Tidal Energy Learns from Wind, Oil

Published Oct 15, 2014 12:10 PM by The Maritime Executive

Jason Deign of Tidal Today spoke to Jim Marnoch, ocean energy manager at SKF, in the lead-up to The International Tidal Energy Summit (24-26 November 2014, Victoria Park Plaza Hotel, London, UK).

In the context of the huge forces at sea, the severe tides and the ‘tidal window,’ what is critical when developing marine technology?

We’re designing fit-for-purpose main-shaft, bearing and sealing arrangements that can withstand high axial forces from the tides. As most people know, it’s not just a simple case of putting a wind turbine on the seabed and hoping for the best. There are significant differences.

We’re taking our knowledge and experience from synergistic industries, particularly wind but also marine oil and gas, or hydro, and customizing what we already have. That’s quite important. We’re designing robust sealing and bearing arrangements for pitch mechanisms. I guess it goes without saying that sealing is absolutely key. In simple terms, we need to keep the lubricant in and the water out.

Obviously if the water gets into the nacelle, it’s basically the end for most of the components, so that’s quite key. Avoiding contamination of the environment is also important. Developers, during the prototype testing phase, will be constantly reviewing measurement data and retrieving the machines say every two years for inspection, but ultimately will want to have the machines performing in some cases up to six and a half years between retrievals, with 20 to 25-year component life.

So we are using our experience from synergistic industries. We are not starting with a blank sheet of paper. We are using what we have already. But you’ve got to recognise that there are differences. The obvious one, of course, compared with a wind turbine for example, is the density of the water, which is 840 times that of air. This is a significant factor.

Survivability, reliability and increased performance are central to the sustainable development of tidal power. What are you going to do to make a difference in these areas and how will it affect the cost of energy?

For me, survivability is more about structural integrity in the harshest of environments. It’s fair to say we are more focused on reliability and performance side of things. Reliability is key. Obviously you want to avoid unplanned interventions and retrievals, or costs. Unplanned means, as in any industry, high cost because you are having to deploy labour and equipment and spare parts and vessels at very short notice. That needs to be avoided at all costs.

From a reliability perspective you want to avoid component failures. Component failures in themselves can be expensive. But, as you find in other industries like oil and gas, component failures can also lead to secondary damage to periphery components.

Because you have got these machines mostly located on the seabed they are not as accessible as a wind turbine, so predictive maintenance and condition monitoring systems can provide useful early warnings of developing faults. To have a useful warning time to plan and react is key.

I always refer to the well-documented reliability-centred maintenance studies conducted back in the ‘60s, where Boeing showed that 89 percent of failures are random in nature, so they are not time-dependent. What that means is when people do planned maintenance it may not be that effective and in fact may cause more problems than it actually solves. So condition monitoring is really quite key for the tidal industry, I feel. The condition monitoring system is installed within the nacelle and has to be reliable itself and function correctly between retrievals, otherwise operators start to run blind.

Realistically, what timeframe do you work to in order to get through the research, development and testing phases and reach the point where your technology can start making an active contribution to the tidal industry?

Based on our experience, from first engagement with our target customers, I’d say 18 months to two years between initial contact with the OEM or technology developer to actually delivering our solutions. Over this time we build the relationship with their design team, gaining their trust and commitment to work with us on a longterm basis. Sometimes there are certain hurdles to overcome in terms of contracts, terms and conditions, warranties and so on, but on the whole these can be resolved.

You find the larger OEMs have well-defined processes for supply chain and procurement that can slow things up a little and there is an expectation that suppliers take on a lot more risk than they normally would, this being reflective of the fact it’s an emerging industry. Indeed, the OEMs themselves are having to take on more risk with their customers, the power companies, so I guess they are keen to share this risk and pass some of it down the supply chain. That’s 18 months to two years from convincing them we should be the ones to work with when it comes to, for example, main shaft bearing design and the periphery components, to delivering the first prototype solutions and them actually arriving on their doorstep. This timescale should be come shorter as experience and knowledge is gained.

Taking a global perspective, we believe the industry is around two years behind where it said it would be at this stage. That said, progress is being made, albeit at a slower pace. I believe that this is reflected in some of the comments from people like Peter Fraenkel [founder of Marine Current Turbines]. If suppliers coming into the tidal sector expect to make good profit from day one, then this is probably an unrealistic expectation.

There needs to be an appreciation that it is an emerging sector and you need to invest now with little return to have a chance of reaping the benefits in years to come. You have to be patient as progress has been slow though some of the major developers are building their full-scale prototypes and will assemble these next year, which is encouraging. For small-scale arrays, I’d probably say, realistically, 2017 onwards. Large-scale, we’re looking at 2022 onwards.

What will you take responsibility for in terms of bringing technology to market and reducing the cost and risk associated with innovation and subsystem development?

When SKF first started to get involved in the sector, a question often asked was “do you want to become an investor in our company?” But this is not really what we’re about. We’ll not take equity stakes individual companies; this would be a conflict of interest and we want to remain impartial. We want to work with all companies that have promising concepts, are a good match for our technologies, and who are likely to reach full commercialisation. Our investment is about time and effort providing engineering support to customers, really helping them optimize the design of their machines.

We have several solutions from other sectors we believe are relevant, that we can build upon, though most if not all require a level of customisation. We might have over 4,500 condition monitoring systems fitted to wind turbines but we have little experience on tidal turbines. We want to work with and learn in tandem with developers.

We will take responsibility for solutions associated with drive train, bearings, seals, lubrication systems, mechatronics, services and condition monitoring, and we have the capability to combine these into a holistic, black box-type solution.

Delivering reliable and cost-effective technologies will be paramount to the ultimate commercial success of the tidal industry. What is the single biggest challenge in doing so, and how do you plan to tackle it?

One problem I’ve seen, not our area at all, but I’ve heard it from developers, is wet-mate connectors. These have been developed to meet the requirements of the offshore oil and gas industry and have a price tag to match. The tidal sector has a need for such a solution but they are not really affordable. There might be a really good solution out there but the solution that has been developed by industry is unaffordable in this emerging sector.

Another example is mechanical seals. Encompassing silicon-carbide faces, and proven over many years in marine sector applications, these are considered expensive. So we need to think, do we really need to use silicon carbide or can we use a cheaper, fit-for-purpose alternative? Not the Rolls-Royce solution, but something that will actually do the job.

We’re talking to many customers and a lot of them are doing similar things in their own way. You could say there is a lot of duplication of effort in many respects. There are different approaches but I guess because we are talking to several companies, we have a more rounded view and can form opinions on the best approaches.

I see there are a lot of government-sponsored bodies involved in technology development in the UK but we have little engagement with them currently and we probably should. I guess it also works two ways; they should try to engage more with us. This is an area for us to explore going forward.

More information: International Tidal Energy Summit