offshore grids for wind power integration - Greenpeace

GLOBAL ENERGY [R]EVOLUTION
A NORTH SEA ELECTRICITY GRID [R]EVOLUTION
results
Over the year, the installed offshore wind power generation capacity
of 68.4 GW would generate 247 TWh of electricity.The average
capacity factor is 41.2%.
Over the year, a single offshore wind farm will experience significant
periods during which the farm is running at full power. Nontheless,
a single wind farm will also experience periods of very low load.
When adding up power generation over the whole North Sea, the
periods of very low and very high power generation are negligible.
Eighty percent of the time the power output is more than 15.5% of
the total installed capacity (Figure 2).
Accumulating the power generation from wind farms over larger
regions can reduce the periods of full load and very low load. In
conclusion, the spatial spread of wind farms over the North Sea leads
to a larger fraction of time during which medium level power is
generated in exchange for a reduction of periods of full load.
Situations of full and no load occur during a negligible fraction of time.
With regard to unit commitment and dispatch of the power system,
this means that the target should not be to operate offshore wind
power in the North Sea as a classical base load plant. Wind power
should rather be seen as a part of a power generation portfolio
that, as a whole, has to be managed in order to supply the variable
demand. For such portfolio management, flexibility is needed in
supply, demand, import and export. Day-ahead and intra-day
forecasting of the wind power generation is required for optimal
dispatch decisions and minimization of reserve requirements.
figure 2: power output of offshore wind power
over two days FOR ONE WIND FARM, ALL WIND FARMS OFF THE
BRITISH EAST COAST AND ACCUMULATED FOR ALL OFFSHORE WIND
FARMS IN THE NORTH SEA
Power(MW)
6
1,000
0
22,238
0
68,400
0
a) London Array I-IV: 1000 MW
b) All Offshore Wind Farms off the British East Coast: 22,238 MW
c) All Offshore Wind Farms in the North Sea: 68.4 GW
0hrs 12hrs 0hrs 12hrs 0hrs
April 3-4, 2006
The calculations for the North Sea show that large variations of
aggregated wind power generation are not very frequent (Figure 3).
For a single wind farm, 35% of all hourly variations are of less
than ±1% of installed capacity. For all wind farms off the British
east coast together, this is the case for 40% of all hourly samples.
For the accumulated generation of all wind farms together in the
North Sea, 42% of all hourly variations are of less than ±1%. In
all cases, more than 50% of all variations are of less than ±2% of
installed capacity.
Variations larger than ±5% occur for 20% of all hourly samples
for the single wind farm. For all wind farms off the British east
coast together they occur only 10% of the time and for the entire
North Sea only 6%.The occurrence of variations beyond ±10%
appears to be negligible.
figure 3: relative frequency of hourly variations
in generation FOR ONE WIND FARM, ALL WIND FARMS OFF THE
BRITISH EAST COAST AND ACCUMULATED FOR ALL OFFSHORE WIND
FARMS IN THE NORTH SEA
Relative Frequency [%]
a) London Array I-IV: 1000 MW
50
40
30
20
10
0
50
40
30
20
10
0
50
40
30
20
10
0
b) All Offshore Wind Farms off the British East Coast: 22,238 MW
c) All Offshore Wind Farms in the North Sea: 68.4 GW
-15 -10 -5 0 5 10 15
Hourly Variation as % of Capacity
Flexibility is the key requirement from a power system that is
largely based on generation from variable renewable sources.
Flexibility can be introduced by:
• distributed generation and storage,
• controllable demand,
• centralized storage,
• reservoir hydro power,
• flexible thermal power stations.