As the global community continuously searches for alternate and sustainable energy solutions to power our needs. Orbital Marine Power – a privately owned company working out of Edinburgh and the Orkneys in the UK – believes they have an answer.

Orbital Marine Power has pioneered the design of an offshore floating structure anchored to the sea floor to harness the predictable and energy rich tidal movements near the isles of Orkney, off the North Coast of Scotland. Their newest design the ‘02’ launched in 2021 claims to be the first commercially operated floating tidal turbine and ‘the most powerful and technologically advanced tidal turbine in the world,’ at 74 metres long and with a claimed (max) shaft output of 2.6MW in water speeds of 3m/s, is capable of powering 2,600 homes in Orkney.

Key points

  • New floating platforms offer lower installation and maintenance costs, and a significantly lower environmental impact than traditional tidal barriers

  • As the technology and operations mature, kwh costs will reduce further (and ensure financial viability)

  • Arrays of tidal turbines will be critical to scale the technology investment and achieve meaningful generation capacity and revenues

How does it work?

Tidal swells and their timings can be easily predicted well into the future and have been by humans for millennia. The moon’s gravity coinciding with that of the sun’s, work together to create the tidal movements that occur across the world 4 times each lunar day. Tidal power is not new, in fact the first remains of a tidal mill dating back to 787 were discovered in Strangford Lough N. Ireland, which was the test site for a recent installation. The world’s first major tidal barrage went into operation on the Rance Estuary in France in 1966, with a capacity of 240 MW. However this was a complex and expensive project, it took 6 years to build, and created a major impact on the local environment.

Orbital Marine Power harnesses this energy in a very similar way to that of a wind turbine with two 20m rotors, connected to generators, which spin during a tidal swell. Driven by water, being 832 times more dense than air, means blades can be smaller and arrays much closer together.  The rotors are fully adjustable, and the pitch can be independently altered to get the most efficiency from the kinetic movement through the water, and therefore the most electrical energy.

But this is a new generation of tidal generator. Being a floating platform, it also has the advantage of easier and cheaper installation and maintenance, as the platform is towed back to a dry dock for maintenance. Unlike the traditional tidal barrages, these smaller floating or semi-fixed structures are a fraction of the cost to build and install and have a far lower environmental impact – avoiding the need for expensive fixed structures which have a heavy impact on marine life and the environment. They can also be towed into placed and installed relatively easily into new locations.

How this could affect the current power grid?

The UK, like many countries, is trying to increase the diversification of its power grids, aiming to stray away from reliance on coal and gas. In addition to large offshore wind capacity, the UK also has several locations where strong tidal currents (>3m/s) occur in relatively shallow water. Introducing tidal energy to the grid is meant to be a complimentary alternate source of clean energy that the grid can use alongside the existing methods, and can also be used to generate clean hydrogen. It is evident that the potential for tidal energy could never feasibly provide the majority sources of energy, however it will undoubtedly help to reduce our reliance on existing methods that are more polluting and less secure. A study into the available energy of tidal power in waters surrounding the UK estimated that 11% of the UK’s grid demand could be met by tidal energy if each area had filled its tidal potential. Estimates for the US are even higher. Orbital have identified two further UK locations where floating tidal generators, with little environmental or shipping impact, could be installed.

With energy security and cost at the top of the agenda, the continued pursuit of tidal energy in UK waters cannot be ignored especially with the environmental benefits and the predictability of output.  

The growing tide of investment

Investment in tidal energy has grown in the last decade but is still a fraction of the investment into other technologies . According to the Ocean Energy Europe report, overall investment into ocean energy sectors increased 50% in 2021 over 2020 in Europe,  a total of $75.5m. This investment is sure to grow as patterns in energy related investments shift, with governments already displaying interest in this sector, drawing more private and public investors to join the trend. Yet, the capacity so far of these new generators  is a small fraction of the capacity from fixed tidal barrages and even smaller still compared to total wind power (see table 1). The outstanding question is can these relatively small single generators be scaled to multiple arrays, in the same way wind turbines were 15 years ago?

Tidal over wind?

