Environmental Engineering Reference
In-Depth Information
1,700 MW in the summer to 5,000 MW in the winter. The main energy sources
within the island are fossil-fuel generation: gas-fired plant, mainly CCGTs, repre-
sent approximately 48 per cent of island capacity, coal-fired plant accounts for
27 per cent, oil-fired plant 11 per cent and peat-fired plant 4 per cent. The
remainder includes one pumped storage station, providing 292 MW, and smaller-
scale hydroelectric plant, CHP and wind generation (Barry and Smith, 2005).
Ireland is exposed to southwest winds and storms blowing across the north
Atlantic. Low pressure cyclones (depressions) regularly pass over or near the
country, with a period of 4-6 days, resulting in large variations in both wind speed
and direction. Storm activity is more intense and frequent during the winter months.
The available wind resource for N. Ireland has been estimated at 106 TWh/yr.
However, considering physical/environmental constraints and economic viability,
the accessible resource is just 8.6 TWh/yr, equivalent to a capacity of about
3,000 MW (Persaud et al. , 2000). Likewise, in the Republic of Ireland, the feasible
resource has been estimated at 344 TWh/yr (ESBI and ETSU, 1997). Against this
background, the EU directive for the Promotion of Electricity from Renewable
Energy proposed renewable energy targets for electricity supply for individual
countries within the European Union (European Commission, 2001). The Northern
Irish and Republic of Ireland have both adopted renewable energy targets of
40 per cent by 2020. The expectation is that wind power will provide the bulk
of the renewable generation, implying a wind capacity on the island approaching
6,000 MW.
For the period 1 January 2004-31 December 2004 metered data has been
collected for the 46 operational wind farms on the island. Within the Republic of
Ireland, metered data is available every 15 minutes, while for N. Ireland the
equivalent 30 minute data has been interpolated to generate 15 minute data. During
the year, wind farm capacity expanded from 248 to 394 MW. Figure 5.8 depicts the
geographical distribution of the wind farms in Ireland in 2004, expressed as the
percentage contribution from each county. It can be seen that the wind farms,
located generally in hilly areas, are well dispersed, although more concentrated in
the northwest of the island. Also included is the Arklow Banks 25 (of a potential
520) MW offshore project, 10 km off the east coast of Ireland, and close to the
major load centre of Dublin. Most of the existing wind farms have been connected
to the distribution system, although connection at transmission level is becoming
more common. The 2004 operational figure of 394 MW corresponded to a wind
energy penetration level of about 4 per cent for the island.
5.3.2.1 System capacity factor
A convenient measure for the available wind resource for a particular wind farm or
region is the capacity factor. The capacity factor is calculated as the actual energy
production over a given period divided by the maximum potential production over
the same period. The capacity factor has been calculated for each quarter of the
year (Figure 5.9). Higher energy production is achieved during the autumn and
winter months, with the capacity factor reaching a maximum value of 60 per cent
during February (not shown), and lower output during spring and summer. Over a
complete year, the average capacity factor for the island is 36 per cent, which for
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