Environmental Engineering Reference
In-Depth Information
Wind and solar energy are available when weather dictates—not on
command. This means that generation does not necessarily correspond to
demand. For example, no power from photovoltaic cells is available without
sunlight; an end user cannot run an air conditioner on wind energy when
the wind is not blowing. Additionally a significant number of solar cells
installed at residences, small businesses, and other sites contribute only a
fraction of the total power required. As a result, utilities must deal with large
numbers of small, widely distributed sources that may or may not be avail-
able when peak demand occurs.
The reverse challenge arises from energy generated when load demand
decreases. Examples of the variabilities of solar and wind energy are shown in
Figures 1.1 and 1.2. The rapid variation in solar power as shown in Figure 1.1
and the lack of availability at certain times cause two types of problems. The
Solar Variability Examples
200
Prescott
3000
150
Scottsdale
2000
Yuma
100
1000
50
0
0
250
750
Minutes since start of day
1250
0
1500
3000
4500
Minutes since 07:30:00 June 22, 2006
FIGURE 1.1
Variability of solar energy. (Courtesy of AzRise.)
Wind & Load Variability Example
Seven days of loads from one municipality assuming peak consumption
& seven days of wind generation from the same region.
300.00
250.00
200.00
150.00
100.00
50.00
0.00
Winter '05/'06 City Peak (MW)
Summer '06 City Peak (mW)
Wind Generation[MW]
0
24
48
72
Hour
96
120
144
168
FIGURE 1.2
Electrical load and wind power available for 7-day period in Fort Collins, Colorado.
