TIP0009

This response to the Parlimentary call for evidence has been prepared by Dr. Stuart Walker, drawing in part on the response submitted to the BEIS call for evidence on marine renewable energy earlier in 2020. This response is submitted by Dr. Walker, and includes contributions from the Marine Renewable Energy group, based at the University of Exeter Penryn campus. The group is a major source of expertise in tidal stream energy and is the largest academic partner in the Interreg TIGER (Tidal Stream Industry Energiser) project, which itself is the largest Interreg project ever funded. The project is a collaboration between UK and French academic partners, industry, and the Offshore Renewable Energy Catapult. Due to the collaborative nature of the field and of this project, this response inevitably incorporates contributions from partners across this project. Contributors include the University of Exeter, University of Plymouth, University of La Havre, University of Caen, Orbital Marine Power, SIMEC Atlantis, QED Naval, and the Marine Energy Council.

I am aware, as I am sure are you, that many of the institutions named above have specific expertise in certain areas of this consultation and have responded directly. Rather than repeating their contributions here, I have provided short answers and highlighted the body or bodies with a high level of specific knowledge.

The most significant area of knowledge which may not be covered by others relates to environmental impact, particularly in the life cycle emissions of tidal stream turbines. I have responded at length to the relevant question, and would be happy to answer any further questions on this or any other aspect of our response.

With best regards,

Dr. Stuart Walker
Research Fellow
University of Exeter

Question 1: What contribution can forms of tidal power play towards the UK’s energy mix? 

As you know, the UK has a significant tidal resource. This resource is estimated at over 30GW and is a significant proportion (greater than 50%) of the total European resource. As with all sources of energy, not all resource is extractable straight away, but current estimates of the extractable resource from key sites in the UK suggest that this technology can deliver around 11% of the UK’s electricity needs.

Tidal energy is predictable. This predictability has a value in the comparison of energy sources which is not acknowledged by current comparison (e.g. direct LCoE comparison). I believe it is important to realise just how great a resource this is to the UK. The response submitted by Dr. Daniel Coles (University of Plymouth) goes into some detail regarding resource assessments, and highlights the importance of this non-intermittency. The response from the Offshore Renewable Energy Catapult highlights the ability of tidal energy, uniquely among renewables, to supply baseload. These factors allow the technology to offer unique benefits which have not been realised while this technology has had to compete directly with mature technologies like offshore wind.

Question 2: Why, despite the considerable marine resources available, have relatively few developers established tidal projects? 

As you will know, there are tidal arrays installed in the Sound of Islay (MeyGen), Bluemull Sound (Nova Innovation) and a thriving test centre at EMEC. A large number of developers have passed through this test centre and have demonstrated the technical proficiency of their devices. However, a large number are subject to the “valley of death” due to the lack of a suitable support mechanism. A few key points:

• O&M is key in tidal stream energy. Devices are difficult to maintain so are robustly designed with built-in redundancy. This allows devices to operate with relatively low operational expenditure, but requires relatively high capital expenditure. This increases investor risk, and in combination with the challenges of competing with technology with 15 years more development time, tidal stream is seen as a risky option.
• I recently undertook a study of all tidal stream deployments around the world to date. The total 57 deployments revealed a number of interesting features. Of pertinence to this question is that of reliability growth. We compared the failure rate of tidal stream turbines at the current total cumulative deployment duration (1.4 million hours as of August 2020) to that of the wind energy sector at the same cumulative deployment duration. This duration was reached in wind energy in around 1994. This analysis suggests that Tidal stream energy and wind energy both experienced around 0.065 major failures per turbine per year after cumulative deployment duration of 1.4 million hours, i.e. the perceived higher failure rate in tidal stream energy does not actually exist.
• The key limitation, as eluded to in above, is that tidal stream energy has been placed in the same “pot” as highly established technologies, and therefore cannot offer the same LCoE due to its much lower cumulative deployment duration. The recent changes to the CfD scheme are positive for tidal stream energy.

Question 3: Are there certain locations where one type of tidal technology is best suited?

Yes. There are technical reasons why certain device types are more suitable in certain locations. These are discussed in the Offshore Renewable Energy Catapult centre’s response to this consultation.

I would like to also highlight some logistical and operational factors which influence the most suitable locations for certain device types. In general, tidal stream turbines can be classified by four main attributes, as illustrated below.

Figure 1 – Four key identifiers of tidal stream energy device types: Ducting, Extractor, Mounting, Foundation.

Ducting (see Figure 2) increases cost relative to non-ducted devices, and also has a small increase on likelihood of failure. Ducting increases flow speed at the energy capture region, so can be used to enhance the effectiveness of a lower flow site. However, in general, ducted devices have historically been associated with more failures than non-ducted devices.

Figure 2 – Percentage failure rates associated with ducted and non-ducted tidal stream energy devices.

