a security of supply. Other legislation currently in draft/planning includes The Marine Bill and within Wales, the Marine Renewable energy strategy , both aiming to improve marine management for optimal energy extraction

An economic analysis anticipates that electricity from tidal stream turbines can initially be produced at 9-18p/KWh (estimated 12-15p/KWh), falling to an anticipated 5-7p/KWh (dependant on production capacity) as technology matures. Initially, installations totalling 1-2.5GW should be targeted throughout Europe, with a majority of this located within the UK [10]. These are the most economically attractive sites and are less than the total resource.

There is currently a large amount of activity in the UK tidal stream development sector, with a wide range of designs in the early stages of development. Support under the Renewables Obligation (RO) as proposed in the forthcoming energy bill could lead to tidal stream devices qualifying for a premium of around 10p/kWh produced to help offset some of the higher start up costs. Creation of the European Marine Energy Centre (EMEC) in Orkney which provides wave and tidal test locations offering monitoring, evaluation and grid connection in order to test prototype devices will aid research and development of tidal stream devices.

Examples of tidal technology

Swanturbines [7]

Axial flow turbine.
Direct Drive – blade and generator on same shaft.
Secured to seabed by gravity base.
Fully submerged.

Marine Current Turbines [8

Axial flow turbine with gearbox.
Mounted on steel pile in seabed.
Turbine moves up and down for maintenance.
First prototype installed off North Devon coast.

SMD Hydrovision [9]

Floating twin rotor design.
Lower support structure cost = cheaper device.
Flexibility of support may increase mechanical issues.

Training Developed as part of WEST

As part of the Welsh Energy Sector Training Programme, three courses giving an introduction to marine renewable energy with a focus on tidal stream energy have been developed. Brief details are outlined below;