The project has attracted a good deal of international interest as a solution to the energy problems of small island communities, with visitors from as far afield as New Zealand. According to NIE's project engineer, George Holland, the effects on life on the island have been dramatic. "People now have access for the first time to the domestic appliances which the rest of us take for granted. Children at the school can use a computer when they want to, rather than waiting for old and unreliable diesel generators to start, and the guest house has a freezer for the first time," he says.
The project is also stimulating development on the island. New houses are being built and existing businesses are facing the future with a confidence which was impossible in the pre-mains era. Business at the island's diving centre has doubled over the year due to the improved amenities it now has on offer, farmers are planning for the future and a new banking facility has opened.
Rathlin is NIE's second wind energy project, following the installation of a 300 kW demonstration turbine, supplied by the UK's Wind Energy Group, at Slievenahanaghan in Co Antrim in 1991. Northern Ireland now has its first Non Fossil Fuel Obligation Order, similar legislation to that which has supported wind and other renewable technologies in England and Wales since 1992. Under the order, NIE will be soon be buying 15 MW of power from renewable energy projects to distribute to users in the province.
Unlike these projects, which will feed into the main grid, the stand-alone system at Rathlin simply serves the isolated island community. Prior to the wind-diesel system's installation in 1992, Rathlin was without mains electricity and islanders survived with kerosene lamps and a few old diesel generators. NIE had twice ruled-out laying a submarine cable from the mainland as too expensive. However, a combination of 55% funding from the European Community's VALOREN programme for regional development and contributions from Northern Ireland's Department of Economic Development made the £1.2 million wind power system possible.
The hybrid power plant is based on three 33 kW MAN wind turbines from Germany, together with three diesel generators and 70 kWh of battery storage. It is automatically controlled by a microprocessor-based supervisory unit, developed by SMA Regelsysteme in Germany, which can be operated by NIE or SMA via modem telephone links.
The mode of operation is dictated by the level of demand, which varies from a night-time low of around 25 kW to peaks of more than 60 kW, usually between six in the evening and midnight when streetlights are on. The control system selects the configuration most appropriate depending on the wind power available and the state of the battery storage system. The wind turbines generate most of the power, with the 60, 100 and 160 kW diesel generators being brought in as necessary -- and in that order -- when wind speeds are too low, or too high, for the wind turbines. The battery storage is always connected to buffer the system during load and wind speed fluctuations -- and can be recharged by the wind turbines. The control centre, batteries, diesel generators and about one year's supply of diesel are located at shore level close to existing harbour facilities.
The two-bladed turbines, all three of which were erected on the same day, have been named Conn, Aedh and Fiachra after a story in Irish mythology with connections to Rathlin. They are located 60 m apart at the highest section of the 12 km long island to catch prevailing south-westerly winds. The system supervisor is able to directly control the power take-off from the turbines to allow balancing of the system demand.
Eleven kilometres of overhead distribution line and 3 km of underground cables carry power to all the homes and business premises on Rathlin, 62 customers in all. The distribution system was carefully planned to minimise its visual intrusion on the island, which has special status as an Area of Outstanding Natural Beauty due to its bird and other wildlife.
Although some minor software adjustments have had to be made to the control system, the installation has performed well in its first year and generated 250,000 kWh. Minor adjustments in the early days are hardly unusual for what is, in effect, a completely new electricity generation, distribution and supply system. The turbines were halted for some days in June and August due to wind speeds below 4 m/s. And gusts as high as 30 m/s in January also prevented their use. Nevertheless, the proportion of power generated by the wind over the whole year, some two-thirds, is very close to that predicted.