Extractor type identifies the energy capture mechanism. Horizontal axis devices are the dominant type, and are responsible for 86% of the total deployment duration of tidal stream energy turbines. This type of device is therefore able to be deployed at lower cost due to increased experience and learning, as well as having a lower independent failure likelihood than vertical axis or kite-type devices. However, whilst horizontal axis devices are the best choice in many situations, kite type devices such as the Minesto device are able to capitalise more successfully on relatively low speed flows due to their design. In areas with mean flow velocities below 2m/s, these devices may be a preferable choice to a horizontal axis device.

Mounting type and foundation type (see Figure 3) are two of the most important factors which influence turbine LCoE, Capex and Opex. We found that turbines installed on the seabed were more likely to fail, whereas floating devices were more likely to be curtailed (i.e. stopped and either returned to shore or maintained in situ) during tests. This suggests that a likely future scenario is that as learning reduces the chance of failure of fixed bottom devices, these devices will be installed in high-flow offshore locations and will be designed for minimum maintenance over their 20 or 25 year lifetime. These devices will be marginally more expensive at Capex but will require minimal intervention over their lifetime. Floating devices allow the most energetic region of the flow to be exploited and can be used in lower mean flow rate sites. These devices can be lower Capex cost and may offer a better solution for slightly lower flow speed sites nearer shore.

 Figure 3 – Percentage failure rates associated with tidal stream energy device foundation types.

Question 4: How could financial support be structured to assist technological and project development in this area? 

Further to the comments on the recent changes the to CfD, I have no further comments to add in this section. Again, the Offshore Renewable Energy Catapult and Marine Energy Council responses both offer detailed responses from experts.

Question 5: How might tidal schemes reduce costs to become commercially competitive with other low carbon or renewable options? 

As discussed, tidal stream energy is already competitive with wind energy when normalised for cumulative duration, so may in fact ultimately become a lower cost technology. The TIGER project has targeted a number of areas for cost reduction, with a key focus on improving LCoE. A number of specific areas in which cost will be reduced in time are as follows:

• Increased rotor swept area and turbine yield will increase generation per turbine and therefore improve LCoE
• Lightweighting of turbine components such as blades and support structure will reduce costs for transport, manufacture and installation.
• Improvements in the environmental credentials of materials (particularly blades) through innovation such as recyclable thermoplastic composites will reduce end of life costs and improve environmental impact.
• Manufacturing at volume will reduce costs, but requires support for developers to cross the commercialisation valley of death before these can be realised.
• Standardisation is possible in many areas of the sector, though as highlighted above, some diversity is necessary and positive. Standardisation is already beginning through projects like TIGER, for example in the development of subsea hubs, which themselves represent a significant cost reduction, cabling, and connectors.

Offshore Renewable Energy Catapult forecasts cost reductions to permit LCoE of £150 per MWh after 100MW installed, £130 after 200MW and £90 after 1GW.

Question 6: What are the environmental impacts of tidal schemes and how can these be minimised? 

Environmental impacts of tidal stream turbines have been demonstrated over and over to be minimal. This perceived risk was introduced early in the sector development but is not supported by the extensive monitoring and research which has been undertaken. This will be covered in detail by other responses, such as the Offshore Renewables Joint Industry Programme (ORJIP) Ocean Energy. Turbine rotational speeds are of the order of 15 revolutions per minute, which has been shown to present very low risk to fish and cetaceans.

Environmental impacts aside from “in-water” impacts are more pressing, and are an area on which we are currently working. The assessment of renewable energy technologies over their full life cycle has not historically been carried out, and in some cases carrying out such an analysis reveals that the impacts of the manufacture, installation, operatation and disposal of (for example) a small domestic wind turbine exceed the offset energy generated over a device lifetime.

Expected impacts of developing, installing and decommissioning a tidal stream project are relatively well understood through extensive monitoring of previous deployments. Short term impacts carry the greatest risk, for example piling of foundations or drilling channels for cable installations. Devices in operation appear to be benign and slow rotation speeds do not appear to present a risk to sealife. Work is ongoing at Exeter on the impact of seabird displacement due to installations in relation to floating offshore wind. This work is being undertaken at the FabTest site in Falmouth bay.

There are environmental risks during installation, maintenance and decommissioning, though these are no greater than those associated with existing marine operations such as shipping, O&G or offshore wind.

Analysis by Offshore Renewable Energy Catapult (Tidal Stream and Wave energy cost reduction and industrial benefit, Offshore Renewable Energy Catapult, May 2018) suggests that marine energy technologies have the potential to reduce CO2 emissions by at least 1MtCO2/yr by 2030 and 4MtCO2/yr 2040 by replacing fossil fuel technology.

