Offshore Renewable Energy: innovation and commercial challenges
Report on Workshop organised by CIRIA held in Cardiff on the 11th November 2003
(CIRIA Construction Industry Research and Information Association).
Welsh Context
The Welsh Assembly officer introduced the workshop by saying the Welsh targets from all renewables resources are, in terms of electricity generation, 4 TWh (terawatt-hours) by 2010. This can be supplied by a capacity of 1500 MW (megawatts) if generating at 30%. This would amount to 27% of current Welsh generating capacity (See Table below). Off-shore wind could be expected to contribute 20% of this figure.
Note: much conventional generating capacity operates only at peak demand, and the generation from wind is generally 25-35% of the declared capacity. In the case of tidal currents, it is expected to be 35-40% of the declared capacity, and higher still for waves.
The wave regime in Wales is less energetic than in Scotland (also less fierce, and so may be more practicable for wave devices). Also, Wales is better for tidal streams in terms of nearness to domestic and commercial consumers.
The Severn Barrage's cost of £10-12bn makes it uneconomic - the Environment Agency representative added comments about the precautionary principle, and advised that renewable energy technology should be of a scale that does not disrupt natural systems. No other barrage schemes were mentioned.
Power from Tidal Currents
Peter Fraenkel gave a talk on Marine Current Turbines, which is also the name of his company.
Tidal currents have good predictability, high energy density (800x wind's) and very low extremes (compared with wind). One needs currents over 2-3m/s (4-6 knots), and sites with less than 20-40m depth at low tide for existing drilling vessels (jack-up barge).
The total UK potential is unknown, but Peter Fraenkel would accept the 1992 DTI estimate that 20% of UK electricity might be obtained from the 8 largest sites. (UK Tidal Stream Review, 1992-03: desk study led by Engineering and Power Development Consultants with Binnie & Partners, Sir Robert McAlpine & Sons, and IT Power. Report published by ETSU and the DTI as T/05/00155, 1993).
When assessing the risk of marine current turbines to marine life, it is to be noted that the average ship propeller rotates 10 times faster than a tidal stream turbine. Moreover the average ship's propeller is a much greater threat since the vessel it is attached to may be moving at a much faster speed than fish or marine mammals, whereas the tidal turbine is of course fixed in one spot.
Peter Fraenkel's own company Marine Current Turbines www.marineturbines.com leads with the 'SeaGen' 300kW turbine now erected 1km offshore from Lynmouth, Devon. Its base is a 2.3 metre diameter tube set in an 18 metre deep hole drilled in the seabed at slack tide (deep enough to allow scour) and carries a horizontal axis turbine with two 11 metre vanes. The rotor is designed to be raised out of the water for maintenance. The commercial prototype will carry twin 500kW, 15 metre rotors. Since the structure is much smaller than a wind turbine base, the installation via a drilling rig is much easier.
Mr Fraenkel predicts a cost of 4p/kWh, with economies of scale decreasing to 3p/kWh as the technology matures. (Off-shore wind is currently projected at 4p/kWh, on-shore wind with the largest turbines is about 2.5p/kWh). The picture of the Lynmouth turbine below comes from www.bwea.com/marine/devices.html.
An array of turbines can be constructed quite close together across a stream because, unlike wind, the current direction is fixed so turbines need little separation. Peter Fraenkel estimated possible generation of about 100MW per sq. km. The environmental impact assessment showed little impact on marine life and landscape. A tidal stream turbine rotates 10 times slower that the average ship propeller and, as already mentioned, the latter is a much greater threat since the vessel it is attached to may be moving at a much faster speed than fish or marine mammals, whereas the tidal turbine is of course fixed in one spot.
Offshore Windfarms
Alex Tindall of RWE/Innogy Ltd. reported that 12 of the 18 offshore sites offered by the DTI (via the Crown Estates) now have all the needed planning and electricity permits.
RWE's own North Hoyle site is near completion, while construction at PowerGen's Scoby Sands project is starting.
The North Hoyle site is 8km offshore from Rhyl in water about 10m deep. All 30 base 'monopiles' are complete - in the form of 4 metre diameter base tubes grouted into the seabed. 25 of the turbines are now installed (2MW turbines), with the first ones due to go electrically live. Someone commented that the turbines have a stronger visual impact than expected from the environmental appraisal.
Note: North Hoyle could generate nearly 0.2 TWh annually, on the basis of 35% average efficiency for a good wind regime.
