OFFSHORE RENEWABLES: COLLABORATING FOR A WINDY AND WET FUTURE? 1. INTRODUCTION P.A. Thompson 1 D. Pridden 2 J.W. Griffiths 3 The last decade has seen significant developments in the efficiency, reliability and economic viability of shoreline and offshore wave power generation. Major advances in offshore oil and gas technology, and particularly in the subsea sector have removed many of the technical barriers to early demonstration and commercialisation since the previous UK Wave Energy programme (1974-84). Pilot devices are now producing electricity in both primary (grid connected) and secondary generation in locations around the world. In a situation not dissimilar to the early developments of the wind energy market there is now an increasing level of private sector investment and confidence amongst device manufacturers, propelling the technology into the commercial arena. There is considerable common ground between the technology and skills required in the offshore oil and gas industry and those required for improvement of the field economics of both marine renewables and offshore wind power generation. A number of shared practical issues will prove to be the key drivers of major expansion in each sector. These include offshore oil and gas technology transfer, low cost offshore installation and improved power transmission and connectivity. This paper describes the current status of the wave energy sector, which currently represents the major part of the marine renewables industry. It also highlights the future requirements of the sector and the scope for a wider offshore industry collaborative effort to accelerate parallel developments in marine renewables and offshore wind. 2. The Wave Energy Resource In 1996 the WEC estimated the global wave energy potential at 2,000TWh\yr. In general, all sites offering over 15 KW/m of crest width have the potential for commercially competitive extraction. Some 320 GW are available along the Atlantic and Mediterranean coastlines. The highest annual wave power level off the European coasts is 75 kw/m off Ireland and Scotland and it decreases gradually to about 30kW/m off northern Norway and off the southern Atlantic Madeira and Canary archipelagos. The accessible UK wave energy resource has been estimated as being up to 840 Twh/year (260% of UK demand). The DTI s Energy Technology Support Unit (ETSU) and other sources have estimated that the practically and economically recoverable resource is nearer 15%-25% of UK demand. 1 British Maritime Technology Ltd 2 Capcis Ltd. 3 SeaPower Europe Ltd.
Figure 2-1: Average annual wave power kw/m of crest width The level of exploitable resource is among many factors, a determinate of geographical location and physical site (shoreline, nearshore or offshore). The relationship of the location of energy production to the end user is a key financial factor, as is the case with offshore wind. The cost of transmission and connection can often outweigh the construction and equipment costs and render a project unfeasible. Wave power is at its strongest in open sea conditions where there are minimal dampening forces. As the waves move closer to land the power of a wave is reduced by the effect of dissipation against the rising seabed and a greater proliferation of contrary wind off the landmass. Upon hitting the shore it is estimated that on average only a tenth of the wave s power remains. Table 2-1: Resource potential by water depth Water depth (m) Average available Average recoverable GW TWh GW TWh 100 80 700 10 87 40 45 394 10 87 20 36 315 7 61 Shoreline <30 <262 0.2 1.75 Total 191 1671 27.2 236.75 Source: Thorpe 1992 3. DEVICE INSTALLATIONS At present about sixteen shoreline and nearshore wave power generators have been installed worldwide. This suggests that the technology is available for efficient power generation, although it has yet to reach full maturation. For example, further developments may be needed in the area of device survivability in extreme wave conditions. The majority of wave energy devices, irrespective of location, utilise the movement of the waves to directly or indirectly drive a Oscillating Water Column (OWC) turbine, with a few others using either fluid driven pistons or piezoelectric conversion.