Currently the most invested in and used renewable energy source is wind farms typically found offshore. They contributed 24% of the total electricity generated in the UK in 2020. However, there are reasons to be optimistic; one major advantage of tidal power lies in the continuity of tidal movements, along with their predictability. We are guaranteed 4 cycles per lunar day and each can be predicted with high accuracy whereas wind varies heavily on seasonal changes and the weather. With current technologies in energy storage lacking in funding and investment the advantages of wind power dwindle somewhat as the extra energy supplied to the grid is random and if not used, it is often wasted. The predictability of tidal energy allows it to be ‘scheduled’ (with tidal timing predictions) into the grid’s energy supply.

However, it Is still worth noting that all things considered, tidal energy is some way from  competing with wind energy and solar farms on a cost per kwh. This is due to the ever-evolving technology and that it is still many decades behind that of large scale offshore and land-based wind farms (as well as solar) which over many years have become a proven renewable resource. As tidal energy is still relatively unproven the cost of investment casts a shadow on potential investors compared to its wind counterpart. In fact, government grants have been a major contributor to the funding and development of Orbital Marine similar to other projects around the world.

Environmental Considerations

Unlike wind turbines, blades beneath the water’s surface do not strike birds or bats, look unsightly or effect local radar systems. Previous environment studies by a sperate company, Sea Gate which operated an earlier fixed turbine in Strangford Narrows N. Ireland, found that that sea mammals tend to stay clear of the turbines due in part to the low-level noise it produces. Orbital site evidence from around 10,000 hours of wildlife observations at EMEC’s (European Marine Energy Centre) sites has indicated no significant long-term changes in the distribution of birds or marine mammals due to the presence and operation of wave and tidal devices. This continues to be monitored as more arrays are installed, and there have been several independent studies published also stating no evidence of impact to local mammals. This of course does not yet mean there is no impact, but the results are promising.

This should be compared with the first generation of large, fixed barrages such as Rance in France which can have a major impact on local marine life and the local environment. The Severn barrage project in the UK has been abandoned due to projections of the high cost (£34b) and environmental impact, despite a relatively large potential contribution to overall UK power needs. Even though, in the new environment, latest news is that this project is being considered again.

An assessment of the total lifecycle emissions of the Orbital Marine platform concluded that while the project can run for 20 years, it can offset from the UK grid mix the carbon emitted by the project within just 1 year and 4 months of operation or 11 months if it is assumed that the electricity being generated is offsetting gas power generation, which is often the case in the UK. The advantage of this kind of carbon footprint also means this type of investment could benefit from carbon offsets.

The future of Orbital Marine Power

Orbital Marine Power started in 2002 and have undertaken many years of testing and development of their tidal systems. They have just raised £4m via a fixed 6% debenture via the Abundance platform (in addition to £7m raised in 2019) for their updated version of the 02 which aims to be even more efficient than the first whilst also reducing the total cost of each unit. The company was recently granted two ‘contracts for difference’ (CfD’s) in the UK allocation round 4 process (AR4). They have also received investment from TechnipFMC ‘a leading technology provider to the traditional and new energy industries with a proven track record of successfully delivering large-scale, fully integrated offshore energy projects to customers around the world.’ With this investment and funding Orbital aims to have four turbines in operation by 2026/27, powering upwards of 7,200 homes and feeding energy into the grid. Estimates based on the improved O2 is that this single unit will generate revenues of £2m per annum, before inflation. Costs, including not just maintenance but berthing and insurance are estimated at £920,000 per year. On an operating cost basis, and using their own figures on maximum output, we estimate the current cost per generated kwh is between the £0.15-0.20 range (excluding R&D capital investment and installation costs). To achieve the same cost level of offshore wind requires a 5-10x reduction. There is some way to go to improve the technology and reduce operating costs, but achievable if compared to the improvements in wind technology over the years.

In conclusion, for tidal energy be more than a drop in the ocean…

The new platforms are the result of many years R&D and investment, including government backed funding, and are improving with time as the technology matures. On their own, these individual projects will generate a return to investors if the technology is proven and can scale to multiple arrays. These large arrays will also be critical if tidal is to make a meaningful contribution to the UK’s or other country energy needs. The advantage is the energy is more predictable, more dependable and better for the environment than many alternatives. The question is who will step forward to make the significant investment and drive scale?

The same question was asked of offshore wind power 15 years ago, with the right investors the UK might well become a leader in tidal power as wind. With the right government backing at a time where we need more reliable renewable energy sources it could shorten the timescale to achieve that.

Author: Will de Vise-Craig 

References and Links