Extracts from the March-April 2003 edition of Renew
These extracts only represent about 25% of it

5. Marine Renewables

The arrival of marine renewables, offshore wind, wave and tidal power, has taken a while, but now at last it seems to be underway- as witness not only the race for offshore wind, and the the launch of a series of new wave and tidal prototypes, but also of a journal Marine Scientist, which covers the new technologies extensively in its first issue (No.1 Autumn 2002).

Offshore wind gets pride of place as the most developed. The new 270m euro Horns Reef project, stretching between 14 and 20 km off the coast of Denmark is the largest so far- with 80 2MW turbines. But wave and tidal power have also come on rapidly. In the first issue of Marine Scientist, tidal current pioneer Peter Fraenkel talks about his hopes and fears for tidal energy, and also comments unusually frankly on wave energy. He says he doesn’t rate onshore wave systems much, except as a stepping stone for larger offshore systems, but then most are using Oscillating Water Columns (OSW) and two way Wells Turbines- the latter being very inefficient. By contrast he liked the Pelamis wave snake, since that used hydraulic energy converters, and the device looked like it could cope with very rough seas.

It certainly is interesting that whereas in the 1970’s and 80’s, the wave prototypes then being tested mostly tried to meet the wave front flank-side on, to take as much power as possible - like the Sea Clam, which had giant compressible bags held against a floating cylinder, with the wave action squeezing air out of them to drive turbines. Now however, the Pelamis is a series of articulated cylinders tethered at the nose, so that it meets the waves nose on and generates energy from the snaking motion caused as they run down its flanks.

Fraenkel is supportative of his UK rivals in the tidal current field, the Northumbria based marine engineering company Engineering Business (EB), with their Stingray hydroplane device. It also seems to be doing very well- as we reported in Renew 140/41 it successfully completed its trials off the Shetlands, and EB say it now plans to redeploy a modified version ‘in the spring’, subject to the appropriate permissions being obtained. In tandem, EB says they will ‘continue to develop its offshore power station concept with the aim of commencing installation of a grid connected 5 MW Stingray farm as early as summer 2004’.

But Fraenkel still feels that propellers, as in his Seaflow marine current turbine, are going to be more efficient. ‘The Victorians discovered that propellers were better than oars’ he said. But it was a friendly contest- and the same with the Norwegian team led by Statoil and ABB (see below) who are also developing a propeller based system, but using a very high tech approach based on offshore gas and oil rig expertise. Fraenkel says ‘it may be the reverse of Scott and Amundsen. Scott took a high tech approach and Amundsen just went on Skis’, and he depicted his project as having adopted something of an ‘agricultural’ approach. But its hardly amateur. After the current round of test off Lynmouth in N. Devon (see Renew 141) on his 11m diameter double bladed prototype, he is planning a twin rotor system, since mounting two rotors on the same pile can cut costs by ‘30-40%’. By 2004 he would like to start work on a ‘tidal turbine farm’ with a group of double rotor machines linked to shore by a marine power cable. Ultimately he says the challenge will be size, the sea is huge and rough and small deices are never going to be as viable as large devices. There was also a ‘minimum critical mass’ of activity that was needed to get the whole thing going seriously. That means big money. For the moment what was happening was ‘a bit too small and underfunded’.

Marine Scientists also reports on Ocean Power Deliverys’ Pelamis wave device. As we have reported before, they have done tests on small one seventh scale prototypes at sea (there is a nice video of a chain of Pelamis cylinders being towed out by dinghy) but soon they plan to install a full scale 150 ft long 750kW machine offshore, possibly using the new £5.5m Orkney wave energy test centre, supported by £6m provided by Norsk Hydro. Eventually the idea is the have 40 such units in a wave farm, which could generate up to 30MW. Under a separate project, Ocean Power Delivery are looking at the feasibility of a 2MW Pelamis scheme, involving four 500kW devices for installation off Canada. As we have reported, the Australian company Energetech have been successful in winning a contract to install a 2MW version of their OWC system, which features parabolic wave focusing device, on Vancouver island. They reckon it can generate at 10 US cents per kWh and the next generation at 4c/kWh. Everyone is understandably cagey about quoting prices, but the Stingray team mentioned 4p-14p/kWh.

There certainty seems to be a lot happening, including some new developments from Universities. Plymouth University has developed a 5kW prototype floating OWC buoy and he RVco Venturi tidal device, now apparently christened Venturis, which was developed initially at Imperial College, is being pushed ahead. It works on the basis that accelerated water drops in pressure and the pressure drop can be used to drive a turbine. A ‘run of the river’ test had been carried out last spring in the Solent and tests are planned for a site on the coast of Humberside.

But the last word should go to Wavegen, who were the first to install a working commercial device- the 500kW Limpet OWC, on Islay. The company is now developing an offshore version, a variant of the ill-fated 2MW OSPREY which was damaged in storms just it came on station in 1992, before it could be properly ballasted on the sea bed. From what we’ve seen it looks somewhat similar, but they are keeping close wraps on it. They have £5m from a consortium led by Merill Lynch and £2.3m from the DTI, for a cluster of three offshore devices- and, according the Marine Scientist, plan to install the first in 2003/4 in shallow water, possibly at 1MW scale.

Marine Scientist is produced by IMarEST Publications,

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Norway tidal first

The tidal current project developed by a consortium of Norwegian companies including Statoil and ABB seems to have won the race to be the first to generate power for the grid. Based on a system similar to that being tested by Marine Current Power in Devon, a windmill-like turbine has been installed on the seabed near Kvalsund at the Arctic tip of Norway. "We will be the first in the world to use tidal currents to generate electricity to be fed into the local grid," Harald Johansen, managing director of Hammerfest Stroem, told Reuters. The initial Norwegian sub-sea turbine only has a capacity of 300 killowatts, but there are plans to expand to 20 mills from 2004, giving enough power for perhaps 1,000 homes. The project there has cost 50 million Norwegian crowns (US$6.7 million) so far and is expected to cost 100 million by completion in 2004.