Marine Energy - Tidal Power

Marine Current Turbine's 300kw machine Photo courtesy of Marine Current Turbine

The waters around the Argyll coastline offer abundant opportunities for the budding tidal stream renewable energy industry. Although the marine tidal turbine technologies tend to follow the same lines as wind turbines, due to the greater energy density (up to 4 times that of air) and hence power available in ocean currents, these devices can be much smaller than their Aeolian counterparts. Tidal power is more dependable than wind due to its predictable nature thus making it a better source of electrical energy for feeding the baseload of the national grid. The tides run almost 6 hours in one direction and then reverse and run for 6 hours in the opposite direction thus giving a power source that is available 24 hours a day unlike wind and solar. At the turn of the tide power levels would fall but since the tide does not turn at the same instant up and down the coast there would always be power production if a number of tidal generators at differing locations were hooked into the grid. 
Many of the companies involved in this sector claim that their machines are less intrusive than on-shore and off-shore wind turbines due to their smaller footprint and lower visual impact. Environmentally these devices are less intrusive and have minimal effect on marine creatures due to the relatively slow rotation speed of the turbine blades.
Above is a photograph of Marine Current Turbine's nacelle device being lowered into the sea off Lynmouth in Devon. This 11m blade turbine produces 300kw and was the first off-shore tidal marine turbine to produce electricity in Europe. In Phase 2 of their 'Sea Flow' project they are planning a larger demonstration device and will follow this up in Phase 3 with a small tidal stream farm similar to the picture below. (Shows a maintenance vessel inspecting a raised turbine unit.)
The Norwegian company, Hammerfest Strom, went one better and connected their 300kv tidal generator machine to the town of Hammerfest's grid thus becoming the first grid connected tidal turbine in the world. MCT's tidal generator uses a load dump and is therefore not grid connected. The Norwegian company believe that they will have their first tidal farm of over 20 second generation devices operational before the end of 2008. This would be the 3rd phase of their 'Blue Concept' project and would result in a tidal farm that would produce 10MW of renewable electricity.
Most of the tidal devices work well in a 4-5 knot current and anything less would be uneconomical in energy production terms. Argyll is blessed with a number of such sites and could see many of these devices being deployed in these waters in the years to come.

MCT Tidal Farm (Artist's Impression) Photo courtesy of Marine Current Turbine

Like off-shore wind, tidal turbine installation costs are expensive due to the need for firm foundations. Innovations such as Aberdeen's Robert Gordon University 'Sea Snail' device (see below) could prove cheaper to install due to its prefabricated nature. This 30 tonne platform device uses hydrofoils or 'sea wings' which harness the seas own power to produce a downward directional thrust to anchor the device to the ocean floor. A turbine is then mounted on this very stable platform. RGU has a 150 kw prototype device deployed in the Eynhallow Sound off of Orkney and should this prove successful hope to deploy a full scale 750 kw device at a cost of £400,000 in the near future. The project attracted £158,000 Scottish Enterprise Proof of Concept funding.
Another device which might overcome the deployment cost barrier is the Rotech Tidal Turbine (RTT). This is being developed by Yorkshire based Lunar Energy Ltd and relies on a concrete plinth for is anchoring platform and this, along with its lack of gearbox, yawing mechanism or blade pitch mechanism, is aimed at low manufcaturing and operation maintenance costs. They hope to have 1MW prototype in action before the end of 2005. 
Aberdeen is also the home of the Energy ITI (Intermediary Technology Institute) who will be investing some of their £15 million per annum budget in R & D in Renewable energy technologies. One of three ITIs set up by Scottish Enterprise and Highlands and Islands Enterprise, the other two being Life Sciences and Techmedia, it is tasked with developing Intellectual Property in the energy field and foresighting for the industry as a whole. Through this high quality market intelligence the Energy ITI identify technologies, particularly in emerging markets, that are likely to be crucial to the Energy industry in Scotland over the coming years.
Argyll and the Islands companies wishing to enjoy the benefits of this new approach should sign up for membership on the ITI Energy web site.
  

In his recent paper 'Tidal Stream Power from the Gulf of Corryvrecken' Sandy Small of Glasgow's College of Nautical Studies suggests that Argyll's famous whirlpool between the islands of Jura and Scarba could be harnessed using tidal devices to produce up to 2 GW of renewable electricity. These devices would have to be very robust to withstand the 6-8 knot spring tide produced by the effects of the whirlpool but, if possible, such an array would rival the output of a conventional power station. Corryvreckan also appears as one of the sites studied by the Energy Systems Research Unit (ESRU) based at Strathclyde University as part of their 'Marine Current Energy Baseload Supply Study' which looked at the potential of marine current energy to meet a proportion of Scotland's baseload electrical energy supply. Sites in Shetland, Orkney, Pentland Firth, Galloway and other West Coast sites are also included in this study. A link to this ESRU marine current study is in the right hand panel 

Another possibility is a road causeway incorporating a tidal fence (an array of tidal turbines) between the islands of Luing and Seil across the Cuan Sound which would replace the current ferry service and produce an on going revenue stream after paying for itself within 10 years. Argyll and Bute Council considered the feasibility study carried out by a major construction company which looked at this very proposition but felt that the overall cost was excessive (£7 million) and that they were already committed to spend the money received from the Scottish Executive on enhancing the ferry service.
Companies such as Blue Energy Canada and Ocean Energy Inc. are hoping to build such a device using the formers Davis Hydro Turbine technology. The project, called 'The Brothers Tidal Fence' will connect the shoreline near the City of Richmond, California to the nearby East Brothers Island in the Bay area. This 1000ft long causeway will produce between 70-100 MW of electricity. If a similar device was constructed at the 650ft Cuan Sound crossing then it could produce 45-65 MW, although it would cost far in excess of the smaller scale project envisioned by Argyll and Bute Council's consultants, more in the region of £50 million. In today's electricity market this kind of generation would add up to a revenue stream of approximately £4.5 million per annum (including ROCs*). With the possibility of attracting European Union, DTI and Scottish Executive funds and with the backing of both island communities this project may not be quite as 'blue sky' as it first appears.
Perhaps the Cuan Sound will become the home of the first grid connected tidal fence in Europe.
While the Norwegian, Canadian and American companies are forging ahead with projects in this field the UK, and Scotland in particular, can benefit enormously by encouraging our domestic companies to continue to invest in R & D. The European Marine Energy Centre in Orkney will soon be constructing tidal generator test facilities to compliment its existing wave device test beds and aims to keep Europe and Scotland on the leading edge of this potentially vital technology.   

*Renewable Obligation Certificates (Scotland) - part of the Scottish Executives subsidy in support of renewable electricity generation.