Feasibility Study | Feasibility Study |
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| Friday, 09 July 2004 | |
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Download the Tiree Renewables Report 1 - Feasibility Study.doc (3.0Mb)
This report was commissioned by Argyll, Lomond and the Islands Energy Agency (ALIEnergy) and the Tiree Development Partnership (TDP) in February 2004, as part of a wider assessment of community-owned renewable energy for the Isle of Tiree. The study scope of work was to establish the following:
Electrical capacity has been assessed in collaboration with the local distribution network operator Scottish and Southern (S+S), who were awarded a short subcontract as part of the overall study. Their assessment is still under way at a detailed level, but initial findings are included in the present report. The maximum renewables generation that can be connected on Tiree without major grid reinforcement is estimated as 2MW based on the export capacity of the undersea cable serving the island (1.5MW) plus the local minimum summer load (500kW). A private wind turbine development has already contracted for 600kW of capacity, so there remains 1400kW available for new renewables projects. An issue still remains over the possibility of a grid fault causing simultaneous disconnection of all embedded generation under maximum system load conditions. In this case only 600kW of generation can be accommodated without exceeding short-term voltage change limits. Technical solutions are being assessed, including the use of static VAr compensators (SVCs) or grid monitor relays set to different sensitivities for individual generators. Wind resource is estimated on the basis of 13-year data from the Met Office weather station at Tiree Airport, where a mean wind speed of 7.2m/s at 12m above ground level has been measured. The wind speed at a hub-height of 45m is estimated to be 8.4m/s. It is likely that most exposed sites on Tiree will have a similar regime and anemometry may be unnecessary unless local terrain effects are anticipated, or a more precise wind speed estimate is needed for turbine verification. Technical constraints to wind turbine installations have been identified as:
RF interference is not expected to be a major problem at most locations due to the sparsity of microwave fixed links on Tiree and (in relation to TV interference) the low population density. In both cases fairly low-cost remedial measures are identified should a problem arise. Road and ferry access will both require more detailed study once type and size of wind turbine have been identified: the public road on the island is likely to have ‘pinch points’ requiring temporary modification to accommodate long vehicles. Likewise the suitability of the scheduled ferry (MV Clansman) for long or heavy vehicles will need to be firmly established, although preliminary information from CalMac suggests it should be adequate. Environmental constraints to the siting of large wind turbines have initially been assessed on the basis of statutorily designated areas using information supplied by SNH, and areas of known high bird activity that lie outwith designated areas, in the latter case using a map supplied by RSPB. While both of the above types of area are regarded as of principal environmental importance, they should not necessarily be regarded as exclusion zones depending on eg the nature of the designation, or the species of bird in the area in question. Visual impact and noise are also commented upon in the report. In the former case it is expected that visibility of a large wind turbine on Tiree is almost inevitable and that landscape impact will require to be assessed on a case-by-case basis. Noise nuisance is potentially avoidable and the use of the DTI best practice guidelines is recommended. Generally speaking a large wind turbine will need to be sited at least 400m from the nearest noise-sensitive property. A map has been drawn up to identify all those locations on Tiree that lie outside designated areas, identified areas of high bird activity, and HIAL airport avoidance zones. For this exercise a wind turbine of approximately 600kW size is assumed, with blade tip height up to 65m. The resulting areas may be regarded as the starting point for further site assessment. They include two locations with potentially good road and grid access, one in the region of Kilkenneth and the other on land east of Ruaig. A scope of work is proposed to narrow down the areas of search for a large community-based wind turbine. It includes consideration of the likely wind resource in terms of fetch and terrain-induced turbulence, proximity to the 11kV power lines, proximity to public roads, separation from habitation, major tourist sites and environmentally sensitive areas, and suitability in respect of land ownership. A brief review is made of suitable wind turbine types for the island considering wind class, electrical characteristics and weak grid capability, and overall track record. Some emphasis is put on the last of these and the need to avoid either commercial or technical risk. It is also noted that a Class I wind turbine, suitable for high wind sites, might be chosen to reduce risk even if conditions indicate a Class II (lower wind speed) machine would be suitable. The possibility of using second hand wind turbines (as on Gigha) is considered. The benefit is significantly lower capital cost for the turbine, hence a major reduction in the overall project cost. The disadvantages are lack of warranties, higher risk regarding the turbine’s maintenance history, and shorter economic lifetime depending on the number of operational hours already accumulated. A financial appraisal for a single wind turbine project on Tiree is made, based on a typical site with reasonable access to 11kV grid and public road infrastructure. Two different turbine sizes are considered, at 300kW and 600kW rating, allowing the impact of scale in regard to balance of plant costs to be assessed. Wind turbine costs and performance are based on commercial data from Enercon for their E30 and E40 wind turbines, both of which are suitable for Class I wind sites and operation on weak grids. The results of the appraisal indicate that the 600kW wind turbine would have a total installed cost of around £563k and a simple payback period of approximately 6 years. Net annual revenue after operating costs is estimated as £96k assuming all output is sold to a licensed supplier under the new Renewables Obligation. For the 300kW wind turbine the installed cost is estimated as £448k, with net annual revenue of £48k and payback period of 9.4 years. The installed cost/kW is some 60% greater than in the preceding example due to lack of competitive pricing at this turbine size, and the higher impact of fixed infrastructure costs in relation to output capacity. It is therefore recommended that a community-owned wind project should be based on units of at least 600kW, if new equipment is to be used. This conclusion does not however apply to the option of second-hand equipment, where the capital cost of the wind turbine would be proportionately less. Second-hand machines may then be a good option for smaller projects of 300kW or less, which may also offer more siting options due to their lower tip height in relation to the airport exclusion zones. Finally, a brief assessment is made of different options for community wind and other renewables on Tiree, based on the assumption of an available generating capacity of 1400kW. The three main scenarios compared for allocating this capacity are:
Solar PV is still expensive, but is commercially available and has ‘grid friendly’ electrical characteristics. The wind plus solar PV mix is therefore technically attractive, and worthy of further assessment; ideally this would include a solar resource assessment, which could be done as a desktop exercise. It is however concluded that maximum benefit to the island would be achieved if some of the 1400kW capacity were left for development by individuals, either privately or in community partnerships. This could encompass both wind and solar energy, with the advantages of this option being (a) to provide more incentive for economic activity and local initiative, (b) to help generate awareness of and expertise in renewables technology on the island, and (c) enhanced security of supply. For these reasons this last option is preferred and a possible mix of new renewables projects could then be:
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