Geoscience Reference
In-Depth Information
Real-Time Dispatch
Real-Time Dispatch
80
80
Geothermal
Wind
Photovoltaic
Solar Thermal
Hydroelectric
NG Reserve
Demand + T&D Losses
Geothermal
Wind
Photovoltaic
Solar Thermal
Hydroelectric
NG Reserve
Demand + T&D Losses
28-Jul-2005
15-Nov-2005
70
70
60
60
50
50
40
40
30
30
20
20
10
10
0
0
2
4
6
8
10 12
Hour of Day
14
16
18
20
22
24
2
4
6
8
10 12
Hour of Day
14
16
18
20
22
24
Figure 13.16. Matching California electricity demand plus transmission/distribution losses (black line) with
100 percent renewable supply based on a least-cost optimization calculation for 2 days in 2005. Natural gas
was available for backup but was not needed during these days. Notes :Systemcapacities: 73.5 GW of wind,
26.4 GW of concentrated solar power (CSP), 28.2 GW of photovoltaics (PV), 4.8 GW of geothermal, 20.8 GW
of hydroelectric, and 24.8 GW of natural gas. Transmission and distribution losses were 7 percent of the
demand. The least-cost optimization accounted for the day-ahead forecast of hourly resources, carbon
emissions, wind curtailment, and thermal storage at CSP facilities, and it allowed for the nighttime production
of energy by CSP. The hydroelectric supply was based on historical reservoir discharge data and currently
imported generation from the Pacific Northwest. The wind and solar supplies were obtained by aggregating
hourly wind and solar power at several sites in California estimated from wind speed and solar irradiance data
for those hours applied to a specific turbine power curve, a specific concentrated solar plant configuration
(parabolic trough collectors on single-axis trackers), and specific rooftop PV characteristics. The geothermal
supply was limited by California's developable resources. From Hart and Jacobson (2011).
2007). The amount of power guaranteed by having the
wind farms dispersed over nineteen sites was four times
greater than the amount of power guaranteed by having
one wind farm.
pressure systems are generally strong, causing winds to
be fast (Section 6.6).
Figure 13.16 illustrates how the combined use of
wind (variable), solar rooftop PV (variable), CSP
(or solar thermal) with storage (variable), geothermal
(baseload), and hydroelectric (dispatchable) can be used
together to match hourly power demand plus trans-
mission and distribution losses on 2 days in Cali-
fornia in 2005. The geothermal power installed was
increased over 2005 levels but was limited by Cali-
fornia's geothermal resources. The daily hydroelectric
generation was determined by estimating the historical
generation on those days from reservoir discharge data.
Wind and solar capacities were increased substantially
over current levels, but they did not exceed maximum
levels determined by prior land and resource availability
studies.
Figure 13.16 illustrates the potential for matching
power demand hour by hour based a computer sim-
ulation that accounts for the variable nature of each
13.8.2. Using Complementary and
Nonvariable Supply to Match Demand
The complementary nature of different renewable
energy resources can also be taken advantage of to
match minutely through seasonally varying power
demand. For example, when the wind is not blow-
ing, the sun is often shining and vice versa .This
occurs physically because, under a high-pressure sys-
tem, descending air evaporates clouds, increasing sun-
light. At the same time, though, pressure gradients are
generally weak, causing winds to be slow, under a high-
pressure system. Conversely, under a low-pressure sys-
tem, rising air increases cloudiness, reducing sunlight
penetrating to the surface. Pressure gradients in low-
 
 
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