Environmental Engineering Reference
In-Depth Information
900
3,500
800
3,000
700
600
2,500
2,000
500
(a)
400
300
1,500
Portion of generation
provided by solar
Avg monthly load
Sunshine W/m
2
1,000
200
100
500
0
0
1 2 3 4 5 6 7 8 9 10111213141516171819202122 2324
Hours
3,500
900
800
700
600
500
400
300
200
100
3,000
2,500
2,000
(b)
STORING
1,500
Portion of generation
provided by solar
1,000
Solar energy stored
Avg monthly load
Sunshine W/m
2
500
0
0
1 2 3 4 5 6 7 8 9 101112131415161718192021222324
FIGURE 7.9
Theoretical load and generation versus time of day for utility power (a) without storage and
(b) with storage.
peak power usage, a utility is able to better match the demand curve with
stored energy and then offer cheaper electricity at peak times.
Figure 7.10 shows data generated by Arizona Public Service (APS) on a
summer day. The available solar energy output with thermal energy stor-
age matches the load almost exactly, whereas the solar output without ther-
mal energy storage begins to decline just as the load peaks. Energy is most
expensive to consumers when the load peaks, around 2 p.m., due to simple
supply and demand principles. By adding storage to a system, a utility can
afford to decrease peak energy costs to consumers.
Heat equivalents up to two days of power plant operation can be stored for
high demand-high price electricity periods that can occur 3-4 hours after