The DTI's Mike Brooke said the government is supporting offshore farms to the tune of £60M. The government is "realistically" expecting 4 to 6 GW by 2010, thus meeting half the renewables target (20 TWh on present consumption, 18 TWh if the 20% efficiency target in the domestic sector is reached - see Table below).
The best sites require to be sited in depths less than 40-50 metres, and to be close to the coast in order to keep down transmission losses and costs.
Support in the next round of offshore permits is being limited to the three areas which the DTI proposed in its consultation paper last November, titled "Future Offshore" (i.e. Thames estuary, the Wash and the NW Morecambe/Liverpool Bay (as announced mid-December).
The DTI is preparing new legislation to permit offshore energy devices outside the 12-mile limit, under the UN Convention on Law of the Sea. It is proposed to make the Crown Estate the licensing authority; to approve development under the Electricity Act (s.36); to establish local Safety Zones (extinguish navigation rights); and, to require guarantees of decommissioning once generation ceases.
Crown Estate
The Crown Estate presentation, given by Emily Forsyth, stated that the Crown Estate acts as landowner, and not as regulator. The Crown Estate earned £3M from its marine estate in 2002/3 (presumably mainly from sand/gravel dredging licences).
The Crown Estate requires £300k deposits from companies bidding for windfarm licences, and it is using the interest on the deposits to fund generic studies in order to secure development in an environmentally acceptable way.
The studies undertaken by COWRE (Collaborative Offshore Wind Research into the Environment) cover wind turbine impacts on birds (esp. Common Scoter) and electromagnetic fields (especially in fish nursery grounds). Reports are on the website www.thecrownestate.co.uk/35_cowrie_04_02_07. The RSPB is the environmental NGO member of COWRIE. Further studies are underway to produce guidance on bird survey methodology and on limiting noise and vibration.
WWF Cymru
WWF Cymru provided a brief, environmentalist's view. It pointed to their 'Turning the Tide — Power from the Seas' paper of Nov. 2002 (not on their Website). To coincide with the public inquiry just started into the proposed Scarweather Sands offshore windfarm in Swansea Bay, WWF Cymru is calling for a new legislative framework in a form of a comprehensive Marine Act and a Minister for the Sea.
WWF Cymru commissioned the new paper 'All at Sea: A Welsh case study for offshore renewable energy' written by Guy Linley-Adams (ex-FoE, now environmental lawyer) which illustrates how the current legislative process stifles the development of much needed offshore renewables www.wwf.org.uk/core/about/cymru_0000001036.asp.
Discussion
The main points brought up in discussion were extending the Grid (who should pay?), and the lack of coherence and 'security' in 2020 if we depend on 80% gas-fired power stations for electricity generation (with 20% renewables).
One critic suggested setting targets in terms of power generated. So, when conservation is included, the "20%" is stretched (particularly in the PIU scenario of 30-40% efficiency improvements by 2020 - extract below). Also, including CHP (with potentially a large amount of household-level micro-CHP) reduces the high dependence on gas-fired power stations.
The DTI's Transmission Issues Working Group was mentioned, as was developing proposals for offshore grid cables to reduce the losses and costs to developers of bringing the electricity ashore.
| Wales | UK Total | Welsh % of Total | |
| Population (millions) | 3 | 60 | 5 |
| Power Generation | |||
| Total Capacity (GW) | 5.5 | 72 | 7.6 |
| Electricity Produced (TWh) | 33.5 | 381 | 8.8 |
| Nuclear capacity (GW) | 1 | 13 | 7.7 |
| Renewables capacity (GW) | 0.33 | 5.3 | 6.2 |
| Renewables production (TWh) | 0.88 | 10.6 | 8.3 |
From the Welsh Assembly's consultation document on Renewable Energy www.wales.gov.uk
Extract from the Energy Review, PIU Report, February 2002 (s.1.19-20).
The conclusion from the PIU report** suggests that to meet possible carbon reduction targets by 2050 it will be necessary to have:
- a reduction of at least 50% in total energy demand through energy efficiency measures;
- at least 50% of total electricity production produced from zero-carbon sources;
- substantial changes in vehicle technology to ones that provide very low carbon emissions.
In support of these broad conclusions the report recommends:
- step change in energy and vehicle efficiencies. In the domestic sector an improvement of 20% by 2010 is proposed, with a further 20% improvement by 2020;
** See also Appendices in the PIU report
www.number-10.gov.uk/su/energy/1.html