Table 3-1: Some recent wave device installations Year Device Type Turbines Country Location KW Status 1998 Pendular N 1 Japan Muroran 30 Test facility 1999 Wave plane N 1 Denmark Jutland 30 Demonstration 2000 OWC S 1 UK Islay 500 Grid-connected 2000 OWC S 2 Portugal Pico Island 1000 Grid connected 2001 Denniss-Auld S 1 Australia Port Kembla 500 Grid connected 2003* OWC N 1 Ireland n/a 2000 Osprey commercial 2004* Pelamis O 2 UK Islay 750 Demonstration 2004* Floating wave vessel N 1 UK Shetland 400 Demonstration * estimated S = shoreline, N = nearshore, O = offshore Work is going on in a number of countries with wave devices at various stages of development. Other countries which are active include: China, Greece, India, Indonesia, Korea, Norway, Spain, Sweden and the USA. Figure 3-1: OWC turbo generators cross-section The Wells turbine has been one of the defining technologies in the development of wave energy. One of the distinct characteristics of wave energy is its bi-directional vertical motion. The Wells turbine utilises the power from both of these motions while maintaining efficient and effective conversion. Source: Wavegen Following on from the successful shoreline LIMPET prototype on the Scottish island of Islay which is now feeding into the UK national grid, a 400kW plant is due to be completed this year on Pico Island in the Portuguese island of the Azores. The electricity is to be generated at an estimated cost of 7-8 cent per kw/h, a rate 50% lower than prototypes in 1990 Figure 3-2: Osprey 1 & 2000 Source: Wavegen Osprey 1 sits on the seabed (up to 15m water depth) with the capture chamber, Wells turbine and generator above the water line. Power is brought ashore via a subsea cable. The new nearshore 2 MW device is of composite steel and concrete construction. A contract is currently in place with the Republic of Ireland to install an Osprey 2000 in Irish waters under the auspices of its AER III (Alternative Energy Requirement III) programme. Multiple Osprey devices can be used to form a larger breakwater but also to reduce the Capex cost through the need for less infrastructure, principally cabling and connections.
Figure 3-3: PELAMIS A 7 th scale model, 375kW Pelamis or Sea Snake is due to be installed off the Scottish island of Islay in early 2002.This will be followed by a full-scale pilot device. Source: OPD Ltd. The Pelamis device is moving towards commercial deployment following the award of a SRO-3 power purchase contract. Developed by Ocean Power Delivery Ltd. of the UK, Pelamis is a semi-submerged, articulated structure composed of cylindrical sections linked by hinged joints. The wave-induced motion of these joints is resisted by hydraulic rams, which pump high-pressure oil through hydraulic motors via smoothing accumulators. The hydraulic motors drive electrical generators to produce electricity. Power from all the joints is fed down a single umbilical cable to a junction on the seabed. Several devices can be connected together and linked to shore through a single seabed cable. The design incorporates standardised offshore and subsea components. Models will be installed in water depths of 20m although the full-scale device is designed for water depths of 50-100m. Electricity generation is estimated at 6 cents per kw/h initially, falling to less than 4 cents per kw/h by the year 2010. A commercial concept envisages up to thirty-nine full size 750kW devices installed in a region with a wave resource of >50kW/m. 4. WAVE ENERGY ECONOMICS There is still no overall consensus on design or location that allows for a long-term definitive financial model based on standardised equipment. As with the early developments of the wind energy industry, larger turbines and more standardised equipment built on a larger scale will undoubtedly lead to improving economic models for wave energy. Many wave devices are still undergoing refinement and early one-off devices have been necessarily over-engineered so critical components can be properly assessed. There remains considerable scope for dramatic cost reductions offered by large-scale manufacturing and longerterm reliability. Yet, the cost of power from these current devices is continually reducing; the last decade has witnessed a 50% reduction in production and operating costs. It does not yet compete with fossil fuel generation but it is already competitive with other renewables. It is also competitive for niche markets such as remote islands, competing against conventional diesel generated electricity supply. Wave energy also offers better than favourable economic comparisons with the onshore wind industry at this stage in its development. Although there is no step-change technology waiting to radically change wave power, the next few years will see a continual but gradual cost reduction.