Tidal stream energy has the particular advantage of predictability, and in addition to significant CO2 emission reduction by replacing fossil fuels, tidal stream energy also has a low environmental impact in terms of embodied carbon dioxide. We feel full assessment of the environmental impact of all renewable energy technologies is important to allow mitigation of any otherwise unforeseen environmental impacts, and would suggest the use of alternative terminology.

It is tempting to consider CO2 as the only important environmental impact in the development of renewable energy, since a key goal is the reduction of CO2 emissions from energy generation, but there are many more impacts. These impacts must be considered in order to understand the relative merits of the technology. By comparing these impacts to benchmarks to identify any of particular concern, these can then be considered in the context of environmental risk associated with a given project, and the most appropriate technology for a given location can be understood.

A key factor is the comparability of assessments, and we would suggest the widespread adoption of the EU Product Environmental Footprint (European Commission Joint Research Centre Product Environmental Footprint (PEF) Guide, 2012, Ref. Ares(2012)873782) method. The 14 impact categories included in this method are given below.

Table 1 - PEF environmental impact categories (taken from European Commission Joint Research Centre Product Environmental Footprint (PEF) Guide, 2012, Ref. Ares(2012)873782)

It is generally assumed the life cycle CO2 emissions associated with the manufacture, installation, operation and decommissioning of a renewable energy device will be many times lower than the offset between the energy generated and the CO2 burden attached to the fossil-fuel energy which it replaces. Existing studies based on example devices did support this assumption, however the following must be considered:

•                               This assumption is only valid if fossil-fuel generation is truly offset. If reliability is sufficiently low to merit the construction (or continued operation) of fossil-fuel generation, then the impact of this should be attributed to the tidal stream device and must be included in life cycle calculations.

•                               It is not reasonable to assume that grid CO2 intensity and environmental impact per kWh remain constant over the 25 year lifetime of a tidal stream device. Changes in grid intensity must be included, which requires dynamic life cycle assessment to be undertaken taking into account forecast decarbonisation projections over the project life cycle.

Existing data on the environmental impact of tidal stream energy is positive, and suggests that despite its relatively early stage, embodied CO2 is lower than competing renewable energy technologies, and is expected to continue to fall.

Figure 3 - Relative carbon dioxide intensity of electricity produced by renewable and non-renewable sources (taken from Walker et al, Tidal energy machines: A comparative life cycle assessment study J Engineering for the Maritime Environment, 2015, Vol. 229(2) 124–140)

Full life cycle assessment includes much more than just carbon dioxide (CO2) or greenhouse gas (CO2e) emissions. A range of upstream and downstream impacts such as marine eutrophication, ozone production, hazardous waste, land use and water use, must all be measured to ensure a project is “net negative” in all its impacts, not just CO2. In this respect tidal stream energy performs well, with comparable impacts to established technologies such as onshore wind, and better performance in some critical categories than alternatives such as photovoltaic solar and nuclear energy.

As part of the TIGER project, a full life cycle assessment is currently being carried out. This is focussed on turbine blades, as these are the most impactful part of the turbine. In common with the wind energy industry, tidal stream turbines typically use glass fibre reinforced or carbon fibre reinforced polymers as their main blade material. These have a significant environmental impact due to manufacture, and also at the end of life, since they cannot be recycled and are currently either stored in landfill or
incinerated.

Figure 4 – Life cycle CO2 emissions of a single 8.85m tidal stream turbine blade, illustrating the major impact of epoxy resin and of incineration at end of life.

Tidal stream turbine developers are working with the TIGER project and with composite manufacturers to test and implement alternatives to this model. Recyclable thermoplastic resins are being tested as part of the project and offer comparable performance to traditional thermoset (non-recyclable) resins. 

Question 7: What are the wider economic benefits and what potential disadvantages could tidal schemes bring to regional areas? 

A key area of economic benefit to the sector is the development of an international industry. The UK has historically been the centre of development of this technology and currently is still leading the world. However, this position is at risk if not supported. There is a risk that as other economies develop tidal stream capability they look to develop a local sector rather than buying knowledge from the UK. If the UK does not continue to develop the sector and provide opportunities and others do, it is likely to the UK will see the departure of academic and industrial expertise.

UK companies have developed strong links with governments and institutions across the world, and particular interest has recently been shown in China, where SIMEC Atlantis installed a 500kW turbine in March 2020.

There are some public support barriers to overcome, but generally the support for tidal stream energy appears to be much greater than has been seen in the wind industry, and in many cases communities are fully supportive and engagement is high. This relies on good communication and fighting misinformation (e.g. making sure communities are aware that turbines rotate slowly and do not present a risk to marine life – many assume “underwater wind turbines”). In our opinion, costs incurred early in the development of the industry to engender this support will be offset by reduced costs as the industry grows, and good public engagement should be embedded in projects.

December 2020