Figure 4-1: Improving economics of wave power (cents/kwh) Slow but steady improvements have improved the economics of wave power and are likely to continue through to 2010. 18 16 14 12 10 8 6 4 2 Limpet Denniss Auld Osprey Hydra Pelamis Source: Aggregate IEA / DWA 0 The three different 1987 1994 2000 2003 2006 2009 locations for wave energy devices have differing economics with variations in capex, installation, maintenance and operational costs. Offshore machines are generally rated to produce more output per wave (kw/m crest) but are faced with higher installation, maintenance and connection costs. Table 4-1: Wave devices - location comparative Shoreline Nearshore Offshore Power potential Low Medium High Connection Simple Difficult Difficult & expensive Servicing Low High Very high Maintenance Low High Very high Opex Low Medium High Capex Low Medium High Conversion method Turbine/generator Turbine/generator Turbine/genset or direct drive It is likely that shoreline and offshore devices will represent the central markets. Shoreline devices with their relatively low Opex, ease of connection and track record should grow progressively in the later part of the decade. Offshore devices with the benefit of increased power capture should grow at a faster rate, as offshore oil industry technology is used in moorings and cabling. Figure 4-2: Production costs by device type The production price of wave energy (8% discount rate) should enable the commercial application of many devices well before 2010. Source: Aggregate IEA/DWA cents/kwh 14 12 10 8 6 4 2 0 Shoreline Nearshore Offshore 1996 2000 2002 2004 2006 2008 2010
5. FUTURE INDUSTRY REQUIREMENTS As more and more devices are installed further offshore in the pursuit of greater productivity and predictability, a number of issues specific to marine renewables will need to be addressed. These include: - wave device survivability in extreme wave conditions. fast-tracking concept evaluation and prototype testing through to commercial deployment of wave and other marine renewable systems, e.g. tidal current turbines Two planned initiatives should help to bridge the crucial credibility gap between design and operational experience as well as accelerating the process of concept evaluation, prototype testing through to commercialisation. The first is Europe s largest dedicated wave research facility, which is to be built at Blyth in Northeast England. Containing a large converted dry-dock the facility is capable of testing full size devices of up to 30kW. This facility is being developed by EEST (Euro-seas Engineering Services and Testing Ltd, UK), a joint venture between CAPCIS Ltd (part of UMIST) and Hedley Purvis Ltd. Also, approval has also been given in-principle to the establishment of a European Test Centre for renewable energy generating devices from wave and tidal streams. The Centre is to sited at Stromness on Orkney and will operable by late summer 2002. A number of other specific issues, common to both the marine renewable and offshore wind sectors, should prove to be the key technological and commercial drivers influencing long-term expansion offshore. The commercial viability of both sectors is greatly influenced by the cost of initial installation and grid connection. Both sectors, therefore, need to develop low cost offshore installation methods and improved power transmission and connectivity solutions. For devices located in an offshore environment the issues of securing the device to the seabed and transmitting the generated power to the shore grow in importance. Fortunately, major advances in offshore oil and gas technology, and particularly in the subsea sector have removed many of the technical barriers. Subsea flexible power cables and connectors, floating mooring systems and subsea pumps and motors have all been developed to have a long life and low operating costs in the subsea or splash zone environments. In terms of power transmission and connection both sectors will require access to cost-effective solutions to embed the generated power into the onshore grid system. Most national grid networks have unsuitable capacity at their extremes. For example, in the UK most wave (and wind) energy is available on the west coasts. The development of a major electrical grid feeder running from the Western Isles to connect with the grid in England would open the way to major developments in wind and wave power. The cost and problems of coastal grid connection and reinforcement will be a major issue impacting the future development and major expansion of offshore wave and wind energy. It is generally recognised that embedded generation, and the associated new equipment, will radically alter the way electrical distribution networks are constructed and operated in the future. The technology of long distance, high voltage cabling offering minimal power degradation is still relatively un-proven. Previously stable and predictable network behaviour will become much more complex in the expanding offshore wind and marine renewable power generation environment and increasingly sophisticated control strategies and equipment will be required.
6. RECOMMENDATIONS This paper has summarised some of the key commercial and technology drivers generic to the emerging wave energy sector and the more established offshore wind industry. There are clear benefits to be realised through improved dialogue and focused cross-sector collaborative effort to address some of the practical issues associated with offshore operations. Steps should be implemented now to achieve this. SeaPower Europe has recently been established as the European trade association for the emerging wave and tidal current energy sectors. Its members already include leading device developers and mainstream engineering businesses who see growing investment opportunities in marine renewable energy. The British Wind Energy Association (BWEA) and SeaPower Europe have agreed to form a strategic alliance to further accelerate growth of the wind and marine renewable energy sectors. An early initiative will be the instigation of a joint industry project focusing on issues, options and possible resolutions related to grid connection and reinforcement in the Western part of Scotland. The difficulties of grid connection and the transfer from coastlines to main demand load centres is undoubtedly the greatest challenge facing the combined UK sectors, and one which no single company or representative body can solve alone. REFERENCES Thorpe 1992, ETSU, "Review of Wave Energy", T W Thorpe 1992 House of Commons Science and Technology Enquiry on Wave and Tidal Energy, 2001 International Ocean Systems July/August 2001 pp26/27 The World Renewable Energy Report 2001-2010, DW Report No. 178-01, Douglas-Westwood Associates